COVER PHOTOGRAPH of San Francisco Bay Region taken April 14, 

1972, at altitude of 65,000 feet from U-2 aircraft. Courtesy National 

Aeronautics and Space Administration (Ames Research Center, 

Moffett Field, Calif.) Front shows city of San Francisco and Golden 

Gate at bottom, San Francisco Bay and city of Oakland in middle, 

Sacramento-San Joaquin Delta and crest of Sierra Nevada at top. 

Back shows Bolinas Lagoon and trace of San Andreas fault at bottom, 

San Pablo Bay in middle, Sacramento valley and crest of Sierra 

Nevada at top. 
Seismic Safety and Land-use PlanningSelected Exam pies from California 

By M. L. BLAIR and W. E. SPANGLE, WILLIAM SPANGLE and ASSC)CIATES 

BASIS FOR REDUCTION OF EARTHQUAKE HAZARDS, 

SAN FRANCISCO BAY REGION , CALIFORNIA 

G E 0 L 0 G I CAL SURVEY P R 0 FE S S I 0 N A L PAPER 941-B 

Methods for using seismic zonation 

and hazard mapping in land-use 

planning and regulation 

Jointly supported by the U.S. Geological Survey 

and the Department of Housing and Urban Development, 

Office of Policy Development and Research, as part of 

a program to develop and apply earth-science information 

in support of land-use planning and decisionmaking 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1979 
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary 

GEOLOGICAL SURVEY 

H. William Menard, Director 

Library of Congress Cataloging in Publication Data 

Blair, M. L. 

Seismic safety and land-use planning-selected examples from California. 

(Basis for reduction of earthquake hazards, San Francisco Bay region, 

California) (Geological Survey professional paper ; 941-B) 

Bibliography: p. B80-B82. 

Supt. of Docs. no.: I 19.16:941-B 

1. Seismology-California. 2. Land use-Planning-California. 

I. Spangle, W. E., joint author. II. Title. III. Series. IV. Series: 

United States. Geological Survey. Professional paper ; 941-B. 

QE535.2U6B56 363.3'4 79-20292 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 

Stock Number 024-001-03231-7 
FOREWORD 

This report is a product of the San Francisco Bay Region Environment and Resources 

Planning Study, an experimental program that was designed to facilitate the use of earthscience information in regional planning and decisionmaking. The study, conducted from 

1970 to 1976, was jointly supported by the U.S. Geological Survey, Department of the Interior, and the Office of Policy Development and Research, Department of Housing and Urban 

Development. The Association of Bay Area Governments actively participated in the study 

and also provided liaison with other regional agencies and with local governments. 

Although the study was focused on the nine-county 74,400-square-mile San Francisco Bay 

region, it explored a problem common to all communities: how best to plan for orderly 

development and growth and yet conserve our natural resource base, insure public health and 

safety, and minimize degradation of our natural and manmade environment. Such planning 

requires that we understand the natural characteristics of the land, the processes that shape it, 

its resource potential, and its natural hazards. These subjects are chieHy within the domain of 

the earth sciences-geology, geophysics, hydrology, and the soil sciences-and information 

from these sciences can help guide growth and development. But the mere existence of' 

information does not assure its effective use. Relatively few planners, elected officials, or 

citizens have the training or experience needed to recognize the significance of basic earthscience information, and many of the conventional methods of presenting earth-science information are ill-suited to their needs. 

The San Francisco Bay Region study has aided planners and decisionmakers by: identifying 

important geologic and hydrologic problems that are related to growth and development; 

providing the earth-science information that is needed to solve these problems; interpreting 

and publishing findings in forms understandable to and usable by nonscientists; establishing 

avenues of communication between scientists and users; and exploring different ways of 

applying earth-science information in planning and decisionmaking. More than 100 reports 

and maps have been produced. These cover a wide range of topics, such as Hood and earthquake hazards, unstable slopes, engineering characteristics of hillside and lowland areas, 

mineral and water resources, solid and liquid waste disposal, erosion and sedimentation, and 

bay-water circulation patterns. 

Seismic safety and land-use planning-selected examples from California is one of the final reports 

in the San Francisco Bay Region study. The authors are city and regional planners and have 

participated in the seismic-safety planning of several California communities. In this report 

they discuss the earth-science data needed for effective planning and the methods that can be 

used by local and regional government to reduce earthquake risk to acceptable levels. Much of 

the discussion is illustrated with examples drawn from experience in California where 

seismic-safety planning is mandated by State law. Although public attitudes, procedures, and 

legal requirements differ in other states, the basic earth-science needs and the planning 

strategies discussed are relevant wherever earthquake hazards are an issue in decisions related 

to public policy. 

This report is the companion volume of an earlier publication, Studiesfor Seismic Zonation qf 

the San Francisco Bay Region (U.S. Geol. Survey Professional Paper 941-A), which dealt chiefiy 

with the geologic and hydrologic causes of earthquake damage. For conformity with the 

earlier report, and because the scientific literature on earthquakes customarily uses metric 

values, measurements in this report are expressed in metric terms followed by their English 

equivalents. R~}) ~/ 

Robert D. Brown, Jr. 

Project Director 

San Francisco Bay Region Study 

III 

CONTENTS 

Page 

Fore~ord __________________________________________________ Bill 

1\bstract -------------------------------------------------- 1 

Introduction---------------------------------------------- 1 

Purpose and scope ---------------------------------- 2 Overvie~ of seismic hazards __________________________ 2 

Seismic hazards defined -------------------------- 4 

Surface faulting ------------------------------ 5 

Ground shaking ------------------------------ 7 

Ground failure -------------------------------- 7 

Tsunamis and seiches ________________________ 7 

Earthquake damage ------------------------------ 7 

Damage to buildings __________________________ 8 

Damage to dams ---------------------------- 8 

Damage to utilities -------------------------- 10 

Damage to transportation systems ____________ 10 

Fire ---------------------------------------- 10 

Earthquake magnitude and intensity ______________ 11 

Professions involved in seismic risk reduction __________ 14 

Land-use planning ___ _________ _ ____________ __ __ __ _ 18 

Geology, engineering geology ______________________ 18 

Civil engineering -------------------------------- 19 

Soils engineering __ _ __________ ____________ __ __ __ _ 19 

Structural engineering____________________________ 19 

1\rchitecture ------------------------------------ 19 

Building inspection _ ________ _ _ ___________ _ __ ____ _ 19 

Governmental frame~ork for reducing seismic risk 19 

Federal programs _______ _________ _ ____________ __ ____ _ 20 

Research and technical information ________________ 21 

U.S. Geological Survey________________________ 21 

National Oceanic and 1\tmospheric 

1\dministration ---------------------------- 21 

National Science Foundation __________________ 21 

Emergency preparedness and disaster relief _______ _ 

Civil Defense Preparedness 1\gency ___________ _ 

Federal Disaster 1\ssistance 1\dministration ___ _ 

Program 1\dministration -------------------------- 1\-95 revie~ _______________________________ _ 

Environmental impact assessment ___________ _ 

Programs of the Department of Housing and 

Urban Development _______________________ _ 

Insurance ---------------------------------------- State role-California _______________________________ _ 

21 

22 

22 

22 

22 

22 

23 

23 

24 

Legislation and advice ---------------------------- 24 

California legislature ________________________ 24 

Governor's Earthquake Council________________ 25 

Joint Committee on Seismic Safety ____________ 25 

Seismic Safety Commissiun ____________________ 26 

Research and information ________________________ 26 

Structural standards------------------------------ 27 

Critical facilities 

Department of Water Resources _____________ _ 

California Department of Transportation _____ _ 

Emergency preparedness and disaster relief _______ _ 

Land-use planning and regulation _______________ _ 

Office of Planning and Research _____________ _ 

California Environmental Quality 1\ct _______ _ 

28 

28 

28 

28 

28 

29 

29 

Page 

Governmental frame~ork for reducing seismic risk-Continued 

1\rea-~ide planning-San Francisco Bay region ________ B29 

1\ssociation of Bay 1\rea Governments ------------ 30 

San Francisco Bay Conservation and Development 

Commission _ __ __ _ _ __ _ _ __ ___ _ _ _ __ __ __ ____ __ __ _ _ _ 31 

California Coastal Zone Conservation Commission _ _ 32 

Metropolitan Transportation Commission ----------

Evaluating seismic risk ----------------------------------

Identifying seismic hazards --------------------------

Surface rupture (1\6-1\12; 1\25-1\30) --------------

Ground shaking (1\52-1\57) ----------------------

Liquefaction (1\68-1\ 74) _______ -------------------

Landsliding (1\75-1\87) --------------------------

Flooding (1\93-1\94) ------------------------------

Selecting the design earthquake ----------------------

Predicting geologic effects ----------------------------

Ground shaking ----------------------------------

Liquefaction and lateral spreading ----------------

Landsliding --------------------------------------

Flooding ---------------------------------------- Seismic zonation _______________________ --------_ 

Inventorying cultural features ------------------------

Current land use -------------------------------- Structures ~ith high and involuntary occupancy ___ _ 

Hazardous structures ___________ -- ____ -----------

32 

33 

33 

33 

34 

34 

34 

34 

35 

36 

36 

40 

40 

40 

40 

46 

48 

48 

48 

Lifelines ---------------------------------------- 48 

Facilities for emergency response ------------------ 49 

Other critical facilities ---------------------------- 49 

1\ssessing seismic risk _______________ -- __ -------------

Dollar loss ________ ------------------------------

49 

49 

49 

50 

Deaths and injuries ------------------------------

Population at risk --------------------------------

Relative risk ------------------------------------ 50 

Scenarios ---------------------------------------- 51 

Determining acceptable risks-------------------------- 52 

Land-use planning and seismic safety ---------------------- 53 

The planning process ---------------------------------- 54 

Identify issues and define objectives---------------- 55 

Collect and interpret data ------------------------ 55 

Formulate plans----------------------------------

Evaluate impacts --------------------------------

Revie~ and adopt a plan -------------------------- 56 

Implement the plan ------------------------------ 56 

56 

56 

Planning examples _________________ ------------------- 57 

Planning to reduce risk from ground shaking ______ 57 

Site investigation and design requirements ____ 57 

1\bating structural hazards-------------------- 58 

Planning to reduce risk from ground failure ________ 58 

Landsliding ________________________ ----------- 58 

Liquefaction _______________ -----------------

Planning to reduce risk from surface rupture ------

Surface rupture-undeveloped areas ----------

Surface rupture-developed areas ___________ _ 

Planning to reduce risk from flooding _____________ _ 

Tsunamis ------------------------------------

Dam and dike failure ------------------------

v 

61 

62 

64 

67 

68 

69 

71 
VI CONTENTS 

Page 

Land-use planning and seismic safety-Continued 

Page 

Land-use planning and seismic safety-Continued 

Putting it all together -------------------------------- Land-capability analysis _________________________ _ 

Land-use policy and regulation ___________________ _ 

Project review ___________________________________ _ 

B69 

71 

73 

76 

Postearthquake reconstruction ________________________ B76 

Earthquake prediction _ _ _ ___ ___ _ _ _ _ _ _ ____ __ __ __ _ _ ____ _ 78 

Conclusions ---------------------------------------------- 78 

References ---------------------------------------------- 80 

ILLUSTRATIONS 

Page 

FIGURE 1- 4. Maps showing: 

1. Plate boundaries and epicenters of 30,000 earthquakes recorded between 1961 and 1967 ____________________ B3 

2. Approximate location of San Andreas fault in California -------------------------------------------------- 4 

3. The shallow, intermediate, and deep-focus earthquakes in the circum-Pacific earthquake belt ______________ 5 

4. Seismic risk zones of the United States ba8ed on damages associated with historic earthquakes _____________ 6 

5. Diagram of four types of fault movement characterized by the sense of movement relative to the fault and 

to the horizontal ---------------------------------------------------------------------------------- 7 

6. Faults in southern California and epicenters associated with San Fernando earthquake -------------------- 9 

7-11. Photographs showing: 

7. Damage to small buildings caused by the San Fernando earthquake -------------------------------------- 10 

8. Damage to hospitals caused by the San Fernando earthquake -------------------------------------------- 12 

9. Slide damage to Van Norman Dam---------------------------------------------------------------------- 14 

10. Damage to Sylmar converter station -------------------------------------------------------------------- 15 

11. Damage to highway interchange _ _ _ __ __ ___ _ __ _ _ __ __ _ _ _ _ __ _ _ __ _ _ _ _ __ _ _ _ _ _ _ ______ __ _ _ _ _ ____ _ _ __ _ _ _ _ __ __ _ _ _ 15 

12. Graph showing relationship between magnitude and energy ---------------------------------------------- 16 

13. Map showing intensity distribution of San Fernando earthquake of February 9, 1971 ______________________ 17 

14. Diagram showing steps in evaluating seismic risk-------------------------------------------------------- 33 

15. Map of California showing behavior of different segments of San Andreas fault __________________________ 36 

16. Map showing location and length of surface rupture associated with a postulated earthquake of magnitude 6.5 on the San Andreas fault _____ __ __________ _ _ _________ _ ________ ____ __ _____________ _________ __ _______ 37 

17. Diagram showing predicted geologic effects of postulated earthquake of magnitude 6.5 on the 

San Andreas fault -------------------------------------------------------------------------------- 38 

18. Generalized geologic map of area crossed by demonstration profile ---------------------------------------- 39 

19. Map showing relative amplification of bedrock motion ---------------------------------------------------- 41 

20-25. Maps showing: 

20. Liquefaction and lateral spreading ---------------------------------------------------------------------- 42 

21. Landsliding ------------------------------------------------------------------------------------------ 43 

22. Flooding ---------------------------------------------------------------------------------------------- 44 

23. Seismic hazard zones ---------------------------------------------------------------------------------- 45 

24. Maximum earthquake intensity predicted on a regional scale -------------------------------------------- 47 

25. Day and night populations, areas of high occupancy, and risk zones, Palo Alto, Calif------------------------ 53 

26. Diagram ofthe planning process------------------------------------------------------------------------ 55 

27-33. Maps showing: 

27. Estimated building damage levels for a 1906-type earthquake, San Francisco, Calif ------------------------ 59 

28. Density of precode, Type C buildings, San Francisco, Calif ------------------------------------------------ 60 

29. Special geologic study areas, San Francisco, Calif -------------------------------------------------------- 61 

30. Risk zones for land-use planning, Santa Clara County Baylands ------------------------------------------ 63 

31. Active and probably active faults and fracture zones for a portion of San Mateo County, Calif ______________ 65 

32. Special Studies Zone for a portion of San Mateo County, Calif -------------------------------------------- 66 

33. Known and inferred fault trace locations and setback lines, Portola Valley, Calif __________________________ 67 

34. Aerial photograph showing Hayward fault traces in urban and urbanizing area ---------------------------- 68 

35. Map showing Hayward redevelopment plan -------------------------------------------------------------- 70 

36. Land-capability map for multi-family residential use ---------------------------------------------------- 74 

37. Natural hazards map, City of San Jose ------------------------------------------------------------------ 77 

38. Seismic safety zones, Santa Clara County---------------------------------------------------------------- 79 
CONTENTS VII 

TABLES 

Page 

TABLE 1. Magnitude/size comparisons between any two earthquakes ------------------------------------------------------ B16 

2. Modified Mercalli intensity scale ------------------------------------------------------------------------------ 16-

3. High priority recommendations of the Task Force on Earthquake Hazard Reduction ------------------------------ 20 

4. Cost of earthquake insurance for residential buildings ---------------------------------------------------------- 24 

5. Recommendations of the Governor's Earthquake Council -------------------------------------------------------- 25 

6. Summary of recommendations of the Joint Committee on Seismic Safety -----------------------'-------------------- 26 

7. San Francisco Intensity Scale for 1906 earthquake -------------------------------------------------------------- 46 

8. Projected total loss from earthquake shaking, 1970-2000 -------------------------------------------------------- 50 

9. Deaths and hospitalized injuries-------------------------------------------------------------------------------- 50 

10. Life loss from dam failure ------------------------------------------------------------------------------------ 51 

11. U.S. population-at-risk by seismic risk zone and state------------------------------------------------------------ 52 

12. Earthquake ratings for common building types ------------------------------------------------------------------ 54 

13. Scale of risks for various building uses ------------------------------------------------------------------------ 54 

14. Risk analysis of a motor inn -------------------~-------------------------------------------------------------- 54 

15. Criteria for permissible land use in Portola Valley -------------------------------------------------------------- 62 

16. Risk zones for settlement and ground failure, Santa Clara·County ------------------------------------------------ 62 

17. Land and building uses appropriate for various risk zones, Santa Clara County------------------------------------ 64 

18. Costs associated with ground shaking resulting from events on the San Andreas, Hayward, or Calaveras faults------ 72 

19. Summary of costs for multifamily residential use ---------------------------------------------------------------- 73 

BASIS FOR REDUCTION OF EARTHQUAKE HAZARDS, 

SAN FRANCISCO BAY REGION, CALIFORNIA 

SEISMIC SAFETY AND LAND-USE PLANNING-SELECTED EXAMPLES 

FROM CALIFORNIA 

By M. L. BLAIR and W. E. SPANGLE, WILLIAM SPANGLE and AssociATES 

ABSTRACT 

Earthquakes are inevitable, but their damaging effects can be 

greatly reduced. Land-use planning and management based on maps 

showing hazards and seismic zones can be particularly effective in 

reducing loss of life, as well as injury and property damage from 

earthquakes. 

Many Federal, State, and areawide programs encourage and support city and county actions to reduce seismic risk. The Federal government provides funds for seismic research, directs emergency preparedness activities, provides disaster relief, considers seismic 

hazards in program administration, and subsidizes insurance in 

tsunamiprone areas. Among the States, California's program for reducing seismic risk is the most comprehensive. Through various 

State agencies, California provides data on seismic hazards, establishes structural standards, regulates construction and operation of 

certain critical facilities, maintains an emergency preparedness 

plan, and requires cities and counties to prepare seismic safety plans. 

Although areawide agencies can reduce seismic risk in many ways, 

those in the San Francisco Bay region do so primarily by establishing 

procedures and criteria for project review to ensure that seismic 

hazards are considered. 

Effective local planning to reduce seismic risk is based on an 

evaluation of the nature and degree of risk-risk being defined as a 

function of the nature, severity, and frequency of seismic hazards 

and of the exposures of persons and property to those hazards. Assessing risk starts with recognizing the overall seismicity of the area 

and identifying the potential for ground shaking, landsliding, 

liquefaction, surface rupture, and flooding. A "design earthquake" is 

then selected as a basis for predicting, as precisely as possible, the 

location and severity of the various seismic effects. Cultural features 

are inventoried and mapped, special attention being given to 

facilities such as large dams whose failure could be catastrophic, 

facilities necessary for disaster response, and high-occupancy structures. Using this information, the degree of seismic risk can be established and expressed in terms of potential dollar loss, deaths, and 

injuries, population exposure, relative risk, or scenarios describing 

the probable effects of a design earthquake. Plans and regulations 

can then be formulated to reduce risk to a level the public is willing 

to accept. 

Local land-use planning and regulation can be used to reduce 

seismic risk, particularly in undeveloped or sparsely developed 

areas. Many cities and counties in California are successfully integrating plans to reduce seismic risk into their general planning programs. Methods include considering seismic hazards in analyzing 

land capability, developing land-use policy and regulations consistent with seismic risk, and establishing project review procedures to 

ensure consideration of seismic hazards in land-use decisions and 

land-development practices. Plans and programs to reduce seismic 

risk can also be formulated to respond to scientifically valid earthquake predictions and to direct postearthquake reconstruction. 

INTRODUCTION 

Then the thunder crashed and rolled, and lightning flashed; and 

there was a great earthquake of a magnitude unprecedented in 

human history. 

The great city of "Babylon" split into three sections, and cities 

around the world fell in heaps of rubble*** 

And islands vanished and mountains flattened out*** 

(Revelations 16: H~-20) 

Earthquakes have inspired fear and awe throughout 

man's time on earth. Often attributed to the nwrath of 

God" or vengeful spirits, earthquakes dramatically 

confront man with the insignificance of his power before the forces of nature. As Charles Darwin (as quoted 

in Elders, 197 4, p. 20) observed in 1835 when the 

ground convulsed beneath him during an earthquake 

in Chile: 

A bad earthquake at once destroys our oldest associations; the 

earth, the very emblem of solidity, has moved beneath our feet like a 

thin crust over a fluid;***One second of time has created in 

the mind a strange idea of insecurity, which hours of 

reflection would not have produced. 

Indeed, individuals are virtually helpless during the 

course of an earthquake. They must nride it out" wherever they happen to be at the time the earthquake 

strikes. But helplessness is. confined to those seconds 

when the ground is shaking; man has the knowledge 

and ability to avert many of the damaging effects of 

earthquakes. 

The basic premise of this report is that actions can 

and should be taken to lessen the impact of earthquakes in seismically active areas. Based on geologic 

and seismologic data, land uses and design and occupancy of structures can be adjusted to reduce 

significantly the loss of life, injury, and damage from 

earthquakes. Failure to make these adjustments will 

result in needlessly high costs in human suffering and 

Bl 
B2 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

property damage when the as yet unpredictable, but 

inevitable, earthquakes occur. 

PURPOSE AND SCOPE 

A major aim of the San Francisco Bay Region Environment and Resources Planning Study has been to 

gather information on the complex effects of earthquakes and to present such information in a form directly applicable to land-use planning and decisionmaking. A report edited by Borcherdt (1975) presents 

the earth-science phase of this study. It consists of a 

series of scientific articles defining earthquake hazards 

and methods of predicting their relative severity 

throughout a planning area. 

Seismic zones delineating the different effects of 

earthquakes, ranked in terms of relative severity, are 

identified in the Borcherdt report. Such seismic zonation provides .the geological and seismological basis for 

relating land-use plans and regulations, structural design criteria, construction practices, and emergency response plans to recognized earthquake hazards. 

A map or set of maps may be prepared showing zones 

having a similar degree of hazard. In conjunction with 

maps of cultural features, these hazard maps indicate 

areas where the same kinds of risk-reduction methods 

may be successfully applied. The seismic zones indicate 

the wide geographic variation in the effects and local 

geologic conditions. If areas subject to severe effects 

can be accurately identified, land use and development 

decisions can reflect potential risk; and significant loss 

of life, injury, and damage can be a voided. 

This report is a companion volume to the Borcherdt 

report (Professional Paper 941-A) and shows how information on seismic hazards can be effectively incorporated into land-use planning and decisionmaking to 

reduce seismic risk. The first report (Professional 

Paper 941-A), was written by earth scientists to present the state-of-the-art for seismic zonation of the San 

Francisco Bay region. This report (Professional Paper 

941-B), is written by planners, and it outlines possible 

applications of seismic hazard information with emphasis on land-use planning and regulation. 

Success in increasing seismic safety requires an interdisciplinary effort including earth scientists, 

engineers, and planners. To be useful, scientific and 

engineering data must be translated to a form understandable to planners and public policy makers. In 

some cases, the engineer can serve as an intermediary 

between scientist and planner. Engineering interpretations relate seismic information directly to issues of 

project feasibility, structural design, and cost; thus 

they provide an important input to planning decisions. 

However, in dealing with broader relationships of 

land-use patterns and intensities of seismic hazards, 

the planner must draw more directly from basic 

geologic and seismologic information. A communication bridge between scientist and planner must be established. This report is an attempt to establish such a 

bridge. In this report, the seismologic information 

needed by planners is summarized as simply as possible consistent with accuracy. Although written by 

planners, the report was carefully reviewed by earth 

scientists at the U.S. Geological Survey, ensuring that 

the geologic information is presented and interpreted 

correctly. 

Seismic hazards are briefly defined to provide the background for a discussion of ways of improving seismic 

safety. Federal, State, and areawide roles in response to 

seismic hazards are summarized, and examples are given 

of specific State and regional programs drawn from 

California and the San Francisco Bay region. 

A systematic approach to assessing seismic risk is 

set forth, and examples of various techniques are 

summarized. Typical planning responses of local government to seismic risk are shown to relate to the nature of the hazard and the level of development in 

areas identified as hazardous. Examples of local planning actions are presented wherever possible. 

The geologic information upon which this report is 

based pertains to the San Francisco Bay region, thus, 

most of the planning examples are drawn from this 

area. The methods of developing and interpreting information and the ways to improve seismic safety used 

by bay region governments are, however, directly applicable to other areas of the country with similar 

seismic hazards and governmental organizations. 

Planners and decisionmakers in most earthquakeprone areas of the United States may find that this 

report provides a useful framework on which to base 

their ongoing planning activities. 

OVERVIEW OF SEISMIC HAZARDS 

Knowledge of the nature and cause of earthquakes 

and their effects has increased tremendously in the last 

decade. Seismology has both contributed to, and benefited from, a revolutionary new concept-the theory of 

plate tectonics. According to this theory, the earth's 

lithosphere or outer shell is formed of a mosaic of a 

dozen or more rigid plates in constant motion relative 

to each other (Dewey, 1972, p. 56). Most of the world's 

large-scale active geologic processes-vulcanism, 

mountain building, formation of oceanic trenches, and 

earthquakes-are concentrated at or near plate 

boundaries (Press, 1975, p. 15). 

Records of seismic activity have been important in 

the development of the plate tectonic theory. As shown 

in figure 1, recorded earthquake epicenters, which tend 
... ~ .. 

.. 

EURASIAN PLATE 

,,., "!::~ 

·"~ ~ 

.j!· 

,; 

,, 

PACIFIC PLATE 

~ 

~ 

SOUTH 

AMERICAN 

PLATE 

..---

FIGURE 1.-Plate boundaries and epicenters of 30,000 earthquakes recorded between 1961 and 1967. The numbers mark an example of each 

boundary: 1 is a midoceanic ridge axis boundary forming the East Pacific Rise; 2 is a transform boundary defined by the San Andreas fault; and 3 

is a subduction zone along the west coast of South America. The arrows show direction of movement (Press, 1975, p. 16). 

r:n 

tr.l 

~ -l.l 

r:n 

~ ~ 

> z 

t:l 

~ t:l 

C:: 

r:n 

tr.l 

~ 

~ 

z 

Q 

to 

w 
B4 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

to cluster along plate boundaries, have been used to 

locate these boundaries. The concept of plate tectonics 

in turn provides a long-missing explanation of the underlying cause of earthquakes occurring along plate 

boundaries according to Press, (1975, p. 15), 

stresses build up where the relative motion of the plates is resisted 

by frictional forces. When the stress increases to the point where it 

exceeds the strength of the rocks of the lithosphere or overcomes the 

frictional forces at the boundary of a plate, fracturing occurs and an 

earthquake results. 

Plate boundaries are of three types, each with distinctive geologic and seismologic characteristics 

(Dewey, 1972, p. 57-59). 

(1). Mid-oceanic ridge axes where plate boundaries 

are diverging. In these areas hot basaltic material is 

welling up from the earth's interior and cooling to form 

new crustal material. Here the focus of earthquakes is 

usually shallow (less than 70 kilometers, 43 miles). 

(2). Transforms where the plates are sliding past 

each other. Lithospheric materials are not created or 

consumed along these boundaries; volcanic activity is 

limited, and earthquakes are shallow. 

(3). Subduction zones where plates are converging, 

one plate diving under the other to be eventually consumed in the asthenosphere-the molten or semimolten layer of the earth's mantle beneath the solid lithosphere. This zone is associated with deep oceanic 

trenches and volcanic island arcs having shallow, intermediate (70-300 km, 43-186 mi), and deep (300-

700 km, 160-434 mi) earthquakes; and with continental areas having primarily shallow earthquakes and 

high mountain ranges created by the compressive force 

of the converging plates. 

Examples of each type of plate boundary are shown 

by the numbers 1, 2, and 3 in figure 1. The San Andreas 

fault system marks the boundary between the Pacific 

and North American plates. The boundary is a 

transform-the plates move past each other. The portion of California, including Los Angeles and part of 

the bay region west of the San Andreas fault is on the 

Pacific Plate which is moving northwest on an average 

of a few centimeters a year (fig. 2). At this rate it would 

take Los Angeles about 10 million years to come 

abreast of San Francisco Bay (Yanev, 1974, p. 26). 

Plate movement is not uniform, however; portions of 

the plate boundary including that passing through the 

bay region have been locked for many years. It is 

considered highly probable that these locked portions 

will eventually give, resulting in earthquakes. 

The San Andreas fault system is part of the 

Circum-Pacific Earthquake Belt, sometimes called the 

"ring of fire". This belt, shown in figure 3, outlining the 

Pacific, Cocos, and Nascan plates, is where intense volcanic and seismic activity takes place. Nearly 80 percent of the world's earthquakes occur along this belt, 

0 

I 

0 

-------, 

I 

I 

Cape Mendocino 

1906 break 

.,... 

0 

100 

I I I 

0 

100 200 

200 Ml LES 

I I 

300 KILOMETERS 

N 

FIGURE 2.- Approximate location of San Andreas fault in 

California. 

accounting for the relatively high seismicity of the 

west coast of North America. 

Not all earthquakes can presently be explained by 

plate movements. Midplate earthquakes, hundreds of 

miles from known plate boundaries, do occur, and scientists are not yet agreed on their causes. In North 

America the most widely felt earthquakes ever recorded were centered in New Madrid, Missouri. The 

largest of these shocks was felt nearly everywhere in 

the United States east of the Rocky Mountains (U.S. 

Geological Survey, 1971, p. 4). 

Figure 4 shows a map of relative seismicity in the 

United States by S. T. Algermissen (1969). This seismic risk map of the United States is based on the 

known distribution of damage from earthquakes. It has 

been incorporated into the 1973 Uniform Building 

Code as the basis for recommending differing structural standards for risk zones 1, 2, and 3. The map 

indicates that most of the country can expect at least 

minor damage from earthquakes. 

SEISMIC HAZARDS DEFINED 

An understanding of plate tectonics is useful in explaining why and where earthquakes are likely to occur. And information based on experience from past 

earthquakes, as summarized in the seismic risk zone 

map of the United States, gives an overall picture of 

the relative seismicity of different parts of the country. 
SEISMIC SAFETY AND LAND-USE PLANNING B5 

\ 

\ 

\ 

Hawaiian Is. 

New Hebndes 

. ·~ .. r !i)o Sa I ·F··· ···

1 • 0 moa s. 

IJI S •• o 

~;w i 0 Tonga Is. 

Caledonia • oj 

. I}) 

~ .. ;.0 

.. /-ew Zealand 

SEISMIC BELTS 

- Belts of shallow-

-,~ \ 

focus earthquakes 

o o o o Intermediate-focus 

earthquakes 

' ....... _ - ••• • Deep-focus earthquakes 

__ ___; 

/ 

/ 

FIGURE 3.-The circum-Pacific Earthquake Belt showing shallow, intermediate, and deep focus earthquakes (figure adapted from 

Strahler, 1971, p. 443). 

However, this is only the tip of the iceberg in defining 

earthquake hazards. 

An earthquake unleashes a complex chain of natural 

events often catastrophic, and difficult to predict. The 

major geologic effects of earthquakes include surface 

faulting (ground rupture), ground shaking, ground 

failure, and flooding from tsunamis and seiches. These 

earthquake hazards are defined below. 

SURFACE FAULTING 

Faults are "planes or surfaces in earth materials 

along which failure has occurred and materials on opposite sides have moved relative to one another in response to the accumulation of stress" (Nichols and 

Buchanan-Banks, 197 4, p. 2). Fault movement does not 

always extend to the surface of the earth, but when it 
us• tos• too" 95• 

r·--r-\-- _;1\-_,__""-._ 0 1 • 

I -----~ 

''-...._ 

"-·f-1 I 

SEISMIC RISK MAP OF THE UNITED-~TATE~-- ZONE 0- No damage. 

ZONE I - Minor damage: distant earthquakes may cause damage 

to structures with fundamental periods greater than 

1.0 seconds;_corresponds to intensities V and VI 

n•l- of the M.M. • Scale. 

ZONE 2- Moderate damage; corresponds to intensity VII of the M.M.• Scale. 

ZONE 3- Major damage; corresponds to intensity VIII and higher of the M.M. • Scale. 

This map is based on the known distribution of damaging earthquakes and ~he 

M. M. • inlenStt.es associated with these earthquakes: evodence of strain release; 

and ~onsideration of ma1or geologic structures and provinces believed to be 

assocoated with earthquake activity. The probable frequency of occurrence of 

damagmg earthquakes in each zone was not considered in assigning ratongs to 

the varlous zones. 

*Modified M4!rcalli Intensity Scale of 1931. 

us• 110" 105° 100" 95° 

90" 

0 100 400 000 

90" as• 

FIGURE 4.-Seismic risk zones of the United States based on damages associated with historic earthquakes (Algennissen, 1969). 

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SEISMIC SAFETY AND LAND-USE PLANNING B7 

does, surface movement often produces a line or narrow 

zone of visible features such as scarps, grabens 

(trenches), fractures, and "mole tracks" or pressure 

ridges. The vertical or horizontal displacement that accompanies surface faulting can destroy structures located astride the fault. 

Faults are often classified according to the direction 

of movement and whether movement is predominantly 

horizontal or vertical. Figure 5 shows the four types of 

fault movement. The San Andreas fault is a rightlateral strike-slip fault. 

GROUND SHAKING 

Ground shaking usually causes the most widespread 

damage (Nichols and Buchanan-Banks, 1974). Ground 

shaking contributes to losses not only directly through 

vibratory damage to manmade structures, but also indirectly by triggering secondary effects such as landslides or other kinds of ground failure. 

GROUND FAILURE 

Most ground failure from earthquake shaking results in displacement in the ground surface due to loss 

of strength of underlying materials. Earthquake shaking may jar loose basically unstable hillside materials. 

Other kinds of ground failure also accompany earthquakes. The most common result from liquefaction-a 

process by which saturated, clay-free sands or silts are 

transformed from a solid to a liquid state. Ground 

failure occurs when the liquefied material is not confined and flows out toward a "free face" . Several forms 

of ground failure may be caused by liquefaction. In the 

San Francisco Bay region, laterally spreading landslides are likely to occur (Youd and others, 1975). Lateral spreading is "movement of a soil mass down a mild 

slope with resulting cracks, fissures, and differential 

settlements within and near the margins of the slide 

mass." (Borcherdt, 1975, p. A94). Any type of ground 

failure can cause severe damage to manmade structures. 

TSUNAMIS AND SEICHES 

Tsunamis are large ocean waves generated by offset 

of the sea floor caused by faulting or large submarine 

landslides. Huge waves, which can travel thousands of 

kilometers at velocities of 500-650 km/hr (300-400 

mi/hr), can be generated by such undersea movement. 

Far at sea, these waves are low and kilometers long; as 

they approach shore, they begin to drag on the bottom, 

slow down, and pile up, sometimes reaching heights of 

15m (50 ft) or more. The effects of tsunamis are in part 

determined by the configuration of the local shoreline 

and the sea bottom (Nichols and Buchanan-Banks, 

1974). 

Right-lateral 

strike slip 

Dip slip 

(reverse or thrust) 

Left -I ate r a I 

strike slip 

Dip slip 

(normal) 

FIGURE 5.-Four types offault movement, characterized by the sense 

of movement relative to the fault and to the horiwntaL Most faults 

in the bay region show right-lateral strike slip, the characteristic 

sense of movement for the San Andreas fault. Movement on 

oblique-slip faults has both strike- and dip-slip components (Borcherdt, 1975, p. A12). 

Seismic seiches, or earthquake-generated standing 

waves, occur within enclosed or restricted bodies of 

water (lakes, reservoirs, bays, and rivers). They are 

periodic oscillations ("sloshing") of water in such 

bodies. Seiches may raise and lower a water surface by 

anywhere from a few centimeters to many meters, 

causing severe flooding and damage from wave action. 

Catastrophic flooding can also result during an earthquake from dam failure or from large-scale landsliding 

into a reservoir or bay. 

EARTHQUAKE DAMAGE 

Singly or in combination, the various seismic 

hazards can raise havoc with the natural and manmade environment. In a matter of seconds, a hillside 

may be sheared in two, whole towns may be leveled, 

and the lifelines of communities may be ruthlessly disrupted. 

The structures destroyed and damaged by an earthquake provide scientists and engineers with examples for the study of seismic hazards and their effects 

on different kinds of structures and facilities. Most of 

our information concerning the damaging effects of 

earthquakes comes from detailed studies carried out in 

the aftermath of an earthquake. 

The moderate San Fernando earthquake (6.4 on the 

Richter scale) has proved especially informative because the development patterns and population density 

in the damaged area are characteristic of suburban 

areas throughout California and other western states. 
B8 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

Buildings, other structures, and public utilities varied 

in age and structural design and were built or installed 

under a variety of code regulations and standards. 

Therefore, the observed effects of this earthquake 

helped to determine the kind of damage that can be 

expected from moderate earthquakes in many areas in 

the western United States. 

The San Fernando earthquake was caused by movement along the San Fernando fault, a north-dipping 

thrust fault (fig. 6). At the surface, fault movement was 

as much as 1.8 meters (6 feet) horizontally and 1.8 

meters (6 feet) vertically. The earthquake triggered 

strong ground shaking, and ground failure (cracking, 

liquefaction, and landslides), causing 58 deaths and 

over $500,000,000 in structural damage (California 

State Legislature, Joint Committee on Seismic Safety, 

1974, p. 215). The loss of life would have been considerably greater if the earthquake, which occurred at 

6:01 a.m., had occurred later in the day when more cars 

were on the road, and more people were walking along 

the streets. 

Study of the San Fernando earthquake showed that 

earthquake forces in the most heavily shaken area of 

the San Fernando Valley far exceeded those used as a 

basis for building-code structural standards, and were 

considerably beyond those anticipated by many engineers for a moderate earthquake (Steinbrugge and 

others, 1971). In areas experiencing the strongest 

ground shaking, many modern, supposedly earthquake-resistant structures collapsed or were severely 

damaged. In other areas damage was within expected 

limits. 

The major effects of the San Fernando earthquake 

are summarized below. 

DAMAGE TO BUILDINGS 

Woodframe dwellings meeting current building-code 

standards performed relatively well (fig. 7 A). Onestory dwellings performed better than two-story 

dwellings. Mobile homes were poorly braced and consequently were damaged (fig. 7B); however, total losses 

were extremely rare (Steinbrugge and others, 1971, p. 

VII). 

Unreinforced masonry buildings performed poorly, 

not only in the area of strong shaking, but also in 

areas, including downtown Los Angeles, 24-40 

kilometers (15- 25 mi) from the epicenter (California 

State Legislature, Joint Committee on Seismic Safety, 

1974, p. 215). 

In the area hardest hit, light industrial buildings 

with wood roofs supported by "tilt-up" reinforced concrete or by reinforced unit masonry exterior walls 

(brick or hollow concrete block) suffered damage averaging nearly 18 percent of building value (fig. 7C). 

These buildings sustained an average loss of less than 

3 percent for the San Fernando Valley as a whole 

(Steinbrugge and others, 1971, p. VII). 

The ability of high-rise buildings to withstand 

ground shaking was only partially tested, because the 

nearest ones were 24--40 km (15-25 mi) from the 

earthquake epicenter. In general, modern steelframe 

and reinforced-concrete highrise buildings performed 

well structurally. However, nonstructural damage to 

interior partitions, windows, ceilings and light fixtures, elevators, and air conditioning and emergency 

power equipment was considerable. In downtown Los 

Angeles (about 24 km (15 mi) from the San Fernando 

Valley) most highrise buildings, built before more 

stringent structural standards were enacted after the 

1933 Long Beach earthquake (M6.3) did not perform 

well; losses ranged from 5 to 26 percent of market 

value (Steinbrugge and others, 1971). 

In the area of strong ground shaking, four major 

hospitals were damaged, did not remain functional, 

and were evacuated (fig. 8A and B). One of these hospitals was a pre-1933 structure, but the other three were 

built since 1960 in accordance with modern codes 

(California State Legislature, Joint Committe!'l on 

Seismic Safety, 1974, p. 216). 

Schools built according to provisions of the Field Act 

(see section on "Structural Standards") fared well, in 

contrast to schools built prior to 1933 and not modified 

to meet the earthquake provisions of that act. 

DAMAGE TO DAMS 

Two hydraulic-fill earthen dams in the area of strong 

shaking were damaged. Damage to the lower Van 

Norman Dam (fig. 9) reduced effective dam height by 

about 9 m (30 ft). Fortunately, the water level was 

about 101!2 m (35 ft) below the crest, and massive failure of the dam was avoided. Had the water level been 

higher, an area inhabited by 80,000 people would have 

FIGURE 6.-Faults in southern California and epicenters associated li> 

with San Fernando earthquake. A, Major historically and geologically recent active faults in southern California (U.S. Geological 

Survey and U.S. National Oceanic and Atmospheric Administration, 1971, p. 7). B, Epicenters of the main shock and aftershocks of 

magnitude 3.0 and greater of the San Fernando earthquake, February 9 through March 1, 1971. The earthquakes were located 

along a north-dipping thrust fault and are shallow toward the 

south edge of the map and deep toward the north (U.S. Geological 

Survey and U.S. National Oceanic and Atmospheric Administration, 1971, p. 17). 
N 

1 

EXPLANATION 

Historically and recently 

active faults 

Possible extensions of historically and 

recently active faults, and related 

inactive faults 

Inferred extensions of active or related 

inactive faults beneath surficial deposits 

or the sea floor 

Fault segments with surface or postulated 

submarine slip during historical earthquakes or with continuous or intermittent 

aseismic fault slippage 

0 

SEISMIC SAFETY AND LAND-USE PLANNING 

120' 118' 

A 

Jl" -~ 3 .0-3.4 -., 

I • 'l' 3.5-3.9 ~ • 4.0-4.4 JO km • 4.5 -5.1 

Main Shock 

B 

J A 

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v 

s 

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E 

E 

B9 

0 50 100MILES 

UNDERWATER CONTOURS IN FEET 

' ' 

R 

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T 

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\ 14' 

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r 

I 

\ 
B10 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

FIGURE 7.-Damage to small buildings caused by the San Fernando earthquake. A. Almetz Street, between Veterans Administration and Olive View (U.S. Geological Survey and U.S. National Oceanic and Atmospheric Administration, 1971, p. 214). 

been inundated (California State Legislature, Joint 

Committee on Seismic Safety, 1974, p. 216). Other 

dams constructed by hydraulic-fill procedures are located throughout California and in other states where 

earthquakes are likely to occur. Those in California 

have been reexamined by the California Division of 

Dam Safety since the San Fernando earthquake, and 

some have been modified or have had allowable reservoir water levels reduced. 

DAMAGE T O UTILITIES 

Within the area of strong shaking, utilities were severely damaged. Displacement along the San Fernando fault cut or damaged underground water, sewer, 

and gas pipes. Damage also occurred from ground 

shaking, landslides, and liquefaction (California Legislature Joint Committee on Seismic Safety, 1974, p. 

216). In addition, electric substations suffered heavy 

damage (fig. 10). Communication systems were damaged, hindering effective response by fire trucks and 

other emergency services. The telephone system was 

severely overloaded, and service was disrupted when 

equipment toppled in the central telephone office in 

Sylmar. Automatic alarm systems suffered from unreadable signals, equipment overload, destroyed lines, 

and insufficient staff to meet the demands of the postearthquake situation (Steinbrugge and others, 1971, p. 

VIII). 

DAMAGE TO TRANSPORTATION SYSTEMS 

The freeway system in the area of strong ground 

shaking was severely damaged. Forty-two bridges or 

overpasses were damaged and five collapsed. The interchange between the Golden State and Foothill freeways collapsed completely, killing two persons (fig. 11). 

Damage to the highway and road systems totaled over 

$36 million (U.S. Geological Survey and U.S. National 

Oceanic and Atmospheric Administration, 1971, p. 5). 

FIRE 

Lack of strong winds and combustible materials 

helped to keep the postearthquake fires under control. 

Firemen quelled 109 earthquake-related fires. Losses 

from fire exceeded $1 million (Steinbrugge and others, 

1971, p. VIII). 

The San Fernando earthquake was a devastating 

experience for the people of southern California. 

Realizing that a higher magnitude earthquake or one 

on a fault closer to a major urban area would have had 

even more catastrophic effects, the State Legislature 

and many State and local agencies began to review 

their actions and operations in terms of seismic risk. 
SEISMIC SAFETY AND LAND-USE PLANNING Bll 

FIGURE 7 (Continued).- B, Mobile home shifted off its foundations (U.S. Geological Survey and U.S. National Oceanic and Atmospheric 

Administration, 1971, p. 219). 

Many of the actions undertaken in California to increase seismic safety stem from the sobering experience of the San Fernando earthquake. 

EARTHQUAKE MAGNITUDE AND INTENSITY 

The severity of an earthquake can be expressed in 

terms of magnitude or intensity. Magnitude is an objective measure of the size or energy release of an 

earthquake at its source. The magnitude rating of an 

earthquake is based on seismic wave amplitude recorded by a seismograph, of specified type, calculated to 

be 100 km (62 mi) from the epicenter. On the Richter 

scale, magnitude is expressed as Arabic whole numbers and decimals. The scale is logarithmic; the wave 

amplitude of each number on the scale is 10 times 

greater than that of the previous whole number. Thus 

the wave amplitude of an earthquake of Richter magnitude 4 is 10 times greater than that of a Richter 

magnitude 3. 

Energy release from an earthquake can be calculated from the measured wave amplitude. As the scale 

is structured, energy release, or earthquake size, increases approximately 32 times for each larger whole 

FIGURE 7 (Continued);-C, Tilt-up wall panel failed, bringing down 

portions of the roof and mezzanine floor, Arroyo light industrial 

tract (U.S. Geological Survey and U.S. National Oceanic and Atmospheric Administration, 1971, p. 202). 

number on the scale. Thus the amount of energy released from a magnitude 4 earthquake is 32 times 

greater than from a magnitude 3. 
B12 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

~ r.-- ::::::--.. ~ ... ~ .... • ..... · ' 

FIGURE 8.-Damage to hospitals caused by the San Femando earthquake. A, Southwest comer of Medical Treatment Building of Olive View 

Hospital, completed in 1970. South stair tower overtumed and collapsed on one-story portion, roof at stair tower is center right (Steinbrugge and others, 1971, p. 45). 

The logarithmic nature of the Richter scale is often 

misunderstood; consequently, the actual difference in 

size or energy release (and potential for damage) between earthquakes of different magnitudes is often 

underestimated. Table 1 shows the relationship between differences in magnitude and differences in 

earthquake size. 

The Richter scale expresses relative values. The actual amount of energy released from a large magnitude 

earthquake is dramatically higher than from a 

moderate earthquake. Figure 12 shows the relationship between magnitude and energy measured in tons 

of TNT. 

The Richter scale is open ended with no upper limit. 

However, the physical strength of the earth's crust 

probably defines the upper limit of the scale. Even the 

most durable geologic formations are considered likely 

to break before strain builds to the point that a 9 magnitude earthquake could occur. The largest recorded 

earthquake was magnitude 8.9. 

Intensity ratings are a totally different way of expressing earthquake severity. Intensity is a subjective 

measure of the observed effects of an earthquake. Although there are several intensity scales, the Modified 

Mercalli intensity scale, in use since 1931, is the most 

common. On this scale, intensity is expressed in 

Roman numerals from I to XII. Table 2 outlines the 

Modified Mercalli intensity scale. On this scale intensities are based on human reactions, the nature of the 

structural damage, and the geologic effects. At any 

given location, intensity from an earthquake varies 

with magnitude, distance from the fault, and local 

geologic conditions. 

Figure 13 shows the intensity pattern of the 1971 

San Fernando earthquake. Intensity was highest (XI) 

near the epicenter, decreasing gradually with distance 

from the fault. However, the width and shape of the 

intensity bands reflect geologic conditions. Because of 

this dependence of intensity on local geology, earthquakes of the same magnitude may produce quite dif-
SEISMIC SAFETY AND LAND-USE PLANNING 

FIGURE 8 (Continued).- B, Air view of Veterans Administration Hospital. Collapsed portion constructed in 1926 

before earthquake resistive design was required (Steinbrugge and others, 1971, p. 55). 

B13 
Bl4 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

FIGURE 9.-Slide damage to lower Van Norman Dam (California State Legislature, Joint Committee on Seismic Safety, 1972, p. 29). 

ferent intensities and intensity patterns. Magnitude 

and intensity are measures of different aspects of an 

earthquake and are related to each other only in the 

general sense that maximum intensities tend to increase with magnitude. 

PROFESSIONS INVOLVED IN SEISMIC RISK REDUCTION 

Reducing seismic risk through land-use planning entails a coordinated effort on the part of professionals 

from many fields. Land-use planners, seismologists, 

geologists, engineering geologists, civil engineers, soils 

engineers, structural engineers, architects, and building inspectors all have direct or indirect roles to play. 

In addition, the contributions of lawyers, public administrators, economists, and other social scientists can be 

major. The overlap in responsibility and expertise 

among these professions complicates assigning a precisely defined role to each . 

In practice, the role of each professional is tailored to 

the strengths of the individuals involved and the na-
SEISMIC SAFETY AND LAND-USE PLANNING B15 

FIGURE 10.-Sylmar Converter Station-collapsed condenser banks (U.S. Geological Survey and U.S. National Oceanic and Atmospheric 

Administration, 1971, p. 248). 

FIGURE 11.- Collapses at interchange between Golden State and Foothill freeways (Steinbrugge and others, 1971, p. 8). 
B16 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

TABLE I.- Magnitude/size comparisons between any two 

earthquakes 

[K.R. Lajoie, written commun., 1976] 

If the difference in magnitude Then the difference in size 

between two earthquakes is . between the two earthquakes is . 

Difference in Magnitude Difference in Energy (Size) ! -:_::: ~----:~~ ::::~:- _:: ::f: f1:;,, ., 0.9 -------------------------------------- 22.4 

0.8 -------------------------------------- 16.0 

0.7 -------------------------------------- 11.2 

0.6 ---------------------------------------- 8.0 

0.5 ---------------------------------------- 5.6 

0.4 ---------------------------------------- 4.0 

0.3 ---------------------------------------- 2.8 

0.2 ---------------------------------------- 2.0 

0.1 ---------------------------------------- 1.4 

Example 1: An M7.5 is 1.4 times larger than an M7.4 

Example 2: An M8.0 is 5.6 times larger than an M7.5 

125 ~ [ 8.9 LARGEST ON RECORD 

120 

==~====~~~==~== i= 50 

z 

1-

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0 

Ul 

~40 

1-

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0 

...J 

...JJ() 

~ 

1-

z 

w 

...J 

~ 20 

:::> 

0 

w 

5 10 

a: 

w 

z 

w 

1952 KERN COUNTY, CA. 

1940 EL CENTRO 

1959 HEBGEN LAK 

HIROSHIMA 

ATOMIC BOM 

1957 

SAN FRANCISC 

AVERAGE 

TORNADO 

1964 ALASKA 

1906 SAN 

FRANCISCO 

0 2 3 4 5 6 7 8 9 10 

MAGNITUDE 

FIGURE 12.-A dramatic demonstration of the vast differences in 

force or energy release between moderate earthquakes, such as 

San Fernando, and great earthquakes, such as San Francisco in 

1906 and Alaska in 1964. Note the incredible span between these 

latter great earthquakes and the magnitude 8.9 shocks, which 

are the largest on record (Yanev, 1974, p. 41). 

ture of the particular problems to be addressed. A core 

of professional competence usually defines each professional's primary responsibility; but in a well-functioning interdisciplinary team each professional 

ventures to the limits of his area of competence fully 

recognizing the probability of overlap with other 

I. 

II. 

III. 

IV. 

TABLE 2.-Modified Mercalli intensity scale 

[1956 version, by Richter, as reported in Nichols and Buchanan-Banks, 1974] 

Not felt 

Felt by persons at rest, on upper floors, or favorably placed. Felt indoors. Hangin~ objects swing. Vibration like passing of 

light trucks. Duratwn estimated. May not be recognized as an earthquake. 

Hanging objects swing. Vibration like passing of heavy trucks; or sensation of a jolt like a heavy ball striking the walls. 

Standing automobiles rock. Windows, dishes, doors rattle. 

Wooden walls and frame may creak. 

V. Felt outdoors; direction estimated. Sleepers wakened. Liquids 

disturbed, some spilled. Small unstable objects displaced or upset. Doors swing. Shutters, pictures move. Pendulum 

clocks stop, start, change rate. 

Felt by all. Many frightened and run outdoors. Persons walk 

unsteadily. Windows, dishes, glassware broken. 

VI. 

VII. 

VIII. 

IX. 

Knickknacks, books, etc., off shelves. Pictures off walls. 

Furniture moved or overturned. Weak plaster and masonry 

D1 cracked. 

Difficult to stand. Noticed by drivers of automobiles. Hanging 

objects quiver. Furniture broken. Weak chimneys broken at 

roof line. Damage to masonry D, including cracks; fall of 

plaster, loose bricks, stones, tiles, and unbraced parapets. 

Small slides and caving in along sand or gravel banks. 

Large bells ring. Steering of automobiles affected. Damage to masonry C; partial collapse. Some damage to masonry B; none to masonry 

A. Fall of stucco and some masonry walls. Twisting, fall of 

chimneys, factory stacks, monuments, towers, elevated 

tanks. Frame houses moved on foundations if not bolted 

down; loose panel walls thrown out. Decayed piling broken 

off. Branches broken from trees. Changes in flow or temperature of springs and wells. Cracks in wet ground and on steep slopes. 

General panic. Masonry D destroyed; masonry C heavily damaged, sometimes with complete collapse; masonry B seriously damaged. General damage to foundations. Frame 

structures, if not bolted, shifted off foundations. Frames 

racked. Serious damage to reservoirs. Underground pipes 

broken. Conspicuous cracks in ground and liquefaction. X. Most masonry and frame structures destroyed with their 

foundations. Some well built wooden structures and bridges 

destroyed. Serious damage to dams, dikes, embankments. 

Large landslides. Water thrown on banks of canals, rivers, 

lakes, etc. Sand and mud shifted horizontally on beaches 

XI. 

XII. 

and flat land. Rails bent slightly. 

Rails bent greatly. Underground pipelines completely out of 

service. 

Damage nearly total. Large rock masses displaced. Lines of 

sight and level distorted. Objects thrown in the air. 

1Masonry A: Good workmanship and mortar, reinforced designed to resist lateral force. Masonry B: GO<Xi workmanship and mortar, reinforced. Masonry C: Good workmanship and mortar, unreinforced. Masonry D: Poor workmanship and mortar and weak materials, like adobe. 

professionals. The extent of direct involvement of specialized professionals in a particular plan to reduce 

seismic risk depends on the nature of the problems involved. In addition to the contributions of individual professionals, the professional societies make substantial 

contributions in examining the role of their members 

in reducing seismic risk and in supporting related research. Many of the professional societies also are examining ways to improve interdisciplinary collaboration. For example, ICED (lnterprofessional Council on 

Environmental Design), which includes engineers, architects, landscape architects, and planners, provides 

for voluntary development of interdisciplinary trust 

and understanding among these professionals. ICED 
38° 

37° 

36° 

35° 

34° 

33° 

32° 

2 • Tonapah 

NEVADA 

Beryl 

(!)3 

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113° 

UTAH 

,------------ -

Olancha 

CALIFORNIA 

"5 • 4• 

5 4 .5 5. •4 • 5 

• • ·5 5 4 .. ,4 v 

5. • Bakersfield 5 

5. 5, •• 5 

5 5, 5. ~ 5 Cantil 5, 4. 

' 5 Wheeler'5 •

5 5 , ,5 • Ridge 

5' 5• .5 5. 

5 

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Lucerne Valley 

5. 

,5 Big Bear City 

f .4 

:I 

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' ~ ' ' ~ 

""-,, !4 ( ~•Kingman "'-,{ • • ARIZONA 

Needles~~-

·l· .... 

, 

Desert r.: 

4, ,Center \ 

5 Blythe~~ ~4 

?·l 

FEBRUARY 9,1971,06:00:41.6 PST 

DOT WITHOUT NUMBER= NOT FELT / \""" • t ,2 I 

4. 4 4 5. ,3 ,2 Cale~/ L!.!-_::_----·i-T /.:Yuma 

--·5 < ................... 

.. 

0 25 50 75 100 125 150 MILES MEXICO 

FIGURE 13.-lntensity distribution of San Fernando earthquake of February 9, 1971 (Scott, 1973, p. 24). 

~ 

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ttl 

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B18 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

has issued a Guide to Interprofessional Collaboration 

in Environmental Design to aid its members who are 

engaged in interdisciplinary projects (ICED, 197 4). 

Land-use planning is a young profession and has 

roots in the Hdesign professions." Many land-use planners come into planning with design training or experience. Land-use planners, as a group, thus have had 

closer ties to engineering, architecture, and landscape 

architecture than to the earth sciences. However, in 

recent years because of increasing costs associated 

with failure to recognize geologic conditions in land 

development, planners and other design professionals 

are working more closely with earth scientists and are 

using more earth-science information. Earth scientists 

have become increasingly aware of the value of th~ir 

information and expertise to land-use planning. For 

example, AEG (Association of Engineering Geologists), 

through meetings, conferences, and publications has 

provided a substantial body of information that 

contributes to a better understanding of the role of the 

engineering geologist (and earth scientists generally) 

in relation to others concerned with reducing seismic 

risk. The publication of the proceedings from their annual meeting in 1973 includes papers by authors from 

many fields. 

The integration of physical and economic planning 

was addressed in a paper (Lakshmanan, 1972) commissioned by the U.N. Centre for Housing, Building and 

Planning. This paper provides useful insights to some 

of the problems planners face in working with professionals from other fields and gives some general guides 

to interprofessional collaboration. Lakshmanan (1972 

writes: 

It is fair to suggest, that in the current state-of-the-art, no such 

overarching framework for integrative economic and physical planning is available. The complexity of issues involved does not hold out 

much promise for such integrative models in the near future. 

A policy of learning by doing and willingness to adapt action with 

experience is warranted. This is a social learning process, learning 

while doing, with a willingness to experiment without excessive 

commitment. The approach is to focus an interdisciplinary team of 

physical and economic planning skills on a broad issue. This will 

require new planning roles and skills in social, economic, and physical design, a good appreciation of implementation processes, and 

knitting together the separate planning systems into a broader developmental planning system. 

LAND-USE PLANNING 

The land-use planner employed by a public agency 

has responsibility for developing plans, regulations, 

and procedures to guide and control the physical development pattern of a planning area. In responding to 

seismic risk through land-use planning, the planner 

can be a key coordinator drawing information from scientists and engineers, developing recommendations for 

public policy, interacting directly with elected decisionmakers and the public, and reviewing and 

evaluating land-development proposals. All of these 

functions require an ability to draw information from 

other disciplines, apply it appropriately to the planning problems at hand, and aid the earth scientists in 

communicating their scientific and technical knowledge to the public. In these tasks, the land-use planner 

will need to interact directly or indirectly with many 

professions. 

In a simple geologic setting with low-intensity development, a team consisting of a land-use planner and 

an engineering geologist frequently is adequate to address the problems related to seismic risk. As intensity 

of development increases or the seismic hazards become more complex, additional, more specialized professionals will need to be involved in addressing the 

problems. The scope and role of key professionals dealing directly with, or making direct application of, 

earth-science information in the discharge of their own 

professional responsibilities are discussed below. 

GEOLOGY, ENGINEERING GEOLOGY 

The geologist or engineering geologist frequently 

works directly with the land-use planner in simple 

situations and, for more complex problems, advises on 

programs, data requirements, and areas of expertise 

needed on the interdisciplinary team. Geologists. and 

engineering geologists have the same basic education 

and frequently have somewhat similar experience. Engineering geology is a specialization within geology, 

emphazing application of geologic information to engineering problems. Many other specializations are 

recognized within the geologic profession, and some are 

particularly important in analyzing specific seismic 

risk problems. 

The geologist, as researcher and interpreter, may be 

a primary member of a team working on seismic risk 

reduction through land-use planning, or he may provide the information used by others. In either case his 

work is basic in formulating public policy, developing 

land-use regulations and project review procedures, 

and reviewing development proposals. Some local 

agencies in California have added geologists to their 

staffs or contracted for geologic services as needed to 

assist the land-use planner in identifying and responding to geologic problems. 

The engineering geologist brings to the land-use 

planning team training and experience in the interpretation of geologic conditions affecting safety and economy of engineering works. He provides a bridge between earth-science researchers, land-use planners, 

engineers, and architects concerned with seismic 

safety policy and its application. 

Geologists are responsible for compiling maps of 
SEISMIC SAFETY AND LAND-USE PLANNING B19 

seismic hazard zones and collaborating with land-use 

planners and engineers in relating levels of risk exposure in hazard zones to land uses and critical facilities. 

They also collaborate in assessing probable damage to 

existing development in relation to seismic hazards. 

Information developed by seismologists dealing with 

the forces, lines of direction, periodicity, and other 

characteristics of earthquakes is fundamental to 

evaluation of the seriousness of seismic problems in 

any given area. This information is the starting point 

for land-use planning to reduce seismic risk, However, 

the planner, and others on the land-use planning team, 

usually depend on published information with 

geologist, engineering geologist, or structural engineer 

serving as interpreter. 

CIVIL ENGINEERING 

Civil engineering is a broad profession with several 

well-recognized areas of specialization, such as soils, 

structural, foundation, sanitary, and transportation. 

However, many civil engineers are engaged in general 

practice and have experience with a wide range of civil 

engineering problems. With this breadth of experience 

the civil engineer can, with collaboration from members of the planning team, provide perspective on the 

general nature of the engineering problems that are 

likely to result from an earthquake. The civil engineer 

can also help identify the engineering specialty needed 

to address seismic risk problems in particular situations. 

SOILS ENGINEERING 

Soils engineering, a branch of civil engineering, 

deals with the mechanical properties of soil and their 

effects on structures. The soils engineer draws information from soils science, geology, and hydrology and 

applies it to specific engineering problems. He carries 

out side investigations and recommends design and 

construction solutions to soil problems such as expansiveness, erodibility, and soil creep. Soils engineers 

prepare soils reports on specific development proposals; 

they may also be employed by public agencies to review 

and evaluate soils reports prepared by others. Soils engineers work closely with engineering geologists and 

civil, foundation, and structural engineers on particular design problems. The soils engineer can provide 

valuable assistance in identifying the limits particular 

soils may place on aseismic construction. 

STRUCTURAL ENGINEERING 

Structural engineering is another specialization 

within civil engineering. This branch of engineering is 

responsible for designing structures. The structural 

engineer collaborates in the design of major public 

facilities and assesses the need for, and costs of, structural measures to mitigate problems associated with 

particular sites. 

ARCHITECTURE 

Architecture is the science and art of designing 

buildings to blend form and function with safety. The 

architect charged with responsibility for preparing 

plans and specifications and providing on-site supervision during construction must work within design parameters recommended by engineering geologists and 

soils and structural engineers to produce a safe building. On any particular project, his interaction with the 

land-use planner is primarily as a member of a design 

team, frequently as the lead professional with responsibility for coordinating the team effort. 

BUILDING INSPECTION 

All the efforts of the professionals can be seriously 

compromised unless building inspection is carefully 

and expertly carried out. The building inspector is the 

public official responsible for seeing that building code 

provisions are adhered to. He reviews final construction plans and inspects construction to insure that local 

code requirements are met. In carrying out his duties, 

the building inspector, who often is not an engineer, 

relies on the engineering or public-works department 

personnel or consulting structural engineers for evaluation of seismic safety and other aspects. 

The land-use planner is often in the position of coordinating the work of these professionals to assist in 

developing plans and policies, framing regulations, establishing review procedures, and reviewing development proposals. Timing may be critical. Basic geologic 

information is needed early to identify and evaluate 

seismic hazards and to assist in developing appropriate 

policies and regulations. The contribution of the engineers is needed primarily at the time of project design and review. A structural engineer, however, is 

also needed during the formulation of seismic safety 

plans to give a general evaluation of the safety of existing and proposed structures in the area. 

GOVERNMENTAL FRAMEWORK FOR REDUCING 

SEISMIC RISK 

Governmental agencies at all levels have a part in 

reducing seismic risk. Under the present system, risk 

reduction through land-use planning is carried out 

primarily by local governments. However, the operations of local agencies affect and are affected by the 

planning and decisionmaking of government agencies 

at Federal, State, and regional levels. These government agencies often preempt or influence local de-
B20 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

cisionmaking by imposing requirements for funds, 

criteria for programs, shared responsibility for specific 

functions such as transportation, and regulations such 

as those concerning environmental quality or the content of local plans. 

To an increasing extent, local governments are dependent on Federal and State funds to carry out their 

responsibilities. This means that plans and programs 

developed at the local level are often framed with an 

eye not only to locally expressed objectives and concerns, but also to Federal and State funding requirements. Thus, individual governmental decisions become part of a network of decisions made by other 

agencies, at different jurisdictional levels over a period 

of time. Because of increasing political, economic, and 

legal interdependency, effective planning by local government often depends on complementary decisions of 

other local, Federal, State, and regional agencies. 

The following sections outline the major Federal, 

State, and regional programs and activities that provide the context for local seismic-safety planning in the 

San Francisco Bay region. Programs directly or indirectly influencing local land-use planning are emphasized. The description of State programs is limited 

to California because California has gone further than 

other states in enacting programs to reduce seismic 

risk. The description of area-wide activities is similarly 

limited to agencies in the San Francisco Bay region. 

Such focusing on California and the bay region allows 

discussion of actual plans and programs illustrating 

various methods of reducing seismic risk consistent 

with the powers and responsibilities of typical state 

and regional governmental agencies. 

FEDERAL PROGRAMS 

The Federal government has a broad constitutional 

mandate to protect the health, safety, and welfare of 

the residents of the United States. Direct Federal efforts to reduce risk from seismic hazards have evolved 

from the Federal commitment to provide disaster relief 

to states and localities devastated by earthquakes. 

With increasing urbanization of seismically active 

areas, particularly the west coast, the potential cost of 

disaster and recovery assistance, borne primarily by 

the Federal government, is awesome. The moderate 

San Fernando earthquake of 1971 caused property 

damage estimated at more than a half billion dollars. 

Federal aid including grants and loans exceeded 

$450,000,000. Approximately $135,000,000 was allocated from the President's Disaster Fund-an amount 

larger than for any natural disastr since the fund's 

establishment (U.S. Senate, 1971, p. 71; U.S. Office of 

Emergency Preparedness, 1971 and 1972, p. 179). 

Expenditures of this magnitude have focused attention on the need to reduce future damages. In 1970, a 

Task Force on Earthquake Hazard Reduction was established by the Office of Science and Technology 

(since disbanded) to ~~develop an appropriate national 

action program for the reduction of the human suffering and property damage attendant upon an earthquake•••" (U.S. Office of Science and Technology, 1970, 

p. 1). Table 3 lists the Task Force's high-priority recommendations. 

These recommendations provide a framework for 

Federal involvement in seismic-hazard reduction. Not 

all of the recommendations are currently being carried 

out in a consistent, coordinated program, but many 

have been incorporated into the activities and proTABLE 3-High-priority recommendations of the Task Force on · Earthquake Hazard Reduction 

[U.S. Office of Science and Technology, 1970, p. 5] 

A. Significant benefits probably beginninq to accrue in the short 

term (less than 5 years after beginnmg of recommended action): 

A-1: 

A-2: 

A-3: 

A-4: 

A-5: 

A-6: 

A-7: 

A-8: 

A-9: 

A-10: 

A-11: 

A-12: 

A-13: 

Engineered earthquake resistance for new governmental facilities. 

Engineered earthquake resistance for new nongovernmental facilities. 

Seismicity (or risk, or probability) maps. 

Earthquake ~eologic hazards maps. Urban plannmg to minimize seismic hazard. 

Earthquake hazards abatement in older 

facilities. 

Cost-benefit studies. 

State and local government role in geologic 

hazards reduction. 

Federal total plan for immediate response. 

Federal responsibility in reconstruction. 

Federal responsibility in earthquake 

insurance. 

Strong motion equipment and analyses. 

Full-scale testing. 

B. Significant benefits probably beginning to accrue in the intermediate term ( 5-l 0 years after beginning of recommended action): 

B-1: 

B-2: 

B-3: 

B-4: 

B-5: 

B-6: 

B-7: 

Applied research on seismic design 

criteria. 

Postearthquake analyses. 

Fault mapping, dating, and specialized 

geologic mapping. 

Local seismic networks. 

State responsibility in earthquake 

hazards reduction. 

Newly discovered hazards and older 

construction. 

Taxes and tax reform. 

C. Significant benefits probably beginning to accrue mainly in the 

longer term ( 10 years or more after beginning of recommended 

action): 

C-1: 

C-2: 

C-3: 

C-4: 

C-5: 

C-6: 

C-7: 

C-8: 

Basic research in earthquake 

engineering. 

Earthquake prediction research. 

Earthquake control research. 

Geodetic research. 

Worldwide seismic network continuation. 

Tsunami hazard research. 

Basic research in seismology. 

Basic research on causes and 

mechanisms of crustal failure. 
SEISMIC SAFETY AND LAND-USE PLANNING B21 

grams of several Federal agencies. At present the Federal Government has four major functions in reducing 

risks from future earthquakes: conducting or funding 

research and providing technical information, encouraging emergency preparedness and providing disaster relief, considering seismic hazards in program 

administration, and requireing insurance. Each of 

these Federal functions is discussed below. 

RESEARCH AND TECHNICAL INFORMATION 

Federal agencies which sponsor research and provide 

technical information concerning seismic hazards include the U.S. Geological Survey, the National Oceanic 

and Atmospheric Administration, and the National 

Science Foundation. 

U.S. GEOLOGICAL SURVEY 

The USGS (U.S. Geological Survey) is responsible for 

carrying out the seismic research and hazard mapping 

recommended by the Task Force on Earthquake 

Hazard Reduction. The USGS publishes maps of faults, 

evaluates their degree of activity, and compiles and 

maintains records of historical and recent seismic activity. Geologists and seismologists investigate therelationship of geologic structure to seismic wave 

amplification and ground shaking, liquefaction potential, and other seismic hazards. Post earthquake 

analysis is carried out in the field by USGS professionals in cooperation with investigators from universities, 

professional organizations, and other groups. 

The USGS also investigates the feasibility of earthquake prediction and control and is responsible for issuing official earthquake predictions. The USGS administers EROS (Earth Resources Observation System) to evaluate the application of data obtained from 

remote sensing. A few previously unknown faults have 

been identified from remote sensing imagery from 

high-altitude aircraft and satellites, but most known 

faults have been recognized and mapped by geologists 

in the field. 

On May 22, 1974, Congress enacted Public Law 

93-288 (88 Stat. 143), which is known as the ((Disaster 

Relief Act of 197 4" to provide an orderly and continuing means of assistance by the Federal Government to State and local governments in carrying out their responsibilities to alleviate the suffering and damage which results 

from***disaster  

By subsequent redelegations of authority, the Director 

of the Geological Survey was 

empowered to exercise the authority, functions, and powers granted 

by Section 202 of the Disaster Relief Act of 1974 with respect to 

disaster warnings for an earthquake, volcanic eruption, landslide, 

mudslide, or other geological catastrophe. 

(Federal Register, vol. 42, no. 70, p. 19292, Tuesday, 

April 12, 1977). Section 202 (a) of the Act states that 

HThe President shall insure that all appropriate Federal agencies are prepared to issue warnings to State 

and local officials." In addition, Section 202 (b) states 

that 

The President shall direct appropriate Federal agencies to provide 

technical assistance to State and local governments to insure that 

timely and effective disaster warning is provided. 

The Federal Register statement cited (p. 19292) describes the Survey's 

capabilities and limitations for advance recognition and warning of 

various kinds of geologic-related hazards and the procedures proposed to carry out the responsibilities delegated under the Act. 

The USGS has undertaken several pilot studies in 

urban areas, such as the San Francisco Bay Region 

Environment and Resources Planning Study, to provide geologic and seismologic information for use in 

land-use planning and decisionmaking. Under the 

Earth Sciences Applications Program, several projects, 

similar to the San Francisco Bay Region Study, have 

been undertaken to provide earth-science information 

for use in land-use planning. Studies have been completed of the Greater Pittsburgh area, Connecticut 

River Valley, Washington-Baltimore region, and the 

Phoenix-Tucson area. Still underway (in 1977) are 

projects in the Puget Sound area, in the Front Range 

Corridor in Colorado, and in Fairfax County, Virginia. 

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION 

NOAA National Oceanic and Atmospheric Administration) is responsible for setting up and maintaining a 

tsunami warning system for coastal areas of the 

United States. The agency's previous functions with 

respect to solid-earth geophysics have been assumed by 

the U.S. Geological Survey, but NOAA still maintains 

and provides data related to seismology. 

NATIONAL SCIENCE FOUNDATION 

The NSF (National Science Foundation) provides 

funds for research by colleges and universities, nonprofit research organizations, and other groups in all 

the scientific disciplines. Under its program, Research 

Applied to National Needs, NSF has funded research to 

investigate the social and engineering aspects of 

seismic-hazard reduction. Such projects have included 

studies of the impacts of hazard-mitigation measures 

and the potential impact of improved capability to predict earthquakes. 

EMERGENCY PREPAREDNESS AND DISASTER RELIEF 

The Civil Defense Preparedness Agency and the Federal Disaster Assistance Administration are the agencies most directly responsible for emergency preparedness and disaster relief. 
B22 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

Civil Defense Preparedness Agency. The main objective of the CDP A (Civil Defense Preparedness Agency), 

established within the Department of Defense in 1972, 

is to improve prospects for survival of the population in 

the event of a nuclear war. A secondary objective ((is to 

improve the readiness of State and local governments 

to respond to peacetime emergencies" (U.S. Civil Defense Preparedness Agency, 1974, p. 6). In this connection, the agency provides planning assistance to state 

and local governments to develop their natural disaster preparedness plans and capabilities and plays a key 

role in coordinating Federal state, areawide, and local 

emergency response plans. Among other activities, the 

CDPA funds emergency planning efforts of other government agencies, makes surplus Federal property and 

equipment available for emergency response, and operates emergency warning and communications systems. 

Federal Disaster Assistance Administration. The 

FDAA (Federal Disaster Assistance Administration), 

in the Department of Housing and Urban Development, is responsible for ((programs concerning disaster 

research, preparedness, readiness evaluation, disaster 

relief, and recovery, and coordination of other agency 

disaster assistance activities (U.S. Office of the Federal 

Register, 1973, p. 253). The agency publishes the Federal Earthquake Response Plan which outlines the 

Federal Government's role in response to a major 

earthquake. FDAA administers the Disaster Relief Act 

of 197 4 enacted to help State and local governments 

alleviate the suffering and damage caused by floods, 

tsunamis, earthquakes, mudslides, and other 

emergencies and major disasters. The Disaster Relief 

Act of 197 4 provides for financial and technical assistance to the states to develop plans, programs, and regulations for hazard reduction, disaster preparedness, 

and disaster relief. The act requires that property to be 

replaced, repaired, or restored with the assistance of 

Federal relief funds be insured, if insurance is available, against future losses. To receive any disaster loan 

or grant, a state or local government must agree to 

evaluate natural hazards in the disaster area and take 

actions to mitigate the hazards, such as control of 

land-use and construction practices (U.S. Congress, 

197 4, Sec. 406). 

PROGRAM ADMINISTRATION 

Federal officials who administer Federal and Federally funded programs have an opportunity to influence 

decisions related to seismic safety. The extent to which 

this is done often depends on how legislation and regulations are interpreted by administrators. 

Two Federally mandated procedures provide the 

basic framework for consideration of seismic risk in 

administering Federal and Federally funded programs: 

(1) review procedures set forth by the U.S. Office of 

Management and Budget (A-95), and (2) environmental impact assessment required by the National Environmental Policy Act of 1969. 

A-95 REVIEW 

A-95 review procedures are d~signed to implement 

the Intergovernmental Cooperation Act of 1968 by insuring that Federally funded projects are consistent 

with State, areawide, and local planning objectives. 

Under these procedures applicants for Federal funds 

for a wide variety of projects must notify designated 

State and regional clearinghouse agencies which review proposed projects for consistency with State, 

areawide, and local plans and programs. The clearinghouse agency forwards the project description to any 

affected agencies for their review and comment. The 

comments are only advisory, but a Federal agency 

must defend in writing any decision to fund a project 

which has received a negative review. This procedure 

at least assures that the review comments of affected 

public agencies are considered. 

Comments may be made concerning the natural 

characteristics of a proposed project site. In seismically 

active areas, the nature and extent of seismic hazards 

are an appropriate and necessary subject of comment 

in the A-95 review process. 

ENVIRONMENTAL IMPACT ASSESSMENT 

The NEP A (National Environmental Policy Act) of 

1969 requires that an EIS (environmental impact 

statement) be prepared for proposed legislation and for 

other Federal actions that may significantly affect the 

quality of the human environment. The statement 

must describe the environmental impact of the proposed action, identify adverse and unavoidable environmental effects, list alternatives to the proposed 

action, describe how local short-term uses of man's environment are related to maintaining and enhancing 

long-term productivity, and identify any irreversible 

and irretrievable commitments of resources. 

Guidelines and procedures for preparing environmental impact statements are issued by the CEQ 

(Council on Environmental Quality) and administered 

by the EPA (Environmental Protection Agency). The 

current guidelines (Council on Environmental Quality, 

1973) help Federal agencies prepare environmental 

impact statements and require that environmental factors, such as seismic hazards, be explicitly considered 

before most Federal actions. To the extent possible, environmental impact assessment and A-95 review are 

coordinated. 
SEISMIC SAFETY AND LAND-USE PLANNING B23 

PROGRAMS OF THE DEPARTMENT OF HOUSING AND URBAN 

DEVELOPMENT 

Although most Federal activities are subject to A-95 

review and environmental impact assessment requirements, each agency develops its own operating 

procedures to carry out the intent of the legislation and 

regulations. The programs of HUD (Housing and 

Urban Development) support planning, community 

development, and housing activities of many state, 

areawide and local governments throughout the country. The way these programs are administered can affect seismic safety in HUD-assisted activities and projects. 

The Housing and Community Development Act of 

197 4 (U.S. Dept. of Housing and Urban Development, 

1975b) combined several HUD programs covering 

urban renewal, neighborhood development, and public 

facilities into a single program funded with Community Development Block Grants. Local community development programs are subject to A-95 review, and 

individual projects funded with Community Development Block Grants are subject to environmental impact assessment. In reviewing applications, HUD may 

challenge statements of fact and program decisions related to seismic safety, and it may require additional 

information from the applicant. Implications of the 

community development program and proposed projects should be evaluated in the review of applications 

for Community Development Block Grants. 

Under the Comprehensive Planning Assistance Program (Section 701 of the Housing and Community Development Act of 1974), HUD provides grants to cities 

and counties, and metropolitan, regional, and State 

planning agencies. Grants may be used for planning to 

mitigate and reduce hazards, among other activities. 

All agencies applying for grants must adopt a land-use 

element by August 23, 1977 (U.S. Department of Housing and Urban Development, 1975a, p. 36862). The 

land-use element must identify areas where growth 

should and should not take place giving comprehensive 

consideration to environmental factors. Planning activities supported by these grants must be conducted in 

accord with the National Environmental Policy Act of 

1969 (Public Law 91-190). HUD (U.S. Department of 

Housing and Urban Development, 1975a, 36860) 

specifies that each agency shall: 

(1) Identify salient elements of the natural and the man-made environments, their interrelationships, and major problems and/or 

opportunities they present for community development; 

(2) Assess those environmental factors which will: 

(i) Minimize or prevent undue damage, unwise use, or unwarranted pre-empting of natural resources and opportunities; 

(ii) Recognize and make prudent allowance for major latent 

environmental dangers or risks (e.g., floods, mud slides, 

earthquakes, air and water pollution); and 

(iii) Foster the human benefits obtainable from use of the natural environment by wise use of the opportunities available (e.g., use of natural drainage systems for park and 

recreational areas, 

HUD has also issued Minimum Property Standards 

which define minimum levels of acceptable design and 

construction for Federally subsidized housing and for 

housing approved for Federally insured mortgages. 

Where earthquakes are a recognized hazard, the standards require a comprehensive soil investigation, special foundation design, and structural design to withstand lateral forces in accord with the latest Uniform 

Building Code (U.S. Dept. of Housing and Urban Development, 1973). 

INSURANCE 

The Task Force on Earthquake Hazard Reduction 

recommended studies of the feasibility of offering 

earthquake insurance at actuarial rates (U.S. Office of 

Science and Technology, 1970, p. 26). Private earthquake insurance has been available since the early 

1900's, but relatively few property owners have purchased it. For example, of the more than half a billion 

dollars in property damage caused by the San Fernando Earthquake, only about $46,000,000 was cov-: 

ered by insurance (Baker, 1971, p. 31). 

The potential for expanding private insurance coverage is limited, because insurance companies are required to maintain reserves sufficient to meet obligations in the event of a major earthquake. Property 

owners have also been reluctant to assume the extra 

cost of earthquake insurance, although it is relatively 

low. Table 4 lists typical costs of earthquake insurance 

in California in 197 4 for residential buildings according to risk classes which are based on structural type. 

A deductible amounting to 5 percent of the building 

value usually applies. 

Several proposals for Federal action to increase the 

extent of insurance coverage for damage from earthquakes and other natural disasters have been made, 

but, to date, the only direct Federal response has been 

enactment of the National Flood Insurance Program in 

1968 (Public Law 90-448) as amended in 1973 (Public 

Law 93-234). Under this program, an individual must 

purchase flood insurance to be eligible for any kind of 

Federal financial assistance, including loans from Fed:-

erally insured or regulated institutions, for acquisition 

of property or construction in identified special floodhazard areas. The insurance is available at rates presently subsidized by the Federal Government in participating communities which have adopted and enforced 

land use and development controls to reduce the flood 

hazard. 

Areas subject to flooding from tsunamis are included 

in the program. When the Federal Insurance Adminis-
B24 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

TABLE 4.-Cost of earthquake insurance for residential buildings 

[Yanev, 1974, p. 234] 

Class 

of 

risk 

II 

III 

IV 

v 

VI 

VII 

VIII 

Building description 

Small wood-frame and frame 

stucco buildings (less than four 

stories). 

Steel-frame and reinforced 

poured -concrete buildings. 

Reinforced concrete-frame (columned) buildings and other 

reinforced shear-wall masonry 

buildings. 

Wood-frame buildings with 

masonry veneers or other 

liabilities. 

Steel-frame and reinforced 

concrete-frame buildings with 

segmented mansonry walls 

(brick, concrete block, etc.). 

Single-family dwellings (less 

than three stories) of reinforced 

masonry; other reinforced 

masonry buildings with 

liabilities. 

Unreinforced brick and larger 

reinforced masonry buildings 

without steel or concrete 

framing. 

Unreinforced masonry, 

masonry-veneer, or adobe 

buildings. 

Cost per $1,000 

coverage 

$1.50 

$2.50 

$3.00 

$3.50 

$3.50 

$4.00 

$7.50 

$25.00 

tration of the Department of Housing and Urban Development (U.S. Federal Insurance Administration, 

1975, p. 13429) has identified such ~~coastal high 

hazard areas," the community: 

Must provide that all new construction or substantial improvements 

within the designated coastal high hazard area be located landward 

of the reach of the mean high tide; Must provide that all new construction and substantial improvements within the designated coastal high hazard area be elevated on adequately anchored piles or 

columns to a lowest floor level (including basement) at or above the 

100-year flood level and securely anchored to such piles or columns: 

Must provide that all new construction and substantial improvements within the designated coastal high hazard area have the 

space below the lowest floor free of obstructions or are constructed 

with "breakaway walls" intended to collapse under stress without 

jeopardizing the structural support of the building so that the impact 

on the building of abnormally high tides or wind-driven water is 

minimized. Such temporarily enclosed space shall not be used for 

human habitation; Must prohibit, within the designated coastal high 

hazard area the use of fill for structural support; Must prohibit, 

within the designated coastal high hazard area, the location of any 

portion of a new mobile home park, expansion to an existing mobile 

home park, and any new mobile home not in a mobile home park. 

These regulations are designed to encourage landuse decisions that minimize losses caused by flooding 

from the sea. 

Federally insured or regulated institutions such as 

banks or savings and loan companies are not permitted 

to provide funds to substantially modify or purchase 

existing structures within coastal high-hazard areas 

unless the. property is insured under the program. 

When more accurate maps of hazard areas are released, the insurance will be available at actuarial 

rates which will reflect the flood risk. 

STATE ROLE-CALIFORNIA 

Officials in nearly every agency of California State 

government need to consider seismic safety in carrying 

out their duties. The location and construction of public 

facilities, management of State lands, provision of 

services, and delegation of powers and responsibilities 

to local governments should all reflect an awareness 

that damaging earthquakes are inevitable. Few, if any, 

populated areas of the State are free from the risk of a 

major earthquake, and most large population centers 

are less than 80 kilometers (50 miles) from faults that 

can generate earthquakes (Jennings, 1975). 

Although the historical record and geologic knowledge are insufficient to precisely establish the frequency of future earthquakes, one estimate is that 

California can expect a great earthquake (Richter 

magnitude greater than 7.7) every 60-100 years, a 

major earthquake (Richter magnitude 7.0-7.7) every 

20 years, and a moderate earthquake (Richter magnitude 6.0-6.9) every 8-10 years (California State 

Legislature Joint Committee on Seismic Safety, 1974, 

p. 200). 

LEGISLATION AND ADVICE 

The State legislature and, more recently, various 

advisory bodies, have led in defining and coordinating 

California's role in reducing seismic risk. 

CALIFORNIA LEGISLATURE 

Legislative actions to reduce seismic risk have almost always followed damaging earthquakes. The 

most far-reaching actions followed the earthquakes of 

1933 in Long Beach, 1964 in Anchorage, Alaska, and 

1971 in San Fernando. Below is a brief chronology of 

legislative actions linked to each of these earthquakes. 

Details of key legislation are provided in relevant sections. 

After the 1933 Long Beach earthquake, the legislature adopted the Field Act establishing seismic stand-

.ards for the construction of school buildings and the 

Riley Act setting forth lateral force requirements for 

certain other buildings. 

After the 1964 Anchorage, Alaska, earthquake and 

in response to two conference reports on this major 

earthquake, the legislature in 1969 established the 

Joint Committee on Seismic Safety to advise it on 

earthquake hazards. 
SEISMIC SAFETY AND LAND-USE PLANNING B25 

After the 1971 San Fernando earthquake the Governor appointed the Governor's Earthquake Council, 

and the Legislature intensified support for the Joint 

Committee on Seismic Safety and passed several 

seismic-safety bills. The major acts include the 

Alquist-Priolo Special Studies Zones Act to reduce risk 

from fault rupture; the Hospital Safety Act to 

strengthen construction standards for hospitals; the 

Dam Safety Act to require evaluation of the safety of 

dams, mapping of potential inundation areas, and 

preparation of evacuation plans; and an amendment to 

the Government Code requiring each county and city 

to adopt a seismic safety element as part of its general 

plan. 

GOVERNOR'S EARTHQUAKE COUNCIL 

In January 1972 the GEC (Governor's Earthquake 

Council) was established to recommend measures to 

reduce future earthquake losses. The recommendations presented in the Council's report of November 

21, 1972 closely parallel those of the Federal Task 

Force on Earthquake Hazard Reduction and emphasize 

measures which can be undertaken administratively 

by the executive branch of State government. Table 5 

summarizes the major recommendations and responsible agencies (California Governor's Earthquake Council, 1972, p. 5-15). 

JOINT COMMITTEE ON SEISMIC SAFETY 

The Joint Committee on Seismic Safety was established by the State Legislature in 1969 as an outgrowth of studies following the 1964 Anchorage, 

Alaska, earthquake. The committee's purpose was to 

~~develop seismic safety plans and policies and recommend to the Legislature any legislation needed to 

minimize the catastrophic effects upon people, property, and operation of our economy should a major 

earthquake strike any portion of California" (California State Senate, 1969, Senate Concurrent Resolution 

No. 128 of 1969, Resolution Chapter 378). The committee, composed of four senators and four assemblymen, 

relied on the technical and professional expertise of 

more than 70 persons who served on five advisory 

groups: engineering considerations and earthquake 

sciences; disaster preparedness; postearthquake recovery and redevelopment; land-use planning; and governmental organization and performance. 

The San Fernando earthquake also spurred the Joint 

Committee's efforts. A special subcommittee was 

formed to conduct a postearthquake investigation, and 

the resulting report provided a basis for many of the 

Committee's legislative recommendations (California 

State Legislature, Joint Committee on Seismic Safety, 

1972). The reports and recommendations of the advisory groups and the committee's basic legislative recommendations are contained in its final report, Meeting the Earthquake Challenge, published in January 

197 4 (California State Legislature, Joint Committee 

on Seismic Safety, 1974). The Committee's recommendations, which emphasize legislative action, are summarized in table 6. 

Perhaps the most important recommendation of both 

the Joint Committee on Seismic Safety and the Governor's Earthquake Council was to create a permanent 

organization within State government to coordinate 

State efforts to improve seismic safety. 

SEISMIC SAFETY COMMISSION 

In July 1975, the California Seismic Safety Commission was established by the Legislature. The 17-

member commission includes geologists; structural, 

civil, mechanical, and soils engineers; architects; planners; representatives of local government; and State 

legislators. The Commission's responsibilities as stated 

in the California Government Code, (1974, Sec. 8897) 

are: 

(a) Setting goals and priorities in the public and private sectors; 

(b) Requesting appropriate state agencies to devise criteria to promote seismic safety; 

(c) Recommending program changes to state agencies, local agencies, and the private sector where such changes would reduce 

the earthquake hazards; 

(d) Reviewing reconstruction efforts after damaging earthquakes; 

TABLE 5.-Recommendations of the Governor's Earthquake Council 

[Adapted and summarized from California Governor's Earthquake 

Subject 

Area 

Research, 

provision of information 

Critical structures 

Emergency 

preparedness 

and response 

Land-use planning 

Insurance _____ _ 

Council, 1972, pp. 5-15] 

Recommended Actions 

Support basic seismological research. Support research in earthquake 

engineering. Fund expanded seismographic network. Develop procedures and provide funds for postearthquake studies. Prepare earthquake geologic hazard maps, seismicity maps. Disseminate earthquake-related information. 

Assess safety of public utility systems and dams. 

Mandate local disaster plans including evacuation procedures. Coordinate Federal, State; areawide, and local disaster plans. 

Require disaster training in schools. Assess emergency operations including medical and communication capabilities. 

Provide incentives and technical guidance for preparation of seismic safety element. Consider local earthquake risk in public 

improvement projects. 

Require geologic reports on private and public projects in seismically active areas. 

Mandate inclusion of disaster coverage in standard fire insurance policies. 

Encourage insurance industry to advise policyholders of disaster coverage. 

'EERI is a private, nonprofit organization. 

State Agencies 

Responsible 

OES (Office of Emergency Sevices). UCB (University of Califomia at Berkeley). 

CDMG (California Division of Mines & Geology). EERI (Earthquake 

Engineering 

Research 

Institute).' 

DGS (Department of General Services). 

PUC (Public Utilities Commission). DWR (Department of Water Resources). 

OES(Office of Emergency Services). 

Department of Conservation. 

Office of Planning and Research. 

Department of Insurance. 
B26 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

TABLE 6.-Summary of recommendations of the Joint Committee on 

Seismic Safety 

[Adapted and summarized from California State Legislature, Joint Committee on Seismic 

Safety, 1972] 

Subject Area Recommended Actions 

Land-use planning __ Provide for effective State review of local 

seismic safety elements. 

Building 

Require geologic and soils reports for 

subdivision and construction activity of 

substantial scope. 

Permit seismic and geologic hazards to be 

considered "blighting" conditions making an area eligible for redevelopment funds. 

Provide for preplanning of postearthquake 

redevelopment. 

Require evaluation of geologic and seismic 

hazards in environmental impact 

statements. 

Employ land-use controls to reduce seismic 

hazards. 

Discourage public investment in hazardous areas. Provide purchasers of real estate with 

property reports disclosing seismic and 

geologic hazards. 

Construction ______ Upgrade engineering standards and building 

Abatement of 

hazardous 

code provisions. 

Assist local agencies in enforcing building 

code standards. 

Develop programs to train building officials 

and other ocal personnel in seismic design. 

Provide geologists, engineers, public safety 

officials, and others with reasonable 

protection from liability. 

buildings _________ _Develop hazard abatement program 

Critical and 

high 

exposure 

concentrating on pre-19331 buildings. 

Inventory potentially hazardous buildings. 

facilities __________ Enforce seismic safety measures in 

Emergency 

preparedness 

construction of schools, hospitals, and 

emergency facilities. 

Review safety of high-rise structures and 

dams. 

measures __________ Ensure that local emergency plans are prepared and maintained as required. 

Establish procedures for review and approval 

of such plans. 

Conduct disaster exercises to test response. 

Increase allocation to State Emergency 

Fund. 

Require communities to prepare 

postearthquake reconstruction plans. 

Research ____________ Increase support of basic and applied 

research. 

Insurance __________ Require purchasers of residential buildings 

'Explained on p. B 10. 

to carry earthquake insurance. 

Explore with Federal Government the 

possibility of comprehensive disaster 

insurance. 

(e) Gathering, analyzing, and disseminating information; 

(f) Encouraging research; 

(g) Sponsoring training to help improve the competence of specialized enforcement and other technical personnel; 

(h) Helping to coordinate the seismic safety activities of government 

at all levels; and 

(i) Establishing and maintaining necessary working relationships 

with any boards, commissions, departments, and agencies, or 

other public or private organizations necessary to further an 

effective seismic safety program for the state. 

To carry out these responsibilities, the Commission 

(California Government Code, 1974, Sec. 8898) may: 

(a) Review state budgets and review grant proposals, other than 

those grant proposals submitted by institutions of postsecondary education to the federal government, in earthquakerelated activities and to advise the Governor and Legislature 

thereon; 

(b) Review earthquake-related legislation proposals, to advise the 

Governor and Legislature concerning such proposals, and to 

propose needed legislation; 

(c) Recommend the addition, deletion, or changing of state agency 

standards when, in the commission's view, the existing situation creates an undue seismic hazard or when new developments would promote seismic safety, and conduct public 

hearings as deemed necessary on the subjects. 

Beginning in January 1977, the Commission's duties 

were expanded to include advising the State Mining 

and Geology Board regarding Special Studies Zones 

(see p. B25) and the State Geologist regarding the 

State Strong-Motion Instrumentation Program. 

RESEARCH AND INFORMATION 

The CDMG (California Division of Mines and Geology) within the Department of Conservation (California State Legislature, Joint Committee oh Seismic 

Safety, 1974, p. 190) has the responsibility to provide: 

(1) information pertaining to earthquake and other geologic 

hazards, (2) to conduct, with city and county governments or 

Federal and other State agencies, large-scale geologic investigations ** *to identify and delineate***geologic hazards in and 

adjacent to metropolitan areas, (3) to organize and monitor a 

strong-motion instrumentation program in the State, and (4) 

to quickly identify potential post-earthquake geologic hazards, 

particularly weakened slopes that could be activated by aftershocks. 

The division is headed by the State Geologist and 

operates under the policy direction of the State Mining 

and Geology Board. 

California Division of Mines and Geology produced 

the Urban Geology Master Plan for California (Alfors, 

1973). This report estimates, for the period 1970-2000, 

losses due to geologic hazards, the amount of losses 

that could be averted by applying current information 

and technology, and the cost of applying loss-reduction 

measures. Earthquake losses are estimated to be $21 

billion from 1970 to 2000. Approximately half of the 

losses could be averted by applying existing riskreduction measures. The cost of applying lossreduction measures is estimated to be about 10 percent 
SEISMIC SAFETY AND LAND-USE PLANNING B27 

of the total projected losses. The study was intended to 

help establish State priorities for measures to reduce 

losses from geologic hazards. 

Calfornia Division of Mines and Geology also administers the Alquist-Priolo Special Studies Zones Act 

(Chapter 7.5, Division 2, Public Resources Code, 1972 

as amended 1974 and 1975). Under this Act, the State 

Geologist maps special studies zones along potentially 

active and recently active fault traces. The zones are 

ordinarily less than 396 meters (a quarter-mile) wide 

unless special considerations indicate the need for a 

wider zone. Once the Special Studies Zones maps have 

been officially issued by CDMG, local jurisdictions 

must require geologic reports prior to approval of most 

new construction within the zones. Individual geologic 

reports are not required, however, for projects consisting of no more than one single-family, wood-frame 

home not exceeding two stories. 

The California Division of Mines and Geology, under 

the direction of the State Mining and Geology Board, 

establishes criteria and policies for content and review 

of the geologic reports, for revising the Special Studies 

Zones maps to reflect new geologic information, and for 

city and county compliance with provisions of the Act. 

Through contracts with cities and counties, CDMG also 

provides geologic information for seismic safety and 

safety elements of the general plan and for other planning purposes. 

STRUCTURAL STANDARDS 

The State OAC (Office of Architecture and Construction) in the Department of General Services administers the California Field Act (Education Code Sections 

15451-15465), which was passed after the 1933 Long 

Beach earthquake destroyed or seriously damaged 

many buildings and almost all public schools in the 

area. The Field Act specifies structural standards for 

construction of new public school buildings and requires that an architect or structural engineer prepare 

plans and supervise construction of school buildings. 

The act does not apply to State colleges and universities or private schools. Similar provisions relating to 

other major buildings are set forth in the Riley Act, 

also adopted in 1933. 

The Field Act has been amended several times as the 

technology of designing and building earthquakeresistant structures has improved. Sections added to 

the Education Code in 1967 require inspection of preField Act school buildings. Those found to be unsafe 

were to be replaced or brought up to code standards by 

June 1975, but some school districts have been granted 

additional time to meet the new requirements because 

of financial problems. Schools built since the Field Act 

was passed in 1933 have performed well during earthquakes (U.S. Office of Emergency Preparedness, 1972, 

p. 76). 

California legislation, also adopted in 1967, requires 

geologic and engineering investigations of any site 

proposed for a school building ((to preclude siting of a 

school over or within a fault, on or below a slide area, 

or in any other location where the geological characteristics are such that the construction effort required 

to make the site safe for occupancy is economically unfeasible•••" (Education Code, Section 15002.1 1967). 

The OAC (Office of Architecture and Construction) 

also develops and enforces standards for hospital construction under contract with the Department of 

Health as required by legislation enacted in 1972 

(California Health and Safety Code, 1972, Sec. 

15000-15023). This legislation was passed after the 

San Fernando earthquake damaged four major hospitals so severely that they had to be evacuated; fifty of 

the fifty-eight deaths attributed to the San Fernando 

earthquake resulted from collapse or damage to hospital buildings. OAC provides architectural and engineering services to State departments in the design 

and construction of State buildings and other facilities 

and prepares and administers the State's building regulations contained in Titles 17, 21 and 24 of the 

California Administrative Code. Since 1971, the Uniform Building Code has been adopted by reference as 

part of Title 24 of the California Administrative Code. 

The Appendix of the 1927 Uniform Building Code, 

published by the International Conference of Building 

Officials, included suggested lateral-force design requirements to increase structural resistance to earthquake ground motion. Lateral-force provisions have 

been modified several times subsequently, largely in 

accord with recommendations of the SEAOC (Structural Engineers Association of California). Sections 

17958 and 17922 of the California Health and Safety 

Code, enacted in 1975, require cities and counties to 

adopt the most recent edition of the Uniform. Building 

Code. Section 2312, Chapter 23, Earthquake Regulations, of the 1976 Uniform Building Code (International Conference of Building Officials, 1976, p. 132-

150) contain the lateral-force requirements which 

apply in seismically active areas of the country. 

Building code requirements typically are minimum 

standards which apply to all structures regardless of 

differing geologic conditions. Local jurisdictions may 

enact requirements more stringent than those of the 

Uniform Building Code and some jurisdictions, notably 

Los Angeles and Long Beach, have attempted to relate 

building standards to geologic conditions of the site. 

Such codes are technically more difficult to prepare and 
B28 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

administer, but as stated by Yanev (1974, p. 53) ~~•••it 

makes no sense to continue to build seemingly sound 

structures on unsound ground." 

CRITICAL FACILITIES 

DEPARTMENT OF WATER RESOURCES 

The DWR (State Department of Water Resources) is 

responsible for constructing and operating the State 

Water Project and for the safety of non-Federal dams in 

California (California State Legislature, Joint Committee on Seismic Safety 1974). Under the Alquist 

Dam Safety Act (Government Code, Section 8589-5, 

1973), DWR and the OES (Office of Emergency Services), identify dams whose failure might lead to injury 

or loss of life. The owner of a dam so identified must 

prepare a map showing the extent of potential flooding 

from dam failure at full reservoir capacity. OES must 

review and approve all such maps, which then serve as 

the basis for emergency evacuation plans drawn up by 

local governments with advice from the State. 

CALIFORNIA DEPARTMENT OF TRANSPORTATION 

The CalTrans (California Department of Transportation), within the Business and Transportation 

Agency, is responsible for building and maintaining 

the State highway system and for planning a balanced 

transportation system. Earthquake-resistant design of 

highway facilities, particularly overpasses and 

bridges, is essential to prevent collapse and possible 

loss of life during an earthquake and to maintain the 

flow of traffic following an earthquake. The vulnerability of freeway overpasses was dramatically illustrated 

by the San Fernando earthquake. As a result, more 

stringent design standards for new construction and 

reconstruction were instituted by the Department of 

Transportation, and additional engineering research 

was strongly recommended (California Division of 

Highways, September 1971). In addition, existing 

highway structures are being evaluated and 

strengthened as funds permit. 

More directly related to land-use planning, the Department also recommends that more attention be paid 

to seismic hazards in locating highways and interchanges. As stated in its report (California Division of 

Highways, 1971, p. 5-6) on the San Fernando earthquake: 

Early in the route location process, active and inactive faults should 

be mapped. A general assessment of the seismic risk of various areas 

within the study zone should then be prepared. 

Consideration must be given to the location of major interchanges. 

They should be sited outside of heavily faulted areas wherever feasible. Where seismic activity is highly probable, consideration should 

be given to avoiding complex multi-level interchanges in favor of 

simple designs with short span structures and maximum use of embankment. 

Early recognition of seismic risk might lead the planner to modify 

alignment or grade in order to minimize high cuts, fills, and bridge 

structures in a given area. Where a freeway must pass through a 

highly seismic area, the best and safest plan will generally be the 

simplest: close to the original ground, with simple, square bridge 

structures. 

These recommendations were incorporated into the 

Department's Highway Design Manual of Instructions 

in March 1975 (Section 7-110.4). 

EMERGENCY PREPAREDNESS AND DISASTER RELIEF 

The OES (Office of Emergency Services), within the 

Governor's office, was established by the Emergency 

Services Act (Chapter 7, Division 1, Title 2 of the Government Code, 1970). The act requires OES to coordinate the emergency activities of all State agencies. 

The OES develops and maintains the State 

Emergency Plan as required by Section 301b of the 

Federal Disaster Relief Act. This plan provides a 

framework for individual State agency and local government plans as well as specifying procedures for delivery of Federal ai~. 

The Emergency Plan also requires that contingency 

plans be prepared for specific potential emergencies, 

including earthquakes. The State Earthquake Response Plan, published by OES, meets this requirement. OES also coordinates postdisaster damage assessment and provides the Governor with information 

needed to declare an emergency or request Federal disaster assistance. The California Earthquake Prediction Evaluation Council, an advisory body to OES 

composed of geologists, seismologists, and geophysicists, reviews and evaluates specific information which 

could lead to an earthquake prediction. If the Council 

finds a significant possibility that an earthquake is 

imminent, OES provides preparedness and response 

information to State agencies and local governments 

and may provide public information to help individuals 

prepare for an earthquake. 

LAND-USE PLANNING AND REGULATION 

Many states have authorized local units of government to plan and regulate future development, but few 

states require local planning. In California, all cities 

and counties are required by State law to prepare and 

adopt a general plan which includes at least the following elements: land use, circulation, housing, conservation, open space, seismic safety, noise, scenic highways, 

and safety. California law further requires that zoning 

and subdivision of land be consistent with the adopted 

general plan. The State Attorney General, a resident, 

or a property owner may bring suit against a city or 

county to force compliance with the consistency provision of State law. 
SEISMIC SAFETY AND LAND-USE PLANNING B29 

In accord with a recommendation of the Joint Committee on Seismic Safety, the requirement for a seismic 

safety element was enacted soon after the San Fernando earthquake. 

Section 65302(£) of the Government Code requires: 

A seismic safety element consisting of an identification and appraisal 

of seismic hazards such as susceptibility to surface ruptures from 

faulting, to ground shaking, to ground failures, or to the effects of 

seismically induced waves such as tsunamis and seiches. 

The seismic safety element shall also include an appraisal of 

mudslides, landslides, and slope stability as necessary geologic 

hazards that must be considered simultaneously with other hazards 

such as possible surface ruptures from faulting, ground shaking, 

ground failure and seismically induced waves. 

This legislation provides the basic framework in 

California for local seismic safety planning requiring, 

in effect, that cities and counties consider seismic 

hazards in formulating and implementing the general 

plan. The CIR (Council on Intergovernmental Relations) (now disbanded) issued guidelines to assist local 

governments in preparing State-required general plan 

elements. The guidelines (California Council on Intergovernmental Relations, 1973, p. IV-24, 25) for preparing seismic safety elements suggested: 

A. A general policy statement that: 

1. Recognizes seismic hazards and their possible effect on the 

community. 

2. Identifies general goals for reducing seismic risk. 

3. Specifies the level or nature of acceptable risk to life and 

property (see safety element guidelines for the concept of 

"acceptable risk."). 

4. Specifies seismic safety objectives for land use. 

5. Specifies objectives for reducing seismic hazard as related to 

existing and new structures. 

B. Identification, delineation, and evaluation of natural seismic 

hazards. 

C. Consideration of existing structural hazards. Generally, existing 

substandard structures of all kinds (including substandard 

dams and public utility facilities) pose the greatest hazard to a 

community. 

D. Evaluation of disaster planning program. 

For near-term earthquakes, the most immediately useful thing 

that a community can do is to plan and prepare to respond to 

and recover from an earthquake as quickly and effectively as 

possible, given the existing condition of the area. The seismic 

safety element can provide guidance in disaster planning. 

E. Determination of specific land-use standards related to level of 

hazard and risk. 

The seismic safety element is related to several other 

required plan elements. As stated in guidelines prepared by the Council on Intergovernmental Relations 

(California Council on Intergovernmental Relations, 

1973, p. IV-27): 

The seismic safety element contributes information on the comparative safety of using lands for various purposes, types of structures, 

and occupancies. It provides primary policy inputs to the land use, 

housing, open space, circulation and safety elements. 

Within this legislative context, several State agencies and programs influence land-use planning with 

respect to seismic hazards. Of particular importance 

are the Office of Planning and Research and the 

guidelines of the California Environmental Quality 

Act, as discussed in the following sections. 

OFFICE OF PLANNING AND RESEARCH 

The OPR (Office of Planning and Research), responsible to the Governor, develops long-range State goals 

and policies for land use and environmental quality, 

evaluates State agency plans and programs for environmental impact, issues guidelines for preparing 

mandatory general plan elements (a function assumed 

from CIR), and provides assistance to local governments in preparing general plans. 

In 1972, the office published Environmental Goals 

and Policies setting forth recommended State actions 

to reduce environmental pollution and to protect environmental resources. The report recommends that 

areas subject to strong earthquake shaking, tsunamis, 

and fault displacement be designated as areas ofttcritical concern". In such areas guidelines should be formulated ttto encourage orderly development and protection from natural calamities while minimizing adverse 

impact upon people or resources•••" (California Office of 

Planning and Research, 1973, p. 3). 

CALIFORNIA ENVIRONMENTAL QUALITY ACT 

The California Environmental Quality Act of 1970, 

based on the National Environmental Policy Act, requires an EIR (Environmental Impact Report) for all 

public and private projects or actions which may have a 

significant effect on the environment and which involve a discretionary decision by a public agency. State 

guidelines and procedures for preparing EIR's are issued by the California Resources Agency. The 

guidelines specify that impacts which upose long-term 

risk to health or safety" be evaluated (California Resources Agency, December 1974, Section 15143, p. 19). 

AI though not specifically mentioned in the act or 

guidelines, seismic hazards are usually considered in 

the environmental impact assessment. 

AREA-WIDE PLANNING-SAN FRANCISCO BAY REGION 

The nine-county San Francisco Bay region is highly 

vulnerable to earthquake damage. A major earthquake 

on any of the faults traversing the region would have 

devastating impact on the entire area. Thus, planning 

to reduce seismic risk and to increase the ability to 

respond to an emergency is appropriately a regional 

concern. The responsibilities of regional agencies 

(those with a jurisdictional area encompassing parts of 

more than one county) related to seismic safety are 

briefly described in the following sections. 
B30 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

ASSOCIATION OF BAY AREA GOVERNMENTS 

ABAG (Association of Bay Area Governments) is the 

only regional agency covering the entire nine-county 

bay area that is responsible for comprehensive planning. Established in 1961 to develop plans and policies 

pertinent to region-wide problems, ABAG is a voluntary association of city and county governments. Implementation of ABAG's regional plans and policies 

depends on decisions by State and Federal agencies, 

other regional agencies, and local governments .. However because ABAG is the A-95 review clearinghouse 

age~cy for the San Francisco Bay region, it can indirectly influence other governmental decisions through 

reviewing requests for Federal funds. Because many 

projects are competing for limited funds, a negative 

finding by ABAG, although advisory, is likely to be 

heeded by the funding agency. ABAG also reviews 

Federal projects proposed for the region for consistency 

with areawide plans. 

ABAG is giving increasing emphasis in its planning 

program to seismic concerns. A report presented to the 

Regional Planning Committee in May 1976, Areas of 

Critical Environmental Concern (ABAG, 1975a), lists 

policies and criteria for identifying critical land and 

water areas. Areas with known earthquake-related 

problems are among the critical areas and, according to 

policy, should be protected from premature or extremely dense development (ABAG, 1975a, p. 44). 

These areas include: 

1. Lands within 50 feet of a known active fault 

trace, as shown on Special Studies Zones 

Maps; 

2. Lands subject to severe ground shaking shown 

as categories A and B on the map of maximum earthquake intensities (Borcherdt and 

others, 1975); 

3. Lands likely to liquefy in a major earthquake 

as mapped by Y oud, Nichols, Helley, and 

Lajoie (1975). 

The report further recommends that land uses 

within 50 feet of a fault trace be limited to agriculture, 

recreation, secondary streets, and parking and that development in areas of severe ground shaking meet or 

exceed the requirements of the most recent uniform 

Building Code. Critical structures -should be located, 

whenever possible, in the less hazardous areas. 

A land capability analysis (Laird and others, 1979) 

prepared by ABAG as part of the San Francisco Bay 

Region Study illustrates a method of analyzing land 

capability for a demonstration area of about 100 square 

miles in the Santa Clara Valley. The cost of damage or 

mitigation measures per acre which can be expected 

from geologic hazards is estimated for selected land 

uses. Such seismic hazards as ground shaking, surface 

rupture, dam failure, dike failure, liquefaction, and 

landslides are considered. The report-relies on information similar to that compiled for the entire San Francisco Bay region by Borcherdt, Gibbs, and Lajoie 

(1975). The report is described more fully on pages 

B72-B73. . In a related effort, ABAG undertook a proJect sponsored by the Federal Civil Defense Preparedne.ss 

Agency to assemble information on disasters and disaster mitigation, to outline a method of evaluating 

risk, and to clarify ABAG's role in civil preparedness. 

(ABAG, 1975b) 

A committee formed to prepare a civil preparedness 

plan for ABAG concluded that ABAG should have no 

operational role in disaster response, but tha~ A.B~G 

should offer technical assistance to member JUnsdictions in ways to reduce hazards, prepare for disasters, 

and plan for postdisaster recovery. 

ABAG prepared uA Method for Evaluating Hazards" 

(ABAG, 1975b) to help local governments set priorities 

for disaster preparedness. 

It sets forth a procedure for describing and analyzing 

hazards and suggests ways a local jurisdiction can decide which hazards are important, what measures can 

effectively reduce them, and appropriate priorities for 

action. 

The theme of ABAG's annual General Assembly in 

February 1976 was earthquake preparedness andresponse. Following a two-day conference (including 

Federal, State and local government staff members, 

elected officials, representatives from private industries and citizens) the Assembly adopted a resolution 

um~king earthquake preparedness and response a high 

ABAG program priority" (Laird and others, 1979) and 

directing the Executive Board to define an ABAG ~rogram emphasizing legislation and advocacy; planning 

and technical assistance; and public information and 

education. As a result, ABAG has appropriated 

$30,000 for 1976-77 for the following work program: 

Legislative advocacy . . . 

a. Monitoring proposed earthquake related legislation; prepanng 

comments as appropriate. 

b. Working with staffs of State legislative committees, advocating 

legislation that would assist local governments' preparedness 

efforts. 

Technical assistance to local governments 

a. Offering information and assistance to member governments in 

using previous ABAG work to upgrade and improve their 

seismic safety programs. 

b. Assisting local governments in using the findings and methods 

contained in the ABAG Land Capability Analysis Report to 

improve local seismic safety programs. 

Plan and project review . . 

a. Completing plan and project review procedures and pohc1es on 

seismic safety. 

b. Conducting plan and project reviews, and preparing review 

comments in relation to seismic safety policies and programs. 
SEISMIC SAFETY AND LAND-USE PLANNING B31 

Legal research 

a. Cataloging legal research into responsibilities and liabilities of 

local jurisdictions for earthquake damage. 

ABAG is also seeking additional funds to augment the 

program and to implement some of the recommendations. 

To carry out policies and criteria related to seismic 

safety, ABAG relies on its project review powers. 

ABAG's (1973) procedures for regional clearinghouse 

review of environmental impact statements contain 

checklists of environmental impacts associated with 

eight different types of projects and include an inventory of mapped environmental information. The procedures also set criteria for determining regional impact. 

The importance of seismic hazards, such as historically 

active faults, high ground-shaking potential, and 

liquefaction potential are recognized, and sources of 

geologic and seismological information are listed. 

SAN FRANCISCO BAY CONSERVATION AND 

DEVELOPMENT COMMISSION 

The BCDC (San Francisco Bay Conservation and 

Development Commission) is a State agency created by 

the State Legislature. BCDC was authorized to prepare 

a comprehensive plan for San Francisco Bay and its 

shores and to control development within its area of 

jurisdiction. The plan was adopted by the State Legislature, and BCDC became a permanent agency 

charged with carrying out the plan. The adopted plan 

has legal status and serves as a guide in the review of 

projects. BCDC shares jurisdiction over land-use decisions with the cities and counties which retain normal 

land use and building-permit controls. However, with 

certain minor exceptions, a permit from BCDC is required for all projects within its area of jurisdiction. 

Thus it, in effect, holds veto power over any project 

proposal in conflict with the San Francisco Bay Plan. 

The BCDC plan and its project-review activities reflect a strong concern for seismic safety. The agency's 

jurisdiction consists primarily of tidelands, marshes, 

salt ponds, and diked and filled land underlain by bay 

mud. Such land is subject to particularly severe seismic 

ground shaking, liquefaction, differential settlement, 

and flooding. Yet in spite of these hazards, diking and 

filling of the bay lands to accommodate urban uses has 

occurred and continues to be a problem. As stated in 

the San Francisco Bay Plan (San Francisco Bay Conservation and Development Commission, 1969, p. 2): 

As the Bay Area's population increases, pressures to fill the Bay for 

many purposes will increase. New flat land will be sought for many 

urban uses because most, if not all, of the flat land in communities 

bordering the Bay is already in use-for residences, businesses, industries, airports, roadways, etc. Past diking and filling of tidelands 

and marshlands has already reduced the size of the Bay from about 

680 square miles in area to little more than 400. Although some of 

this diked land remains, at least temporarily, as salt ponds or managed wetlands, it has nevertheless been removed from the tides of the 

Bay. 

Despite the risks involved, the State recognizes that 

some bay filling may be desirable or necessary if the 

benefits outweigh the disadvantages. The San Francisco Bay Plan recommends approval to fill if one of the 

following four conditions is met: (1) the filling is in 

accord with the bay plan policies as to the bay-related 

purposes for which filling may be needed ( such as, 

ports, water-related industry, and water-related recreation) and is shown on the bay plan maps as likely to be 

needed, (2) the filling is in accord with bay plan policies 

as to purposes for which some fill may be needed if 

there is no other alternative (such as, airports, roads, 

and utility routes), (3) the filling is in accord with the 

bay plan policies as to minor fills for improving 

shoreline appearance or public access, ( 4) the filling 

would provide for new public access to the bay on privately owned property and for improvement of 

shoreline appearance-in addition to what would be 

provided by the other bay plan policies-and the filling 

would be for bay-oriented commercial recreation and 

bay-oriented public assembly purposes. The question of 

safety of the fill must also be addressed before BCDC 

can issue a permit for filling. 

With respect to the safety of fills, the plan (San Francisco Bay Conservation and Development Commission, 

1969, p. 15) makes the following findings: 

Virtually all fills in San Francisco Bay are placed on top of Bay mud 

which presents many engineering problems. The construction of a 

sound fill depends in part on the stability ofthe base upon which it is 

placed. Safety of a fill also depends on the manner in which the filling 

is done, and the materials used for the fill. Similarly, safety of a 

structure on fill depends on the manner in which it is built and the 

materials used in its construction. Construction of a fill or building 

that will be safe enough for the intended use requires (1) recognition 

and investigation of all potential hazards-including (a) settling of a 

fill or a building over a long period of time, and (b) ground failure 

caused by the manner of constructing the fill or by shaking during a 

major earthquake-and (2) construction of the fill or building in a 

manner specifically designed to minimize these hazards. While the 

construction of buildings on fills overlying Bay deposits involves a 

greater number of potential hazards than construction on rock or on 

dense hard soil deposits, adequate design measures can be taken to 

reduce the hazards to acceptable levels. 

Policies to reduce potential earthquake damage to 

structures built on filled land include (San Francisco 

Bay Conservation and Development Commission, 

1969, p. 17):. 

1. The Bay agency should appoint a Fill Review Board consisting of geologists, civil engineers specializing in soils engineering, structural engineers, and architects competent 

to and adequately empowered to (a) establish and revise 

safety criteria for Bay fills and structures thereon, (b) review all except minor projects for the adequacy of their 

specific safety provisions, and make recommendations concerning these provisions, (c) prescribe an inspection system 

to assure placement of fill according to approved designs, 

and (d) gather, and make available, performance data de-
B32 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

veloped from specific projects. These activities would complement the functions of local building departments and 

local planning departments, none of which are presently 

staffed to provide soils inspections. 

2. Even if the Bay plan indicates that a fill may be permissible, 

no fill or building should be constructed if hazards cannot 

be overcome adequately for the intended use in accordance 

with the criteria prescribed by the Fill Review Board. 

3. To provide vitally needed information on the effects of earthquakes on all kinds of soils, installation of strong-motion 

seismographs should be requried in all future major land 

fills. In addition, the Bay agency should encourage installation of strong-motion seismographs in other developments 

on problem soils, and in other areas recommended by the 

U.S. Coast and Geodetic Survey, for purposes of data comparison and evaluation. 

The proposed Fill Review Board was established as 

the Engineering Criteria Review Board, composed of 

geologists, structural engineers, civil engineers, soils 

engineers, and other professionals as recommended in 

the plan. The board reviews and evaluates soils and 

geologic reports submitted by applicants for permits to 

fill. Significant improvement in the seismic engineering of fills and design of structures has resulted from 

the board's insistence on a thorough evaluation of 

geologic hazards at a project site (San Francisco Bay 

Conservation and Development Commission, 197 4a, p. 8). 

The policies and review procedures incorporated into 

the bay plan provide the means to assure that development within BCDC's jurisdiction is carried out in 

accordance with an acceptable degree of risk. However, 

as stated in a report of the Bay Plan Evaluation Project 

(San Francisco Bay Conservation and Development 

Commission, 197 4b, p. 19) a ~~more precise definition of 

what level of risk is acceptable for design of structures 

on the Bay" is needed. Such a definition requires a 

detailed risk analysis involving both seismic and nonseismic hazards. 

CALIFORNIA COASTAL ZONE CONSERVATION 

COMMISSION 

The CCZCC (California Coastal Zone Conservation 

Commission) and subordinate regional commissions 

were created by State legislation adopted, by initiative, 

in 1972. The CCZCC, working with the six regional 

commissions, prepared a plan for the future of the 

California coastal zone. While the plan was being prepared, the commissions controlled all development, 

through a permit process, to ensure consistency with 

the objectives of the establishing legislation and the 

emerging plan policies. Coastal areas of the bay region 

are represented by two regional commissions: Central 

(San Mateo County) and North Central (San Francisco, 

Marin, and Sonoma Counties). 

The California Coastal Plan was adopted by the 

CCZCC in September, 1975, and forwarded to the Governor and State Legislature in December, 1975. In 

1976, the California Coastal Act was enacted, establishing the policies and governmental mechanism for 

ensuring wise use of the State's coastal areas. The act 

requires local governments within the coastal zone to 

adopt local coastal programs to implement the policies 

of the Coastal Act. It is stated in one policy that new 

development shall ~~minimize risks to life and property 

in areas of high geologic, flood, and fire hazard," and 

shall ~~assure stability and structural integrity, and 

neither create nor contribute significantly to erosion, 

geologic instability, or destruction of the site or surrounding area•••" (California Public Resources Code, 

1976, Sec. 30253). 

Local coastal programs are to be submitted to the 

appropriate regional commission for certification. 

After the local coastal programs in a region have been 

certified, or by January 1, 1981, the regional commissions are to be disbanded. The State Coastal Commission is to designate sensitive coastal resource areas 

which require special protection in local coastal programs. To remain in force after two years, the designations must be affirmed by the State Legislature. 

Permits for specific coastal zone developments will 

be required, and the Coastal Act establishes procedures to be followed before and after a local coastal 

program is certified. Guidelines for preparing local 

coastal programs will be issued by the State Coastal 

Commission in Spring 1977. In keeping with the policy 

framework in the act, full consideration of seismic and 

other geologic hazards is likely to be required of local 

programs. 

METRO PO LIT AN TRANSPORTATION COMMISSION 

The MTC (Metropolitan Transportation Commission) was created to coordinate development of regional 

transportation facilities. It was charged with preparing 

and adopting a Regional Transportation Plan dealing 

with major highways, mass transit, transbay bridges, 

airports, and harbors. It must also develop a 

transportation improvement program and a financial 

program for carrying it out. 

MTC also cooperates with ABAG in the A-95 review 

process by providing comments related to transportation. MTC's approval is required for certain projects 

including transbay bridges, public multicounty transit 

systems on exclusive rights-of-way, all applications 

from local governments or districts for State or Federal 

funds related to transportation, and construction of the 

State Highway System. In addition to the projectreview function, MTC administers the public transit 

funds derived from State and local sales taxes on 

gasoline for the nine bay region counties. 

MTC adopted the Regional Transportation Plan in 

1973 and revisions on several subsequent occasions. 
SEISMIC SAFETY AND LAND-USE PLANNING B33 

With respect to seismic safety, the plan recognizes the 

importance of the transportation system to postearthquake evacuation, rescue, and relief efforts. Accordingly, the following policy was adopted: ~~Earthquake 

and seismic technology shall be used in the planning, 

location and construction of new transportation 

facilities" (Metropolitan Transportation Commission, 

1974, p. 14). This policy ensures that seismic hazards 

are considered in the review of transportation projects 

undertaken by MTC. 

EVALUATING SEISMIC RISK 

Seismic safety planning is the process of evaluating 

seismic risk and formulating public policy to reduce 

that risk. Methods of evaluating seismic risk are described in this section; formulating public policy is discussed in the following section. To evaluate risk, it is 

necessary to understand the distinction between 

hazard and risk. A seismic hazard is an effect of an 

earthquake such as surface faulting, ground shaking, a 

tsunami, liquefaction, landsliding, and other forms of 

ground failure. Seismic risk is the exposure of individuals and structures to potential injury or damage from 

seismic hazards. For example, the presence of an active 

fault is clearly a hazard; however, the degree of risk 

depends on the location, type of construction, and occupancy of structures with respect to the fault. Given 

present knowledge of seismic phenomena, little can be 

done to modify the hazard, that is, control tectonic processes, but much can be done to control risk or exposure 

to seismic hazards. This is the purpose of seismic safety 

planning. 

Risk evaluation consists of: evaluating seismic 

hazards, and assessing the degree of exposure of individuals and structures to those hazards. The techniques and specifics of the evaluation may differ, but 

the basic procedure is becoming fairly well established. 

Figure 14 outlines the usual steps in evaluating risk 

from seismic hazards. Each step is described briefly in 

the following sections. 

IDENTIFYING SEISMIC HAZARDS 

The first step in evaluating risk in any area is to 

determine the potential for damaging earthquakes by 

reviewing the seismic history of the area and identifying any active or potentially active faults. Such faults 

are identified from historic, geologic, or seismic evidence of surface displacement (Borcherdt, 1975, p. A5). 

Evaluating earthquake potential or seismicity of an 

area requires information concerning: 

(1) the location of faults capable of generating damaging earthquakes, (2) the magnitude of earthquakes anticipated on these 

faults, (3) the amount of fault displacement anticipated, (4) the nature and areal distribution of deformation accompanying earthquakes or fault movement; and (5) the frequency of recurrence of 

earthquakes on a known fault (Borcherdt, 1975, p. A29). 

Work done in the bay region provides an example of 

the necessary first step in evaluating regional seismic-· 

ity. Here some 30 faults have been identified as being 

active or potentially active and therefore potentially 

capable of producing damaging earthquakes (Borcherdt, 1975, p. A30). These faults have been mapped 

at scales ranging from 1:250,000 to 1:24,000 and their 

earthquake potential evaluated. These data provide a 

detailed description of the seismicity of the bay area 

(Borcherdt, 1975, fig. 3 and table 1). As in this exainple, where damaging earthquakes can be expected, the 

various seismic hazards need to be identified and evaluated. 

The following discussion of individual seismic 

hazards in the San Francisco Bay region illustrates 

this process. The discussion is based almost entirely on 

the technical data in Part A of this report, and major 

topics are keyed to pages in Part A (Borcherdt, 1975). 

SURFACE RUPTURE (A6-Al2; A25-A30) 

Faults which have displaced the surface of the earth 

in the recent geologic past can be expected to do so 

again and are classed as active or potentially active. 

Not all earthquakes result in surface rupture and, in 

any one earthquake, surface rupture is unlikely to 

occur along the full length of a major fault. Also the 

likelihood and amount of potential surface displacement vary for different faults and even for different 

segments of the same fault. However, because even 

small vertical or horizontal displacements can severely 

damage structures astride a fault, planners should 

consider rupture a hazard on all the identified active or 

potentially active faults in the San Francisco Bay region. Special geologic investigations to determine the 

nature and amount of anticipated displacement are 

needed to locate and design those utility lines and 

other lifelines which must cross a fault. 

Surface rupture along active faults may also result 

from fault creep-a process consisting of slow, intermittent, or fairly continuous fault movement which 

can amount to as much as an inch per year. It is 

usually recognized by surface evidence such as offsets 

and breaks in curbs, sidewalks, streets, fences, and 

FIGURE 14.-Steps in evaluating seismic risk. 
B34 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

other structures. The presence of creep and its rate can 

be verified by installing and monitoring instruments 

along the fault. 

Another aspect of evaluating hazard from surface 

rupture is defining the width of the zone of surface 

deformation associated with fault displacement (Borcherdt, 1975, p. A25). Precise delineation of this zone 

may require extensive subsurface investigation 

(usually including trenching) to locate all active traces 

and other evidences of surface deformation. Such information is seldom available, so the width of the zone 

is commonly estimated from geologic evidence or from 

historic records. 

Widths of zones of deformation are discussed (Borcherdt, 1975, p. A25) in these terms: 

Until proved otherwise by geologic site investigations, prudence suggests zone widths of 184m (600ft) for the largest strike-slip faults 

and 1,800 m (6,000 ft) for the largest dip-slip faults. In the San 

Francisco Bay region, most dip-slip faults are relatively short (less 

than 16 km or 10 mi), and for these, narrower zone widths are appropriate. 

GROUND SHAKING (A52-A57) 

Ground shaking is a major cause of earthquake 

damage. The severity of shaking depends on the magnitude and type of movement, distance from the fault, 

and local geology. The most violent ground shaking 

generally occurs in a fairly narrow band adjacent to the 

fault and the intensity of shaking tends to decrease 

with distance from the fault, but local geologic conditions may modify this pattern. That unconsolidated 

sedimentary deposits may amplify bedrock motion and 

produce strong ground shaking far from the fault is 

evident in the damage patterns of many major earthquakes. Borcherdt (1975, p. A64) states: 

***The effects of ground shaking are expected to be least for sites 

underlain by bedrock, intermediate for those sites underlain by alluvium, and greatest for those sites underlain by artificial fill and 

bay mud. 

In the bay region, the relative potential ground 

shaking can be estimated from the damage patterns of 

the 1906 earthquake, from empirical studies of 

amplification of bedrock motion in different earth materials, and from the predicted relationship between 

distance from the fault and intensity. Current estimates of the potential for shaking are given by Borcherdt, Gibbs, and Lajoie (1975). 

LIQUEFACTION (A68-A74) 

Liquefaction is the transformation of a loose, watersaturated, granular material (such as sand) from a 

solid to a liquid state. It can be caused by ground shaking and may in turn cause major ground failure. The 

relative potential for liquefaction in the southern San 

Francisco Bay region was mapped (Borcherdt, 1975, p. 

A70) using the following criteria: 

The liquefaction-potential criteria can now be summarized as follows: Saturated clay-free granular sediments with relative densities 

less than 65 percent are considered to have high liquefaction potential, even in a moderate earthquake; clay-free granular sediments 

with relative densities greater than 90 percent are considered to 

have low liquefaction potential, even in a major earthquake; and 

saturated clay-free granular sediments with relative densities between 65 and 90 percent have moderate liquefaction potential that 

depends on intensity and duration of ground shaking and textural 

properties of the sediments. 

((Potential" is the key word here. For liquefaction to 

occur, liquefiable materials must be within about 30 

meters (100 feet) of the surface, saturated, and subjected to strong ground shaking. In addition, ground 

failure from liquefaction occurs only if the liquefied 

materials are not confined. For some geologic units, 

like bay mud, geologic site investigations are necessary to determine that a particular site is not underlain by liquefiable materials. 

LANDSLIDING (A75-A87) 

Earthquakes may trigger many landslides, particularly during the wet season. The potential for landsliding is a function of basic slope stability and is highest 

in unconsolidated, soft sediments or surficial deposits; 

on steep slopes; where seasonal rainfall is high; where 

vegetation is shallow rooted or sparse; where erosion 

rates are high; and where ground shaking is intense. 

Maps showing relative slope stability for the entire 

San Francisco Bay region are available at a scale of 

1:125,000 (Nilsen and Wright, 1979). These maps 

evaluate relative landslide potential on an areawide 

basis. Although they do not predict which landslides 

will move in an earthquake, they do show those areas 

in which landslides are most likely. Geologic site investigation is needed to pinpoint the landslide potential within these areas. 

FLOODING (A93-A94) 

Earthquakes may cause flooding from tsunamis and 

seiches. The susceptibility of a coastal area to tsunami 

damage depends on local topography and elevation 

with respect to the potential size and direction of incoming waves. Potential tsunami runup areas can be 

generally delineated, and are often based on a 

maximum probable event. Potential runup areas in the 

San Francisco Bay region are mapped by Ritter and 

Dupre (1972). 

The hazard from seiches is more difficult to evaluate. 

Generally speaking, any area adjacent to a large reservoir, lake, or other enclosed body of water is susceptible 

to flooding from seiches. Overtopping of dams or 

shoreline flooding can also be generated by landslides 

falling into bodies of water. The potential depends on 

the location of unstable slopes with respect to lakes, 

reservoirs, and bays. 
SEISMIC SAFETY AND LAND-USE PLANNING B35 

Major flooding may be caused by the failure of dams 

or dikes during an earthquake. Areas around the 

southern San Francisco Bay are particularly 

susceptible to flooding from dike failure. Many dikes 

are built mostly of fine-grained sediments dredged 

from the bay and are located on deposits of bay mud. 

Such dikes are particularly prone to failure during an 

earthquake. The areas susceptible to flooding from 

dike failure vary with tidal level at the time of an 

earthquake, but they have increased in size over the 

years because of ground subsidence brought about by 

the withdrawal of ground water in the south bay area. 

In accordance with the Alquist Dam Safety Act (see 

section on ttCritical facilities"), areas which would be 

flooded in the event of dam failures have been mapped 

throughout California. These areas are extensive in 

the San Francisco Bay region and are of significant 

concern because of their size and location. Studies are 

being made to identify more specifically the likelihood 

of individual dam failure in the event of a major earthquake. It is also essential to evaluate the probable 

depth and velocity of flood waters and, where areas 

below dams are developed, the length of warning time 

residents may have. 

SELECTING THE DESIGN EARTHQUAKE 

The severity of seismic hazards is directly related to 

several characteristics of earthquakes. Information 

concerning possible earthquake magnitude and lOcation are needed to estimate the possible surface 

rupture, ground shaking, ground failure, and flooding 

in an area. The hypothetical earthquake that is used as 

the basis for assessing seismic effects is called the design earthquake. Criteria for establishing the magnitude of the design earthquake are described below. 

Maximum earthquake magnitude and frequency can 

be estimated, based on: 

(1) the geologically determined rate of slip and historic records of 

ground deformation, (2) the seismic history of the fault and the surrounding tectonic regime, (3) geologic evaluation of the tectonic setting, and (4) the empirically derived relation between magnitude of 

earthquakes and fault length or other parameters (Borcherdt, 1975, 

p. A17). 

It is realistic to assume that the largest historic earthquake can recur on the same fault or a geologically 

similar fault and that potential magnitude increases 

with fault length. Based on seismic history and faultlength relations, assuming that half the fault length 

would break in a maximum magnitude earthquake, 

the largest expected earthquake on the San Andreas 

fault is 8.5 on the Richter scale and, on the Hayward 

fault, 7.0-7.5 (Borcherdt, 1975, p. A10). 

A magnitude at, or close to, the maximum expected 

is usually chosen for the design earthquake in evaluating risk for planning purposes. Becaus~ earthquake effects cannot yet be predicted in detail, a conservative 

approach based on the largest magnitude foreseen by 

competent geologists is prudent, especially when planning for areas or structures with intensive use or for 

facilities which are critical to the safety and continued 

functioning and recovery of a community during and 

after an earthquake. 

Choice of size of the design earthquake is also influenced by projected frequency of occurrence. If an earthquake of maximum magnitude can be expected to occur 

once every thousand years, for example, one of lesser 

magnitude may be reasonably chosen for the design 

earthquake. However, recurrence intervals, particularly for major earthquakes, are difficult to determine; the historic record is too short, and even careful 

geologic studies do not always clearly define recurrence 

intervals. 

Although magnitude and frequency appear to be related linearly-small earthquakes occur more often 

than large ones (Chinnery and North 1975, p. 1198)-

this relationship is a poor guide for evaluating risk, 

because in a given area the pattern is highly variable. 

Different segments of the same fault may behave differently. For example, the segment of the San Andreas 

fault running through Marin County and the San 

Francisco peninsula has been relatively quiet since 

1906, whereas the same fault near Hollister is the 

source of frequent relatively small earthquakes. Figure 15 shows the maximum magnitude, maximum 

strike slip (horizontal displacement), and recurrence 

interval estimated for different segments of the San 

Andreas fault (Wallace, 1970, p. 2881). 

The magnitude chosen for the design earthquake 

should not necessarily be the maximum magnitude 

that may be expected on the fault segment closest to 

the planning area. For example, the Hollister area may 

experience more damage from a magnitude 8 on the 

fault segment to the north than from a magnitude 6 on 

a closer segment of the fault. All faults and fault segments near the planning area need to be carefully 

evaulated in selecting the design earthquake. Because 

damaging effects are related to the length of fault displacement which in turn is related to the length of the 

fault, the design earthquake is usually the maximum 

event expected on the largest active fault affecting an 

area. 

A design earthquake may represent the expected effects of a single large earthquake or a series of earthquakes of different magnitudes. The design earthquake does not indicate the overall seismicity or 

susceptibility to damage-from lesser magnitude earthquakes or from earthquakes on other nearby faults. 

However, if appropriate measures are taken to reduce 
B36 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

-----l N 

0 

0 100 200 Ml LES 

I I 1 

I 11 

0 100 200 300 KILOMETERS 

Behavior category 2 3 4 

Maximum magnitude 7-8+ 6-7 S-6 

Maximum strike slip (m) 1.2-10 0.3-1.2 0.1-0.3 <0.1 

Recurrence interval (yrs) 100-1000 10-100 <10 >10 

FIGURE 15.-Behavior of different segments of San Andreas fault 

(Wallace, 1970, p. 2881). 

risk from the design earthquake, risk from lesser 

events are correspondingly reduced. 

PREDICTING GEOLOGIC EFFECTS 

Predicting the effects of a design earthquake involves relating information available on the seismic 

hazards to the design earthquake. Since the seismic 

hazards are closely related to geologic conditions, the 

evaluation depends on the level of detail and accuracy 

of the basic geologic mapping. Predicting the geologic 

effects of an earthquake in a given area is termed 

useismic zonation", which is defined as ((the delineation 

of geographical areas with different potentials for surface faulting, ground shaking, flooding, liquefaction, 

and landsliding during future earthquakes of specific 

size and location" (Borcherdt, 1975, p. A1). Such 

studies are essential in evaluating risk for planning 

purposes. 

The geologic effects of a postulated earthquake of 

magnitude 6.5 on the San Andreas fault are predicted 

(Borcherdt, 1975, p. A88-A95) along a demonstration 

profile extending from Sky Londa west of the fault on 

the San Francisco peninsula across the bay to Coyote 

Hills (fig. 16). The moderate magnitude of6.5 was chosen because reliable strong-motion data obtained 

within 50 km (31 mi) of the causative fault were available for earthquakes of moderate size (magnitude 

5.0--6.9) but not for magnitude 7.0 and larger earthquakes. With such data it is possible to statistically 

predict ground-motion values for competent geologic 

materials (ranging from bedrock to firm alluvium) for 

sites at distances greater than 10--20 km (6--12 mi) 

from the causative fault (Borcherdt, 1975, p. A32). 

The maximum magnitude expected along this segment of the fault is 8.5, and a magnitude closer to this 

would usually be used for the design earthquake for 

planning in the area of the demonstration profile. 

However, the methods used to predict the geologic effects of a 6.5 M earthquake are the same as for an 8.5, 

and any ranking of geographic areas on the basis of 

relative hazard would be the same. An 8.5 M earthquake would cause more severe effects over a larger 

area than a 6.5. 

Figure 17 shows the predicted geologic effects of the 

postulated 6.5 M earthquake along the demonstration 

profile. The method described can be applied to other 

large areas in the San Francisco Bay region where 

comparable geologic information is available. This information was translated into a series of hazard maps 

for use in assessing seismic risk by extending the several geologic effects to areas with similar underlying 

geologic material in an area roughly centered along 

the profile. 

Figure 18 shows the generalized geology of the area 

crossed by the demonstration profile and zones of potential surface deformation for the postulated earthquake. A surface-rupture length of 40 km (25 mi) plus 

or minus about 10 km (6 mi) is postulated on the San 

Andreas fault (see fig. 16). Displacement on the San 

Andreas of about 1 m (3ft) is estimated. The zone of 

potential surface deformation can vary in width from a 

few meters to a few tens of meters. The hatched lines in 

figure 18 showing deformation zones are not to scale; 

they simply indicate that surface deformation is not 

necessarily confined to the line depicting the fault location. The zone of predicted surface deformation should 

be considered highly hazardous in a risk evaluation. 

Structures within it could experience severe damage 

from displacement of the ground and from intense 

shaking; however, detailed investigations may reveal 

sites within the zone which can accommodate structures with acceptable safety. 

GROUND SHAKING 

Predicting relative severity of ground shaking is one 

of the most difficult tasks of seismic zonation. Two 

steps are involved in estimating relative ground shaking at the surface: predicting bedrock shaking, and 

predicting amplification of bedrock shaking in unconsolidated deposits. Shaking was predicted for four sites 
30' 

15' 

SEISMIC SAFETY AND LAND-USE PLANNING 

PACIFIC 

OCEAN 

EXPLANATION 

30' 

Estimated surface rupture for postulated 

earthquake (magnitude 6.5) 

"""""' Fault trace 

Demonstration profile 

.... 

Site for which ground shaking was calculated 

for postulated earthquake (magnitude 6.5) 

0 5 10 MILES 

0 5 10 KILOMETERS 

15' 

B37 

FIGURE 16.-Location of demonstration profile and estimated length of surface rupture associated with a postulated earthquake of magnitude 

6.5 on the San Andreas fault, southwestern San Francisco Bay region (Borcherdt, 1975, p. A89). 
600 

About 1m (3 ftl right-lateral offset likely SURFACE FAULTING 

I I Off set possible _________ __ ~o rf ~c :_ u~i~g i~ y • - - -------------- GROUND SHAKING 

Strong bedrock shaking (75-125 cm/s; 30-50 in./ s) decreasing with distance to moderate bedrock shaking (10-30 em Is; 5-15 in. IS) 

Amplification for frequenc1es < 1. 5 Hz Increased ampl ification for frequencies < 1.5 Hz 

FLOODING 

Not possible Partial inundation possible 

-------------------------- --. 

LIQUEFACTION 

_______ No potential (exc:_p!_ ':'_ ~ke_ ~n~ ~n~a~~e<!_s ~ _ _ _ _ _ Low potentia l High potential (where clean granular layers exist) 

Several large and small 

landslides likely 

-· 

/Sky Londa 200 

LANDSLIDING 

Severa l smal l landslides likely Few small landslides likely 

Lateral spreading associated with liquefaction 

N ANDREAS FAULT ZONE 

Moderate 

potential 

(/) 

a: 

w 

1-

w 500 

~ 

z 400 

z 

0 

1-

<( 

> 200 w 

_J 

w 

EXPLANATION 

- Baymud 

iiTJTII) Holocene alluvium 

[2] L ate Pleistocene alluvium 

(/) 

a: 

w 

1-

w 

~ 

z 

z 

0 

i= 

<( 

> 

w 

_J 

100 

0 

w 100 

0 Pliocene and early Pleistocene 

1-

w 

w 

u.. 

0 ~ 

z 

0 

~ w 

...J 

w 

deposits 500 

EJ Pre-Tertiary and 

Tertiary bedrock 

~ Landslide deposit 

Water table 

I J Fault 

200 

0 5 10 15 MILES 

0 5 10 15 20 Kl LOMETERS 

DISTANCE 

FIGURE 17 .-Predicted geologic effects of a postulated earthquake (magnitude 6.5) on the San Andreas fault (see fig. 16 for location of demonstration profile and estimated length 

of surface rupture). The severity of each earthquake effect is indicated qualitatively by thickness underlining and quantified to the extent permitted by the current state of 

the art or seismic zonation on a regional scale. The severity of the predicted earthquake effects generally depend on the type of underlying geologic material. Geologic cross 

section compiled by K. R. Lajoie (Borcherdt, 1975, p. A91). 

t:C 

C.:~ 

00 

~ t:l 

~ 0 

z 

0 

"%j 

t'j 

~ 

~ c:::: 

~ 

~ 

~ SJJ 

~ z 

(1 

~ 

~ 0 

~ >< 

~ 0 

0 

z 
32° 

22' 

30" 

SEISMIC SAFETY AND LAND-USE PLANNING B39 

EXPLANATION 

Bay mud 

Holocene alluvium 

Late Pleistocene alluvium 

Pliocene and early Pleistocene Santa 

Clara & Merced formations +-+-

Pre-Tertiary and Tertiary bedrock 

Franciscan, marine sandstone, Page 

Mill Basalt 

General zone of predicted surface deformation from the design earthquake 

General zone of possible deformation 

Borcherdt and others, 1975 differentiation of 

Holocene and Pleistocene alluvium added 

0 2 3MILES 

0 2 3 4 KILOMETERS 

FIGURE lB.-Generalized geology of area crossed by demonstration profile (Borcherdt and others, 1975) and zones of potential surface 

deformation for the postulated earthquake. 

along the demonstration profile (fig_ 19)_ Site 1 is 9 km 

(5.6 mi) from the fault; site 2, 14 km (8.7 mi); and sites 

3 and 4, 22.5 km (13.1 mi). 

Bedrock motion is estimated to be 75-125 cm/s 

(30-50 in./s) at site 1, decreasing with distance from 

the fault to 10-30 cm/s (8-12 in./s) at sites 3 and 4. 
B40 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

However, bedrock motion is amplified by the unconsolidated materials present at sites 2 and 3. This 

amplification of bedrock motion depends on the frequency and varies with the nature of unconsolidated 

deposits and the distance from the earthquake source. 

Figure 19 shows the potential for amplification of bedrock motion in the area crossed by the demonstration 

profile. As stated by Borcherdt (1975, p. A93): 

The model calculations suggest that a substantial amplification of 

bedrock shaking in the frequency range below 1.5 hertz could be 

expected for all parts of the demonstration profile underlain by alluvial deposits, with increased amplifications for the parts underlain 

by bay mud. The predicted amplifications are large enough to suggest that ground shaking for frequencies below 1.5 hertz may be 

stronger at the sites underlain by bay mud and alluvium than at 

sites underlain by bedrock much closer to the fault. 

LIQUEFACTION AND LATERAL SPREADING 

Relative potential for liquefaction and lateral 

spreading from the postulated earthquake is illustrated in figure 20. Liquefaction potential is considered 

highest where beds or lenses of clay-free granular sediments occur within the bay mud. Lateral spreading, 

which is the most common kind of ground failure to 

result from liquefaction in the San Francisco Bay region, is the movement of soil mass toward a free face or 

down a gentle slope. Cracks, fissures, and differential 

settlement in or near the margins of the slide mass 

commonly result from lateral spreading (Borcherdt, 

1975, p. A94). 

LANDSLIDING 

The relative stability of upland slopes, as mapped by 

Nilsen and Wright (1979) is shown in figure 21. The 

slope stability categories shown are based on geology 

and slope and are independent of earthquakes. But an 

earthquake during the wet season could be expected to 

trigger more and larger landslides than normally occur. Unstable areas like those between Sky Londa and 

the San Andreas fault are susceptible to earthquakeinduced landslides even in the dry season, and small 

landslides can be expected where slopes are moderately 

unstable (Borcherdt, 1975, p. A94). 

FLOODING 

For the postulated earthquake, flooding is most 

likely to occur from the failure of earthen dikes located 

on bay mud along the margins of southern San Francisco Bay. The extent of potential flooding depends on 

topography and the tide level at the time of dike failure. Figure 22 shows possible flooding throughout the 

bay mud unit extending inland to the 1850 bay 

shoreline. Flooding could extend farther inland in 

some areas if ground subsidence has occurred. For the 

postulated earthquake, flooding from tsunami runup, 

seiches, or dam failure is not considered likely in the 

area shown in figure 22. 

SEISMIC ZONATION 

Figures 19-21 are hazard maps expressing the relative severity of potential earthquake hazards and, together, constitute a preliminary seismic zonation. A 

composite map of hazard zones can be compiled by 

judging the relative risk posed by each hazard. For 

example, the area shown in the figures is divided into 

high, moderately high, moderate, and low hazard zones 

as follows: 

High: the San Andreas and Canada fault zones, 

bay mud, and slope-stability category 5; 

Moderately high: Holocene alluvium, slope stability category 4, and areas near the San Andreas 

and Canada faults; 

Moderate: Late Pleistocene alluvium, and slope 

stability category 3; and 

Low: the remainder of the study area. 

The limits of these zones are not exact; also the degree of hazard within each zone may vary locally. 

These local variations can be more precisely defined by 

more detailed investigations and mapping. 

Figure 23 shows four possible hazard zones. These 

zones have the following characteristics: 

1. Bay mud is in the highest hazard zone because 

it has relatively high potential for liquefaction and for lateral spreading; it is subject to 

strong ground shaking; and it is subject to 

flooding. 

2. The zones of predicted surface deformation are 

in the highest hazard zone because structures 

astride a fault are vulnerable to serious damage or destruction in the event of sudden surface rupture. 

3. Slopes that are unstable under nonseismic conditions are in the highest hazard zone because they are likely to fail in the postulated 

earthquake. Moderately unstable slopes are 

considered slightly less likely to fail and are 

in the moderately high hazard zone. Slopes 

that are stable or marginally stable may fail 

during the postulated earthquake and are in 

the moderate hazard zone. Other slopes are 

relatively stable and are in the low hazard 

zone. 

4. Areas underlain by Holocene alluvium have 

moderate potential for liquefaction and lateral spreading and may have high surface 

ground shaking because of amplification of 

bedrock motion. They are in the moderately 

high hazard zone. 

5. Although areas underlain by late Pleistocene 
37° 

22' 

30" 

SEISMIC SAFETY AND LAND-USE PLANNING 

EXPLANATION 

Amplification for frequencies less than 1.5 hertz 0 2 3 

• Strong 

D Moderate 

DSiight 0 2 3 4 5 

~ Bedrock - no amplification 

FIGURE 19. - Relative amplification of bedrock motion. 

B41 

4 5 MILES 

6 7 KILOMETERS 

alluvium have a low potential for liquefac- 6. Areas next to the San Andreas and Canada 

tion and lateral spreading, bedrock motion faults are in the moderately high hazard zone 

may be greatly amplified. These areas are in because of the potential for strong ground 

the moderate hazard zone. shaking. 
B42 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

EXPLANATION 

• High potential for liquefaction and 

lateral spreading where clay-free 

granular layers are present 

Moderate potential for liquefaction 

and lateral spreading where clayfree granular layers are present 

D Low potential for liquefaction and 

lateral spreading where clay-free 

granular layers are present 

~ Land areas underlain by bedrock with 

little potential for liquefaction 

0 

0 

2 3 MILES 

2 3 4 KI L OMETERS 

FIGURE 20.-Relative potential for liquefaction and lateral spreading from the postulated earthquake. 
37° 

22' 

30" 

EXPLANATION 

Stable 

D Generally stable 

D Generally stable to marginally stable 

SEISMIC SAFETY AND LAND-USE PLANNING 

• Moderately unstable 0 

• Unstable 0 2 

FIGURE 21.-Relative stability of upland slopes. 

B43 

2 3 4 M l LES 

3 4 5 6 KILOMETERS 
B44 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

37° 

22' 

30" 

EXPLANATION 

D Partial flooding possible 

0 

0 

2 

2 3 

3 4 5 Ml LES 

4 5 6 7 KILOM ETERS 

FIGURE 22.- Possible flooding throughout the bay mud unit from dike failure. 

When an area can be assigned to more than one 

hazard zone, the highest hazard zone is shown. The 

resulting map (fig. 23) shows relative hazards from all 

the seismic effects considered. It does not show which 

hazard dominates at a given location. Because different measures are effective in mitigating different 

seismic hazards, maps showing the relative severity of 

individual hazards are almost always needed to formulate plans for reducing seismic risk. 

The composite seismic hazard zone map provides a 

general overview of relative hazards from the postulated 

earthquake. Preparing a composite map identifies 

areas with multiple hazards and areas where, because 

the hazard is greatest, the most severe damage from 
SEISMIC SAFETY AND LAND-USE PLANNING B45 

37° 

30' 

37° 

22' 

30" 

EXPLANATION 

~ High ha zard 

D Moderately high hazard 

D Moderate hazard 

D Low hazard 

0 

0 

2 3 4 5 MILES 

2 3 4 5 6 7 KILOMETERS 

FIGURE 23.- Seismic hazard zones. 

the earthquake can be expected. These areas should be 

carefully investigated before making land-development decisions and given particular consideration 

when planning for emergencies. Such a map cannot 

substitute for detailed investigations, but it can indicate where such investigations are most needed. The 

seismic hazards zone map is only 8.8 accurate as its 

elements. Because ground shaking is difficult to predict regionally, it is less accurately reflected in the 

composite map than other seismic hazards. As pre-
B46 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

sented here, the map shows relative differences in 

amplification of bedrock motion in unconsolidated deposits, but it does not indicate differences in bedrock 

motion. Areas near the fault shown in the low hazard 

zone may, because of strong bedrock shaking, be more 

hazardous than indicated. 

Another approach to seismic zonation, which partly 

avoids this problem, was suggested by Borcherdt, 

Gibbs, and Lajoie (1975), whose map of the South San 

Francisco Bay region (scale 1:125,000), shows 

maximum earthquake intensity for a large (7.5M8.3M) earthquake on the San Andreas or Hayward 

fault. Intensities of the 1906 San Francisco earthquake 

are related to geologic units and distance from the fault 

to predict the maximum intensity throughout the region. Intensity is expressed in terms of the San Francisco Intensity Scale (table 7) developed by H. 0. Wood 

(1908, p. 224, 225) to describe the 1906 San Francisco 

earthquake. 

Figure 24 shows the maximum intensities predicted 

for the area shown in figure 23. It is not possible to tell 

from this map which hazards are present in a given 

location. High intensities may be from strong ground 

shaking, ground failure, or some other hazard. However, the intensity map fairly accurately depicts 

relative ground shaking from a large earthquake. 

Comparing this map with the seismic hazard zone map 

indicates that the intensity map probably understates 

landsliding and flood potential. 

Hazard evaluation for risk assessment depends, first 

of all, on the detail and accuracy of the geologic information available for an area, but it also depends on the 

purpose of the evaluation, the size and diversity of the 

planning area, and the power of the agency undertaking the evaluation. If geologic maps are highly generalized, hazard evaluation must, of necessity, first 

focus on identifying those areas most likely to be 

hazardous, then further data can be collected and appropriate geologic information submitted with any 

major development proposals. Better hazard evaluations can be made as more detailed geologic data become available. 

If the hazard evaluation is to be used primarily for 

earthquake preparedness, hazard zones based on intensity may be appropriate. For such purposes, it is 

more important to know the expected level of damage 

than the exact cause of the damage. If, on the other 

hand, the evaluation is to be used primarily to prepare 

land-use plans and regulations and to suggest measures to reduce seismic risk, it is important to evaluate 

each seismic hazard individually and in as much detail 

as the information permits. 

Hazard evaluation for a geologically homogeneous 

region, regardless of size, can be quite generalized. 

TABLE 7.-San Francisco Intensity Scale for 1906 Earthquake 

[From Borcherdt, 1975, p. A3] 

Grade Intensity Description 

A Very Violent The rending and shearing of rock masses, 

earth, turf, and all structures along the line 

of faulting; the fall of rock from 

mountainsides; many landslips of great 

magnitude; consistent, deep, and extended 

fissuring in natural earth; some structures 

totally destroyed. 

B Violent Fairly general collapse of brick and frame 

buildings when not unusually strong; serious 

cracking of brickwork and masonry in excellent structures; the formation of fissures, step 

faults, sharp compression anticlines, and 

broad, wavelike folds in paved and asphaltcoated streets, accompanied by the ragged 

fissuring of asphalt; the destruction of foundation walls and underpinning structures by 

the undulation of the ground; the breaking of sewers and water mains; the lateral displacement of streets; and the compression, 

distension, and lateral waving or displacement of well-ballasted streetcar tracks. 

C Very Strong Brickwork and masonry badly cracked, with 

occasional collapse; some brick and masonry 

gables thrown down; frame buildings lurched or listed on fair or weak underpinning structures, with occasional falling from underpinning or collapse; general destruction of chimneys and of masonry, brick, or cement 

veneers; considerable cracking or crushing of 

foundation walls. 

D Strong General but not universal fall of chimneys; 

cracks in masonry and brickwork; cracks in 

foundation walls, retaining walls, and curbing; a few isolated cases of lurching or listing 

of frame buildings built upon weak underpinning structures. 

E Weak Occasional fall of chimneys and damage to 

plaster, partitions, plumbing, and the like. 

More detail is needed to evaluate seismic hazards in 

geologically diverse areas where hazard potential will 

vary significantly throughout the area. 

The power of the agency evaluating seismic hazards 

also affects the scope and detail of the effort. For example, a regional council of governments, with powers 

limited to planning and reviewing applications of local 

governments for Federal funds, may find generalized 

hazard evaluation sufficient for framing broad policies 

and determining what information should be submitted with applications for funds. Local governments, on 

the other hand, need a more detailed evaluation as 

basis for land-use plans, land-development regulations, project-review criteria and procedures, 

building-code requirements, plans for public facilities 

and emergency responses. 

INVENTORYING CULTURAL FEATURES 

Evaluating seismic hazards is only part of assessing 

seismic risk. The other part is assessing the vulnerability ofland uses and building occupancies to earthquake 
37° 

30' 

37° 

22' 

30" 

SEISMIC SAFETY AND LAND-USE PLANNING B47 

\ 

\ 

. \ AC\ I 

EXPLANATION 

~ Very violent D Very strong 

0 2 3 4 5 Ml LES 

-Violent c::::J Strong 0 2 3 4 5 6 7 KILOMETERS 

FIGURE 24.-Maximum earthquake intensity predicted on a regional scale. 

damage. The next step in assessing seismic risk in the used to determine the exposure of structures and 

area crossed by the demonstration profile would be to people to damage or death and injury from an earthinventory cultural or manmade features. quake. 

This information, considered in relation to the indi- Because of limitations of time and budget and the 

vidual and composite seismic hazards maps, would be fact that the demonstration profile crosses several 
B48 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

jurisdictions, an inventory of cultural features was not 

undertaken as part of this study. Instead, the key elements of such an inventory are first described in general terms, which are then followed by examples of 

various methods of combining hazard data with cultural data to assess seismic risk. 

Risk depends on the uses of land and buildings and 

on the ability of a public agency to respond to a disaster. Evaluating seismic risk thus requires an inventory 

of (1) current land use; (2) structures with high occupancy; (3) structures that are hazardous because of age 

or type of construction; and (4) critical facilities including lifelines, facilities or structures needed for 

emergencies, and facilities and structures whose failure would be catastrophic, such as dams or nuclear 

power plants. 

CURRENT LAND USE 

Maps or aerial photographs of current land use, 

viewed in conjunction with hazard maps, provide an 

overview of risk. Data concerning the number of dwelling units, rate of occupancy, location of businesses, and 

number of employees are used in estimating the daytime and nighttime population of specific areas. Land 

use, population density, and hazard maps should be 

prepared at the same scale. Map overlays are particularly useful. In populous areas, computer modelling 

may be justified. The distinction between land uses 

should be fine enough to separate structural types, 

heights, and intensity of use. For example, residential 

uses should be broken down at least into single-family 

and multiple-family categories and into height and 

structural categories. 

ST RUCTURES WITH HIGH ANIJ 

INVOLUNTA RY OCCUPANCY 

High-occupancy structures such as large apartment 

buildings, office buildings, major employment and 

shopping centers, theaters, auditoriums, and stadiums 

should be identified and noted on the hazard map. 

Buildings with high involuntary occupancy such as 

hospitals, schools, prisons, and convalescent homes 

form a separate and particularly vulnerable group. 

Most discussions of risk distinguish between a risk 

that is voluntarily assumed, such as the choice of a 

home site, and a risk that is involuntary, such as being 

in school or jail. Presumably structures occupied involuntarily should be safer than those voluntarily occupied. The distinction is especially important in those 

cases where public policy or laws require certain 

classes of people, such as prisoners or students, to occupy structures which have fairly high occupancy. 

As a practical matter, only limited volition is possible in choosing the structure in which to work, live, or 

even spend leisure time. A choice of working in a relatively unsafe building or not working at all, or living in 

a structurally unsound house or leaving the area is 

often not a real choice. Most people fall somewhere 

between being voluntary or involuntary occupants of a 

building. In addition, information concerning the relative safety of structures is often not known. The relative safety of buildings is rarely considered by the job 

seeker, and the home seeker who would like a house 

designed as earthquake resistant may not be able to 

afford it. 

Similarly, determining what occupancy rate 

should be classed as "high" depends upon the character 

of the development area. A community with predominantly low-density residential development might logically class two-story garden apartments as high occupancy in its risk evaluation. Conversely, a central city 

might apply that term only to structures more than 10 

stories high. 

The location of structures with high or involuntary 

occupancy can be shown on the land-use map or separately, depending on the graphic methods used. Information concerning whether occupancy is for 24 hours, 

daytime, or nighttime should also be noted. 

HAZARDOUS STRUCTURES 

Structures built before seismic safety requirements 

were imposed by local building code or State law need 

to be identified, noted on the map, and evaluated to 

determine if they were constructed with unsafe materials or methods. Particular attention should be given 

to masonry buildings. Also, poorly attached parapets, 

cornices, and other appendages should be noted. Failure of a building or parts adjacent to a street may be 

hazardous not only to occupants but to passersby. This 

type of information may be available from the agency 

or department responsible for building inspection; if 

not, it will need to be obtained. 

LIFELINES 

Lifelines are the utility services and communication 

and transportation lines necessary for the continued 

functioning of the community. Water supply lines, gas 

lines, electric transmission lines, telephone lines, 

major highways, and railway lines should all be included on the maps. Related facilities such as telephone exchanges, water and natural gas storage areas, 

airports, harbors, bridges, highway interchange structures, and power stations should also be identified. The 

location of shut-off valves, auxiliary suppliers, emergency power generators, and back-up communication 

systems should be noted where applicable. In addition, 

information on age, condition, and other factors will be 

needed in order to assess the likelihood of failure during an earthquake. 
SEISMIC SAFETY AND LAND-USE PLANNING B49 

FACILITIES FOR EMERGENCY RESPONSE 

The degree of risk partially depends on a community's ability to respond to a disaster situation. Command 

and communication centers, hospitals, medical offices 

and supply centers, fire stations, and police stations 

should all be noted on the maps. Buildings such as 

schools, churches, and theaters which could be used to 

provide temporary shelter or centers for dispensing 

emergency aid should also be identified. 

Emergency resources may also be available from 

nearby communities under mutual aid agreements. 

However, because a major earthquake is likely to damage highways, communication lines, airports and other 

links to nearby communities, local facilities need to be 

sufficient to sustain a community until aid from outside can be obtained. Areas within a community which 

could become isolated should also be identified and 

evaluated for an emergency situation. 

OTHER CRITICAL FACILITIES 

Structures whose destruction or damage could have 

catastrophic effects include nuclear power plants, large 

dams, and storage facilities for toxic materials. These 

and similar facilities in, or potentially affecting, a 

planning area should be identified, and the area of potential damage mapped. For example, areas subject to 

flooding from dam failure or dike collapse should be 

shown on the map. 

ASSESSING SEISMIC RISK 

When information describing seismic hazards, land 

use, and the structural and disaster response characteristics of a planning area has been assembled, decisions concerning the nature and degree of seismic risk 

can be made. Risk can be expressed in a variety of ways 

and with varying degrees of precision. 

DOLLAR LOSS 

Estimates of the dollar loss from all earthquakes 

over a period of time, or from a design earthquake, can 

be used to express seismic risk. Alfors, Burnett and 

Gay (1973) have estimated the total dollar loss from 

earthquake shaking, fault displacement, landsliding, 

tsunamis, and other natural hazards which can be expected in California from 1970 to 2000 assuming current 

hazard mitigation practices. The total loss includes the 

cost of property damage, life-loss, injury, and intangible loss. The analysis explicitly relates hazard zones to 

population levels. Standard 7¥2 minute topographic 

quadrangles were selected as unit cells and were assigned to high, moderate, and low-hazard severity 

zones. The percent of population in each zone during 

the 30-year period is estimated, yielding an estimate of 

person-years exposure from 1970 to 2000. This figure is 

multiplied by the expected average total loss per capita 

per year to attain the total loss figures. The calculations for earthquake shaking are shown in table 8. 

Projected total losses, 1970-2000, are $76,000,000 

from fault displacement, $9,852,000,000 from landsliding, and $40,800,000 from tsunamis. Similar estimates 

were made of losses from other natural hazards. 

Using dollars to express loss allows a comparison of 

total risk from several different hazards, including risk 

of life loss, injury, and property damage. This comparison is important in assigning priorities for public 

action and expenditure. It also provides a basis for determining the benefits of various risk-reduction measures if the costs of applying such measures are known. 

The Alfors study also estimates the cost of applying 

risk-reduction measures to arrive at a benefit/cost ratio 

for each hazard. 

Alfors, Burnett, and Gay (1973) assess Statewide 

risk in order to maximize the benefits of State actions 

to reduce risk from natural hazards. More specific 

studies of natural hazards would be needed if such an 

analysis were made at the regional or local level. But 

in many cases the time and expense necessary to do a 

thorough assessment in terms of dollar losses is not 

justified. In addition, lack of data and lack of ability to 

evaluate hazards may be significant barriers to risk 

assessment. 

DEATHS AND INJURIES 

Risk can also be expressed as the expected loss of life 

and injury from a hazard over a period of time, or from 

a single event such as an earthquake of specified magnitude. The risk may be stated as a total of the expected deaths and injuries or as a rate per unit of population. Algermissen's (1972) estimates of the expected 

loss of life and injury from an 8.3 magnitude earthquake on either the San Andreas or Hayward fault 

were based on death and injury rates from historic 

earthquakes adjusted for types of structures and for 

daytime and nighttime conditions in the bay region. 

He estimated 2,300 deaths would result from damage 

or collapse of residential structures if the earthquake 

occurred at 2:30 a.m. when most people are at home. 

An additional 550 deaths would occur in hospitals if 

the earthquake were on the San Andreas fault, and 820 

if it were on the Hayward. The largest number of 

deaths, 10,360, would occur with an 8.3 magnitude 

earthquake on the San Andreas fault at 4:30 p.m. during the evening commute period. A comparable earthquake at the same time of day on the Hayward fault 

would cause 6,650 deaths (table 9); deaths and injuries 

due to dam failure are not considered in these estimates. 
B50 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

~ABLE B.-Projected total loss from earthquake shaking, 1970-2000 

[Alfors and others 1973, p. 96 and Alfors, John, oral commun., 1977] 

Number of urban 

7-'h-minute 

quadrangles of each Estimated percent of Estimated person-years exposure 

Geology Points 

(expectable total 

average loss rate) 

(dollars per capita Projected total loss 

Earthquake severity zone severity total population 1970-2000 per year) 1970-2000 

High ------------------------ 181 37% Moderate ____________________ 242 50 

Low ------------------------ 57 12% 

Total ------------------------------------------------------

The potential number of deaths from dam failure is 

horrendous. Table 10 shows the number of people exposed to risk from the failure of major bay region dams 

and the maximum possible and probable deaths should 

a dam fail during the night or day. 

Estimates such as these can be used to express risk 

as a death rate per unit of population per unit of time. 

ABAG (1975b, p.14) uses estimates derived from the 

Algermissen study to calculate risk from an 8.3 magnitude earthquake on either fault. Assuming 6,600 

deaths, a population of 5 million, and a recurrence 

interval of 170 years for an 8.3 magnitude event, the 

following calculation is made: 

Risk = ___ 6~,6_0_0_d_e_a_t_hs __ _ 

5 million population 

x 1 quake 

170 years 

= 7. 7 deaths per year per 1 million persons 

Such calculations are useful primarily in comparing 

the risk of death from earthquakes with other natural 

and man-made risks. For example, the actual risk of 

death from all causes is about one in 100 persons per 

year (ABAG, 1975b, p. 14). 

POPULATION AT RISK 

One of the simplest ways to express risk is in terms 

of the number of people exposed to a hazard. This can 

be done simply by estimating the population of each 

delineated seismic hazard zone. Ayre (1975) uses the 

generalized seismic risk map for the United States (see 

fig. 4, p. 10) as the basis for such an estimate. The 

results, shown in table 11, indicate that approximately 

31 million people (15 percent of the population) live in 

risk zone 3-the zone with the highest seismic risk. 

Over half of these people live in California 

(17 ,000,000). Assessment of this type is useful only to 

provide an overview of risk exposure. To develop riskreduction policies and programs at the regional or local 

level, hazardous areas must be delineated more precisely, and types of structures and patterns of occupancy must be studied in relation to the hazards. 

In order to study risk, the City of Palo Alto (1976) 

took a census of population density during the day and 

during the night (fig. 25). Buildings with high occu289,050,000 

385,400,000 

96,350,000 

770,800,000 

31 

27 

14 

$ 8,961,000,000 

10,406,000,000 

1,349,000,000 

$20,716,000,000 

TABLE 9.-Deaths and hospitalized injuries 

[Adapted from Algermissen, 1972, p. 121] 

Magnitude 

Time of 

Day 

San Andreas fault 

8.3 ______________ 2:30a.m. 

2:00p.m. 

4:30p.m. 

7.0 ______________ 2:30a.m. 

2:00p.m. 

4:30p.m. 

6.0 ______________ 2:30a.m. 

2:00p.m. 

4:30p.m. 

Hayward fault 

8.3 ______________ 2:30 a.m. 

2:00p.m. 

4:30p.m. 

7.0 ______________ 2:30a.m. 

2:00p.m. 

4:30p.m. 

6.0 ______________ 2:30a.m. 

2:00p.m. 

4:30p.m. 

Total 

Deaths 

2,850 

9,460 

10,360 

500 

1,640 

1,990 

25 

80 

100 

3,120 

7,200 

6,650 

1,040 

3,200 

2,240 

330 

730 

700 

Total 

Hospitalized 

Injuries 

10,800 

34,400 

40,360 

1,900 

6,200 

11,680 

100 

320 

390 

11,600 

28,500 

24,900 

3,860 

9,900 

8,160 

1,220 

2,600 

2,550 

pancy were then located on a map together with generalized hazard zones. It became clear that buildings 

with high occupancy either during the day or night 

were located in zones of moderate or low hazard. The 

Palo Alto study (1976, p. 55) states: 

Measures to lessen risk to human life and property should focus upon 

identified areas of population concentration and be keyed to areas of 

greatest natural hazard and areas of known or suspected structural 

hazard. 

RELATIVE RISK 

Levels of seismic risk are commonly expressed in 

relative terms. The important point to remember is 

that a map of seismic hazard zones does not show exposure to hazards; information must include types of 

structures and occupancy characteristics. The term 

seismic risk map or zones is often used in a misleading 

sense. 

The report by the Tri-cities Seismic Safety and Environmental Resources Study (Armstrong, 1973), illus-
SEISMIC SAFETY AND LAND-USE PLANNING B51 

TABLE 10.-Life loss from dam failure 

[The figures represent the worst conditions as they may currently exist, assuming unsafe dams. All of these dams are (or will be) re-evaluated for safety, and appropriate corrections will be made if unsafe. From Algermissen, 1972, p. 132. Asterisks indicate flgures not available.] 

Maximum Possible 

Individuals Exposed 

Dam Day Night 

~~~~b~o, ~;-s;i~~~;-------------------------- 95,000 91,000 

and San Pablo Upper San Leand~~---------------------------- 49,000 51,000 

and Chabot---------------------------------- 86,000 109,000 

Lower Crystal Springs ------------------------ 61,000 57,000 

Calaveras, James 

Turner, and Del 

Valle ________________________________________ 125,000 136,000 Only Calaveras________________________________ 35,000 40,000 

Only Del Valle-------------------------------- 21,000 24,000 

Lexington ------------------------------------ * 72,000 

Andrson and Coyote -------------------------- * 18,000 

trates a means of evaluating risk for a given structure 

or proposed project. Each of the following four factors is 

assigned a high, medium, or low-risk rating: geology of 

the general area, geology of the site, structures, and 

building uses. The rating for the geology of the general 

area is determined from the risk zones shown by 

Algermissen (1979). A rating of local geologic conditions is obtained by using the best information available on risk from active faults, slope stability, liquefaction, tsunamis, seiches, and ground shaking. 

Structural hazards are rated according to type of building construction. Table 12 lists common structural 

types of buildings in order of increasing susceptibility 

to damage in an earthquake. Table 13 provides the 

basis for rating various building uses. The term ~~ordinary" risk in table 13 applies to structures which 

would: resist minor earthquakes without damage; resist moderate earthquakes without structural damage, 

but with some nonstructural damage; resist major 

earthquakes of the intensity of severity of the strongest 

experienced in California, without collapse, but with 

some structural as well as nonstructural damage. In 

most structures it is expected that structural damage, 

even in a major earthquake, could be limited to repairable damage (Armstrong, 1973, p. 162). Using the four 

risk levels, the Tri-cities study gives several examples 

of risk assessment for particular uses of specific sites. 

Table 14 is an example of one such assessment for a 

motor inn. Note that this seemingly simple analysis 

depends on quite specific information concerning seismic hazards at the site, and the structural and use 

characteristics of the structure. The procedure is 

adaptable to assessing existing risk levels or changes 

in risk if changes in land use are proposed. Thus risk, 

although not quantified, is expressed in a way that can 

be applied directly to many planning decisions. 

Maximum Possible Estimated 

Deaths Probable Deaths 

Day Night Day Night 

11,000 7,000 7,000 5,000 

29,000 30,000 20,000 25,000 

50,000 52,000 30,000 35,000 

30,000 31,000 20,000 25,000 

30,000 34,000 20,000 24,000 

8,000 7,000 5,000 5,500 

15,000 19,000 10,000 13,000 

* 20,000 * 15,000 

* 5,000 * 3,000 

SCENARIOS 

Another technique for expressing risk is through a 

scenario, a fictional but realistic description of a disaster and the chain of related events, told in the order in 

which they occur. 

Scenarios are especially effective in awakening public concern for seismic safety because they are dramatic. A good scenario requires accurate, specific 

information and should clearly identify areas and 

structures of greatest risk. It can serve as a basis for 

developing policy, and, more important, it can 

dramatize the need for reducing risk. 

However risk is expressed, the assessment should be 

as clear and understandable as possible. Elaborate 

statistical studies of risk, although useful for some 

purposes, are not needed for most planning purposes. 

As stated in San Diego County's general plan (San 

Diego County, 1975, p. v-2): 

The problem with quantitative approaches lies in the complexity of 

principles upon which risk judgments are made. Risk is a function of 

the underlying lithology of the site and its proximity to an earthquake epicenter (sic) and varies with the use of the structure as well 

as the type, kind and quality of construction. Given those independent factors and economic and social impacts, the mechanical determination of an arbitrary level of risk is too simplistic. 

Statistical expressions of risk based on historic records are particularly chancy when applied to infrequent, catastrophic events, such as major earthquakes, if the historic record is fairly short. One event 

greatly affects loss, injury, and death rates for years to 

come. Conversely, if no major earthquake has occurred 

during the period studied, an unduly ~ptimistic picture 

of the degree of risk is conveyed. 

The foregoing examples of risk assessment evaluate 

existing risk levels, but risk assessment needs to be a 

flexible tool. It can also be used to assess the risks 
B52 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

TABLE 11.-U.S. population-at-risk by seismic risk zone and state 

[From Ayre, 1975] 

State Total Population ZoneD 

Alabama ________________________ 3, 444,165 1,056,000 Alaska ___________________________ 300,382 0 

Arizona ----------------------- _1, 722,482 0 

Arkansas ---------------------_1,923,295 0 

California ______________________ 19,953,134 0 

Colorado ________________________ 2,207 ,259 0 

Connecticut ____________________ 3,032,217 0 

Delaware ________________________ 548,104 0 

Florida ________________________ 6,789,443 5,503,000 

Georgia ________________________ 4,589,575 0 

Hawaii __________________________ 768,324 30,000 Idaho ____________________________ 712,567 0 

Illinois ------------------------11,113,976 0 

Indiana --------------------- ___ 5,193,669 0 Iowa ____________________________ 2,825,041 0 

Kansas ------------------------2,249,071 0 Kentucky ______________________ 3,219,311 0 

Louisiana ______________________ 3,643,180 0 ~aine ____________________________ 993,663 0 ~aryland ______________________ 3,922,399 0 ~assachusetts ----- _____________ 5,689,170 0 ~ichigan ______________________ 8,875,083 0 ~innesota ______________________ 3,805,069 0 ~ississippi _____________________ 2,216,912 269,000 ~issouri _______________________ _4,676,501 0 

Montana ________________________ 694,409 0 

Nebraska ----------- ___________ 1,483, 791 0 

Nevada __________________________ 488,738 0 

New Hampshire __________________ 737,681 0 

New Jersey ______________________ 7,168,164. 0 

New ~exico --------------------1,016,000 0 

New York ______________________ 18,236,967 0 

North Carolina __________________ 5,082,059 0 

North Dakota ____________________ 617,761 0 

Ohio --------------------------10,652,017 0 

Oklahoma ______________________ 2,559,253 0 

Oregon -----------------------_2,091,385 0 

Pennsylvania __________________ 11,793,909 0 

Rhode Island ____________________ 946,725 0 

South Carolina __________________ 2,590,516 0 

South Dakota ____________________ 665,507 0 

Tennessee ______________________ 3,923,687 0 

Texas __________________________ 11,196, 730 9,859,000 

Utah ---------------------- ____ 1,059,273 0 

Vermont ________________________ 444,330 0 

Virginia _______________________ _4,648,494 0 

Washington ____________________ 3,409,169 0 

Washington, D.C. ________________ 756,510 0 

West Virginia ----------------- _1, 7 44,237 0 

Wisconsin ______________________ 4,417,731 0 

Wyoming ________________________ 332,416 0 

Totals __________________ 203,223,000 16,717,000 (100%) (8%) 

inherent in proposed land use or occupancy change. 

Procedures for assessing risk should be designed to accommodate new information concerning seismic 

hazards, changes in structural conditions, occupancies, 

and other risk parameters. 

DETERMINING ACCEPT ABLE RISKS 

Public actions to reduce risk involve at least an 

implicit determination of ((acceptable risk." Acceptable 

risk, from the point of view of the public agency, is that 

level of risk at which no governmental response is conEstimated Population-at-Risk by Seismic Risk Zone 

Zonel Zone2 Zone3 

1,126,000 1,263,000 0 

6,000 25,000 270,000 

0 1,742,000 30,000 

1,473,000 166,000 284,000 

0 2,636,000 17,317,000 

2,207,000 0 0 

2,948,000 85,000 0 

548,000 0 0 

1,286,000 0 0 

1,777,000 2,812,000 0 

637,000 39000 63,000 

0 513,000 200,000 

9,951,000 895,000 268,000 

2,350,000 2,608,000 236,000 

2,825,000 0 0 

1,907,000 342,000 0 

1,349,000 1,467,000 403,000 

3,643,000 0 0 

318,000 675,000 0 

3,734,000 189,000 0 

0 1,980,000 3,709,000 

8,875,000 0 0 

3,805,000 0 0 

1,674,000 217,000 57,000 

3,079,000 1,389,000 209,000 

240,000 313,000 142,000 

1,206,000 278,000 0 

0 300,000 189,000 

0 738,000 0 

7,168,000 0 0 

536,000 480,000 0 

13,211,000 2,481,00 2,545,000 

2,172,000 2,910,000 0 

618,000 0 0 

7,863,000 2,789,000 0 

2,399,000 160,000 0 

539,000 1,539,000 13,000 

11,347,000 183,000 264,000 

84,000 863,000 0 

0 1,577000 1,013,000 

666,000 0 0 

1,165,000 1,810,000 949,000 

1,325,000 13,000 0 

40,000 48,000 972,000 

0 444,000 0 

2,435,000 2,213,000 0 

0 1,240,000 2,169,000 

757,000 0 0 

1,509,000 236,000 0 

4,418,000 0 0 

308,000 19,000 5,000 

115,091,000 40,442,000 30,973,000 

(57%) (20%) (15%) 

sidered necessary. Acceptable risk is rarely expressed 

in quantitative terms, but is embodied in the riskreduction policies, regulations, and standards adopted 

by the public agency. 

Acceptable risk is a measure of willingness to incur 

costs to reduce risk. Aiming for a totally risk-free environment is unrealistic; some balance must be sought 

between risk and the costs of reducing it. The balance 

actually struck by a governmental agency represents 

its choice of an acceptable level of risk. The choice can 

be made explicitly by public bodies based on evaluation 
SEISMIC SAFETY AND LAND-USE PLANNING B53 

2:00 P.M. / 2:00A.M. POPULATION ON WEEKDAYS, BY CENSUS TRACT 

~;::~s ~~:h~~~~~~~~;~::n iliiiiliii 5046 56 I 500 

509) 

5094 

5106 

510'7 

5109 

s 110 

Sill 

5 11 2 

5113 

5114 

5115 

5116 

5 11 7 

Cum me rcial, indu strial , or 

mult·family wit h more than 

10 units 

Srhool 

Buildings wilh J or more stories 

EB Hosoitals 

® Jail 

••• Plan ning area bound:uy 

s 116 

A 

Reference- data gath<.-red in the field 

and from bui l ding inspect ion 

records by rhe Palo Alto 

Planning Department 

COMPOSITE 

RISK ZONES 

References compilation by Palo Alto 

Planni ng Depart ment of fl ood risk 

a reas (HUD Flood Insurance Admin istrat ion Data) ground shakin g, ground 

failure, and landslide hnard areas 

lUSCS data) 

c 

EXPLANATION 

High risk 

FIGURE 25.-Census of population density for Palo Alto, Calif. A, At 2:00a.m., most people are in woodframe houses, structures which are 

likely to suffer the least damage from a great earthquake. At 2:00p.m., people are in school, at work, on the roads, and in commercial 

buildings which are areas of high population density and greater structural hazard. B, Areas of high population density. C, Fault line 

areas have the greatest risk for manmade structures. High risk is also associated with bay mud, landslide-prone hillsides, and areas 

susceptible to flooding. Moderate risk areas involve potential liquefaction, ground shaking, and some flooding. Low risk areas are 

susceptible to some liquefaction and some ground shaking. 

of the level of risk and the means and costs of reducing 

that risk. Such an evaluation is particularly relevant 

when a public agency is considering land-use plans and 

regulations, siting and design of major public facilities, 

renewal or rehabilitation of existing built-up areas, 

emergency-preparedness plans, and building-code requirements. 

LAND-USE PLANNING AND SEISMIC SAFETY 

Increasing seismic safety through land-use planning 

is at present primarily a function of local government, 

and local actions are central to reducing seismic risk. 

Most of the power to adopt and administer land-use 

and development regulations and building codes is now 
B54 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

TABLE 12. - Earthquake ratings for common building types 

fThis table is not complete. Additional considerations would include parapets, building interiors, utilities, building orientation, and frequency response (Armstrong, 1973, p. 167)] 

TABLE 14.-Risk analysis of a motor inn 

[(From Armstrong, 1973, p. 174)] 

Relative damageability Factors Situation of motor inn Risk 

Simplified description of structural types (in order of increasing 

susceptibility to damage) 

Small wood-frame structures, i.e., dwellings 

not over 3,000 sq. ft., and not over 3 stories __ ____ ___________ _ 1 

Single or multistory steel-frame buildings 

with concrete exterior walls, concrete floors, 

and concrete roof. Moderate wall openings __________________ 1.5 

Single or multistory reinforced-concrete 

buildings with concrete exterior walls, 

concrete floors, and concrete roof. 

Moderate wall openings ------- ---- -------- -----------------2 

Large area wood-frame buildings and other 

wood-frame buildings ___________________ ____ ____ _______ 3 to 4 

Single or multistory steel-frame buildings 

with unreinforced masonry exterior wall 

panels; concrete floors and concrete roof ___________ ______ ____ _______ ________________ __ __ _______ _ 4 

Single or multistory reinforced-concrete 

frame buildings with unreinforced masonry 

exterior wall panels, concrete floors 

and concrete roof ___________________ ___ ________ ______________ 5 

Reinforced concrete bearing walls with 

supported floors and roof of any materials 

(usually wood) ____ ____ ____ ______ ______ __________ ___________ _ 5 

Buildings with unreinforced brick masonry 

having sandlime mortar; and with 

supported floors and roof of any materials 

(usually wood) -------- ------- --- ----- -------------- - -- - -7 up :Bearing walls of unreinforced adobe, un- reinforced hollow concrete block, or 

unreinforced hollow clay tile ----- ---- ----- Collapse hazards 

in moderate shocks 

TABLE 13.-Scale of risks for various building uses 

[Adapted from Scale of acceptable Risks of the Structural Engineers Association of California, in Armstrong, 1973, p. 162] 

Level of risk to public Kinds of structures 

Failure of a single structure may affect substantial 

populations 

Extremely high ______ Structures whose continued functioning is 

critical, or whose failure might be catastrophic: nuclear reactors, large dams power 

inter-tie systems, plants manufacturing 

explosives. High _____ ____ _____ __ Structure whose use is critically needed after 

a disaster: important utility centers, hospitals, fire, police and emergency communcation facilities, and critical transportation 

elements, such as bridges & overpasses; 

also smaller dams. 

Failure of a single structure will affect primarily only the 

occupants 

Possible high risk 

to occupants _____ ___ Structures of high occupancy, or whose use 

An "ordinary" level 

after a disaster will be particularly convenient: schools, churches, theaters, large 

hotels and other high-rise buildings housing large numbers of people, other places 

normally attracting large concentrations of 

people, civic buildings such as fire stations, 

secondary utility structures, extremely 

large commercial enterprises, most roads, a lternate or noncritical bridge and overpasses. 

of risk ______________ The vast majority of structures: most commercial and industrial buildings, small 

hotel and apartment buildings, and 

single-family residences. 

Geology ____ ____ ______ __ Tri-Cities area, 

several fault 

systems nearby. 

Site __ ___ ___ ____ ________ On fault zone, 

perhaps directly 

over fault trace. 

landslide 

adjacent. 

Structure __ ___ __ _______ Multistory 

utilities. 

Building ____ ____ ______ __ Large number 

use of occupants. 

High 

High to 

very 

high 

Medium 

Medium 

to high 

Total risk for all factors ____ ____ ______ _________ High 

lodged with local government. Also, the primary responsibility for emergency response by police, fire, and 

public works agencies is locaL Local areas may be isolated after an earthquake and depend entirely on local 

emergency services to protect life and property for a 

significant period of time before outside aid is available. This section describes how local land-use planning and decisionmaking can reduce seismic risk. 

THE PLANNING PROCESS 

Planning is the process of devising and carrying out 

a course of action to reach an objective. As an organized 

governmental activity, planning seeks to improve the 

decisions of public bodies and administrators. Comprehensive planning affects the future development of 

an area and involves all major determinants of growth 

and change-economic, political, social, and physicaL 

To be effective for seismic risk reduction, the comprehensive planning process must result in specific 

land-use decisions. The process described here provides 

for a land-use plan as a key component of the comprehensive plan; it forms a link between more general 

goals and policies and the pattern ofland development. 

A land-use plan includes objectives, policies, and 

proposals for the type, pattern, and intensity of land 

use. It typically specifies the general location of different types of land uses, transportation lines, and public 

facilities. A functional plan defines needed facilities 

and operations for a specific function of government 

such as transportation, water development, flood control, or emergency response; it is more specific than a 

comprehensive plan and usually covers a shorter 

period of time. Any plan, when adopted by the governing body of an agency, becomes official public policy. 

The development of comprehensive, and functional 

land use plans generally consists of six steps: (1) iden-
SEISMIC SAFETY AND LAND-USE PLANNING B55 

tifying problems and general goals and objectives, (2) 

collecting and interpreting data, (3) formulating plans, 

(4) evaluating impacts, (5) reviewing and adopting 

plans, and (6) implementing plans. These steps, shown 

in figure 26, are all interrelated. Plan formulation 

often indicates the need for additional information; additional information may reveal the need for additional 

information or modification of the plan. 

The steps in the planning process constitute a rational, systematic approach to informed decisionmaking and are applicable to most governmental activities. 

The product is a logical and internally consistent plan, 

or set of plans and programs, to guide public and private decisions. The planning process is ongoing; it 

produces refinements, revisions, and new plans, and 

implements programs as additional information is obtained, new issues and problems are raised, or changes 

in public attitudes are recognized. Public participation 

is essential throughout the planning process. Success 

in implementing a plan depends on widespread public 

support which can only be gained if all major segments 

of the public participate in the planning process, and 

not always then. 

Decisions occur throughout the process, ranging 

from the decision to engage in a planning effort, to the 

final approval of a plan and adoption of implementing 

regulations, programs, and procedures. Elected public 

officials have the final responsibility for most key policy decisions although persons in nonelective positions 

actually make many important day-to-day decisions. 

Where earthquakes are a recognized hazard, seismic 

safety is an important part of comprehensive land-use 

and functional planning. Comprehensive plans deal 

with the social, economic, and physical ramifications of 

seismic risk and methods of reducing it; and functional 

plans with the procedures, actions, and resources 

needed for improving seismic safety in a given government function, such as transportation, water 

supply, and fire protection. But because the degree of 

seismic risk depends on the location of structures and 

facilities in relation to seismic hazards, the land-use 

plan is a key document for expressing a community's 

response to seismic risk; seismic safety can be addressed in every step of the land-use planning process. 

IDENTIFY ISSUES AND DEFINE OBJECTIVES 

Reviewing available information to identify the 

major land-use issues and problems helps define the 

scope of the plans and the limits of the planning area. 

The issues and problems are then analyzed in relation 

to existing development, current land-use plans and 

policies, projected economic and population growth, 

and other anticipated changes. Based on this analysis, 

a tentative set of goals, objectives, and priorities is 

formulated. In this step potential seismicity is evaluated to identify seismic safety problems and define objectives for reducing risk. Accounts of historic earthquake damage in the area, or regional seismicity maps 

such as the Seismic Risk Map of the United States (fig. 4), 

can indicate the relative importance of considering seismic risk in land-use planning in a given area. 

COLLECT AND INTERPRET DATA 

Previously compiled data are evaluated for adequacy, and a program for acquiring and interpreting 

new data is prepared. The data needed include descriptions of the economic, social, cultural, political, 

and natural characteristics of the planning area as a 

basis for estimating the future requirements for spePublic initiative and response 

IDENTIFY 

PROBLEMS 

AND DEFINE 1---,.. 

GOALS AND 

OBJECTIVES 

COLLECT 

AND 

2 

INTERPRET 1---PI 

DATA 

3 

FORMULATE 

PLANS 

4 

EVALUATE 

IMPACTS 

Feedback for review and revision 

FIGURE 26.-The planning process. 

REVIEW 

AND 

ADOPT 

PLANS 

5 6 

IMPLEMENT 

PLANS 
B56 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

cific kinds of land uses. Geologic and other information 

describing the natural features of the planning area is 

needed to describe natural hazards and resources relevant to land-use decisions. 

Because collecting and interpreting data is expensive and time-consuming, this study should be closely 

related to the issues and objectives of the planning program. A careful analysis of available general information can pinpoint those areas where more detailed data 

and analyses are needed. In some instances existing 

development or readily identifiable physical conditions 

may so restrict the land-use options that little new information is needed. 

The degree of seismic risk is assessed during this 

step. Cooperation between planners and earth scientists, particularly seismologists and geologists and 

structural and soils engineers, is needed to identify and 

evaluate seismic hazards in relation to existing and 

potential land and building uses. 

FORMULATE PLANS 

Based on data and analyses gathered in the previous 

step, alternative policies, criteria, standards, and proposals are evaluated for responsiveness to the goals 

and objectives already identified. The environmental, 

social, political, and economic impacts of the policies 

and proposals are tested as a part of the process of 

selecting alternatives for presentation to the policy 

bodies. The evaluation of the alternatives is the heart 

of plan formulation. The plan should provide sufficient 

detail and definition to guide future growth and change 

in the planning area. The level of detail needed depends on the complexity of the planning area, the nature of the decisions anticipated, and the authority of 

the agency. 

Policies related to seismic hazards should be incorporated into the comprehensive plan. As previously 

noted, California law provides for this by requiring all 

city and county general plans to include a seismic 

safety element. This element usually consists of a description and evaluation of seismic hazards, together 

with policies and recommendations for improving 

seismic safety. These policies and recommendations 

should be reflected in the land use, open space, safety, 

circulation, and other general plan elements. The 

land-use/seismic risk relationships of alternative policy options should be thoroughly considered in plan 

formulation. Policies and critieria for seismic safety 

should be specific enough to provide a basis for land use 

and development regulations and building code requirements. 

EVALUATE IMPACTS 

The impact evaluation, begun as a part of plan formulation, is formalized in this step for the land-use 

plan (or alternatives) selected for presentation to the 

policy body responsible for plan approval or adoption. If 

formal reports on environmental impact are required, 

by State or Federal law, the scope of the report is well 

defined. The method of analysis may be either quantitative or qualitative. California law requires an 

environmental impact report for any plan or plan element which might have significant environmental impact. 

The environmental, social, and economic impacts of 

proposed measures to reduce risk should also be evaluated. The loss of life and the amount of damage from an 

earthquake depends on the land-use pattern. To aid in 

the decisionmaking, the levels of risk associated with 

alternative land-use patterns should be stated as explicitly as possible. 

REVIEW AND ADOPT A PLAN 

The plan or plan alternatives and the report evaluating impact are reviewed by the legislative body of the 

planning jurisdiction. Public hearings are scheduled 

and publicized to encourage the widest possible public 

response to the plan proposals. In California, cities and 

counties are required to hold public hearings before 

official adoption of any element of the general plan. 

Although comment and criticism by individuals and 

institutions is sought earlier in the planning process, 

new questions and issues are often raised at this point 

and plan policies and proposals may be modified as a 

result. 

After plan review, the plan may be adopted as an 

official statement of policy and a commitment to a future course of action. All states do not require that 

local general plans be adopted officially as does 

California. However, because many Federal grant programs require formally adopted plans as a condition of 

eligibility, the practice is expected to become more 

widespread. Measures needed to implement the plan 

must be specified and clearly understood by the legislators and their constituents and, because circumstances and priorities change, procedures for amending 

an adopted plan also should be established. 

IMPLEMENT THE PLAN 

Implementing a land-use plan depends on coordinating, scheduling, and carrying out a variety of measures. Land-use regulation alone may fail to reduce 

seismic risk significantly, particularly if the hazard 

exists primarily in developed areas. Therefore, regulations need to be combined with other measures such as 

public acquisition of land, urban renewal, redevelopment, and code enforcement. Implementing a plan is 

an intensely political process, and it directly affects the 

legal rights, economic and social status, and living and 

working environment of individuals in a community. Im-
SEISMIC SAFETY AND LAND-USE PLANNING B57 

plementation thus depends on the active support of residents and organizations within a planning jurisdiction. 

The powers to implement plans and the methods 

used to implement them are different for each state 

and for each jurisdictional level. For example, most 

regional agencies rely on a project review process, 

while local governments have broad powers to regulate 

land use and development, tax, acquire land, and construct and operate facilites. Despite this diversity, 

most implementing measures fall logically into one of 

three categories: 

1. Controlling land use and development through 

zoning, subdivision, and grading ordinances, 

and building and housing codes; 

2. Reviewing projects, both public and private, for 

conformity with an approved general plan 

and for environmental impact pursuant to 

State or Federal laws or regulations (such as 

the U.S. National Environmental Policy Act 

of 1969 or the U.S. Office of Management and 

Budget Circular A-95); and 

3. Developing and executing governmental programs for acquiring land, constructing public 

facilities, providing public services, or redeveloping and rehabilitating substandard 

parts of the community. 

PLANNING EXAMPLES 

Examples of plans, regulations, and administrative 

procedures to reduce seismic risk are described below. 

These examples are drawn mainly from cities and 

counties in California. Because the State requires each 

city and county to adopt a seismic safety element as 

part of its general plan, many examples of local plans 

to reduce seismic risk are found in California and illustrate methods that can be used elsewhere. Most of the 

examples are from the San Francisco Bay region because it has an array of earthquake hazards, much scientific data that can be used for planning, and a diverse 

assortment of planning agencies. 

Planning to reduce seismic risk varies for different 

earthquake hazards. Planning to reduce risk from surface rupture is reasonably straightforward where active faults are recognized and mapped, as they are in 

California. On the other hand, dealing with problems 

of ground shaking is more difficult because few maps of 

potential levels of gro"und shaking are available. Reducing risk requires adjusting both land uses and 

structural types to the anticipated intensity, frequency, and duration of shaking. In addition, areas of 

severe ground shaking are usually more extensive 

than the fairly narrow bands which are subject to surface rupture. 

Methods to reduce seismic risk also depend on the 

degree of development of a planning area. Land-use 

planning to reduce seismic risk is most effective and 

least costly in areas just being considered for development. 

PLANNING TO REDUCE RISK FROM GROUND SHAKING 

To reduce risk from ground shaking requires the collaboration of planners, structural engineers, and earth 

scientists. Planners provide information about the 

present and future locations of high-occupancy structures, critical facilities, and hazardous structures, and 

the planning techniques available to control the future 

development. Structural engineers provide advice regarding criteria for safe building design, the safety of 

existing structures, and techniques to reduce existing 

structural hazards. Earth scientists evaluate the ground 

response characteristics of a postulated earthquake. 

Seismic safety objectives are most likely to be attained when they coincide with other planning objectives. For example, preserving the margins of San 

Francisco Bay for ecological and environmental reasons is consistent with seismic safety objectives because these areas, underlain primarily by bay mud, are 

susceptible to severe ground shaking and several forms 

of ground failure. Land-use regulations are likely to 

receive wider public support and withstand legal challenge better if they meet more than one objective. 

The result of such joint efforts can be a land-use plan 

in which differences in expected ground shaking levels 

influence the location and intensity of proposed future 

development. This matching can only be done in areas 

where there is a significant variation in predicted 

levels of ground shaking. Even then, it should be recognized that land-use decisions properly reflect economic, social, and political, as well as other natural 

conditions; a perfect match of land uses and seismic 

risk is rarely achieved. 

Ground shaking problems can often be directly handled in undeveloped areas by requiring seismic and 

geologic site investigations before approving development proposals and establishing and enforcing building design and construction standards consistent with 

the seismic risk. In developed areas, the problems can 

be handled by abating existing structural hazards 

through removal or strengthening of parapets and 

other building appendages, basic structural improvement, changes in occupancy, or demolition. Examples 

of such plans and actions follow. 

SITE INVESTIGATION AND DESIGN REQUIREMENTS 

The San Jose seismic safety element (Duncan and 

Jones, 1974) is based on a thorough geotechnical study 

of the San Jose planning area by Cooper, Clark, and 

Associates. This study defines the complex relationship 

between ground-shaking characteristics and structural 
B58 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

type and height as follows (Cooper, Clark, and Associates, 197 4, p. 63): 

The effect of ground motion on buildings depends not only on the 

characteristics of the ground motion, but also on the characteristics 

of the buildings. The fundamental periods for typical single-story, 

10-story, and 40-story buildings, are on the order of 0.2, 1.0, and 4.0 

seconds, respectively. If a building is subjected to a series of ground 

vibrations having the same period as its fundamental period, large 

amplitude motions and high internal stresses develop. On the other 

hand, if the same building is subjected to base vibrations having a 

period very different from its fundamental period, comparatively 

small internal stresses will be induced. Accordingly, it is desirable to 

develop as great a difference as possible between the fundamental 

period of a building and the fundamental period of the estimated 

ground surface motion. 

The San Jose geotechnical report divides the planning area into seven ground-response zones based 

primarily on depth to bedrock. Expected ranges of 

maximum ground surface accelerations and fundamental periods were estimated for each zone. This information can be used to highlight areas where 

ground-shaking characteristics could cause serious 

damage to particular types of structures. For example, 

highrise buildings may sustain more damage in areas 

of deep alluvium than single-story structures. The 

study indicates these areas where ground response 

may cause severe problems and where further investigation should be undertaken before development decisions are made. 

The San Francisco Community Safety Plan (San 

Francisco Department of City Planning, 1974) evaluates the possibility of ground shaking in a similar way, 

observing that the effect of ground shaking on buildings can be compensated for by proper design and engineering. The report recommends uspecial soilsengineering and geologic investigations in areas of potentially strong ground shaking" (San Francisco, Department of City Planning, 1974, p. 23), and building 

code standards incorporating safety factors consistent 

with the building type, use, and site conditions. 

ABATING STRUCTURAL HAZARDS 

A particularly difficult and costly problem is the 

abatement of existing structural hazards. The San 

Francisco plan estimated the damage that would result 

from an earthquake similar to the one in 1906 by 

analyzing data on the age, use, construction type, 

number of stories, and floor area of existing structures 

in relation to the geologic conditions that affect ground 

motion. The damage potential of each block was 

classified as severe, heavy, moderate, or slight (fig. 27). 

Individual buildings were not analyzed. Precode, Type 

C buildings were also noted. Precode buildings are 

those constructed before 1948 when comprehensive 

lateral force requirements to resist earthquake shaking were included in the San Francisco building codes; 

Type C buildings have masonry or concrete exterior 

bearing walls with wood floors and roofs. More than 

1,400 residential buildings with nearly 35,000 living 

units and 2,800 nonresidential buildings were identified as precode, Type C construction. Their density 

was mapped by census tract (fig. 28). At 1975 construction costs, replacing these buildings would cost more 

than one billion dollars (San Francisco Department of 

City Planning 197 4, p. 20). 

Objectives and policies to abate structural hazards 

pertain to areas where damage levels are expected to 

be severe such as in precode, Type C structures, (fig. 8), 

and in Special Geologic Study Areas (fig. 29) which 

have potential for ground failure or flooding. Priority is 

assigned to ~~(1) areas with high concentrations of potentially hazardous precode, Type C buildings; (2) 

areas with high population densities; and (3) those 

structures for which there is a critical community 

need" (San Francisco, Dept. of City Planning 1974, p. 

42). 

Eliminating existing structural hazards often conflicts with other community objectives and is politically 

difficult to achieve. Although San Francisco adopted an 

ordinance in 1969 requiring removal or strengthening 

of unsafe parapets and building appendages, little has 

been done to enforce the ordinance. 

Concern over both private and public costs, resistance of property owners, the absence of political support, and concern for the effect on the architectural 

character of the city are reasons for the lax enforcement of the parapet ordinance. The Community Safety 

plan emphasizes preserving architectural character. 

Voluntary compliance with the ordinance had resulted 

in ua severe loss of building character and appearance" 

(San Francisco Dept. of City Planning, 1974, p. 56). 

PLANNING TO REDUCE RISK FROM GROUND FAILURE 

The most damaging forms of earthquake-induced 

ground failure are landsliding and failures caused by 

liquefaction. 

LANDSLIDING 

Plans and regulations to reduce risk from slope failure are similar under seismic and nonseismic conditions. Where unstable slopes are identified, land uses 

can be restricted, geologic investigations can be required before development is allowed, and grading and 

foundation design can be regulated. 

The Town of Portola Valley has taken strong actions 

to reduce future losses from landslides. Spurred by incidents in the wet winter of 1969, the town retained a 

geologist to assemble the information needed to improve land-use decisions by avoiding landslide hazards. 

A geologic map at a scale of 1:6,000 was complied and 

was used to prepare a landslide potential map (officially titled the Land Movement Potential of Undis-
SEISMIC SAFETY AND LAND-USE PLANNING B59 

tO 

,- .... --

\ 

\ 

I 

DAMAGE 

- Severe 

• Heavy 

D Recently demolished or to be demolished. 

Information not available or not in study 

0 Moderate 

D Slight Source. John A. Blume 8 Associa!H, Engineers, June 1974 

FIGURE 27.-Estimated building damage levels for a "1906-type" earthquake, San Francisco Calif. (San Francisco Department of City 

Planning, 1974, p. 18) 

turbed Land Map) at the same scale. Provisions were 

added to the local zoning, subdivision, and grading ordinances, requiring that geologic information be submitted for review and approval by the Town Geologist 

before development. Even with the establishment of 

review procedures, it became evident that a consistent 

policy would be needed to relate the types of permissible land use to the possibilities of landslides. To assist 

in formulating such a policy, the town council appointed an eight-member geologic committee, chaired 

by the Town Geologist and composed of three geologists, two engineering geologists, a soils engineer, an 

attorney, and a planner. The committee recommended 

criteria to relate land uses to the stability categories 

shown in table 15. The geology map, landslide potential map, and criteria for permissible land use were 

adopted by resolution of the town council to guide 

land-development decisions. The town council felt that 

land-use regulation through zoning or other specific 

restrictions was not warranted because the landslide 

potential of individual parcels within each mapped 

category may vary, and because site investigation may 
B60 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

c::::::::J .01- 4. 91 k·.·.· .. '·''''''''"''' 5-19.9 

~~~:~ Units per gross acre 

-60-85.64 

DENSITY OF PRECODE (1948) TYPE C RESIDENTIAL UNITS 

(by 1970 Census Tracts) 

DENSITY OF PRECODE (1948) TYPE C NON-RESIDENTIAL BUILDINGS 

(by 1970 Census Tracts) 

FIGURE 28.-Precode, Type C buildings in San Francisco, Calif. (San Francisco 

Department of City Planning, 1974, p. 53). 
SEISMIC SAFETY AND LAND-USE PLANNING B61 

::m~;:.::::;:;.;;~~ potential ground failure hazards 

'11'/////fi Potential inundation hazards 

FIGURE 29.-Special geologic study areas, San Francisco, Calif. (San Francisco Department of City Planning, 197 4, p. 44). 

show that a given parcel is more or less stable than 

mapped. The resolution provides for incorporating in 

the official map any new information from site investigations. 

Portola Valley's response to landslide problems is to 

avoid hazardous areas-a response consistent with the 

town's existing and planned pattern of low-density residential development and policies for preserving the 

natural environment. In jurisdictions fostering urbanization or in already intensively developed areas, special site and building design or engineering to mitigate 

the risk from slope failure may be emphasized. 

The San Francisco Community Safety Plan includes 

landslide-prone areas in Special Geologic Study Areas 

(fig. 29). The plan (San Francisco Department of City 

Planning, 197 4, p. 43) states: 

Special site investigations should be required in these potential 

hazard areas to determine the actual hazard, if any, for all proposed 

new development. Based upon the finding of the site investigation 

and determination of type and degree of hazard present, appropriate 

engineering design should be required to ameliorate the hazard. If 

proper engineering design is not technically or economically feasible, 

development of the site should not be permitted. 

Even if it is technically feasible, mitigating landslide 

problems is often expensive, not only for the property 

owner, but also for the public agency which must maintain roads, utilities, and other essential facilities. 

Whenever possible, it is wise to encourage open space 

or low-intensity uses for landslide-prone areas. 

LIQUEFACTION 

Reducing risk from liquefaction is one aim of the 

Santa Clara County Baylands Plan (Planning Policy 
B62 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

Committee of Santa Clara County, 1972); this plan 

covers an area subject to liquefaction as well as other 

types of seismic and nonseismic ground failure. 

Geologic and structural engineering consultants identified the natural hazards of the planning area and 

defined their implications for land use. The resulting 

report divided the planning area into risk zones based 

on potential for settlement and ground failure under 

both seismic and nonseismic conditions. Table 16 lists 

the risk zones and the nature of the hazard in each. 

Figure 30 is a map of the risk zones. Table 17 relates 

the land and building uses to the risk zones. 

The plan adopts these uses with the stipulation that 

any developer in the baylands provide data from test 

boring and sample testing in depth, to demonstrate 

that a proposed development site is not in a higher risk 

zone than shown. An Advisory Review Board was recommended to advise public agencies on the adequacy of 

engineering investigations, design, and construction 

methods in the bay lands. 

Based on the plan, the county adopted an ordinance 

requiring a soils report for all major subdivisions unless specifically exempted. Geologic reports and site investigations are required for all subdivisions on or adTABLE 15.-Criteria for permissible land use in Portola Valley 

Land Houses stability Roads (parcel acreage) Utili- Water symbol Public Private 1

/4-Ac l-Ac 3-Ac ties tanks 

MOST Sbr y y y y y y y 

STABLE Sun y y y y y y y 

Sex [Y] y [Y] y y y [Y] 

Sls [Y] [Y] [N] [Y] [Y] [Y] [NJ 

Ps [Y] [Y] [N] [Y] [Y] [Y] [N] 

Pmw [N] [N] [N] [N] [N] [N] [N] 

Ms [NJ [NJ N N N N N 

Pd N [N] N N N N N 

Psc N N N N N N N 

Md N N N N N N N 

LEAST 

STABLE 

Pf [Y] [Y] (Covered by zoning [NJ [N] 

ordinance) 

LEGEND: y Yes (construction permitted) 

[Y] Normally permitted, given favorable geologic 

data and/or engineering solutions 

N No (construction not permitted) 

[N] Normally not permitted, unless geologic data 

and (or) engineering solutions favorable 

s Stable 

p Potential movement 

M Moving 

LAND br bedrock within 3 feet of surface 

STABILITY d deep landsliding 

SYMBOLS: ex expansive shale interbedded with sandstone 

f permanent ground displacement within 100 

feet of active fault zone Is ancient landslide debris mw mass wasting on steep slopes, rockfalls 

and slumping s shallow landsliding or slumping sc movement along scarps of bedrock landslides un unconsolidated material on gentle slope 

jacent to potentially hazardous areas as depicted on 

official county hazard maps. The map ~~Risk zones for 

land-use planning'' (fig. 30) is one of the official hazard 

maps. Geologic reports are normally required for development in risk zones C and D and may be required 

in risk zones A and B. 

PLANNING TO REDUCE RISK FROM SURFACE RUPTURE 

Planning to reduce risk from surface rupture varies 

with the degree of development in the fault zone. In 

California, the Alquist-Priolo Special Studies Zones 

Act (see section on ~~Research and Information") defines 

minimum local actions. 

The most effective way to avoid risk from surface 

rupture is to prevent construction of buildings for 

human occupancy across known active or potentially 

active fault traces. It is very difficult, if not impossible, 

to construct a building which can survive significant 

ground displacement without extensive structural 

damage. Preventing such construction depends on the 

accuracy and scale with which the fault has been 

mapped. 

As better information is available, actions in addition to those based on preliminary findings can be 

taken. 

Potential surface rupture should always be considered in site selection for critical public and private 

facilities, structures for human occupancy, and structural design for lifelines. Preliminary soils and 

geologic reports may be required with major development proposals, and detailed site investigation required if the preliminary report indicates potential 

hazards. A geologist is often needed to help review 

these reports and to help determine when more information is needed. 

TABLE 16.-Risk zones for settlement and ground failure established 

by subsurface conditions in the baylands of Santa Clara County 

[Adapted from Santa Clara County Planning Policy Committee, 1972] 

Risk Zone Surface Effect 

A ____________ Little risk of settlement 

or ground failure 

BnL __________ Significant settlement 

Cs ____________ Moderate to substantial 

settlement and/or differential settlement 

Dn ____________ Substantial settlement 

and (or) differential 

settlement 

DsL __________ Failure of ground 

surface 

__ do __ 

Subsurface Cause 

Liquefaction of confined 

granular layer in 

alluvium (seismic 

loading) 

Consolidation of bay mud or soft clay (static 

loading) 

Consolidation of uncon- trolled dump fill or sanitary land fill 

(static loading) 

Liquefaction of granular 

surface layer 

(seismic loading) 

Lateral spreading toward 

free face (seismic loadin ) 
EXPLANATION 

Risk 

~ 

~ 

zone A 

Risk 

~ 

~ 

zone B 

Based on possibility of deep liquefaction 

~::::~s:<l Risk zone C 

Based on probability 

of settlement 

r-o-~-z-a Risk zoneD 

lased on possibility of 

shallow liquefaction 

NOTE: 

.s-4./)1" 

Rk.t.l)l"c/.sco 

Risk ~ zoneD 

Based 011 possibility of 

lateral spreading 

Risk zoneD 

Based on presence of 

uncontrolled dump fill 

Limit of study area 0 4000 

I I I I I I I 

0 1000 2000 METERS 

The delineation of risk zones is based on limited subsurface information. Risk zone 

designations could change as more detailed subsurface information becomes available. 

"V~ 

~"V 

~+. (\< 

c..¢ 

~() 

~ 0~ 

IS')\ 

c..¢ ~ 

FIGURE 30.-Risk zones for land-use planning, Santa Clara County Bay lands (Santa Clara County Planning Policy Committee, 1972). 

N 

1 00 

t;rj 

~ 

00 

~ 

0 

t;rj 

~ 1-3 

to<: 

~ t:::l 

s: 

z 

t:::l 

(:: 

00 

t;rj 

~ 

> z 

z 

z 

0 

to 

m 

~ 
B64 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

TABLE 17.-Land and building uses appropriate for various risk 

zones, Santa Clara County 

[Adapted from Santa Clara County Planning Policy Committee, 1972, p. 22] 

Land and Building Uses Risk Zones 

A B C D 

Group A Buildings 

Hospitals and nursing homes ________________ x Auditoriums and theatres ____________________ x 

Schools ------------------------------------ x Transportation and airport __________________ x Public and private office ____________________ x 

Major utility -------------------------------- x 

Group B Buildings 

Residential-multiple units ____________________ x x Residential- 1 and 2 family __________________ x x Small commercial __________________________ x x 

Small public -------------------------------- x x Small schools-one story ______________________ x x 

Utilities ------------------------------------ x x 

Group C Buildings 

"Industrial park" commercial ________________ x x x Light and heavy industry ____________________ x x x Small public, if mandatory __________________ x x x Airport maintenance ________________________ x x x 

Group D Buildings 

Water-oriented industry ____________________ x x x 

Wharves and docks -------------------------- x x x Warehouses -------------------------------- x x x 

Group D Open Space 

Agriculture, marinas, public and private open 

spaces, marshlands and saltponds, and small 

appurtenant buildings ___________ x x x x 

SURFACE RUPTURE-UNDEVELOPED AREAS 

A draft of the San Mateo County seismic safety element lists ways to reduce risk from surface rupture 

based primarily on fault mapping at a scale of 1:62,500. 

A portion of this map is shown in figure 31. The 

policy options relevant to largely undeveloped areas 

include: 

1. ((Restrict development within active or potentially active fault zoneS***" (San Mateo 

County, 1975, p. 72) 

2. ((Encourage the State Public Utilities Commission to establish increased design and 

construction standards for utility systems 

traversing active or potentially active fault 

zoneS***" (San Mateo County, 1975, p. 75) 

3. ((Prohibit development of critical use structures in any active or potentially active fault 

zoneS***" (San Mateo County, 1975, p. 77). 

Geologic, seismic, and soil investigations of individual 

sites are recommended before making land-development decisions in the designated fault zones. 

Figure 32 is an example of a Special Studies Zones 

map at a scale of 1:24,000. For regulatory purposes, the 

zone boundaries are very accurately located using a 

coordinate system, but the faults and the fault zones 

are much more complex and irregular. The fault loca"-

tion shown in figure 32 is derived from the 1:62,500 

map (fig. 31) which in turn was based on field mapping 

of the fault and analysis of stereopairs of aerial phows 

at different scales. Direct regulation through zoning 

requires maps that are detailed and accurate enough ~o 

show the distance of existing and proposed structures 

from the fault. 

The fault mapping done for Portola Valley in 1970 by 

W. R. Dickinson (fig. 33) provides the basis for the 

town's fault setback requirements adopted in 1973 (or:. 

dinance 1973-119) as part of the zoning ordinance. The 

ordinance prohibits structures for human occupancy 

within 15 m (50 ft) of a uknown" fault trace. uKnown" 

locations are based on surface expressions or subsur~ 

face studies which fix the location of the trace. No use 

more intensive than a single-family, one-story, woodframe house, or house of similar earthquake-resistant 

design, is permitted in the band from 15m (50ft) to 38 

m (125ft) on either side of a known fault trace. 

Setback distances for an uinferred" fault trace are 

larger-no structures for human occupancy are permitted within 30m (100ft) of the inferred location and 

only single-family homes are allowed for an additional 

23m (75ft). ((Inferred" locations are based on the presence of a limited number of surface or subsurface indications of a fault trace. The actual position of the 

((inferred" location is subject to greater error than the 

((known" location, and therefore the width of potential 

risk band is increased. A property owner may contract 

for detailed geologic investigation to locate an uinferred" trace more precisely. In such cases, the ordinance provides that the trace be reclassified as 

((known" and the setback requirement correspondingly 

reduced. 

Outside the setback lines shown in figure 33, all proposals for development more intensive than singlefamily residences are reviewed by an engineering 

geologist employed by the town to determine if the site 

might be subject to significant offset or ground warping 

related to surface rupture. 

Existing structures in the fault zone are not affected 

by the setback ordinance. Had the town chosen to make 

the fault zone into a zoning district rather than requiring setbacks, existing structures would have become 

nonconforming and subject to eventual removal, depending on the zoning ordinance provisions covering 

nonconformity. 

Generally speaking, as the fault mapping becomes 

more precise, the area subject to regulation becomes 

smaller. The Alquist-Priolo Special Studies zones for 

Portola Valley encompass a significantly larger area 
SEISMIC SAFETY AND LAND-USE PLANNING B65 

FIGURE 31. -Active and probably active faults and fractures and fracture zones for a portion of San Mateo County, Calif. at a scale of 

1:62,500 (Brown, 1972). The rectangle outlined is shown at larger scale in figure 32. 
B66 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

FIGURE 32.-Special Studies Zones for a part of San Mateo County, Calif., at a scale of 1:24,000. The area outlined is shown at larger scale in 

figure 33. 
SEISMIC SAFETY AND LAND-USE PLANNING B67 

than that subject to the setback regulations of the 

town. Specific geologic investigation often narrows the 

area of potential surface rupture, but where site investigations produce uncertain or unforeseen results, a 

wider zone of potential surface rupture may be included. 

Fault maps used for planning should be systematically updated as new geologic and seismic information 

becomes available. Excavations for road cuts or construction projects, geologic and geophysical site 

studies, and wells drilled near a known or suspected 

fault may provide new evidence of subsurface faulting. 

Where the public interest is affected, geologic investigations to locate fault traces more exactly may appropriately become the responsibility of the public agency. 

All information pertaining to fault location at a given 

site should become part of the title record for the 

parcel. 

SURFACE RUPTURE-DEVELOPED AREAS 

Where an active or potentially active fault passes 

through urban or urbanizing areas, the basic planning 

problem is how to prevent new construction and how to 

remove existing structures from on or near an active 

fault trace with equity and a minimum economic impact on the community. Some local jurisdictions decide 

that the effort simply is not worth the economic and 

social costs, and the risk is accepted. 

At the least, agencies faced with this risk should 

prepare a plan to prevent rebuilding after an earthEXPLANATION 

quake in areas subject to surface rupture. Such a plan 

can be similar to a redevelopment plan, that is, specific 

enough to assure relocation of structures away from 

areas of potential surface rupture, but general enough 

to allow flexibility in responding to conditions existing 

after the earthquake. 

During redevelopment under various Federal, State, 

or private programs, structures can be removed from 

an active fault trace. Such removal is appropriate in 

older areas where there is structural deterioration. The 

redevelopment area needs to be large enough to retain 

the fault zone as open space and still provide enough 

buildable space to make a project economically 

feasible. 

Although high-occupancy or critical facilities in active fault zones should be removed, public investment 

in such facilities may be so high as to make such action 

uneconomic. 

The Hayward fault runs through a highly urbanized 

and rapidly growing part of the East Bay (fig. 34). 

Many schools, public facilities, commercial, industrial, 

and residential buildings are located on or near the 

fault. Although no major earthquake has occurred on 

this fault in more than 100 years, tectonic creep makes 

continuing maintenance and repair necessary. The 

fault is active and is considered capable of producing 

an earthquake of magnitude 7.0-7.5 accompanied by 

surface rupture. 

The City of Hayward, crossed by the fault, adopted a 

seismic safety element in 1972. In it fault traces were 

0 500 FEET 

Fault trace location known I 11 ,, I I 0 150 METERS 

Fault trace location inferred 

FIGURE 33.-Known and inferred fault trace locations and setback lines, Portola Valley, Calif., at a scale of 1:6,000 (Dickinson, 1970). 
B68 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

mapped at a scale of 1:12,000, and a "fault corridor" 

was defined including the mapped fault traces and 15 

m (50ft) on either side. This corridor was declared an 

area of high seismic risk, and creation of a zoning combining district applying to the corridor was recommended. 

This seismic safety element further recommended 

that existing structures or portions of structures identified as hazardous be declared public nuisances and, as 

such, subject to repair, rehabilitation, or removal. 

Structures within the fault corridor would be subject to 

the nonconforming use provisions of the zoning ordinance upon adoption of the earthquake-fault combining district. 

In accord with these recommendations, the Hayward 

City Council considered designating an EarthquakeFault Combining District within which construction of 

the following types of structures over an active fault 

trace would be prohibited: residences, facilities required for emergency response, structures over 23 m 

(75 ft) in height, or high-occupancy buildings such as 

schools, churches, and theaters. Seismic, soils, and 

geologic reports would be required for new structures 

and additions to existing structures intended for 

human occupancy. Before the Council adopted the 

combining district, the Alquist-Priolo Act, with similar 

provisions, was passed by the State legislature, and so 

the city dropped the matter. 

The Hayward fault corridor runs through the middle 

of the older downtown section of the city. The city hall 

and police station, formerly located astride the fault, 

have been relocated to a new city-center complex a few 

blocks from the fault (fig. 35). Concern over economic 

decline of the downtown area led to a revitalization 

plan (Hayward, 1975a). The plan envisions an Lshaped downtown area linking the BART (Bay Area 

Rapid Transit) station and the new city center. An increase in development was recommended in the area 

bounded by Foothill Boulevard, C Street, Main Street 

and Hazel Avenue (fig. 35). Because this area is in the 

Special Studies Zone, no new development or substantial redevelopment could be approved without a 

geologic investigation. The city contracted with a consulting firm to conduct geological and geophysical investigations, including trenching, in this part of the 

proposed redevelopment area. The study concluded 

that no fault traces were present in the area (Burkland 

and Associates, 1975). 

The consultant's report provided the basis for a request by the city to the CDMG (California Division of 

Mines and Geology) that the area be removed from the 

Alquist-Priolo Special Studies Zone. The study, if approved by CDMG, will meet the requirements of the act 

for geologic investigations, and development may be 

FIGURE 34.-Hayward fault traces in urban and urbanizing area 

(from Nichols and Buchanan-Banks, 1974). 

permitted in the area. This is one of the few examples 

of a public agency assuming the responsibility and cost 

(in this case $18,000) of conducting the geologic investigations required by the State law. In most instances, 

the burden falls on the individual property owner. 

Four blocks of the redevelopment area between Main 

Street and Mission Boulevard are crossed by the Hayward fault. Consequently, the plan calls for meeting 

the needs for additional downtown parking by expanding parking lots in this area as parcels become available. The city proposes to use tax increment financing 

permitted under the California Community Redevelopment Law (California State Legislature, 1963), HUD 

Community Development Block Grant funds, parking 

revenues, and other available funds for public improvements in the redevelopment area. 

The official redevelopment plan (Hayward, 1975b) 

does not directly address the risk from surface rupture 

in the fault zone. However, implementing the plan 

could significantly reduce risk from surface faulting. If 

carried out in accordance with State law and the 

adopted policies of the Hayward Earthquake Study 

(Hayward, 1972), the plan will meet seismic safety objectives as well as its stated objectives of revitalizing 

the downtown area and increasing the space available 

for parking. 

PLANN ING TO REDUCE RISK FROM FLOODING 

Tsunamis and failures of dams or dikes are the major 
SEISMIC SAFETY AND LAND-USE PLANNING B69 

source of earthquake-induced flooding. Reducing the 

flood hazard can be accomplished by regulating construction in flood-prone area, by the use of warning 

systems, by planning for evacuation, and by building 

various structures to confine or control flooding. 

TSUNAMIS 

Because damaging tsunamis are infrequent in 

United States coastal areas, few coastal communities 

have tsunami-preparedness plans. A tsunami warning 

system in the Pacific basin, directed by the National 

Oceanic and Atmospheric Administration, is the major 

attempt to reduce risk. Sea walls, breakwaters, or 

other structures designed to protect coastal areas from 

storm surges may also prevent damage from small 

tsunamis; but the cost of protecting communities from 

the largest foreseeable tsunami by engineering works 

is unacceptably high (Ayre, 1975, p. 106). 

Planning to reduce tsunami risk may be stimulated 

by the Federal Coastal Zone Management Act of 1972 

(U.S. Congress Public Law 92-583); this act authorizes 

Federal grants to coastal states to prepare management programs for coastal zones. These programs must 

identify and list "areas of significant hazard if developed due to storms, slides, floods, erosion, settlement, 

etc." (U.S. National Oceanic and Atmospheric Administration, 1975, p. 1687). 

Potential tsunami runup areas are also included in 

"coastal high hazard areas" and subject to the requirements of the National Flood Insurance Program 

outlines in Section II. 

Because of Federal and State requirements, the 

land-use plans of coastal cities and counties are now 

more likely to include risk from tsunamis than in the 

past. The Seismic Safety Element for Monterey County 

is one of the few that contains policy directly relating 

to tsunami risk. The following policies (Monterey 

County, 1975, p. 34), based on very general mapping of 

areas of historic tsunami runup, were adopted by the 

caunty: 

1. In general, known tsunami runup areas should be avoided 

by new development except marine installations requiring location in proximity to water. 

2. Where development presently exists an adequate warning 

and evacuation system is essential. 

3. All reasonable measures will be taken by this jurisdiction to 

reduce potential damage. Such measures will include establishing and enforcing standards of construction for 

structures within harbors and known runup areas, and 

formulating post-disaster plans for debris clearance and 

emergency repairs to essential facilities. 

More precise delineation of potential runup areas 

and estimates of probable frequency of occurrence 

would make it possible to implement plan policies in 

tsunami runup areas by zoning for low-intensity or 

marine-oriented uses, establishing setback or elevation requirements for proposed structures or imposing 

design and construction standards. 

DAM AND DIKE FAILURE 

Reducing risk from dam or dike failure is particularly critical in seismically active areas because of the 

enormous potential for loss of life and destruction of 

property. Preliminary estimates of property damage 

from the recent failure of the Teton Dam in Idaho in a 

sparsely populated area are around $1 billion. Dam or 

dike safety is chiefly the responsibility of the engineer, 

builder, and operator, and, in the past, little effort has 

been made to control downstream land use as a means 

of reducing the change of catastrophic losses. In the 

future, risk of dam failure may be considered in landuse planning by placing restrictions on development of 

lands below the dams. 

Dike failure is of particular concern to communities 

along the edge of San Francisco Bay. Many dikes rest 

on unstable bay mud and are composed of materials 

unlikely to withstand severe ground shaking. The area 

subject to flooding from dike failure depends on the tide 

level and elevation of the land. The Alviso area of San 

Jose, situated about 2% m (8 ft) below sea level, is 

particularly vulnerable to severe flooding as well as 

other environmental hazards. 

In recognition of this, the comprehensive plan of the 

City of San Jose recommends that land uses in close 

proximity to water retention levees or dams with 

moderate or high potential for seismic failure shall be 

carefully regulated (San Jose, 1976, p. 19). No residential or employment growth or land-use change through 

1990 is projected for the Alviso area. This decision was 

reached after two basic alternatives for the future of 

the area were explored: (1) Build flood control levees 

and maintain and upgrade the existing community, or 

(2) relocate Alviso residents to other parts of San Jose 

(San Jose, 1976, p. 35). Based on an analysis of comparative costs and existing public investment in Alviso, the planers concluded that Alviso should remain 

where it is, and flood-protection levees should be provided. Long-term development options for the area are 

contingent upon a structural solution to the flood 

hazard. 

Planning for the Alviso area is a good example of the 

complex considerations involved in land-use decisions. 

The result is not optimum from the point of view of 

reducing seismic risk, but it represents a balancing or 

risk with other important economic and social factors 

and objectives. 

PUTTING IT ALL TOGETHER 

The effects of an earthquake are varied, and the ability to predict and evaluate the potential severity and 
B70 

Parking Lot 

Expansion in 

Fault Corridor 

Parking Lot 

at B and Watkins 

(Immediate Acquisition) 

REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

CITY CENTER - CAPWELLS 

ACTIVITY CENTER 

I 

5 00' 

~-_....,..... ____ Parking Structures 

in "Koy" Blocks 

'2~rfiei~---:::ll~--- B Straet Improvements 

Zo n e boundary 

ba- Foothill and 

BART 

EXPLANATION 

l int%tM%il RETAIL AND OFFICE 

~ OFFICE AND RESIDENTIAL 

F5559 RESIDENTIAL 

[-:~-:. -:->: :-' :.:1 PUBLIC 

:::~·: :: ;.\ •;1 OPEN SPACE 

A - MAJOR STREET 

I l SECONDARY STREET 

I• PARKING LOT 

I I PARKING STRUCTURE 

PEDESTRIAN WAY 

............... ) BIKEWAY 

b0000] SPECIAL TREATMENT 

PRELIMINARY ACTION PROPOSAL F IGURE 35_ - Hayward redevelopment plan. 
SEISMIC SAFETY AND LAND-USE PLANNING B71 

location of each effect differs, therefore, it is often necessary and desirable to respond to risk from each seismic hazard separately. A land-use plan, however, reflects the desires of a community for the future and is 

based on a multitude of often conflicting objectives and 

priorities. Reducing seismic risk requires integrating 

all the related seismic concerns into an overall plan for 

community development. Three methods are used to 

achieve this end: land-capability analysis, systematic 

consideration of seismic risk in land-use policy andregulation, and project review requirements within a 

general policy framework. These methods are complementary, not mutually exclusive. Each method relates to a particular phase of the planning process. A 

land-capability study is a way of interpreting data for 

direct application in plan formulation. Designating 

land uses involves formulating a plan and regulating 

land use. Project review is largely reactive, dealing 

with development proposals as they come rather than 

prescribing specific uses ahead of time; it emphasizes 

plan implementation. Each method is discussed below. 

LAND-CAPARILITY ANALYSIS 

In any area, the existing natural features and processes present a range of constraints and opportunities 

for different uses of land. Land-capability studies systematically record judgments concerning the effects of 

these factors on the value of the land for selected uses. 

The factors considered usually include topography, hydrology, geology, soils, vegetation, and climate. 

Methods of evaluating land capability differ. A study 

may be largely descriptive, pulling together in narrative form information concerning the natural features 

and processes relevant to a particular land use; or a 

study may involve a fairly sophisticated effort to quantify, weight, and aggregate the factors relevant to 

specific uses for all lands within a planning area. In 

any case, judgment is needed, and the studies should be 

carried out by planners with the assistance of experienced earth scientists. Land-capability analysis involves four basic steps: 

1. Defining the scope of the study and the land use 

or uses to be considered. 

2. Determining the factors affecting capability for 

the use or uses selected. 

3. Gathering, analyzing, and presenting the pertinent inforniation. 

4. Evaluating the relative capability of the land 

units to support the selected use or uses. 

The relative importance of each factor, as well as the 

range of conditions within each, can be expressed numerically. The main advantage of numerical analysis 

is the greater ease in combining many judgments into 

an overall rating ofland capability. Such analyses vary 

greatly in precision, however, depending on the quality 

of data, the qualifications ofthe analysts, and the method 

used. 

Land capability studies vary in focus as well as in 

method. A common variation is an analysis which 

rates land within a study area in terms of relative risk 

from selected natural hazards. A study may be very 

detailed, dividing an area into small units which are 

evaluated for a specific use such as a sanitary landfill; 

or it may be general, dividing an area into large units 

which are evaluated for a broad category such as urban 

development. 

The Seismic Safety Element of Santa Barbara 

County uses techniques of land-capability analysis to 

rank areas, on a grid system, in terms of relative seismic and geologic hazards. The following hazards were 

evaluated: ground shaking, tsunamis and seiches, 

liquefaction, slope stability, expansive soils, soil creep, 

compressible/collapsible soils, and high ground water. 

Surface rupture was considered separately because, as 

an essentially linear phenomenon, it is difficult to incorporate into a grid analysis. 

Each grid cell was rated 1-3 for each hazard based 

on the following system: 1 equals none or low hazard; 2 

equals moderate hazard; and 3 equals high hazard. 

Each hazard was given a weight representing its importance relative to the other hazards. The weight was 

based on three considerations: consequences severe or 

moderate consequences (such as loss of life or property 

damage), frequency of occurrence, and difficulty of prevention or mitigation. The hazards were then assigned 

the following weights: 

Seismic severity (ground shaking) __ ____ 18 

Tsumani-seiches ---------------------- 19 

Liquefaction -------------------------- 15 

Slope stability ------------------------ 23 

Expansive soils ---------------------- 7 

Soil creep ---------------------------- 4 

Compressible/collapsible soils ____ ______ 11 

High groundwater -------------------- 3 

Total ------------------------------ 100 

(100 is the lowest possible score assuming a 

rating of 1 for all hazards) 

For each grid cell, a weighted rating for each hazard 

was obtained by multiplying the weight by the rating. 

The weighted ratings for all hazards are then totalled 

for each grid cell. This total is called the GPI (geologic 

problem index). The GPI was calculated for each 90-

acre grid cell county-wide and for each 5-acre grid cell 

in four urban areas. The range of GPI's was 100-236 

(300 max.). No cell received a maximum GPI because 

some problems are confined to flatlands or hillsides, 

and no one cell had a high rating for all hazards. For 

convenience, GPI's were grouped into five categories; 
B72 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

GPI range Category Severity 

100-125 ________ __ I low 

126-145 __________ II low-moderate 

146-180 ____________ III moderate 

181-210 ____________ IV moderate-severe 

210-up ____________ V severe 

Computer mapping of the five categories was used to 

show the relative severity of geologic hazards throughout the county and in the four urban areas in greater 

detail. The system employed in Santa Barbara County 

includes a "variability number" to indicate differences 

in reliability of the hazard ratings for particular grid 

cells resulting from potential local variations, quality 

of data, and other factors. Areas with the same GPI 

rating or in the same severity category may have different variability numbers which can affect planning 

recommendations. 

The Santa Barbara study is a good example of the 

incorporation of seismic considerations into a land 

capability analysis. Although the hazard ratings were 

not related to particular land uses, the GPI does provide an overview of relative seismic and geologic 

hazards throughout the county. The ratings can be related to levels of acceptable risk for different categories 

of use, thus providing a guide for land-use planning. 

Based on the GPI, the seismic safety element recommends that the county: 

1. Consider areas in category V for open space, 

recreational or agricultural use, or possible 

low-density use, because cost of safe development may be high. 

2. Consider areas in category IV for low-density 

use or nondevelopment. 

The relative costs of measures needed to mitigate 

adverse natural conditions affect the values assigned 

in a land-capability study. In a pilot study of a part of 

the Santa Clara Valley, the Association of Bay Area 

Governments (Laird and others, 1979), expressed land 

capability in terms of the dollar costs required to mitigate hazards or to compensate for property damage and 

loss of natural resources. 

The ABAG study included such geologic and hydrologic hazards as ground shaking, surface rupture, 

flooding, bearing-materials problems (potential for 

shrink/swell, settlement, liquefaction, and subsidence), 

slope stability, erosion/sedimentation, and septic-tank 

limitations. The study also included an evaluation of 

natural resources. Lands in the study area were evaluated for a range of uses: agricultural or rural, semirural residential, single-family residential, multifamily residential, regional commercial, downtown 

commercial, industrial manufacturing, and freeway. 

The total cost associated with each natural constraint and resource for each land use was estimated. 

Table 18 lists for each land use the estimated costs 

associated with different intensities of ground shaking. 

Estimated costs per acre are obtained by multiplying 

the value of buildings, personal property, and utilities 

by the percent damage expected by the annual frequency of occurrence, and dividing by a discount rate to 

reduce future values to present levels. In this case costs 

were based on an anticipated damage level associated 

with each land use. 

Cost information for the identified natural resources 

and hazards for each 24.9-acre grid cell was aggregated 

for each land use. The resulting number indicates for 

each cell the estimated dollar cost per acre of developing that cell with that land use. The range of total costs 

was divided into six capability levels and a landcapability map for each use was printed by computer. 

Figure 36, a land-capability map for a part of the Santa 

Clara Valley study area, is derived from table 19, 

which shows the costs associated with all the hazards, 

constraints and resources for multi-family residential 

use. 

Analysis of land capability provides only part of the 

information needed for land-use decisions. Economic, 

social, political, and esthetic considerations are also 

important. The physical capability of a parcel ofland to 

support an intensive use may be poor, but other factors, 

such as location and accessibility, land cost, absence of 

alternative lands, or overriding public need, may well 

indicate that the parcel should be intensively developed. 

A study which systematically evaluates economic, 

social, and political factors, in addition to physical 

capability, is often called a "land-suitability study". A 

land-capability study can be undertaken as part of a 

broader land-suitability study. However, on occasion, 

capability is, or should be, the determining factor. 

Areas with very low capability for sustaining a parTABLE 18.---Costs associated with ground shaking resulting from 

events on the San Andreas, Hayward, or Calaveras faults 

[Laird and others, 1979] 

Cost per acre (in dollars) 

San Francisco Intensity Scale 

Land use A B c D E 

Rural or agricultural 40 30 10 5 1 

Semi-rural 

residential ______ 300 300 100 40 4 

Single-family 

residential ______ 4,000 3,000 1,000 500 50 

Multi-family residential ______ 20,000 20,000 5,000 2,000 200 

Regional 

shopping centers 50,000 40,000 10,000 4,000 800 

Downtown 

commercial ___ ___ 70,000 50,000 20,000 5,000 1,000 

Industrial _______ _ 40,000 30,000 10,000 3,000 700 

Freeways - ------- 10,000 10,000 10,000 0 0 
SEISMIC SAFETY AND LAND-USE PLANNING B73 

TABLE 19.-Summary of costs for multifamily residential use 

[Laird and others, 1979] 

Hazard, constraint, 

or resource 

Severe 

Costs for 

mal categories 

(in do lars per acre) 

(scale from severe to slight) 

Slight 

Surface rupture --------------------------------------------------800 800 0 

Ground shaking, San Andreas, Hayward _____ ______ _____________ 20,000 

Ground shaking, Southern Hayward ___ ____ _____________________ __ 2,000 20,000 5,000 2,000 200 

2,000 500 200 20 

Ground shaking, Calaveras _____ ______ ________ _____ ____ ___ _____ 20,000 5,000 2,000 200 

Stream flooding _____ ___ ________ ______ ________ __ __________ ___ ___ 40,000 0 

Darn failure __________ ____ _____ __ _______ ___________________ _________ o 

Dike failure _____ ________ _____ _____ _______ __ _____ ___ ____ ______ 80,000 

Shrink/swell soils _______ ______ _____ _______________ __ ____ __ __ ___ 20,000 

0 

7,000 0 0 Settlement _____ ___________ __ __ ____ __ ____ ____ ___ ________ _______ 30,000 30,000 20,000 2,000 

~~'b~fd~~~~n ~~~~~~~ ~~~~~~~~~~~ ~~~~~~ ~~~~~~~~~~ ~~~~~~~~~~~ ~~~g 3,000 300 20 0 

Landslides __ _______ ____ _____ _____________ ___ ____ __ _____ ___ __ 200,000 100,000 50,000 9,000 0 

Soil creep __ ___________ ____ __________________ ______ _______ ___ _40,000 40,000 0 0 

Erosion and sedimentation __ _______ ____ __________________ ____ ____ _ 200 30 10 0 

Septic tanks _____ ______ ______ _______ ___ __ __ ____________ ____ ____ _____ 0 

Sand and gravel ________ ______ ___ ______ _____ __________ _____ ___ 20,000 0 Mercury ___ _____ ___ ________ ___________ ____ ________ __________ ________ o 

Agricultural land ____ ______________ _________________________ ___ 5,000 0 

ticular use can sometimes be eliminated from further 

consideration, allowing the planner to focus attention 

on more realistic options. 

Land-capability studies are becoming increasingly 

important to land-use planners at all governmental 

levels. They assure that physical characteristics of the 

land will be systematically considered in land-use 

planning. The earth-science information requirements 

for such studies vary with the total land area and the 

specific use to be studied. For example, fairly general 

data may be appropriate for an initial analysis of land 

capability for regional open space. On the other hand, a 

study undertaken, at any governmental level, to locate 

specific sites with good capability for sanitary landfill 

will require detailed information. 

Land-capability analysis allows seismic-risk constraints to be considered along with other natural 

characteristics in making land-use decisions. The 

hazard information developed in the process of seismic 

zonation is combined with other natural characteristics and given a numerical weight. Capability analysis 

relates seismic and other hazards directly to potential 

land uses. Land-capability studies may usefully serve 

as an intermediate step in identifying areas where 

hazards are present and where detailed consideration 

of risk is needed in deciding land uses, structural design, and occupancy. 

LAND-USE POLICY AND REG ULAT ION 

Many cities and counties in California have completed the seismic safety elements of their general 

plans. For many of these jurisdictions, the preparation 

of these elements was their first experience in using 

geologic information systematically in a planning task. 

The typical seismic safety element is a preliminary 

step toward developing a comprehensive program to 

reduce seismic risk. Because of limited experience in 

using existing geologic data, most seismic safety elements emphasize the need for more data. If detailed 

data were available and the planning staff was experienced, more specific recommendations for immediate 

action resulted. While most seismic safety elements 

contain recommendations for land-use policy, few 

jurisdictions have yet integrated seismic safety policies 

and programs into their comprehensive plans. This 

kind of planning will come about when more cities and 

counties combine the various required general plan 

elements into a comprehensive document. 

The recently adopted General Plan 1975 for the City 

of San Jose is one of the first to consider seismic risk as 

an integral part of a comprehensive plan. The land-use 

pattern of San Jose is a classic example of urban sprawl 

resulting from very rapid development following World 

War II. An aggressive annexation policy and a 

growth-oriented political climate led to more than a 

fivefold increase in city population from 1950 to 

1975- from just under 100,000 to 54 7 ,500. During the 

five-year period 1969-1974, an average of769 hectares 

(1,900 acres) was converted to urban uses each year 

(San Jose, 1976, p. 7). Increasingly, land with development constraints was being pressed into urban use. 

The San Jose General Plan 1975 is a guide for 

managing growth to match the city's ability to extend 

urban services, avoid development of unsuitable lands, 

and achieve a more efficient urban form and a better 

balance of land uses. The first step was the adoption in 

1970 of a set of urban development policies. These 

policies are now incorporated into the General Plan 
B74 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

. t--:----- ' IH . " ' ~ 

f 

I 

~ 

~~ 

I , '\ '" I 

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1 

I 

~ -;. 

f I 

t I ' I ' J I I 

I 

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I , • ~ 

l I ( ~ . N ' I ~ . ·I ... + ... 

1 I { t ftt' 

/ t 1 I \ I \ 

' [ ..-" (9 / f 

' / " 1 ; t- y . I I t . ~.-."\ 

I I/ I= ,. ~ 

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FIGURE 36.-Land-capability map for multi-family residential use (Laird and others, 1979, p. 75). 
SEISMIC SAFETY AND LAND-USE PLANNING B75 

1975. Future development is to be limited to a designated urban service area for the 15-year time span of 

the plan. Within the urban service area approximately 

8,134 hectares (20,100 acres) were undeveloped in 

1975. Of these, 1,052 hectares (2,600 acres) were already approved for private development; 425 hectares 

(1,050 acres) committed to public uses; 399 hectares 

(985 acres) under Williamson Act Contract\ 301 hectares (7 45 acres) programmed for public acquisition; 

and 770 hectares (1,920 acres) considered ill-suited for 

development because of size, shape, slope, soil subsidence flooding, or location in an airport safety zone 

(San Jose, 1976, p. 7). 

The plan contains specific policies related to lands 

considered unsuitable for urban development within 

the urban service area as well as throughout the area. 

Based on a goal of striving to minimize risk from natural hazards, the plan (San Jose, 1976, p. 19) contains 

the following general policies: 

1. The City shall not permit urban development in 

those areas where such development would 

constitute a significant potential danger to 

the health, safety, and welfare of the residents. 

'The California Land Conservation Act of 1965 (California Government Code, 1965), also 

called the Williamson Act, permits landowners to enter into contracts with cities and counties in which the landowners agree to maintain land in agricultural use in exchange for tax 

assessments based on the economic return from agricultural use of land. 

EXPLANATION 

Level Symbol 

Total Cost Range (in dollars per acre) 

0.01 1 o. 00 

2 10.01 100.00 

3 100.01 1000.00 

4 1000.01 10000.00 

5 11111 10000.01 100000.00 

6 IIIII 100000.011000000.00 

FIGURE 36.-Continued. 

No. Of Cells 

In Level 

0 

0 

0 

16 

4644 

2877 

2. Low levels of (acceptable exposure to risk' shall 

be established for land uses and structures in 

which failure would be catastrophic, which 

are required during emergencies, or which 

involve involuntary or high human occupancy. 

3. Risks from natural hazards shall be reduced as 

much as possible in areas where human activity is necessary or already exists, and 

where the natural and man-made environment can be safely integrated. 

4. Preventative measures for known natural 

hazards shall be taken simultaneously with 

new development. 

5. Site-specific information on natural hazards 

shall be required for proposed new development and where identified hazards preclude 

safe human interaction, development shall 

yield to natural processes. 

6. Provision shall be made for the continuation of 

essential public services during natural 

catastrophes. 

7. The City shall promote an awareness and caution among San Jose residents regarding possible natural hazards including soils conditions, earthquakes, flooding, and fire hazards. 

Specific policies regarding seismic safety call for rehabilitating or removing structural hazards ((without 

creating undue hardship or relocation policy problems" 

(San Jose, 1976, p. 19); restricting construction near 

creek channels where liquefaction is a hazard; requiring geotechnical studies to determine the extent of 

seismic hazards prior to approval of development proposals; regulating land uses in areas prone to flooding 

from dike or dam failure; and requiring detailed 

dynamic ground motion analysis and suitable structural design for critical facilities (San Jose, 1976, p. 

19). 

These and other policies apply to areas designated as 

hazardous on maps which are part of the Geotechnical 

Report prepared by Cooper, Clark, and Associates 

(197 4) as background for the Seismic Safety Element. 

A generalized natural hazards map (fig. 37) is incorporated in the General Plan 1975. 

The importance of avoiding development in hazardous areas is reflected in the land-use policies and 

land-use diagram. For example, the following policies 

of the General Plan 1975 (San Jose, 1976, p. 21, 25) are 

related to specific land uses: 

Solid waste disposal land fill sites shall be discouraged on lands 

which are susceptible to landslides, seismically induced ground failure, •••dam inundation***. Residential development shall not be allowed to occur in areas where such development might be hazardous 

to human habitation***Densities permitted by the General Plan on 
B76 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

slopes greater that 15 percent may be allowed to be transferred***. 

The land-use diagram shows the area underlain by 

bay mud as open space, agriculture, and light industry. 

Areas adjacent to major creeks which may be subject to 

ground failure are shown as open space. Hillside areas 

to the northeast and southwest of the valley floor are 

designated for nonurban uses. In these areas, slope 

failure and surface rupture during an earthquake are 

potential hazards. 

To implement the plan, new zoning districts limiting 

the density of residential development in hillside and 

other outlying areas are to be prepared. Geologic 

hazards are to be systematically considered in thereview of development proposals. Where warranted by 

geologic investigation, designated land uses can be altered because the geologic hazards may be overriding. 

The 1975 plan evaluates the full range of factors affecting the future development of the San Jose area. Conflicts 

among economic, social, and environmental objectives are 

recognized and resolved into a plan and an implementing 

program that explicitly incorporates seismic safety concerns into the decisionmaking process. 

PROJECT REVIEW 

Another means of integrating seismic risk and 

land-use planning is to develop, within a general policy 

framework, project review requirements and procedures. Such requirements and procedures are appropriate when detailed data on seismic hazards are not 

available. Generalized data can be used to alert planners and decisionmakers to potential problems. Such a 

system generally identifies areas where seismic, 

geologic, or soils investigations are required before 

development proposals are approved. Specific report 

requirements, procedures for evaluating reports and 

requiring hazard mitigation, and criteria for determining the acceptability of proposed projects can be developed to incorporate seismic safety concerns. 

Project review can be very effective if it assures that 

seismic risk is considered in site selection, structural 

design,a nd occupancy of major development proposals. 

Although the developer has the responsibility for collecting data, the public agency must have sufficient 

information and geologic expertise to evaluate the 

geologic and seismic reports submitted with the proposals. 

Santa Clara County emphasizes project review. The 

Seismic Safety Plan (1975) describes the seismic and 

geologic hazards in the county and general policies to 

mitigate or avert undue seismic risk in existing or future development. The essence of the plan, however, is 

contained in the recommendations for geotechnical site 

investigations (Santa Clara County, 1975, p. 19-20): 

In order to maximize public safety and minimize seismic hazards, 

additional local geotechnical studies should be performed prior to 

further development in many areas of the County. These studies 

should consider the data in this report as general background and 

regional material and should determine the extent of particular 

seismic hazards on each site in relation to the specific intended use. 

These geotechnical investigations should be multidisciplinary, including component studies of seismology, engineering geology, planning, hydrology, architecture, design engineering, structural engineering, and soil engineering. These interrelated components 

should be coordinated so that all pertinent factors are considered. 

To review and approve these geotechnical investigations, it is recommended that the County should develop an adequately trained 

and funded staff team including the various disciplines mentioned 

above. 

To help decide if a geologic or geotechnical investigation should be required, the county uses a Relative 

Seismic Stability Map prepared by the California Division ofMines and Geology at a scale of1:62,500. Figure 

38 is a part of the reduced version of this map which is 

included in the Seismic Safety Plan. The original map 

is incorporated, by reference, in a county ordinance setting forth soils and geologic report requirements 

(Santa Clara County Board of Supervisors Ordinance 

No. NS-1203.31, December 1974). Soils and geologic 

reports may be required when applications are submitted for subdivisions, building site review, grading permits, and building permits. 

Soils reports are to be prepared by a civil engineer 

registered by the State and geologic reports by an engineering geologist certified by the State. The county 

staff includes an engineering geologist and other experts competent to evaluate the reports and the 

mitigating measures proposed. The report requirements and evaluated procedures are part o.f the total 

review process, and they ensure that geologic and 

seismic hazards are considered adequately in land-use 

decisions and land-development practices. 

POSTEARTHQUAKE RECONSTRUCTION 

After a damaging earthquake, economic, social, psychological, and political pressures coalesce to hasten 

rebuilding. Often this leads to restoring area, buildings, and services to their previous condition without 

regard for site or structural hazards revealed by the 

earthquake, or hazards previously identified, but not 

heeded. If properly planned and carried out, reconstruction following an earthquake can greatly reduce 

risk from future events. 

The San Francisco Community Safety Plan (San 

Francisco Department of City Planning, 1975) stresses 

the opportunities presented during reconstruction to 

carry out the objectives of the comprehensive plan. The 

plan (p. 38) recommends that the city: 

Adopt contingency legislation to provide for anticipated needs following a disaster and to reduce pressures for unnecessarily rapid reconstruction. 

Create a reconstruction planning committee to insure that development following a major disaster takes place in a timely fashion 

according to established objectives and policies. 
EXPLANATION 

High landslide susceptibility (high landslide susceptibility bordering creeks 

omitted due to scale) 

~ Fault traces 

~ Potential salt water inundation 

[§]1 High ground failure susceptibility 

CJ Soil creep (highly ex pansive soils above IS percent slope) 

~ Very weak soilsfrecent 

young bay mud 

• Potential major destruction 

due to dam inundation 

(any structure left standing must be considered a 

total loss) 

SEISMIC SAFETY AND LAND-USE PLANNING B77 

·-·-·-·-· Sphere of influence 

0 5000 METERS 

0 10,000 FEET 

FIGURE 37.-Natural hazards map, City of San Jose. 
B78 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAy REGION 

The proposed Reconstruction Planning Committee 

would have the following duties (San Francisco Department of City Planning, 1974, p. 63-64): 

1. Insure that postearthquake building code and 

design standards are as advanced in terms of 

seismic safety as possible. 

2. Implement objectives, policies, and criteria of 

the Comprehensive Plan. 

3. Recommend contingency legislation to be 

enacted now, but taking effect after an earthquake to authorize such actions as provision 

of temporary housing. 

4. Determine priorities for allocating resources 

particularly building materials. ' 

5. Seek joint agreements with lending institutions, insurance companies, and Federal disaster assistance agencies to require a valid 

building permit before money for new construction is released. 

6. Develop an information booklet setting forth all 

requirements pertinent to reconstruction and 

sources of financial assistance. 

EARTHQUAKE PREDICTION 

Current research in earthquake prediction appears 

quite promising and has attracted considerable public 

attention. Although the science of prediction is still in 

its infancy, many seismologists in the United States 

believe that within the next decade or two, they will be 

able to predict at least some earthquakes. However 

p.redictions that specify the location, magnitude, and 

time of damaging earthquakes with accuracy and 

enough lead time to take measures to reduce risk are 

probably a long way off. 

Credible earthquake prediction may have short-term 

a?~e.r~e economic and social impacts, but the poss~bihtles for reducing loss of life, injury, and substantial property damage make prediction a worthwhile research objective. The value of such predictions is well 

stated in a recent article by Frank Press (1975 p. 14-

15): ' 

~reliminary results of current investigations indicate that predictions of strong earthquakes could be made many years in advance. It 

also appears likely that a method for making short-term predictions, 

as short as weeks or even days, will be developed. With this dual 

capability it should become possible to devise a remedial strategy 

that could greatly reduce casualties and lower property damage. For 

example, the long-range prediction of a specific event could greatly 

reduce casualties and lower property damage. For example, the 

long-ra~ge prediction of a specific event could spur the strengthening 

of ex1stmg structures in the threatened area and motivate authorities there to enforce current building and land-use regulations 

and to revise such codes for new construction. A public-education 

campaign on safety procedures could also be instituted. 

Short-term prediction could mobilize disaster-relief operations and 

set in motion procedures for the evacuation of weak structures or 

particularly flammable or otherwise hazardous areas. The shutdown 

of special facilities, such as nuclear power plants and gas pipelines, 

and the evacuation of low-lying coastal areas subject to tsunamis, or 

"tidal waves," could also follow a short-term forecast. 

In brief, long-term earthquake prediction could spur 

public agencies to take those actions which are recomPJ.ended in seismic safety and emergency preparedness 

plans. High priorities could be assigned to such measures if an earthquake were predicted, thus substantially reducing the risks. Short-term predictions could 

avert little property damage but could reduce dramatically the risk of death or injury. 

Planning responses to seismic risk are just as, or 

even more, relevant if accurate prediction becomes 

possible. The jurisdiction with a development pattern 

which avoids intensive use of hazardous areas and 

which provides for sound structural design and construction and carefully located and designed emergency 

response facilities will be well prepared for that inevitable 

earthquake whether or not it is predicted. 

CONCLUSIONS 

Over the past decade, remarkable progress has been 

made in understanding the nature, cause, and effects of 

earthquakes. Planners are still developing methods 

and procedures to make effective use of the data. 

Methods which more fully integrate safety concerns in 

land-use planning and decisionmaking can be expected 

to emerge. 

Success in seismic safety planning requires public 

awareness of the nature of seismic risk and the potential for reducing it. Historically, safety has not been an 

important factor in locating urban settlements, and 

overcoming apathy toward seismic risk is a formidable 

task. Typically, the spurt of public interest following 

each damaging earthquake gradually dwindles away. 

Recent California seismic safety planning has occurred 

because of the State law adopted after the San Fernando earthquake of 1971. It is to be hoped that these 

planning efforts will continue and ultimately will result in significant reduction of losses in future earthquakes. 

Success in reducing seismic risk requires a comprehensive program including preparing for disaster 

response, establishing and enforcing structural design 

standards, and planning for safe land and building 

uses. The land-use planning component of the program 

is particularly important because if seismic hazards 

are properly recognized in the land-use patterns, disaster response and structural design requirements can be 

correspondingly reduced. Reducing risk through 

land-use planning requires an interdisciplinary effort 

involving earth scientists, engineers, and planners. 

A land-use plan provides the framework for many 

public actions including land-use and development regulations, building code provisions, and project review 
0 5 Ml LES 

0 5 K I L OMETERS 

FIGURE 38.- Seismic safety zones, Santa Clara County. 

• • 

EXPLANATION 

W h er e geologic in vestigation is 

norma ll y requ ired 

W h ere geol og ic investiga t ion may 

be requ ired 

W h ere geo l og ic investi gat ion i s 

not normall y requ ired 

Reproducible cop ies of th i s map i n 

greater detail are ava il able f or a sma ll 

charge at the Santa Clara County Transportation Agency under the title of 

Relat ive Seism ic Stabil ity Map at a 

scale of one i nc h equals one m i le 

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B80 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

procedures and criteria. The basic objective ofland-use 

planning for seismic safety is to reduce exposure to 

seismic hazards by relating land uses to degrees of 

seismic hazards. In formulating a land-use plan, the 

social and economic benefits of particular locations for 

particular uses must be weighed against the costs for 

structural measures needed to reduce risk to acceptable levels. In developed areas, the value of existing 

buildings and infrastructure must be weighed against 

costs of damage and injuries from earthquakes. 

In the future, more effective land-use planning to 

reduce seismic risk will be possible as more accurate 

and detailed information becomes available and planners become more experienced in its application. Maps 

showing where ground shaking, slope instability, and 

liquefaction may occur will be particularly useful to 

land-use planners. Further research in structural response to seismic forces is needed to develop more 

realistic building code requirements. 

The relative costs of applying various risk reduction 

measures are usually unknown but are greatly needed. 

In addition, the public and private costs associated 

with various land uses and structural types in hazardous areas need to be studied. Legal mechanisms and 

funds are required to help reduce existing structural 

hazards. If these additional tools are provided, local 

public agencies in cooperation with knowledgeable 

citizens and decisionmakers will be well equipped to 

plan for seismic safety. 

REFERENCES 

Alfors, J. T., Burnett, J. L., and Gay, T. E., Jr., 1973, Urban geology 

master plan for California: California Div. Mines and Geology, 

Bull. 198, 112 p. 

Algermissen, S. T., 1969, Seismic risk studies in the United States in 

Proceedings of the fourth world conference on earthquake engineering: Santiago, Chile, v. 1, p. 19-27. 

---(principal investigator), 1972, A study of earthquake losses in 

the San Francisco Bay area: Nat!. Oceanic Atmospheric Admin., 

U.S. Dept. Commerce, 220 p. 

Armstrong, Dean, 1973, The seismic safety study for the general 

plan: Sacramento, Calif., California Council on Intergovernmental Relations, 199 p. 

Association of Bay Area Governments, 1973 Procedures for regional 

clearinghouse review of environmental impact statementsPhase two: Assoc. Bay Area Govts., Berkeley, Calif., 225 p. 

--- 1975a, Areas of critical environmental concern. Review draft: 

Assoc. Bay Area Govts., Berkeley, Calif., 83 p. 

---1975b, Hazards evaluation for disaster preparedness planning: Assoc. Bay Area Govts., Berkeley, Calif., 37 p. 

---1976, Earthquake preparedness- ideas for action: Assoc. Bay 

Area Govts., Berkeley, Calif. unpaged. 

Association of Engineering Geologists, 1973, Geology, seismicity, 

and environmental impact: Special Publication, Los Angeles, 

University Publishers, 446 p. 

Ayre, R. S., 1975, Earthquake and tsunami hazards in the United 

States-A research assessment: Nat!. Sci. Found.-RA-E-75-

005, Univ. Colorado, Boulder, 149 p. 

Baker, L. C., Jr., 1971, Availability and desirability of earthquake 

insurance in earthquake risk: Conference proceedings Sept. 

22-24, 1971, sponsored by the Joint Committee on Seismic 

Safety to the California Legislature, report of the Special Subcommittee to the Joint Committee on the San Fernando Earthquake Study, p. 31-33. 

Borcherdt, R. D., ed., 1975, Studies for seismic zonation of the San 

Francisco Bay region-Basis for reduction of earthquake 

hazards, San Francisco Bay region, California: U.S. Geol. Survey Prof. Paper 941-A, 102 p. 

Borcherdt, R. D., Gibbs, J. F., and Lajoie, K. R., 1975, Maps showing 

maximum earthquake intensity predicted in the southern San 

Francisco Bay region, California, for large earthquakes on the 

San Andreas and Hayward faults: U.S. Geol. Survey Misc. Field 

Studies Map MF- 709, 3 sheets, scale 1:125,000. 

Brown, R. D., Jr., 1972, Active faults, probable active faults, and 

associated fracture zones, San Mateo County, California: U.S. 

Geol. Survey Misc. Field Studies Map MF-355, scale 1:62,500. 

Burkland and Associates, 1975, Geological and geophysical investigation in downtown Hayward: Burkland and Assoc., Mountain 

View, Calif., 22 p. and appendix. 

California Council on Intergovernmental Relations, 1973, 

Guidelines for local general plans, Sacramento: Calif. Council on 

Intergovernmental Relations, Sacramento, 106 p. 

California Division of Highways, 1971, The effect on state highways 

of the San Fernando earthquake February 9, 1971: Calif. Div. 

Highways, Sacramento, Calif., 62 p. and appendixes. 

---1975, Highway design manual of instructions: Calif. Div. 

Highways, Sacramento, Calif., Section 7- 110. 

California Division of Mines and Geology, State Mining and Geology 

Board, 1975, Policies and criteria of the State Mining and Geology Board with reference to the Alquist-Priolo Special Studies 

Zones Act, 3 p. 

California Education Code, 1933, sees. 15451-15465. 

--1967, sec. 15002, Field Act. 

California Government Code, 1965, California Land Conservation 

Act of 1965 (Williamson Act): California Govt. Code, sees. 

51,200-51,295. 

---1970, sec. 65302, Emergency Services Act. 

---1973, sec. 8589-5, Alquist Dam Safety Act. 

---1974, sees. 8890-8899, Seismic Safety Commission Act. 

California Governor's Earthquake Council, 1972, First report of the 

Governor's earthquake council: Sacramento, Calif., 65 p. 

California Office of Planning and Research, 1973, Summary report-Environmental goals and policy: Sacramento, Calif., 29 p. 

California Public Resources Code, 1972, sees. 2621-2625, Alquist/ 

Priolo Special Studies Zones Act. 

---1976, California Coastal Act: sees. 30000 to 30900. 

California Resources Agency, 1974, Amendments to guidelines for 

implementation of the California Environmental Quality Act, 

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---Joint Committee on Seismic Safety, Gates, George 0., ed. 

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public policy: Calif. Joint Comm. on Seismic Safety, Sacramento, 

Calif., 127 p. 

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1974, Meeting the earthquake challenge, final report to the 

Legislature, January 1974: Calif. Div. Mines and Geology, Special Publication 45, 223 p. 

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SEISMIC SAFETY AND LAND-USE PLANNING B81 

Cooper, Clark, and Associates, 1974, Technical report, geotechnical 

investigation, city of San Jose's sphere of influence for the city of 

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Hayward, 1972, Hayward earthquake study: Planning Commission 

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Monterey County, 1975, County-wide seismic safety element for the 

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B82 REDUCTION OF EARTHQUAKE HAZARDS, SAN FRANCISCO BAY REGION 

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