Earthquake Losses to 

Single-Family Dwellings: 

California Experience

U.S. GEOLOGICAL SURVEY BULLETIN 1939-A

Prepared in cooperation with the

State of California Department of Insurance

/§

L

---. =. i

wt. 9<m

III
Cover: Damage caused by the 1933 Long Bench California, earthquake. 

Photograph by Harold Er^le, 1933.
Chapter A

Earthquake Losses to 

Single-Family Dwellings: 

California Experience

By KARL V. STEINBRUGGE and ST. ALGERMISSEN

Prepared in cooperation with the

State of California Department of Insurance

U.S. GEOLOGICAL SURVEY BULLETIN 1939

ESTIMATION OF EARTHQUAKE LOSSES TO HOUSING IN CALIFORNIA
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L Peck, Director

Any use of trade, product, or firm names in this publication is for descriptive 

purposes only and does not imply endorsement by the U.S. Government.

UNITED STATES GOVERNMENT PRINTING OFFICE: 1990

For sale by the

Books and Open-File Reports Section

U.S. Geological Survey

Federal Center

Box 25425

Denver, CO 80225

Library of Congress Catalog-in-Publication Data

Steinbrugge, Karl V. 

Earthquake losses to single-family dwellings.

(U.S. Geological Survey bulletin ; 1939-A) (Estimation of earthquake losses to 

housing in California)

"Prepared in cooperation with the State of California Department of 

Insurance."

Includes bibliographical references.

Supt. of Docs, no.: I 19.3:1939-A

1. Insurance, Earthquake California. 2. Earthquakes California.

I. Algermissen, Sylvester Theodore, 1932- . II. California. Dept. of 

Insurance. III. Title. IV. Series. V. Series: Estimation of earthquake losses 

to housing in California.

QE75.B9 no. 1939-A 557.3 [368.1'22] 90-3436 

[HG9981.3S.C2]
CONTENTS

Abstract Al 

Introduction Al

Acknowledgments A2

Data sources and loss-over-deductible compilation A2 

1971 San Fernando earthquake A3 

Data sources A3

Single-family wood-frame dwellings, no exclusions A4 

All wood-frame dwellings, excluding sites with geologic effects A4 

One-story wood-frame dwellings, excluding sites with geologic 

effects A12

1983 Coalinga earthquake A12 

Data sources A12

One-to-four-family wood-frame dwellings A12 

One-to-four-family wood-frame dwellings, excluding special 

cases A12

One-to-four-family wood-frame dwellings Insurance company 

experience A12

1933 Long Beach earthquake A21

Relationships among construction, geologic effects, and loss over deductible A21 

1971 San Fernando earthquake A21 

1983 Coalinga earthquake A23 

Non-insurance data A23 

Insurance claim data A27

Loss distribution and probable maximum loss (PML) A34 

Distribution curve A35

Uncertainties concerning degrees of damage A35 

Other uncertainties A35

Insurance company data on probable maximum loss (PML) and loss 

distribution A36 

Judgmental considerations A36

Probable maximum loss (PML) for magnitude 6.5 earthquakes A36 

Loss over deductible for magnitude 6.5 earthquakes A37 

Transferability to other earthquakes A37

Earthquakes of magnitudes other than 6.5 A37 

Probable maximum loss (PML) A42 

Loss over deductible A42 

1987 Whittier Narrows earthquake A43 

Insurance Source C A43

Geographic distribution of losses A43

Region with paid earthquake claims A43 

Areas with highest number of paid claims A45 

Deductibles and losses over deductible A45

Adjustment for magnitude 8.25 earthquake and uncertainty factor

of 1.5 A46

Commentary on loss-over-deductible results A46

Contents III
1987 Whittier Narrows earthquake Continued 

Insurance Source D A48

Distribution of losses A49

By type of first floor A49 

By number of stories A50 

By age group A50 

By geographic distribution A50 

Loss over deductible A53

Loss attenuation with distance from seismic energy release A53 

Overview, findings, and recommendations ASS 

Overview ASS

Intensity observations as an alternative data source AS6

ASS

f*ftjfcable-maximum-loss (PML) approach ASS 

Loss-over-deductible approach A60 

Applications to simpler methods A61 

Other findings A61 

Recommendations A61 

References cited A62

Appendix: Probable-maximum-loss background information A64 

Definition of probable maximum loss A64 

Origin of wood-frame-dwelling probable maximum loss A64 

Sensitivity: Loss over deductible versus dwelling PML changes A65

FIGURES

1. Graph showing loss over deductible versus deductible for 1971 San Fernando 

earthquake A27

2. Isoseismal map of the 1906 San Francisco earthquake showing the location of 

Coalinga A28

3. Graph showing loss over deductible versus deductible for 1983 Coalinga 

earthquake A29

4. Graph showing loss over deductible versus deductible for 1971 San Fernando 

and 1983 Coalinga earthquakes and comparing our data and Insurance 

Source A data (applicable to dwellings of all ages) A32

5. Graph showing loss over deductible versus deductible for 1971 San Fernando 

and 1983 Coalinga earthquakes and comparing our data and Insurance 

Source A data (applicable to post-1949 dwellings) A32

6. Graph showing distribution of dwellings versus loss at 0 percent deductible 

for the 1983 Coalinga earthquake and comparing our data and Insurance 

Source A data A40

7. Graph showing distribution of dwellings versus loss at 0 percent deductible 

for the 1983 Coalinga earthquake and comparing our data and Insurance 

Source A data A40

8. Map showing the epicenter of the 1987 Whittier Narrows earthquake and the 

location of the population-weighted ZIP centroids for data from Insurance 

Source C A44

IV Contents
9. Graph showing distribution of dwellings versus deductible, based on 

replacement cost of all earthquake-insured dwellings A46

10. Map showing the epicenter of the 1987 Whittier Narrows earthquake and the 

location of the population-weighted ZIP centroids for data from Insurance 

Source D A54

11. Graph showing average loss for each ZIP versus distance from fault rupture 

for the 1987 Whittier Narrows earthquake ASS

12. Graph showing average loss for 1-mile interval versus distance from fault 

rupture for the 1987 Whittier Narrows earthquake ASS

13. Graph showing intensity versus distance from fault rupture for earthquakes in 

northern California AST

14. Map showing the city of San Fernando and the Sylmar and Pacoima districts 

of Los Angeles, which were part of the 1971 San Fernando earthquake 

region A59

15. Graph showing recommended loss over deductible versus deductible, based 

on equations 4-6 A60

TABLES

1. Types of data acquired from dwelling inspections after the 1971 San 

Fernando earthquake A3

2. Dwelling loss experience for the 1971 San Fernando earthquake: Loss over 

deductible. All one-story, one-and-two-story, split-level, and two-story 

dwellings, including sites with geologic effects A5

3. Dwelling loss experience for the 1971 San Fernando earthquake: Loss

distribution by number of dwellings. All one-story, one-and-two-story, splitlevel, and two-story dwellings, including sites with geologic effects A6

4. Dwelling loss experience for the 1971 San Fernando earthquake: Loss 

distribution by percent of dwellings. All one-story, one-and-two-story, splitlevel, and two-story dwellings, including sites with geologic effects A8

5. Dwelling loss experience for the 1971 San Fernando earthquake: Loss over 

deductible, in millions of 1985 dollars. All one-story, one-and-two-story, 

split-level, and two-story dwellings, including sites with geologic 

effects A10

6. Dwelling loss experience for the 1971 San Fernando earthquake: Loss over 

deductible, excluding sites with geologic effects All

7. Dwelling loss experience for the 1971 San Fernando earthquake: Loss over 

deductible, excluding sites with geologic effects and one-and-two-story and 

split-level dwellings A13

8. Dwelling loss experience for the 1971 San Fernando earthquake: Loss

distribution by number of dwellings, excluding sites with geologic effects and 

one-and-two-story and split-level dwellings A14

9. Dwelling loss experience for the 1983 Coalinga earthquake: Loss over 

deductible. All inspected wood-frame dwellings A16

10. Dwelling loss experience for the 1983 Coalinga earthquake: Loss distribution 

by number of dwellings A17

11. Dwelling loss experience for the 1983 Coalinga earthquake: Loss distribution 

by percent of dwellings A19

12. Dwelling loss experience for the 1983 Coalinga earthquake: Loss over

deductible, excluding dwellings that had shifted on their foundations or were 

posted as hazardous or had been demolished before time of 

inspection A22

Contents
13. Dwelling loss experience for the 1983 Coalinga earthquake: Loss distribution 

by number of dwellings, excluding dwellings that had shifted on their 

foundations or were posted as hazardous or had been demolished before time 

of inspection A24

14. Dwelling loss experience for the 1983 Coalinga earthquake: Loss over 

deductible, based on Insurance Source A data A26

15. Overview of dwelling loss experience for the 1971 San Fernando earthquake: 

Loss over deductible A27

16. Overview of dwelling loss experience for the 1971 San Fernando earthquake: 

Loss over deductible A29

17. Dwelling loss experience for the 1983 Coalinga earthquake: Loss over

deductible, Insurance Source A, insured values and paid claims; excluding 

dwellings that had shifted on their foundations or were posted as hazardous 

or had been demolished before time of inspection or were higher than one 

story A30

18. Dwelling loss experience for the 1983 Coalinga earthquake: Loss over 

deductible, Insurance Source A, realtor market values, less land values; 

excluding dwellings that had shifted on their foundations or were posted as 

hazardous or had been demolished before time of inspection or were higher 

than one story A31

19. Comparison of loss over deductible between our data and Insurance Source 

A data for the 1971 San Fernando and 1983 Coalinga earthquakes A33

20. Dwelling loss experience for the 1983 Coalinga earthquake: Loss distribution 

by number of dwellings, Insurance Source A; excluding dwellings that had 

shifted on their foundations or were posted as hazardous or had been 

demolished before time of inspection or were higher than one story A38

21. Probable Maximum Loss of wood-frame dwellings in magnitude 6.5 

earthquakes A40

22. Loss over deductible for conventional wood-frame dwellings A41

23. Number of dwellings with losses over deductible in Whittier and La Habra, 

on the basis of percent deductible A47

24. Comparison of loss over deductible and percent deductible, Insurance 

Source C A48

25. Summary of losses over deductible, Insurance Source C A48

26. Adjusted percent loss over 5 percent deductible for magnitude 5.9 and 8.25 

earthquakes, Insurance Source C A49

27. Dwelling loss experience for the 1987 Whittier Narrows earthquake: 

Insurance Source D A51

28. Modified Mercalli Intensities and dwelling percent losses: Five California 

earthquakes AST

29. Modified Mercalli Intensities and dwelling percent losses: 1971 San Fernando 

earthquake ASS

VI Contents
Earthquake Losses to 

Single-Family Dwellings: 

California Experience

By Karl V. Steinbrugge1 and ST. Algermissen

ABSTRACT

Most of the present methods for quantifying earthquake 

monetary losses to California wood-frame dwellings are 

based on summarized information on the 1933 Long Beach 

earthquake and on the partially analyzed 1971 San Fernando 

earthquake. Loss over deductible, for example, was not 

studied in the published reports that followed the 1971 San 

Fernando earthquake.

We reexamined the extant data from these two 

earthquakes, plus those from the 1983 Coalinga and 1987 

Whittier Narrows earthquakes, and other, less well 

documented events in the contexts of dwelling market value 

and insured value. Differences between market value and 

insured value are significant for older houses.

Transfer of data from specific earthquakes to 

generalized loss-estimation methods requires commonality 

of data. Unusual construction characteristics and unusual 

geologic effects were eliminated from the data to achieve 

commonality. For example, information from the 1983 

Coalinga earthquake shows that many dwellings were unanchored, which was contrary to the then generally accepted 

California practice; this circumstance was the result of 

houses moved to the city and placed on new foundations 

without anchors. In 1971 San Fernando earthquake, surface 

faulting and related ground movements at dwelling sites 

intensified damage. After standardizing the data, we 

developed a transfer function for earthquakes of other 

magnitudes.

A vital part of any loss-estimation method is the 

expected dwelling damage in the near vicinity of a fault 

rupture during a great earthquake. We examine two key 

factors, probable maximum loss and loss over deductible, 

from the standpoints of market value and insured value.

Manuscript approved for publication, April 18, 1990. 

1 Structural Engineer, El Cerrito, California.

Our analysis included one-story, one-and-two-story, 

split-level, and two-story structures. There are four age 

groups: pre-1940,1940-49, post-1949, and all ages. Further 

subdivision is by type of first floor: supported wood floor and 

concrete slab on grade. Although measurable differences in 

expected monetary losses exist among most of these 

dwelling characteristics, the most important from a practical 

standpoint are two age groups: pre-1940 construction and 

post-1939 construction. Available data allow the inclusion of 

any of the other dwelling characteristics that may be of user 

interest. The definition of the probable maximum loss, if 

applied to dwellings, has practical difficulties due to 

uncertainties in the evaluation of the loss-distribution curves. 

We propose an alternative method based on loss-overdeductible experience, in the forms of a graph and equations.

INTRODUCTION

This study examines two key factors in earthquake 

monetary loss estimation applied to California dwelling 

earthquake insurance: (1) probable maximum loss 

(PML), and (2) loss over deductible. The term PML, as 

used in California insurance practice, is defined in detail 

in the appendix. Loss over deductible is the entire loss 

minus a percentage of the dwelling value (either market 

or insured value). For an insured dwelling, loss over 

deductible is the insured loss, in other words, the loss that 

will be reimbursed by the insurer. Dollar deductible may 

be used instead of percent deductible in some cases.

Dwelling-loss data was acquired from field 

inspections and also, for three earthquakes, from 

insurance companies' paid-claims information. Presentation of the analyses of these two kinds of data sources is 

carried on in parallel from the standpoints of PML and 

loss over deductible. We analyzed the weaknesses and

Earthquake Losses to Single-Family Dwellings: California Experience A1
strengths of each approach to loss estimation. All data 

sources for each earthquake are independent of each 

other.

The private sector obviously has an interest in 

earthquake insurance. Dwelling-loss estimation is 

important to private commercial entities, such as savings 

and loan associations, banks, and mortgage holders. In 

the public sector, state insurance regulators have an 

interest in post-earthquake solvency of insurance 

companies. The California Department of Insurance 

issues an annual report on this subject (California 

Department of Insurance, 1981, and annually thereafter).

Loss information from non-insurance sources must 

be examined considering the basis on which the data 

were gathered. In a general sense, consider the 

"personal" versus "impersonal" viewpoints on loss and 

how each affects published loss statistics. For example, a 

wood-frame dwelling suffers minor interior and exterior 

plaster cracking but no structural damage. This could 

become a $100 "personal" loss if the homeowner pays for 

the paint and plaster patch and makes his own repairs for 

$100 out-of-pocket costs (with no outside labor). If, 

however, the loss is covered by other sources such as 

insurance, then the loss becomes "impersonal" from the 

homeowner's standpoint because someone else pays; the 

cost of the repairs if done by commercial painters might 

reasonably be $1,000, or 10 times the "personal" cost.

Similar loss interpretations are applicable to nondwellings. For example, in the 1964 Alaskan earthquake, 

a major private school had substantial non-structural 

damage, mostly in the form of cracked plaster and tile 

damage in the lavatories. The cost of commercial repair 

of damage to this just-completed structure was beyond 

the school's resources. After considerable deliberation, 

the maintenance staff pointed out that they could make 

the repairs for only the cost of materials during school 

vacation periods. The cost of repairs became manageable 

because no new labor costs were included. The reported 

cost of repairs then became a "personal" basis rather 

than the much higher "impersonal" basis.

Readers with insurance backgrounds may have 

seen references to various magnitude scales in articles on 

earthquakes. The more common of these scales are: (a) 

local magnitude, MLt or Richter magnitude; (b) bodywave magnitude, mb \ (c) surface-wave magnitude, Ms \ (d) 

moment magnitude, Mw (Stover, 1988, p. 5). We use 

local magnitudes. Differences among these magnitude 

scales are not important for this study.

Acknowledgments

Confidence in loss-estimation methods is a direct 

function of comparisons with reality. Reality is the actual 

amount of money that changes hands and, for this study, 

is on an impersonal-loss basis. We are grateful for the 

detailed proprietary loss data made available by the State

Farm Insurance Company and the Hartford Fire 

Insurance Company on the 1983 Coalinga earthquake. 

The State Farm Insurance Company and the California 

Department of Veterans Affairs supplied similar data on 

the 1987 Whittier Narrows earthquake.

The experience and insights of Frank E. McClure 

on loss-estimation methods significantly contributed to 

this study, and we thank him for his incisive comments.

Partial financial support for this study was provided 

by the State of California Department of Insurance 

through Richard J. Roth, Jr., Assistant Insurance 

Commissioner, and by the U.S. Geological Survey.

DATA SOURCES AND 

LOSS-OVER-DEDUCTIBLE COMPILATION

Principal sources of dwelling-loss data are the 1971 

San Fernando, 1983 Coalinga, and 1987 Whittier 

Narrows earthquakes. Some useful, but limited, data are 

also available from the 1933 Long Beach shock. 

Numerical information also exists from the 1906 San 

Francisco earthquake, but changes in construction 

practices limit its relevance.

Variations in dwelling construction have been 

limited to those that lay persons can identify without 

technical assistance or much knowledge of construction 

practices. This criterion allows the development of lowcost dwelling inventories where large numbers of 

structures are involved. The usual dwelling variants are: 

(1) age; (2) construction of the first floor; and, to a lesser 

extent, (3) number of stories. Regional differences in 

construction practices throughout California are also 

factors. For example, the wood-frame dwellings in San 

Francisco's Sunset District are not typical of usual 

California dwelling construction from an earthquakebracing standpoint. The reason for this is that these 

dwellings arc on narrow sites with automobile parking 

and utility rooms on the ground floor. As a result, the 

inherent earthquake bracing found in conventional 

housing is commonly reduced due to fewer crosswalk

PML's, dcductibles, and losses over deductible are 

normally given as percentages, unless context indicates 

otherwise. The methods used here apply equally to dollar 

deductibles; one needs only to divide the dollar 

deductible by value to obtain the percent deductible.

The term "value" can have various meanings, two 

of which are of principal interest. "Insured value" is 

obtained from data from insurance sources and is used 

with insurance paid claims. The equivalence of insured 

value to replacement value in this study is discussed in a 

following section. "Market value" is obtained from noninsurance data, with the exception of some of the 

information on the 1933 Long Beach earthquake, which 

is of assessor origin. Numerical relationships among 

these meanings arc discussed in following sections.

A2 Estimation of Earthquake Losses to Housing In California
1971 San Fernando Earthquake

Data Sources

Data sources are of two types: field inspections, 

which were not related to insurance claims, and 

insurance claim records.

Three published reports are of interest: Steinbrugge and others (1971), Steinbrugge and Schader 

(1973), and McClure (1973). McClure (1973) provided a 

useful perspective with respect to the other data because 

the McClure study represents a thoroughly examined 

sample of damage to 169 dwellings. Data for Steinbrugge 

and others (1971) and Steinbrugge and Schader (1973) 

were developed from a field inspection of more than 

12,000 single-family wood-frame dwellings by Pacific 

Fire Rating Bureau personnel. First, a pilot survey was 

necessary to determine the most heavily damaged areas. 

These areas were then located on a map and divided into 

convenient subareas. The inspection form identified each 

dwelling by address and block, age group, stories, firstfloor construction, and degree of damage to the principal 

construction components. (Construction components are

exterior wall types, brick chimneys if they exist, 

foundation type, and so forth.) Specifics of the inspection 

form are summarized in table 1.

The completed data forms for the 1971 report were 

reexamined after original publication. After instances of 

erroneously entered data were corrected, a total of 

12,075 correct inspection reports existed. The original 

forms no longer exist, but much of their data had been 

computerized for non-insurance studies. The street 

addresses of dwellings surveyed are no longer available; 

present information only locates each dwelling by a tract 

number, which is a grouping of city blocks. See figure 14 

for the size and location of each of these tracts along with 

the average percent loss to each tract.

The word description of the degree of damage to 

each construction component of each dwelling (table 1) 

was converted to a percent loss of dwelling value. 

Dwelling value was pre-earthquake market value, less 

land value, and was established by local realtors who 

were paid as consultants to the authors of the 1971 report 

(Steinbrugge and others, 1971). Percent loss of dwelling 

value for each component was summed to obtain the 

percent loss for the entire dwelling. Percent losses for

Table 1. Types of data acquired from dwelling inspections after the 1971 

San Fernando earthquake

[For all one- to four-family dwellings of all types of construction. The guidelines below 

were used by the field inspectors to identify word descriptions of degrees of damage for 

San Fernando. The guidelines used for Coalinga may be found in the appendix to 

Steinbrugge and others (1990). Descriptions used for Coalinga were very similar to those 

for San Fernando, except for changes due to local construction variants]

Location

Age group:

Pre-19HO, 1940-1919, Post-1919

Number of stories:

1, 2, U2, split level (there were no basements)

First floor type:

Supported wood or concrete slab on grade

Foundation damage:

None, slight, moderate, severe

Structural damage above foundation: 

None, slight, moderate, severe

Interior damage for plaster, gypsumboard, wood panel, or other: 

None, slight, moderate, severe

Exterior damage for stucco, wood, or other: 

None, slight, moderate, severe

Brick veneer by percent of wall(s) veneered, and

 by damage: None, slight, moderate, severe

Brick chimney by number of chimneys: none, 1, or 2, and

 by damage: None, slight, moderate, severe, total

Brick chimney: When found damaged, was it reinforced? 

Geologic effects in terms of observed ground movements

Swimming pool damage:

None, slight, moderate, severe

Earthquake Losses to Single-Family Dwellings: California Experience A3
each component were developed by a construction 

specialist who had access to or was able to obtain 

repair-cost figures from contractors who made repairs in 

the area. Percent losses were to the nearest 1 percent. 

Repair-cost figures were broken down by construction 

component, building value (less than $20,000, low value; 

$20,000430,000, medium value; and more than $30,000, 

high value), and period of construction (pre-1940, 

1940-49, and post-1949). Repair costs were not distorted 

by the increased work volume because there was a 

sufficiently large skilled-labor pool available and 

demands on construction materials were not large 

enough to distort local markets.

Single-Family Wood-Frame Dwellings, 

No Exclusions

Table 2, which applies to all inspected single-family 

wood-frame dwellings, shows losses over deductible for 

the range of 0-20 percent deductible. This kind of 

information had not been previously published. Dwelling 

inventory includes one-story, one-and-two-story, splitlevel, and two-story categories. The few brick-veneered 

dwellings are also included. Below-ground basements do 

not exist in this region.

Loss-over-deductible tables, such as table 2, may 

be readily computed if a number of individual dwellings 

have known values and losses. Assume a $100,000 

dwelling with a $15,000 loss. For this structure, a 1 

percent loss over deductible would be:

Loss over deductible » $15,000 - ($100,000 x 1 percent) 

= $14,000, but never less than zero.

This is repeated and summed for the entire inventory of 

dwellings, each with a specific value and loss. Dollar 

deductibles may be used as well as percentages.

Ages were visually determined. Pre-1940 

architectural styles are identifiable from post-1949 styles. 

Older wood-frame structures have not performed as well 

in earthquakes as newer structures for a variety of 

reasons. Rot, termite infestation, and other deterioration 

between a wooden first floor and the ground surface have 

weakened many structures. Older houses commonly are 

not well anchored to their foundations, in some cases, not 

at all. Concrete foundations in older structures may not 

be reinforced, may not be continuous, and may have 

cracked due to settlements. A few older foundations may 

be brick or stone that lack earthquake resistance.

Wood floors are above the ground surface and 

normally have crawl spaces beneath them. These floors 

are supported by wood posts and commonly by wood 

"cripple" studs, which extend from the concrete 

foundation up to the wood floor. These studs may 

overturn during an earthquake if wood siding nailed to 

them has deteriorated, resulting in heavy damage to the 

dwelling. If the dwelling has a concrete floor slab on

grade, and the structure is not anchored to the slab, 

dwelling failure is limited to the structure sliding off its 

foundation. Loss-over-deductible data that pertains to 

different floor construction types and age groups are 

included in table 2.

Table 3 is the loss distribution, by number of 

dwellings, using the same data as for table 2. The column 

headings on table 3 and similar tables are explained in 

detail in the "Loss distribution and probable maximum 

loss" section later in this report. Table 4 is similar to table 

3, except that it shows the loss distribution, by percent of 

dwellings. Table 5 shows loss over deductible, in 1985 

dollars, for the range of 0-10 percent deductible. Lossover-deductible tables, such as table 2, are readily 

developed from field surveys of observed damage as well 

as from insurance claims. Loss and value are determined 

from each field survey, the deductible is applied to value 

less land value, and the final results are summed. Lossdistribution tables, such as table 3, are similarly 

developed.

Table 2, and other similar tabulations such as table 

17, may also be useful for rate-deductible relationships. 

For example, using table 2, the loss over deductible at 5 

percent deductible for post-1949 dwellings with wood or 

concrete floors is 4.82 percent, whereas at 12 percent 

deductible for pre-1940 dwellings it is 4.90 percent. All 

other things being equal, except the deductible, rates 

should be the same for both age groups because they 

have approximately the same expected loss.

All Wood-Frame Dwellings, 

Excluding Sites With Geologic Effects

The inspection forms allowed the inspector to note 

if ground disturbance was observed at or adjacent to the 

site. This disturbance could be in various forms, such as 

faulting, displaced sidewalks, liquefaction, and ground 

movements from unidentified sources (see plates in 

Steinbrugge and others, 1971; also plates in Oakeshott, 

1975). Because inspection emphasis was on dwelling 

damage, it is quite likely that a number of dwellings were 

incorrectly coded as having no observable ground 

disturbance.

Table 6 shows loss over deductible for the range of 

0-20 percent deductible, excluding dwellings on sites 

with geologic effects or soil amplification. Counterparts 

to tables 3-5 are not included in this report.

Intensified damage, which is attributed to 

amplification of ground motions, was observed where the 

San Fernando Valley alluvial deposits meet the San 

Gabriel Mountains on the north side of the valley. The 

Olive View Hospital, the Veterans Hospital, and woodframe dwellings between and near these facilities are 

located in this area. All dwellings in this area were 

excluded even if no disturbed soil was observed.

A4 Estimation of Earthquake Losses to Housing in California
Table 2. Dwelling loss experience for the 1971 San Fernando earthquake: Loss over deductible. All one-story, 

dwellings, including sites with geologic effects

Percent Loss Over Deductible

CO

<o

I

<§w

No. of 

Dwell. 0% ded.

1.

2.

«3.

Wood floors:

Age Group: Pre-1940

1940-49

Post- 4 9

**A11 ages

Concrete floors:

Age Group: Pre-1940

1 940-49

Post-49

"All ages

Wood or concrete floors:

Age Group: Pre-1940

1940-49

Post-49

"All ages

509

2,714

1,396

4,709

108

1,769

5,153

7,106

634

4,541

6,652

12,075

12.87

9.48

10.72

10.22

6.17

7.99

8.37

8.24

11.84

8.93

8.91

9.03

1$ ded. 2% ded. 3% ded. 4$ ded. 5% ded. 6$ ded. 

12.07

8.62

9.83

9.35

5.56

7.26

7.56

7.46

11.07

8.12

8.08

8.22

11.27

7.76

8.94

8.50

4.94

6.54

6.76

6.68

10.31

7.32

7.26

7.41

Percent Loss

1.

2.

«3

Wood floors:

Age Group: Pre-1940

1940-49

Post-49 

**A11 ages

Concrete floors:

Age Group: Pre-1940 

1940-49

Post-49 

**A11 ages

. Wood or concrete floors:

Age Group: Pre-1940 

1940-49

Post-49

"All ages

No. of

Dwell .

509

2,714

1,396 

4,709

108 

1,769

5,153 

7,106

634 

4,541

6,652

12,075

10$ ded.

6.15

1.87

2.67 

2.59

1.17 

1.82

1.19 

1.36

5.44 

1.88

1.54

1.88

11$ ded.

5.82

1.69

2.41 

2.36

0.96 

1.59

1.00 

1.15

5.13 

1.68

1.33

1.67

12* ded.

5.57

1.58

2.26 

2.23

0.82 

1.45

0.86 

1.01

4.90 

1.55

1.18

1.52

10.49

6.91

8.06

7.65

4.34

5.83

5.96

5.90

9.56

6.52

6.44

6.61

9.72

6.07

7.19

6.81

3.74

5.12

5.17

5.14

8.83

5.73

5.63

5.82

8.95

5.23

6.31

5.96

3.14

4.42

4.38

4.37

8.09

4.94

4.82

5.03

8.19

4.39

5.44

5.12

2.56

3.73

3.60

3.62

7.36

4.16

4.03

4.24

Over Deductible

13$ ded.

5.34

1.50

2.12 

2.11

0.69 

1.31

0.77 

0.91

4.69 

1.44

1.08

1.41

14$ ded.

5.13

1.42

2.00 

2.00

0.55 

1.17

0.68 

0.81

4.49 

1.34

0.98

1.31

15$ ded.

4.94

1.35

1.89 

1.91

0.47 

1.08

0.63 

0.7t

4.32 

1.26

0.91

1.23

16$ de

4.76

1.28

1.80 

1.82

0.42 

1.00

0.57 

0.68

4.16 

1.18

0.85

1.16

 Includes unknown floor types not included above. 

"Includes unknown dwelling ages not included above,
Table 3. Dwelling loss experience for the 1971 San Fernando earthquake: Loss distribution by number of dwellings. All on

two-story dwellings, including sites with geologic effects

Estimal

s 

O

2,

m

1

1

<D

g"

*»

<D 

*»

X

O

2.

(O

3"

O

fiL

__5*

WOOD-PRE40 

% NO. SUM

LOSS

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

DWELL

101

2

6

9

0

2

96

3

11

104

5

46

7

7

17

1

2

6

0

3

0

1

6

1

1

4

3

4

1

1

9

0

0

7

0

3

1

1

1

0

3

5

2

1

1

1

. PCT

19.8

20.2

21.4

23.2

23.2

23.6

42.4

43.0

45.2

65.6

66.6

75.6

77.0

78.4

81.7

81.9

82.3

83-5

83.5

84.1

84.1

84.3

85.5

85.7

85.9

86.6

87.2

88.0

88.2

88.4

90.2

90.2

90.2

91.6

91.6

92.1

92.3

92.5

92.7

92.7

93.3

94.3

94.7

94.9

95.1

95.3

WOOD- 404 9 

NO. SUM

DWELL.

375

11

27

14

0

1

187

5

12

1526

61

210

58

7

32

6

3

9

1

6

3

0

14

1

11

3

6

16

5

4

26

3

3

15

6

2

2

1

0

0

1

3

1

2

0

1

PCT

13.8

14.2

15.2

15.7

15.7

15.8

22.7

22.8

23.3

79.5

81.8

89.5

91.6

91.9

93.1

93.3

93.4

93-7

93-8

94.0

94.1

94.1

94.6

94.7

95.1

95.2

95.4

96.0

96.2

96.3

97.3

97.4

97.5

98.0

98.3

98.3

98.4

98.5

98.5

98.5

98.5

98.6

98.6

98.7

98.7

98.7

WOOD-POST49 

NO. SUM

DWELL

155

5

2

14

3

3

48

3

7

766

31

144

27

13

31

8

7

14

2

2

5

2

11

2

9

4

1

2

3

2

8

4

2

4

3

1

2

1

0

3

0

2

2

0

3

0

. PCT

11.1

11.5

11.6

12.6

12.8

13.0

16.5

16.7

17.2

72.1

74.3

84.6

86.5

87.5

89.7

90.3

90.8

91.8

91-9

92.0

92.4

92.6

93.3

93.5

94.1

94.4

94.5

94.6

94.8

95.0

95.6

95.8

96.0

96.3

96.5

96.6

96.7

96.8

96.8

97.0

97.0

97.1

97.3

97.3

97.5

97.5

WOOD-ALL CONC-PRE40 

NO. SUM NO. SUM

DWELL.

652

19

35

39

3

6

334

11

30

2436

98

408

95

27

84

15

12

29

3

11

8

3

32

4

21

11

11

22

10

7

43

7

5

26

9

6

6

3

1

3

4

10

5

3

4

2

PCT DWELL. PCT

13.8

14.2

15.0

15.8

15.9

16.0

23.1

23.3

24.0

75.7

77.8

86.5

88.5

89.0

90.8

91.1

91.4

92.0

92.1

92.3

92.5

92.5

93.2

93.3

93.8

94.0

94.2

94.7

94.9

95.1

96.0

96.1

96.2

96.8

97.0

97.1

97.2

97.3

97.3

97.4

97.5

97.7

97.8

97.8

97.9

98.0

42

0

1

0

0

3

19

0

1

19

1

7

0

0

7

2

0

2

0

0

0

0

1

0

0

2

0

0

0

0

0

0

0

0

0

1

0

0

0

0

0

0

0

0

0

0

30.9

38.9

39.8

39.8

39.8

42.6

60.2

60.2

61.1

7H.7

79.6

86.1

86.1

86.1

92.6

94 . 4

94 . 4

96.3

96.3

96.3

96.3

96.3

97.2

97.2

97.2

99.

99.

99.

99.

99.

99.

99.

99.

99.

99.

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

CONC-4049 

NO. SUM

DWELL.

490

6

9

14

1

29

215

1

42

559

3

145

8

6

85

2

4

17

0

24

14

0

15

1

7

8

1

2

3

5

2

0

2

1

3

17

1

0

7

0

1

3

1

0

0

0

PCT

27.7

28.0

28.5

29-3

29.4

31.0

43.2

43.2

45.6

77.2

77.4

85.6

86.0

86.4

91.2

91.3

91.5

92.5

92.5

93.8

94.6

94.6

95.5

95.5

95.9

96.4

96.4

96.6

96.7

97.0

97.1

97.1

97.2

97.3

97.5

98.4

98.5

98.5

98.9

98.9

98.9

99.1

99.2

99.2

99.2

99.2

CONC-POST49 

NO. SUM

DWELL

1000

14

14

41

14

68

252

17

45

2459

23 '»

270

253

39

128

31

18

23

2

15

14

7

36

10

13

16

a

18

15

11

9

7

2

6

1

12

0

1

4

0

0

3

3

0

2

5

. PCT

19-4

19.7

19.9

20.7

21.0

22.3

27.2

27.6

28.4

76.1

80.7

85.9

90.8

91.6

94.1

94.7

95.0

95.5

95.5

95.8

96.1

96.2

96.9

97.1

97.4

97.7

97.8

98.2

98.5

98.7

98.9

99.0

99.0

99.1

99.2

99.4

99.4

99.4

99.5

99.5

99.5

99.6

99.6

99.6

99.7

99.7

CONC-ALL 

NO. SUM

DWELL .

1551

20

25

56

16

103

491

19

91

3055

238

427

265

47

225

36

23

42

2

39

28

7

55

11

20

26

9

21

18

16

12

7

4

7

4

31

1

1

11

0

1

6

4

0

2

5

PCT

21.8

22.1

22.5

23.2

23-5

24.9

31.8

32.1

33.4

76.4

79.7

85.7

89.5

90.1

93.3

93.8

94.1

94.7

94.7

95.3

95.7

95.8

96.6

96.7

97.0

97.4

97.5

97.8

98.0

98.3

98.4

98.5

98.6

98.7

98.7

99.2

99.2

99.2

99.4

99.4

99.4

99.5

99.5

99.5

99.5

99.6

BOTH-PRE

NO. S

DWELL

149

2

7

10

0

5

117

3

12

125

6

53

9

8

24

3

2

a

0

3

0

1

7

1

1

6

3

4

1

1

9

0

0

7

0

4

1

1

1

0

3

5

2

1

1

1

. P

23

23

24

26

26

27

45

46

48

67

68

77

78

79

83

84

84

85

85

86

86

86

87

87

87

88

89

89

89

90

91

91

91

92

92

93

93

93

93

93

94

95

95

95

95

95
COo"

£

5

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£

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c

m

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c 

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Earthquake Losses to Single-Family Dwellings: California Experience A7
Table 4. Dwelling loss experience for the 1971 San Fernando earthquake: Loss distribution by percent of dwellings. All one

two-story dwellings, including sites with geologic effects

m

a

3

At

A 

§

5

3

J3

fl»«"

JTw

i

0

X

§

2.

<o

3*

O

SL

1

35*

WOOD-PRE40

%

LOSS

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

%

DWELL

20

0

1

2

0

0

19

1

2

20

1

9

1

1

3

0

0

1

0

1

0

0

1

0

0

1

1

1

0

0

2

0

0

1

0

1

0

0

0

0

1

1

0

0

0

0

SUM

. PCT

19.8

20.2

21.4

23.2

23.2

23.6

42.4

43.0

45.2

65.6

66.6

75.6

77.0

78.4

81.7

81.9

82.3

83.5

83.5

84.1

84.1

84.3

85.5

85.7

85.9

86.6

87.2

88.0

88.2

88.4

90.2

90.2

90.2

91.6

91.6

92.1

92.3

92.5

92.7

92.7

93.3

94.3

94.7

94.9

95.1

95.3

WOOD- 4049

,

DWELL.

13.8

0.4

1.0

0.5

0.0

0.0

6.9

0.2

0.4

56.2

2.2

7.7

2.1

0.3

1.2

0.2

0.1

0.3

0.0

0.2

0.1

0.0

0.5

0.0

0.4

0.1

0.2

0.6

0.2

0.1

1.0

0.1

0.1

0.6

0.2

0.1

0.1

0.0

0.0

0.0

0.0

0.1

0.0

0.1

0.0

0.0

SUM

PCT

13.8

14.2

15.2

15.7

15.7

15.8

22.7

22.8

23.3

79.5

81.8

89.5

91.6

91.9

93.1

93.3

93.4

93.7

93.8

94.0

94.1

94.1

94.6

94.7

95.1

95.2

95.4

96.0

96.2

96.3

97.3

97.4

97.5

98.0

98.3

98.3

98.4

98.5

98.5

98.5

98.5

98.6

98.6

98.7

98.7

98.7

WOOD-POST49

,

DWELL

11.1

0.4

0.1

1.0

0.2

0.2

3.4

0.2

0.5

54.9

2.2

10.3

1.9

0.9

2.2

0.6

0.5

1.0

0.1

0.1

0.4

0.1

0.8

0.1

0.6

0.3

0.1

0.1

0.2

0.1

0.6

0.3

0.1

0.3

0.2

0.1

0.1

0.1

0.0

0.2

0.0

0.1

0.1

0.0

0.2

0.0

SUM

. PCT

11.1

11.5

11.6

12.6

12.8

13.0

16.5

16.7

17.2

72.1

74.3

84.6

86.5

87.5

89.7

90.3

90.8

91.8

91.9

92.0

92.4

92.6

93.3

93.5

94.1

94.4

94.5

94.6

94.8

95.0

95.6

95.8

96.0

96.3

96.5

96.6

96.7

96.8

96.8

97.0

97.0

97.1

97.3

97.3

97.5

97.5

WOOD-ALL

%

DWELL.

13-8

0.4

0.7

0.8

0.1

0.1

7.1

0.2

0.6

51.7

2.1

8.7

2.0

0.6

1.8

0.3

0.3

0.6

0.1

0.2

0.2

0.1

0.7

0.1

0.4

0.2

0.2

0.5

0.2

0.1

0.9

0.1

0.1

0.6

0.2

0.1

0.1

0.1

0.0

0.1

0.1

0.2

0.1

0.1

0.1

0.0

SUM

PCT

13.8

1N.2

15.0

15.8

15.9

16.0

23.1

23.3

2H.O

75.7

77.8

86.5

88.5

89.0

90.8

91.1

91.4

92.0

92.1

92.3

92.5

92.5

93.2

93.3

93.8

94.0

94.2

94.7

94.9

95.1

96.0

96.1

96.2

96.8

97.0

97.1

97.2

97.3

97.3

97.4

97.5

97.7

97.8

97.8

97.9

98.0

CONC-PRE40

%

DWELL

38.9

0.0

0.9

0.0

0.0

2.8

17.6

0.0

0.9

17.6

0.9

6.5

0.0

0.0

6.5

1.9

0.0

1.9

0.0

0.0

0.0

0.0

0.9

0.0

0.0

1.9

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.9

0.0

0.0

0.0

0.0

0.0

o.o

0.0

0.0

0.0

0.0

SUM

. PCT

38.9

38.9

39.8

39.8

39.8

42.6

60.2

60.2

61.1

78.7

79.6

86.1

86.1

86.1

92.6

94.4

94.4

96.3

96.3

96.3

96.3

96.3

97.2

97.2

97.2

99.1

99.1

99.1

99.1

99.1

99.1

99.1

99.1

99.1

99.1

100.0

100.0

100.0

100.0

reo.o

100.0

100.0

100.0

100.0

100.0

100.0

CONC-4049

*

DWELL.

27.7

0.3

0.5

0.8

0.1

1.6

12.2

0.1

2.4

31.6

0.2

8.2

0.5

0.3

4.8

0.1

0.2

1.0

0.0

1.4

0.8

0.0

0.8

0.1

0.4

0.5

0.1

0.1

0.2

0.3

0.1

0.0

0.1

0.1

0.2

1.0

0.1

0.0

0.4

0.0

0.1

0.2

0.1

0.0

0.0

0.0

SUM

PCT

27.7

28.0

28.5

29.3

29.4

31.0

43.2

43.2

45.6

77.2

77.4

85.6

86.0

86.4

91.2

91.3

91.5

92.5

92.5

93.8

94.6

94.6

95.5

95.5

95.9

96.4

96.4

96.6

96.7

97.0

97.1

97.1

97.2

97.3

97.5

98.4

98.5

98.5

98.9

98.9

98.9

99.1

99.2

99.2

99.2

99.2

CONC-POST49

%

DWELL

19.4

0.3

0.3

0.8

0.3

1.3

4.9

0.3

0.9

47.7

4.5

5.2

4.9

0.8

2.5

0.6

0.3

0.4

0.0

0.3

0.3

0.1

0.7

0.2

0.3

0.3

0.2

0.3

0.3

0.2

0.2

0.1

0.0

0.1

0.0

0.2

0.0

0.0

0.1

0.0

0.0

0.1

0.1

0.0

0.0

0.1

SUM

. PCT

19.4

19.7

19.9

20.7

21.0

22.3

27.2

27.6

28.4

76.1

80.7

85.9

90.8

91.6

94.1

94.7

95.0

95.5

95.5

95.8

96.1

96.2

96.9

97.1

97.4

97.7

97.8

98.2

98.5

98.7

98.9

99.0

99.0

99.1

99.2

99.4

99.4

99.4

99.5

99.5

99.5

99.6

99.6

99.6

99.7

99.7

CONC-ALL

%

DWELL.

21.8

0.3

0.4

0.8

0.2

1.4

6.9

0.3

1.3

43.0

3.3

6.0

3.7

0.7

3.2

0.5

0.3

0.6

0.0

0.5

0.4

0.1

0.8

0.2

0.3

0.4

0.1

0.3

0.3

0.2

0.2

0.1

0.1

0.1

0.1

0.4

0.0

0.0

0.2

0.0

0.0

0.1

0.1

0.0

0.0

0.1

SUM

PCT

21.8

22.1

22.5

23.2

23.5

24.9

31.8

3?. 1

33.4

76.4

79.7

85.7

89.5

90.1

93.3

93.8

94.1

94.7

94.7

95.3

95.7

95.8

96.6

96.7

97.0

97.4

97.5

97.8

98.0

98.3

98.4

98.5

98.6

98.7

9B.7

99.2

99.2

99.2

99.4

99.4

99.4

99.5

99.5

99.5

99.5

99.6

BOTH-PRE4

j

DWELL

23.5

0.3

1.1

1.6

o f o

0.8

18.5

0.5

1.9

19.7

0.9

8.4

1.4

1.3

3.8

0.5

0.3

.1.3

0.0

0.5

0.0

0.2

1.1

0.2

0.2

0.9

0.5

0.6

0.2

0.2

1.4

0.0

0.0

1.1

0.0

0.6

0.2

0.2

0.2

0.0

0.5

0.8

0.3

0.2

0.2

0.2

SUM

. PC

23.5

23.8

24.9

26.5

26.5

27.3

45.7

46.2

48.1

67.8

68.8

77.1

78.5

79.8

83.6

84.1

84.4

85.6

85.6

86.1

86.1

86.3

87.4

87.5

87-7

88.6

89.1

89.7

89.9

90.1

91.5

91.5

91.5

92.6

92.6

93.2

93-4

93.5

93-7

93.7

94.2

95.0

95.3

95.4

95.6

95.7
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6 (0 > co vorEarthquake Losses to Single-Family Dwellings: California Experience A9
Table 5. Dwelling loss experience for the 1971 San Fernando earthquake: Loss over deductible, in millions of 198

split-level, and two-story dwellings, including sites with geologic effects

1. Wood floors:

Age Group: Pre-1940 

1940-49 

Post-49 

"All ages

2. Concrete floors:

Age Group: Pre-1940 

1940-49 

Post-49

 All ages

*3« Wood or concrete floors: 

Age Group: Pre-1940 

1940-49 

Post-149

**A11 ages

No. of 

Dwell.

509

2,714

1,396

Dollar Loss Over Deductible, in millions (1985 dollars) 

0% ded. 1% ded. 2% ded. 3% ded. 4$ ded. 5% ded. 6% ded. 

5.43

21.79

13.46

5.09

19.80

12.37

4.75

17.82

11.28

4.42

15.87

10.19

4.09

13.93

9.12

3.76

11.98

8.05

3-43

10.04

6.98

4,709 41.45 37.97 34.50 31.07 27.67 24.27 20.88

 Includes unknown floor types not included above. 

**Includes unknown dwelling ages not included above,

108

1,769

5,153

7,106

0.60

12.63

42.54

56.44

0.54

11.50

38.43

51.08

0.48

10.38

34.34

45.74

0.42

9.26

30.26

40.43

0.36

8.16

26.24

35.19

0.30

7.06

22.23

29.96

0.25

5.98

18.31

24.86

634

4,541

6,652

12,075

6.27

35.02

57.17

100.15

5.86

31.86

51.89

91.15

5.45

28.72

46.62

82.19

5.05

25.61

41.37

73.29

4.66

22.52

36.19

64.48

4.26

19.43

31.03

55.71

3.87

16.37

25.96

47.07
Table 6. Dwelling loss experience for the 1971 San Fernando earthquake: Loss over deductible, excluding sit

Percent Loss Over Deductible

1. Wood floors:

Age Group: Pre-1940 

1940-49 

Post-49 

"All ages

2. Concrete floors:

Age Group: Pre-1940 

1940-49 

Post-49 

**A11 ages

*3« Wood or concrete floors: 

Age Group: Pre-1940 

1940-49 

Post-49 

"All ages

No. of

Dwell.

468

2,391

1,184

4,123

106

1,675

4,343

6,185

589

4,117

5,596

10,515

0$ ded.

11.40

8.29

9.13

8.87

6.40

7.49

7.69

7.61

10.43

8.00

8.02

8.10

1$ ded.

10.61

7.45

8.25

8.02

5.78

6.78

6.91

6.85

9.67

7.21

7.22

7.31

2$ ded.

9.82

6.61

7.37

7.18

5.17

6.07

6.14

6.10

8.93

6.42

6.43

6.53

3$ ded.

9.05

5.78

6.50

6.34

4.56

5.37

5.36

5.35

8.19

5.65

5.63

5.75

4$ ded.

8.30

4.95

5.64

5.52

3.94

4.68

4.60

4.61

7.47

4.88

4.85

4.98

5$ ded.

7.55

4.13

4.78

4.69

3.33

3.98

3.84

3.87

6.74

4.11

4.06

4.21

6$ ded.

6.80

3.31

3.92

3.87

2.75

3.30

3.09

3.15

6.03

3.34

3.29

3.45

5"

CD

% 

CD

8*

<o

<o w

O

Percent Loss Over Deductible 

No. of 

Dwell. 10J ded. 11? ded. 12$ ded. 13$ ded. 14$ ded. 15$ ded. 16$ ded. 

1. Wood floors:

Age Group: Pre-1940 

1940-49 

Post-49 

"All ages

2. Concrete floors:

Age Group: Pre-1940 

1940-49 

Post-49 

"All ages

*3. Wood or concrete floors: 

Age Group: Pre-1940 

1940-49 

Post-49 

"All ages

468

2,391

1,184

4,123

106

1,675

4,343

6,185

589

4,117

5,596

10,515

4.89

0.92

1.24

1.46

1.26

1.48

0.78

0.99

4.21

1.18

0.90

1.19

4.60

0.78

1.03

1.28

1.04

1.27

0.62

0.81

3.93

1.01

0.73

1.02

4.39

0.72

0.92

1.19

0.88

1.15

0.51

0.70

3.73

0.93

0.62

0.91

4.20

0.68

0.83

1.12

0.72

1.03

0.45

0.62

3.55

0.85

0.55

0.83

4.03

0.64

0.75

1.05

0.56

0.92

0.40

0.55

3.38

0.77

0.48

0.76

3.88

0.60

0.69

0.99

0.48

0.84

0.36

0.50

3.25

0.72

0.44

0.71

3.74

0.57

0.64

0.94

0.42

0.77

0.33

0.45

3.13

0.67

0.40

0.66

 Includes unknown floor types not included above. 

 Includes unknown dwelling ages not included above.
Exclusion of sites with special geologic effects is to 

provide a common geologic basis for transferring 

information to other areas that do not have special 

geologic conditions. In this manner, each site, area, or 

region elsewhere will require a geologic or soil factor in 

the loss-estimation algorithm. This important factor can 

not be overlooked in any adequate loss-estimation 

method.

One-Story Wood-Frame Dwellings, 

Excluding Sites With Geologic Effects

Another analysis further restricted the data to 

one-story dwellings, thereby eliminating one-and-twostory, split-level, and two-story structures.

Table 7 shows loss over deductible for the range of 

0-20 percent deductible. Table 8 is the loss distribution, 

by number of dwellings; a detailed discussion of this table 

may be found in "Loss distribution and Probable 

Maximum Loss." Counterparts to tables 4 and 5 are not 

included in this report.

1983 Coalinga Earthquake

Data Sources

Data sources are of two types. The first type that is 

discussed is the information gained from field inspections 

that were not related to insurance claims. This is followed 

by a discussion of information from insurance claim 

records.

The 1983 Coalinga earthquake was examined for 

dwelling losses of many kinds, including loss over 

deductible (Steinbrugge and others, 1990). Examination 

of losses over deductible and PML's have been expanded 

here.

All one-to-four-family dwellings in Coalinga 

(population 6,769 as of 1983) were examined after the 

1983 Coalinga earthquake to determine location by 

street address, city block, age group, stories, floor 

construction, and degree of damage to construction 

components. The inspection form was similar to that 

used for the 1971 San Fernando earthquake (table 1), 

but modified for local conditions.

At least three sides of each house were inspected, 

and the interiors of almost 60 percent of the houses were 

also examined. A total of 1,982 of the 2,041 inspected 

dwellings provided useful data.

Percent losses to each construction component 

were based on 1971 San Fernando experience, modified 

by experience from Coalinga contractors.

Dwelling values were pre-earthquake market 

values, less land values, as established by local realtors 

who were paid as consultants to the authors.

One-to-Four-Family Wood-Frame Dwellings

The 1983 Coalinga inspections included all oneto-four-family dwellings, whereas the 1971 San Fernando 

inspections were limited to single-family dwellings. This 

difference is not considered to be significant due to the 

few non-one-family dwellings in Coalinga and San 

Fernando.

There were no below-ground basements in either 

Coalinga or San Fernando.

All masonry-veneered dwellings were excluded in 

Coalinga but not in San Fernando. Few houses in San 

Fernando and Coalinga were veneered. If veneered, the 

amount was usually small, such as 1-10 percent of the 

total wall area. In Coalinga, 75.1 percent of those with 

small amounts of veneer had slight or no damage. The 

difference in treatment of brick veneer in the data bases 

of San Fernando and Coalinga does not have a significant 

impact on the results of this study.

Table 9 shows the loss over deductible for the 

range of 0-20 percent deductible. Tables 10 and 11 are 

the loss distributions, by number of dwellings and by 

percent of dwellings, respectively. A counterpart to table 

5 is not included in this report.

One-to-Four-Family Wood-Frame Dwellings, 

Excluding Special Cases

The San Fernando commentary on age of dwelling 

and type of first-floor construction also applies to 

Coalinga.

By "special cases" is meant those dwellings that 

had shifted on their foundations or were posted as 

hazardous or had been demolished before time of 

inspection. Most of these, by far, had shifted on or fallen 

off their foundations.

An unusual construction characteristic was found 

in the dwellings that had been moved into the city of 

Coalinga from the nearby oil fields. These houses were 

not moved into any one particular area and were set on 

any available vacant lot. Perhaps 200 such dwellings were 

moved to Coalinga between about 1930 and the late 

1950's. It is estimated that 90 percent of the dwellings 

imported prior to 1940 or 1945 were placed on wooden 

sills (directly on the earth). Dwellings moved to Coalinga 

after 1945, particularly after 1950, probably were placed 

on concrete foundations but apparently were not bolted 

thereto. In these latter instances, where failure was 

observed, the wooden foundation sills had been placed 

directly on the smooth (troweled in many cases) top 

surface of the concrete foundations. This construction 

peculiarity has not been found in other cities. The results 

of excluding these "special cases" are shown in table 12,

A12 Estimation of Earthquake Losses to Housing in California
Table 7. Dwelling loss experience for the 1971 San Fernando earthquake: Loss over deductible, excluding sites 

and split-level dwellings

Percent Loss Over Deductible

w 

to

to

w

O

2L

I 

5"

 o

(D

55"

o

o

1.

2.

 3-

Wood floors:

Age Group: Pre-1940

1940-49

Post-49

 All ages

Concrete floors:

Age Group: Pre-1940

19HO-49

Post-49

"All ages

. Wood or concrete floors:

Age Group: Pre-1940

19HO-49

Post-49

 All ages

No. of 

Dwell.

465

2,379

1,148

4,072

106

1,668

4,142

5,965

586

4,097

5,353

10,237

0} ded.

11.41

8.26

8.72

8.73

6.40

7.50

7.56

7.52

10.44

7.99

7.83

7.99

1} ded.

10.63

7.42

7.85

7.89

5.78

6.79

6.78

6.77

9.68

7.20

7.03

7.21

2} ded.

9.84

6.58

6.97

7.05

5.17

6.09

6.01

6.02

8.94

6.41

6.24

6.43

Percent Loss

1.

2.

 3

Wood floors:

Age Group: Pre-1940

19HO-49

Post- 49

 All ages

Concrete floors:

Age Group: Pre-1940 

1940-49

Post-49

**A11 ages

. Wood or concrete floors:

Age Group: Pre-1940 

1940-49

Post-49

**A11 ages

No. of 

Dwell.

465

2,379

1,148

4,072

106 

1,668

4,142

5,965

586 

4,097

5,353

10,237

10} ded.

4.92

0.89

0.87

1.34

1.26 

1.48

0.67

0.92

4.23 

1.17

0.73

1.11

11} ded.

4.63

0.76

0.68

1.18

1.04 

1.28

0.51

0.75

3.95 

1.00

0.57

0.94

12} ded.

4.42

0.70

0.59

1.09

0.88 

1.16

0.41

0.64

3.75 

0.92

0.46

0.83

3} ded.

9.07

5.75

6.10

6.22

4.56

5.38

5.24

5.27

8.20

5.63

5.44

5.65

4} ded.

8.32

4.93

5.24

5.39

3.94

4.69

4.48

4.53

7.48

4.86

4.66

4.88

5} ded.

7.57

4.10

4.39

4.57

3.33

3.99

3.72

3.79

6.76

4.09

3.88

4.11

6} ded.

6.83

3.28

3.53

3.75

2.75

3.32

2.97

3.07

6.05

3.33

3.11

3.35

Over Deductible

13} ded.

4.23

0.66

0.51

1.02

0.72 

1.04

0.36

0.56

3.57 

0.84

0.40

0.76

14} ded.

4.05

0.62

0.45

0.95

0.56 

0.92

0.30

0.49

3.40 

0.76

0.34

0.69

15} ded.

3.91

0.58

0.40

0.90

0.48 

0.85

0.27

0.44

3.27 

0.71

0.31

0.64

16} ded.

3.77

0.55

0.36

0.86

0.42 

0.77

0.25

0.40

3.14 

0.66

0.28

0.60

 Includes unknown floor types not included above. 

 Includes unknown dwelling ages not included above.
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A14 Estimation of Earthquake Losses to Housing in California
E

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58

excluding sfa

dwellings, of 

CD

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the San 1971Continued 35 

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Earthquake Losses to Single-Family Dwellings: California Experience A15
Table 9. Dwelling loss experience for the 1983 Coalinga earthquake: Loss over deductible. All inspected wood-

w

8 

o

(O

1. Wood floors:

Age Group: Pre-19lO 

19HO-H9 

Post-19 

**A11 ages

2. Concrete floors:

Age Group: Pre-19lO 

19HO-19 

Post-19 

"All ages

*3« Wood or concrete floors: 

Age Group: Pre-1910 

19HO-19 

Post-19 

"All ages

1. Wood floors:

Age Group: Pre-19lO 

igUO-19 

Post-19 

"All ages

2. Concrete floors:

Age Group: Pre-19lO 

igUO-19 

Post-19 

"All ages

*3- Wood or concrete floors 

Age Group: Pre-19lO 

19HO-19 

Post-19 

"All ages

No. of 

Dwell.

802 

289 

360 

1,177

19 

35 

396 

155

815 

329 

763 

1,982

No. of 

Dwell .

802 

289 

360 

1,177

19 

35 

396 

155

815 

329 

763 

1,982

0} ded.

28.20 

11.79 

11.88 

22.30

17.05 

11.37 

9.23 

9.71

28.19 

15.18 

11.90 

20.16

10} ded.

19.17 

6.92 

6.11 

13-73

9.11 

3.60 

2.00 

2.11

19.17 

7.32 

3-95 

11.86

1} ded.

27.25 

13.89 

13.91 

21.35

16.16 

10.13 

8.33 

8.81

27.21 

11.27 

10.97 

19.22

2} ded. 3} ded.

26.31 

12.99 

12.95 

20.12

15.26 

9.19 

7.15 

7.95

26.30 

13.37 

10.05 

18.29

Percent Loss 

11} ded. 12} ded.

18.71 

6.39 

5.15 

13.05

8.63 

3.17 

1.61 

2.06

18.73 

6.79 

3.15 

11.25

18.02 

5.89 

1.89 

12.12

8.16 

2.77 

1.35 

1.76

18.02 

6.30 

3.03 

10.69

25.36 

12.10 

12.00 

19.18

11.37 

8.57 

6.60 

7.09

25.35 

12.18 

9.16 

17.38

1} ded.

21.17 

11.28 

11.09 

18.60

13.17 

7.71 

5.83 

6.31

21.16 

11.65 

8.32 

16.52

Over Deductible 

13} ded. 11} ded.

17-39 

5.15 

1.13 

11.86

7.71 

2.51 

1.15 

1.51

17.38 

5.87 

2.70 

10.20

16.76 

5.02 

1.01 

11.32

7.32 

2.31 

O.Q6 

1.31

16.75 

5.16 

2.11 

9.71

5} ded.

23-58 

10.16 

10.20 

17-72

12.63 

6.89 

5.08 

5.55

23-57 

10.83 

7.51 

15.66

15} ded.

16.17 

1.67 

3.66 

10.83

7.00 

2.11 

0.83 

1.19

16.16 

5.12 

2.17 

9.32

6} ded.

22.69 

9.61 

9.31 

16.81

11.79 

6.11 

1.35 

1.81

22.68 

10.02 

6.71 

11.82

16} ded.

15.60 

1.33 

3.35 

10.38

6.68 

2.00 

0.72 

1.07

15.59 

1.80 

1.96 

8.93

 Includes unknown floor types not included above. 

"Includes unknown dwelling ages not included above.
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\ co o^roonai irivOf-eoo>^^'-'-'-'-^-«-'-'-cM(\iojoj'evi(M?JfEarthquake Losses to Single-Family Dwellings: California Experience A17
£ Table 10. Dwelling loss experience for the 1983 Coalinga earthquake: Loss distribution by number of dwellings Continued

? 

»

$ WOOD-PRE10 WOOD-1019 WOOD-POST19 WOOD-ALL CONC-PRE10 CONC-1019 CONC-POSTlg CONC-ALL BOTH-PREl

6

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5

2§ 

35*

*

LOSS

16

17

18

19

50

51

52

53

51

55

56

57

58

59

60

61

62

63

64

65

>65

NO.

DWELL

1

0

16

0

18

0

2

3

0

0

3

0

1

0

2

1

0

1

0

0

82

SUM

. PCT

80.2

80.2

82.2

82.2

88.2

88.2

88.it

88.8

88.8

88.8

89.2

89.2

89.3

89.3

89.5

89.7

89.7

89.8

89.8

89.8

100.0

NO.

DWELL.

0

0

2

0

1

0

0

1

0

0

0

1

0

0

0

1

0

0

0

0

5

SUM

PCT

96.2

96.2

96.9

96.9

97.2

97.2

97.2

97.6

97.6

97.6

97.6

97.9

97.9

97.9

97.9

98.3

98.3

98.3

98.3

98.3

100.0

NO.

DWELL

0

0

0

2

0

0

0

0

0

0

0

0

1

0

0

0

0

0

0

0

5

SUM

. PCT

97.8

97.8

97.8

98.3

98.3

98.3

98.3

98.3

98.3

98.3

98.3

98.3

98.6

98.6

98.6

98.6

98.6

98.6

98.6

98.6

100.0

NO.

DWELL.

1

0

18

2

50

0

2

It

0

0

3

1

2

0

2

3

0

1

0

0

91

SUM

PCT

87.7

87.7

88.9

89.0

92.1

92.1

92.6

92,8

92.8

92.8

93.0

93.1

93.2

93.2

93.1

93.6

93.6

93.6

93.6

93.6

100.0

NO.

DWELL

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

1

SUM

. PCT

91.7

91.7

91.7

91.7

91.7

91.7

91.7

91.7

91.7

91-7

91.7

91.7

91.7

91.7

91.7

91.7

91.7

91.7

91.7

91.7

100.0

NO.

DWELL .

0

0

0

0

0

0

0

0

0

0

0

0

0

0

1

0

0

0

0

0

0

SUM NO.

PCT DWELL

97.

97.

97.

97.

97.

97.

97.

97.

97.

97.

97.

97.

97.

97.

0

0

1

0

0

0

0

0

0

0

0

0

0

0

100.0 0

100.0 0

100.0 0

100.0 0

100.0 0

100.0 0

100.0 1

SUM

. PCT

99.5

99.5

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99-7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

100.0

NO.

DWELL.

0

0

1

0

0

0

0

0

0

0

0

0

0

0

1

0

0

0

0

0

2

SUM

PCT

99.1

99.1

99.3

99.3

99.3

99.3

99.3

99.3

99.3

99.3

99.3

99.3

99.3

99.3

99.6

99.6

99.6

99.6

99.6

99.6

100.0

NO.

DWELL

1

0

17

0

51

0

2

3

0

0

3

0

1

0

2

1

0

1

0

0

86

SUM

. PC

80.

80.

82.

82.

88.

tttt.

88.

88.

88.

88.

89.

89.

89.

89.

89.

89.

89.

89.

89.

89.

100.
Coalinga distribution earthquake: Loss by Table theofdwellings Dwelling experience for loss19831. percent 

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Earthquake Losses to Single-Family Dwellings: California Experience A19
Estimation ofEarthquake Losses

0

Q

c

2.

<o

5*

O 

SL

I

5*

Table 11. Dwelling loss experience for the 1983 Coalinga earthquake

WOOD-PRE40 WOOD-4019 WOOD-POST19 WOOD-ALL CONC-PRE40

%

LOSS

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

>65

,

DWELL

0

0

2

0

6

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

10

SUM

. PCT

80.2

80.2

82.2

82.2

88.2

88.2

88.4

88.8

88.8

88.8

89.2

89.2

89.3

89.3

89.5

89.7

89.7

89.8

89.8

89.8

100.0

,

DWELL.

0.0

0.0

0.7

0.0

0.3

0.0

0.0

0.3

0.0

0.0

0.0

0.3

0.0

0.0

0.0

0.3

0.0

0.0

0.0

0.0

1.7

SUM

PCT

96.2

96.2

96.9

96.9

97.2

97.2

97.2

97.6

97.6

97.6

97.6

97.9

97.9

97.9

97.9

98.3

98.3

98.3

98.3

98.3

100.0

t

DWELL

0.0

0.0

0.0

0.6

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.3

0.0

0.0

0.0

0.0

0.0

0.0

0.0

1.4

SUM

. PCT

97.8

97.8

97.8

98.3

98.3

98.3

98.3

98.3

98.3

98.3

98.3

98.3

98.6

98.6

98.6

98.6

98.6

98.6

98.6

98.6

100.0

%

DWELL

0.1

0.0

1.2

0.1

3.1

0.0

0.1

0.3

0.0

0.0

0.2

0.1

0.1

0.0

0.1

0.2

0.0

0.1

0.0

0.0

6.1

SUM

. PCT

87.7

87.7

88.9

89.0

92.1

92.1

92.6

92.8

92.8

92.8

93.0

93.1

93.2

93.2

93.1

93.6

93.6

93.6

93.6

93-6

100.0

*

DWELL

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

5.3

SUM

. PCT

91.7

91.7

91.7

91.7

91.7

91.7

91.7

94.7

91.7

94-7

91.7

91.7

91.7

94.7

94.7

94.7

94.7

94.7

94.7

91.7

100.0

: Loss distribution by percent of dwellings Continue

CONC-1049 CONC-POST49 CONC-ALL BOTH-PRE40

f

DWELL

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

2.9

0.0

0.0

0.0

0.0

0.0

0.0

SUM

. PCT

97.1

97.1

97.1

97.1

97.1

97.1

97.1

97.1

97.1

97.1

97.1

97.1

97.1

97.1

100.0

100.0

100.0

100.0

100.0

100.0

100.0

I

DWEL

0.0

0.0

0.3

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.3

SUM

L. PCT

99.5

99.5

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

99.7

100.0

t

DWELL

0.0

0.0

0.2

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.2

0.0

0.0

0.0

0.0

0.0

0.4

SUM

. PCT

99.1

99.1

99.3

99.3

99.3

99.3

99-3

99.3

99.3

99.3

99.3

99.3

99.3

99.3

99.6

99.6

99.6

99.6

99.6

99.6

100.0

*

DWELL

0.1

0.0

2.0

0.0

6.0

0.0

0.2

0.4

0.0

0.0

0.4

0.0

0.1

0.0

0.2

0.1

0.0

0.1

0.0

0.0

10.2

SUM

. PCT

80.2

80.2

82.2

82.2

88.3

88.3

88.5

88.9

88.9

88.9

89.2

89.2

89.3

89.3

89.6

89.7

89.7

89.8

89.8

89.8

100.0
which shows loss over deductible for the range of 0-10 

percent deductible. Table 13 is the loss distribution, by 

number of dwellings. Counterparts to tables 4 and 5 are 

not included in this report.

One-to-Four-Family Wood-Frame DwellingsInsurance Company Experience

Due to unusual legal problems, claims were paid by 

many companies under non-earthquake insurance 

policies even though the damage was due to earthquake. 

As a result, additional loss information became available 

from claims paid under the 10 percent earthquake 

deductible.

Insurance-loss experience was obtained from two 

insurance companies. Table 14 shows the loss over 

deductible (for the range of 0-20 percent deductible) 

experience for one company with information on 367 

dwellings, which represents almost 20 percent of our 

1,982 inspected dwellings. The second company provided 

similar loss information on 29 additional dwellings.

1933 Long Beach Earthquake

The loss data for the 1933 Long Beach earthquake 

lack detail and are not as extensive as data for the 1971 

San Fernando and 1983 Coalinga earthquakes. However, 

the 1933 losses have major historic importance because 

they were the basis for many of today's lossover-deductible practices, including those used by the 

California Department of Insurance.

Published wood-frame-dwelling data on the 1933 

Long Beach earthquake are in a supplement to a study by 

Martel (1936). Martel (1936, p. 161) stated,

The principal source of data, the building department of the county assessor's office, yielded assessed values and reductions in assessed value 

due to earthquake damage, when granted, for all 

the buildings. This information was supplemented and checked by use of Compton city 

building permits and by field surveys.

The results of considering the damage percentage for wood frame residences *** as to location indicated that a central area, several blocks 

wide and extending north and south to the city 

limits, received slightly higher damage than either the east or west sides of Compton. However, since many old buildings of low value were 

in this area, the small increase in percentage 

damage of this area over the rest of the town 

does not definitely indicate much difference in 

intensity.

The extent of damage for wood frame residences *** is very low; in fact in 95 percent of

these buildings the damage was less than 5 percent ***.

A second source of information is a file of 590 

one-page insurance summary reports in the "Adjuster's 

Special Report, Southern California Earthquake" (K.V. 

Steinbrugge, unpub. data). These reports on each 

property include location, construction (brick, frame, or 

"fireproof), occupancy, property covered (type of 

coverage), value, insured value, loss, and other data. Only 

32 wood-frame dwellings in Long Beach and Compton 

were included in these reports.

The following tabulates the Martel and insurance 

(adjuster) information:

Martel (1936)

Damage

In percent

0-4

5-24

25-49

50 and greater

Demolished

1 Number of

dwellings

4,334

131

63

36

11

Percent of

dwellings

94.7

2.9

1.4

0.8

0.2

Insurance (adjuster)

^Number of

dwellings

8

18

6

None

None

Percent of

dwellings

15

56

19

None

None

1Compton, Calif.

2Compton and Long Beach, Calif.

Because the insurance adjustment reports indicate that 5 

or 10 percent deductibles were typical of these policies, 

persons with losses under the deductible most likely 

never filed claims and thereby data on such losses are 

probably not included in the range of 0-4 percent 

deductible.

Although the Martel (1936) data are the better of 

the two, they are of limited utility. Relationships among 

assessed values, market values, insured values, and 

replacement values are not clear. Dwelling construction 

has changed since 1933. In the interim, deterioration has 

occurred to many of the remaining dwellings. Performance of pre-1933 dwellings in future earthquakes is 

expected to be poorer than in the 1933 Long Beach 

earthquake.

Prior to the 1971 San Fernando earthquake, and 

also thereafter, it was common California insurance 

practice to use a 7 percent PML, which was judgmentalty 

determined from Mattel's (1936) statement "*** in 95 

percent of these buildings the damage was less than 5 

percent ***." The California Department of Insurance 

continued this practice.

RELATIONSHIPS AMONG 

CONSTRUCTION, GEOLOGIC EFFECTS, 

AND LOSS OVER DEDUCTIBLE

1971 San Fernando Earthquake

Recent and present dwelling construction falls into 

the "wood or concrete floors, post-1949" category in

Earthquake Losses to Single-Family Dwellings: California Experience A21
fi

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& 

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m 

o>

o 

S2.

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Table 12. Dwelling loss experience for the 1983 Coalinga earthquake: Loss over deductible, excluding dwellin

were posted as hazardous or had been demolished before time of inspection

Percent Loss Over Deductible

Dwell. 0* ded. 1* ded. 2* ded. 3* ded. 1* ded. 5* ded. 6* ded. 7

1 . Wood floors:

Age Group: Pre-1910 

1940-19

Post-19

"All ages

2. Concrete floors:

Age Group: Pre-1910 

19HO-19

Post-19

"All ages

*3. Wood or concrete floors:

Age Group: Pre-1910

1910-19

Post-19

"All ages

167 

130

226

532

9

23

300

335

177

151

530

873

8.35 

8.16

10.51

9.28

5.78 

8.57

7.52

7.53

8.21

8.12

8.78

8.58

7.61 

7.67

9.55

8.13

5.00 

7.65

6.65

6.67

7.17

7.62

7.87

7.72

6.88 

6.90

8.62

7.60

1.22 

6.71

5.81

5.82

6.71

6.83

6.99

6.89

Percent Loss

1 . Wood floors:

Age Group: Pre-1910

19UO-19

Post-19

"All ages

2. Concrete floors:

Age Group: Pre-1910

19UO-19

Post-19

"All ages

 3. Wood or concrete floors

Age Group: Pre-1910

19UO-19

Post-19

 All ages

No. of

Dwell.

167

130

226

532

9

23

300

335

.

177

151

530

873

10* ded.

2.28

2.02

2.17

2.11

0.00

0.96

0.77

0.76

2.15

1.81

1.37

1.60

11* ded.

2.00

1.75

1.63

1.75

0.00

0.65

0.52

0.51

1.89

1.57

1.00

1.27

12* ded.

1.75

1.52

1.25

1.15

0.00

0.39

0.36

0.35

1.65

1.31

0.71

1.02

6.15 

6.15

7.70

6.78

3.11 

5.87

5.00

5.01

6.01

6.06

6.11

6.07

5.15 

5.13

6.81

6.01

2.67 

5.01

1.29

1.28

5.30

5.31

5.36

5.32

1.75 

1.72

5.99

5.21

2.00 

1.22

3.59

3.58

1.60

1.61

1.60

1.58

1.07 

1.01

5.11

1.18

1.33 

3.39

2.91

2.89

3-92

3.89

3.85

3.85

Over Deductible

13* ded.

1.53

1.30

0.98

1.21

0.00

0.30

0.28

0.27

1.15

1.11

0.58

0.81

11* ded.

1.32

1.09

0.77

1.01

0.00

0.22

0.21

0.20

1.21

0.95

0.11

0.69

15* ded.

1.16

0.91

0.62

0.86

0.00

0.13

0.16

0.15

1.09

0.81

0.35

0.58

16* ded.

0.99

0.78

0.50

0.71

0.00

0.01

0.12

0.11

0.91

0.67

0.28

0.18

 Includes unknown floor types not included above. 

 Includes unknown dwelling ages not included above.
tables 2, 6, and 7. The reader should compare losses over 

deductible for this category in tables 2 and 6 at 10 percent 

deductible. (The 10 percent deductible was chosen 

because it is presently a common insurance deductible.) 

Inclusion of geologic factors increases the loss over 

deductible from 0.90 percent (table 6) to 1.54 percent 

(table 2), or a 71 percent increase. Any use of this 1971 

San Fernando information for loss estimates in other 

regions should not ignore the distortions in loss data 

from geologic effects.

Table 7 shows losses over deductible for only 

one-story dwellings, thereby excluding oneand-two-story, split-level, and two-story dwellings. 

Compare tables 6 and 7 for wood or concrete floors in 

the post-1949 age group at 10 percent deductible. 

Including split-level, one-and-two-story, and two-story 

dwellings, the loss over deductible increases from 0.73 

percent (table 7) to 0.90 percent (table 6), or a 23 percent 

increase. This 23 percent increase is the result of only a 

243-dwelling increase in the number of one-and-twostory, split-level, and two-story dwellings (from 5,353 to 

5,596). Certainly the modern one-story dwelling in San 

Fernando performed well compared to those of other 

heights.

Modern post-1949 houses of all heights performed 

significantly better than did pre-1940 dwellings; this has 

also been observed in studies of all other recent 

California earthquakes. Newer dwellings are far more 

likely to be bolted to their foundations than are older 

ones. Also, deterioration has not yet taken its toll on the 

newer dwellings.

Dwellings with concrete first floors on grade 

performed better than did those with supported wooden 

first floors, noticeably so with increasing age.

Figure 1 is a graphic representation of much of the 

information in tables 2 and 6. The curves can be 

reasonably approximated by straight lines from 0 to 10 

percent deductible, but not from 0 to 20 percent 

deductible. This family of curves has similar 

characteristics.

Table 15 is an overview comparison among losses 

over deductible without regard to the type of first-floor 

construction. This table uses the same data as figure 1. 

The 5 and 10 percent deductibles are or have been 

commonly used, and some interest has been shown in a 

15 percent deductible.

1983 Coalinga Earthquake

Non-Insurance Data

Losses over deductible for wood-frame dwellings, 

without exclusions for the 1983 Coalinga earthquake, are 

shown in table 9. Comparing table 9 with table 2 shows 

Coalinga losses over deductible to be much larger than

those for San Fernando. San Fernando information in 

table 2 includes losses from faulting, liquefaction, and 

other geologic effects not found in Coalinga. The 

Coalinga magnitude was 6.7, slightly higher than 6.4 for 

San Fernando; these magnitudes are reasonably equal 

for the purpose of damage comparisons. Coalinga was 

close to the epicenter and energy release, whereas San 

Fernando was astride the faulting; both fall within the 

PML zone as defined for insurance purposes.

One strong reason for the discrepancies between 

Coalinga and San Fernando losses over deductible lies 

with the approximately 200 dwellings moved to Coalinga 

and not anchored to their foundations. It is possible to 

place upper and lower bounds on these special cases of 

unanchored houses. Values in table 9 are the upper 

bounds because they include all losses over deductible 

for all reasons, except ensuing fire. Values in table 12 are 

the lower bounds because they include all losses over 

deductible for one-to-four-family wood-frame dwellings, 

excluding possible aberrations such as dwellings that had 

shifted on their foundations or were posted as hazardous 

or had been demolished before the time of inspection. 

Dwellings that had been moved to Coalinga were not new 

dwellings and belonged in the pre-1940 or 1940-49 age 

group. However, fallen older dwellings on cripple studs 

were not necessarily structures that had been moved to 

Coalinga.

A second reason appears to be the amplification of 

ground motions, which resulted in increased damage. 

There are certain areas that, during earthquakes, are 

shaken more severely than are other, nearby areas and 

yet do not have "poor ground" as commonly understood 

for the purpose of earthquake insurance. Figure 2 is an 

isoseismal map of the 1906 San Francisco earthquake. 

Coalinga is about 80 miles from the southern end of the 

1906 San Francisco earthquake's rupture on the San 

Andreas fault. It will be noted that higher seismic 

intensities were observed in Coalinga, Los Banos, and 

elsewhere on the western side of San Joaquin Valley than 

at many locations that were actually closer to the 1906 

faulting. Figure 2 indicates that Coalinga may have 

experienced intensities equal to those experienced in 

parts of San Francisco.

Damage at Coalinga from the 1906 event was 

summarized by Lawson (1908, v. 1, pt. 2, p. 318) as 

follows:

The tops of a few of the walls of brick buildings 

were slightly damaged as shown by the accompanying photograph [note: parapet fell from a 

two-story structure]. A few dishes and bottles 

were thrown from the shelves, and water was 

slopped out of the tanks, but not capsized. At 

the oil wells no damage was done either to wells 

or pipe lines. At a pumping station, the brick lining of the furnace was slightly cracked. Considerable oil was thrown from the tanks. In a large

Earthquake Losses to Single-Family Dwellings: California Experience A23
m

Table 13. Dwelling loss experience for the 1983 Coalinga earthquake: Loss distribution by number of dwellings, excluding dw

or were posted as hazardous or had been demolished before time of inspection

WOOD-PRE10 WOOD-1019 WOOD-POST19 WOOD-ALL CONC-PRE10 CONC-1019 CONC-POST19 CONC-ALL BOTH-PR

£*

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iw 

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(0

ET

£0

5*

LOSS

0

1

2

3

1

5

6

7

8

9

10

11

12

13

11

15

16

17

18

19

20

21

22

23

21

25

26

27

28

29

30

31

32

33

31

35

36

37

38

39

10

11

12

13

11

15

NO. SUM NO. SUM NO. SUM 

DWELL. PCT DWELL. PCT DWELL. PCT

11

1

0

5

1

1

31

0

2

31

1

5

6

0

9

0

1

3

0

1

2

0

5

1

3

1

0

0

0

1

1

0

0

0

0

1

0

0

0

0

0

0

0

1

0

0

26.3

26.9

26.9

29.9

30.5

31.1

19.7

19.7

50.9

71.3

71.9

71.9

78.1

78.1

83.8

83.8

86.2

88.0

88.0

90.1

91.6

91.6

91.6

95.2

97.0

97.6

97.6

97.6

97.6

98.2

98.8

98.8

98.8

98.8

98.8

99.1

99.1

99.1

99.1

99.1

99.1

99.1

99.1

100.0

100.0

100.0

27 20.8

3 23.1

2 21.6

5 28.5

0 28.5

1 29.2

11 10.0

2 11.5

8 17.7

31 71.5

2 73.1

5 76.9

2 78.5

1 79.2

7 81.6

0 81.6

3 86.9

5 90.8

1 91.5

1 92.3

0 92.3

0 92.3

3 91.6

0 91.6

1 95.1

1 98.5

0 98.5

0 98.5

1 99.2

0 99.2

0 99.2

0 99.2

0 99.2

0 99.2

1 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

9 1.0

6 6.6

1 8.1

12 13.7

2 11.6

2 15.5

10 19.9

2 20.8

5 23.0

36 38.9

17 16.5

35 61.9

21 72.6

11 78.8

15 85.1

5 87.6

1 89.1

3 90.7

1 92.5

1 91.2

2 95.1

0 95.1

1 96.9

1 98.7

0 98.7

1 99.1

2 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

NO. 

DWELL,

81

10

6

23

3

1

56

5

15

101

21

15

32

16

31

5

11

11

5

9

1

0

12

5

1

6

2

0

1

1

1

0

0

0

1

1

0

0

0

0

0

0

0

1

0

0

SUM NO. SUM NO. SUM NO. SUM NO. SUM NO. S

. PCT DWELL. PCT DWELL. PCT DWELL. PCT DWELL. PCT DWELL. 

15.2

17.1

18.2

22.6

23 .'I

23-9

31.1

35.3

38.2

57.7

61.7

70.1

76.1

79.1

85.0

85.9

88.0

90.0

91.0

92.7

93.1

93.1

95.7

96.6

97.1

98.5

98.9

98.9

99.1

99.2

99.1

99.1

99.1

99.1

99.6

99.8

99.8

99.8

99.8

99.8

99.8

99.8

99.8

100.0

100.0

100.0

2 22.2

0 22.2

0 22.2

0 22.2

1 33.3

0 33-3

2 55.6

0 55.6

0 55.6

1 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

2 8.7

0 8.7

1 13.0

1 17.1

0 17.1

0 17.1

1 21.7

3 31.8

1 39.1

5 60.9

2 69.6

1 73.9

1 91.3

0 91.3

0 91.3

0 91.3

1 95.7

1 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

10 13.3

8 16.0

10 19.3

27 28.3

7 30.7

2 31.3

13 35.7

6 37.7

12 11.7

89 71.3

12 75.3

26 81.0

22 91.3

5 93.0

6 95.0

1 96.3

1 96.7

3 97.7

2 98.3

2 99.0

0 99.0

0 99.0

2 99.7

0 99.7

0 99.7

0 99.7

0 99.7

1 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

11 13.1

8 15.5

11 18.8

29 27.5

8 29.9

2 30.1

17 35.5

9 38.2

13 12.1

98 71.3

11 75.5

28 83.9

26 91.6

5 93-1

6 91.9

1 96.1

2 96.7

1 97.9

2 98.5

2 99.1

0 99.1

0 99.1

2 99.7

0 99.7

0 99.7

0 99-7

0 99.7

1 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

16

1

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5

2

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38

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6

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5

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3

1

0

0

0

1

1

0

0

0

0

1

0

0

0

0

0

0

0

1

0

0

2

26

26

29

30

31

19

19

51

72

73

76

79

79

81

81

87

88

88

91

92

92

91

95

97

97

97

97

97

98

98

98

98

98

98

99

99

99

99

99

99

99

99

100

100

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Earthquake Losses to Single-Family Dwellings: California Experience A25
Table 14. Dwelling loss experience for the 1983 Coalinga earthquake: Loss over deductible, based on Insura

m

ft

o

w 

I*

Percent Loss Over Deductible

1. Wood floors:

Age Group: Pre-1940 

1940-49 

Post-49

**A11 ages

2. Concrete floors:

Age Group: Pre-1940 

1940-49 

Post-49 

»»A11 ages

*3. Wood or concrete floors 

Age Group: Pre-1940 

1940-49 

Post-49

 All ages

1. Wood floors:

Age Group: Pre-1940 

1940-49 

Post-49

 *A11 ages

2. Concrete floors:

Age Group: Pre-1940 

1940-49 

Post-49 

"All ages

*3. Wood or concrete floors 

Age Group: Pre-1940 

1940-49 

Post-49

 All ages

No. of

Dwell.

138

72

63

279

3

14

84

103

144

87

148

394

0* ded.

26.40

8.24

5.25

16.49

5.33

16.86

5.04

7.33

26.10

10.69

5.15

15.70

1* ded.

25.50

7.50

4.35

15.65

4.33

15.93

4.26

6.52

25.21

9.92

4.32

14.86

2% ded.

24.70

6.96

3.48

14.91

3.67

15.14

3.62

5.85

24.42

9.33

3.57

14.14

3* ded.

23.96

6.43

2.73

14.23

3.00

14.36

3.00

5.21

23.69

8.76

2.90

13.46

4* ded.

23.27

5.90

2.10

13.60

2.33

13.79

2.52

4.72

23.01

8.22

2.35

12.86

5% ded.

22.59

5.42

1.63

13.03

1.67

13.29

2.10

4.27

22.33

7.72

1.91

12.31

6% ded

21.94

5.00

1.30

12.52

1.00

12.86

1.76

3.91

21.69

7.30

1.57

11.84

Percent Loss Over Deductible

No. of

Dwell .

138

72

63

279

3

14

84

103

144

87

148

394

10* ded.

19.75

3.75

0.62

10.93

0.00

11.57

1.15

3.17

19.55

6.01

0.92

10.42

11* ded.

19.29

3.58

0.54

10.63

0.00

11.29

1.07

3.06

19.10

5.82

0.84

10.16

12* ded.

18.86

3.44

0.46

10.36

0.00

11.00

1.00

2.95

18.67

5.64

0.76

9.92

13* ded.

18.42

3.32

0.40

10.10

0.00

10.71

0.93

2.84

18.25

5.48

0.70

9.68

14* ded.

17.99

3.21

0.35

9.84

0.00

10.43

0.86

2.74

17.83

5.33

0.64

9.45

15* ded.

17.57

3.11

0.30

9.59

0.00

10.14

0.81

2.65

17.42

5.20

0.59

9.23

16* de

17.16

3.03

0.25

9.35

0.00

9.86

0.77

2.57

17.02

5.07

0.55

9.01

 Includes unknown flbor types not Included above.

 includes unknown dwelling ages not included above.
12

10

*AII ages

* Post-1949

.Pre-1940

*Pre-1940

Post-1949

All ages

5 10 15 

DEDUCTIBLE, IN PERCENT

20

Figure 1. Graph showing loss over deductible versus 

deductible for 1971 San Fernando earthquake. Computations 

are based on 1971 market values, less land values. Asterisk (*) 

indicates that dwellings at sites with faulting, liquefaction, and 

other geologic effects are excluded.

reservoir containing No. 10 oil (very heavy), the 

oil was thrown up 10 inches on the northeast 

and southwest sides. In a pump having No. 16 

grade, the oil was splashed 3 feet up the sides.

Although some people may question the accuracy 

of the reported 1906 intensity at Coalinga, it can not be 

doubted that the intensities along the western edge of the 

San Joaquin Valley were unexpectedly high. It is 

reasonable to believe that 1906 ground motions at 

Coalinga were amplified due to local geology and that the 

1983 ground motions at Coalinga were also amplified, for 

the same reason.

Figure 3 is a graphic representation of most of the 

information in tables 9 and 12. The curves can be 

reasonably approximated by straight lines from 0 to 10 

percent deductible, but not from 0 to 20 percent 

deductible. This family of curves is similar in form to that 

shown in figure 1 because the computational 

methodologies are similar.

Table 15. Overview of dwelling loss experience for the 

1971 San Fernando earthquake: Loss over deductible

[One-story wood-frame dwellings. Values are market values, less land 

values. PRE40 (pre-1940), 4049 (1940-1949), POST49 (post-1949), 

excluding dwellings where the field inspector noted ground 

disturbance, such as faulting or ground movement (for example, 

sidewalk movement with respect to adjoining soil), and also excluding 

dwellings with apparent soil-amplification damage where San 

Fernando Valley alluvial deposits meet the San Gabriel Mountains to 

the north of the valley. Also excluding one-and-two-story, split-level, 

and two-story dwellings]

____ t Loss Over Deductible___________

Post-49 Pre-10

Excluding Special Cases* 

All ages Post- 1*9 Pre-itO

9.0 

5.0 

1.9 

1.2

8.9 

1.8 

1.5 

0.9

11.8 

8.1 

5.1 

1.3

8.0 

1.1 

1.1 

0.6

7.8 

3-9 

0.7 

0.3

10.1 

6.6 

1.3 

3-3

Number o."

dwell. > 12,075 6,652

Table > 2 2

631 10,237 5,353 586

2777

Table 16 is an overview comparison among losses 

over deductible without regard to the type of first-floor 

construction. This table uses the same data as figure 3.

Insurance Claim Data

Data (from Insurance Source A) in table 14 have 

no exclusions, whereas data in table 17 exclude dwellings 

that had shifted on their foundations or were posted as 

hazardous or had been demolished before the time of 

inspection, or had more than one story. Tables 17 and 18 

contain this insurance company loss experience on two 

different value bases: insured value and market value 

from 0 to 20 percent deductible.

Curves 3 and 4 in figure 4 are the Insurance Source 

A losses over deductible for dwellings of all ages, with 

exclusions as noted on the figure. Curves 1 and 2 are 

from our data, also with exclusions as noted on the figure. 

The two insurance curves (#3, #4) have similar shapes 

as do our two curves (#1, #2). There is a noticeable 

difference between the shapes of the insurance curves 

(#3, #4) and our curves (#1, #2). Improvements in our 

loss-estimation methodology should reduce the 

differences in the shapes of the curves. These four curves 

are based on tables 6,12, 17, and 18.

Figure 5, similar to figure 4, is additionally limited 

to post-1949 construction. Previous comment pertaining 

to figure 4 also applies tojigure 5. Figures 4 and 5 are 

representative of dwelling losses near the earthquake's 

energy release for magnitudes around 6.5.

Earthquake Losses to Single-Family Dwellings: California Experience A27
Isoseismal Map Of 

1906 SAN FRANCISCO EARTHQUAKE

Adapted and simplified from Map 23 of the Atlas to 

the "Report of the State Earthquake Investigation 

Commission" (Carnegie Institution of Washington).

Rossi-Forel intensities on the original have been 

converted to Moditied Mercalh intensities.

0 10 20 30 40 50

SAN FRANCISC 

IX 

VII

SAN FRANCISCO

Figure 2. Isoseismal map of the 1906 San Francisco earthquake showing the location of Coalinga.

A28 Estimation of Earthquake Losses to Housing in California
Table 16. Overview of dwelling loss experience for the 

1971 San Fernando earthquake: Loss over deductible

[One-stoiy wood-frame dwellings. Values are market values, less land 

values. PRE40 (pre-1940), 4049 (1940-1949), POST49 (post-1949), 

excluding dwellings that had shifted on their foundations or were 

posted as hazardous or had been demolished before time of 

inspection]

__________t Loss Over Deductible__________

Deduct.

0

5

10

15

Number 

dwellings

Po3t-i»9 Pre-UO

Excluding Special Cases* 

All ages Post-Ug Pre-UQ

20.2

15.7

11-9

9.3

1,982

11.9 

7.5 

K.O 

2.2

763

28.2

23.6

19.5

16.2

8U5

8.6

1.6 

0.6

873

8.8 

K.6 

1.1) 

0.1

530

8.2 

4.6 

2.2 

1.1

177

Table 19 is of special interest. Our data for the 

1971 San Fernando and 1983 Coalinga earthquakes are 

usually similar. Coalinga insured losses using insured 

values are low if compared to our market values for both 

Coalinga and San Fernando; a partial exception is the 

pre-1940-dwelling category. These differences can be 

examined two ways.

The first approach compares the aggregate losses 

from all paid claims with the aggregate losses for the 

same dwellings computed by our independent methods. 

A total of 331 dwellings were matched in the two 

dwelling inventories. Our methods produced an 

estimated $2,559,000 aggregate loss, whereas the 

aggregate paid claims was $2,375,000 (both in 1983 

dollars) (Steinbrugge and others, 1990, table 20.15). This 

similarity indicates that our loss-estimation methods are 

adequate if dwelling values (market versus insured) are 

not involved.

The second approach involves an examination of 

the impacts of insured values versus market values on 

loss over deductible. Insured value is the face value of the 

policy. Except for new dwellings, market values are 

commonly less than replacement values. Visual 

observations confirmed this for older dwellings in 

Coalinga. An insured partial dwelling loss is paid in full 

until the stated value in the policy is reached. For 

example, a damaged older Coalinga dwelling would 

receive new or equivalent repair up to the face value of 

the policy. One exception is a new type of policy that 

replaces total losses regardless of policy amount. Even if 

not insured to full replacement value and for losses less 

than the policy face value, losses would be paid in full 

without respect to depreciation of finishes and other 

items, such as paint and plaster. As expected, losses over 

deductible for insured values in table 19 are less than 

those for market values.

Market values are constantly varying by location 

and over time. Dwelling market values, including land 

and without regard to age, averaged $192,600 in southern

30

25

a 20

cc

CC 

LLJ

o

(0 

g10

*AII ages /

*Post-1949

*Pre-1940

Post-1940

All ages

Pre-1940

10 15 

DEDUCTIBLE. IN PERCENT

20

Figure 3. Graph showing loss over deductible versus 

deductible for 1983 Coalinga earthquake. Computations are 

based on 1983 market values, less land values. Asterisk (*) 

indicates that dwellings that had shifted on their foundations or 

were posted as hazardous or had been demolished before 

time of inspection are excluded.

California as of April, 1988 (Real Estate Research 

Council of Southern California, 1988). From the same 

source, in April of 1981 it was far less at $129,900. The 

average market value, including land, for the San 

Francisco Bay Area was $213,800 as of April, 1988 (Real 

Estate Research Council of Northern California, 1988), 

and is also changing rapidly. Insured values may lag in 

relationships to market value.

As a numerical example of the impacts of different 

kinds of values, consider an older house that has a 

replacement value of $200,000, a market value (less land 

value) of $150,000, a cost to repair earthquake damage of 

$25,000, and a 10 percent deductible of 'Value." Losses 

over deductible would be:

Market value basis ($25,000-$15,000)/$150,000, 

or 6.7 percent.

Insured value basis ($25,000-$20,000)/$200,000, 

or 2.5 percent.

Earthquake Losses to Single-Family Dwellings: California Experience A29
m 

o»

i

.o

§

Table 17. Dwelling loss experience forthe t983 Coalinga earthquake: Loss over deductible, Insurance Source A

dwellings that had shifted on their foundations or were posted as hazardous or had been demolished before time 

<O

I

§ 

1. Wood floors:

Age Group: Pre-1940 

1940-49 

Post-49 

"All ages

2. Concrete floors:

Age Group: Pre-1940 

1940-49 

Post-49

**A11 ages

*3. Wood or concrete floors: 

Age Group: Pre-1940 

19HO-49 

Post-49

**A11 ages

Percent Loss Over Deductible

No. of

Dwell.

31

33

42

109

1

8

60

69

32

41

102

178

0$ ded.

9.35

5.27

5.31

6.30

1.00

5.88

3.58

3.81

9.09

5.39

1.29

5.3"<

1$ ded.

8.58

4.45

4.38

5.48

0.00

5.00

2.83

3.04

8.31

4.56

3.47

4.53

251 ded.

7.97

3.88

3.50

4.79

0.00

4.25

2.23

2.43

7.72

3.95

2.75

3.88

3* ded.

7.42

3.33

2.76

4.18

0.00

3.50

1.65

1.84

7.19

3.37

2.11

3.28

4* ded.

6.87

2.79

2.17

3.63

0.00

3.00

1.22

1.41

6.66

2.83

1.61

2.77

5* ded.

6.39

2.27

1.76

3.18

0.00

2.50

0.85

1.03

6.19

2.32

1.23

2.35

6$ ded.

5.97

1.88

1.48

2.83

0.00

2.13

0.60

0.77

5.78

1.93

0.96

2.03

1. Wood floors:

Age Group: Pre-1940 

1940-49 

Post-49 

"All ages

2. Concrete floors:

Age Group: Pre-1940 

1940-49 

Post-49 

"All ages

*3. Wood or concrete floors; 

Age Group: Pre-1940 

1940-49 

Post-49 

"All ages

Percent Loss Over Deductible

No. of

Dwell. 10* ded.

31

33

42

109

1

8

60

69

32

41

102

178

4.87

0.73

0.79

1.91

0.00

1.38

0.20

0.33

4.72

0.85

0.44

1.30

11* ded.

4.68

0.61

0.69

1.78

0.00

1.25

0.17

0.29

4.53

0.73

0.38

1.20

12$ ded.

4.48

0.52

0.60

1.66

0.00

1.13

0.13

0.25

4.34

0.63

0.32

1.11

13* ded.

4.29

0.42

0.52

1.55

0.00

1.00

0.10

0.20

4.16

0.54

0.27

1.03

14* ded.

4.10

0.36

0.48

1.46

0.00

0.88

0.07

0.16

3.97

0.46

0.24

0.96

15* ded.

3.90

0.30

0.43

1.37

0.00

0.75

0.05

0.13

3.78

0.39

0.21

0.89

16* ded

3.71

0.24

0.38

1.28

0.00

0.63

0.03

0.10

3.59

0.32

0.18

0.82

 Includes unknown floor types not included above. 

""Includes unknown dwelling ages not included above.
Table 18. Dwelling loss experience for the 1983 Coalinga earthquake: Loss over deductible, Insurance Source A, realto

dwellings that had shifted on their foundations or were posted as hazardous or had been demolished before time of ins

Percent Loss Over Deductible

S1

.o

1. Wood floors:

Age Group: Pre-1940 

1940-49 

Post-49

* All ages

2. Concrete floors:

Age Group: Pre-1940 

1940-49 

Post-49

** All ages

 3. Wood or concrete floors 

Age Group: Pre-1940 

1940-49 

Post-49

**A11 ages

No. of

Dwell.

31

33

42

109

1

8

60

69

32

41

102

178

0* ded.

15.42

8.55

8.00

10.06

1.00

8.13

5.62

5.84

14.97

8.46

6.60

8.43

1% ded.

14.68

7.70

7.05

9.22

0.00

7.13

4.85

5.04

14.22

7.59

5.75

7.60

251 ded.

14.06

6.97

6.14

8.48

0.00

6.25

4.17

4.35

13.63

6.83

4.98

6.88

3% ded.

13.45

6.33

5.29

7.78

0.00

5.63

3.55

3.74

13.03

6.20

4.26

6.21

4$ ded.

12.84

5.76

4.48

7.12

0.00

5.00

2.95

3.14

12.44

5.61

3.58

5.58

5% ded.

12.23

5.18

3.81

6.51

0.00

4.38

2.45

2.64

11.84

5.02

3.01

5.01

f>% ded.

11.65

4.61

3.21

5.94

0.00

3.88

2.02

2.20

11.28

4.46

2.51

4.49

7% 

11

4

2

5

0

3

1

1

10

3

2

4

Percent Loss Over Deductible

6*

3 

(0

to

(A

1. Wood floors:

Age Group: Pre-1940 

1940-49 

Post-49

 All ages

2. Concrete floors:

Age Group: Pre-1940 

1940-49 

Post-49

 *A11 ages

 3- Wood or concrete floors: 

Age Group: Pre-1940 

19110-49 

Post-49

 *A11 ages

No. of

Dwell.

31

33

42

109

1

8

60

69

32

41

102

178

10* ded.

10.19

2.58

1.76

4.36

0.00

2.25

1.07

1.19

9.88

2.51

1.35

3.13

11* ded.

9.87

2.18

1.52

4.06

0.00

2.13

0.93

1.06

9.56

2.17

1.18

2.89

12* ded.

9.58

1.82

1.36

3.80

0.00

2.00

0.83

0.96

9.28

1.85

1.05

2.70

13* ded.

9.35

1.52

1.21

3.59

0.00

1.88

0.75

0.87

9.06

1.59

0.94

2.53

14* ded.

9.16

1.24

1.10

3.40

0.00

1.75

0.68

0.80

8.88

1.34

0.85

2.39

15* ded.

8.97

1.03

1.00

3.25

0.00

1.63

0.62

0.72

8.69

1.15

0.77

2.27

16* ded.

8.77

0.85

0.93

3.11

0.00

1.50

0.57

0.67

8.50

0.98

0.72

2.16

17

 Includes unknown floor types not included above. 

 Includes unknown dwelling ages not included above,
o cc -

O 

cc 4

1983 Coalinga - Note 3

1971 San

1983 Coalinga - Note 4

Fernando- Note 1

1983 Coalinga-Note 2

5 10 15 

DEDUCTIBLE, IN PERCENT

20

1971 San Fernando - 

1983 Coalinga - Note 4

5 10 15 

DEDUCTIBLE. IN PERCENT

Figure 4. Graph showing loss over deductible versus 

deductible for 1971 San Fernando and 1983 Coalinga 

earthquakes and comparing our data and Insurance Source 

A data (applicable to dwellings of all ages).

Note 1: Our data, excluding dwellings at sites with faulting, liquefaction, and 

other geologic effects. Data from table 6.

Note 2: Our data, excluding dwellings that had shifted on their foundations or 

were posted as hazardous or had been demolished before time of inspection. 

Data from table 12.

Note 3: Insurance Source A data, using insured values and paid claims and 

excluding dwellings that had shifted on their foundations or were posted as 

hazardous or had been demolished before time of inspection. Data from 

table 17.

Note 4: Insurance Source A data, using realtor pre-earthquake market values, 

less land values, and excluding dwellings that had shifted on their foundations 

or were posted as hazardous or had been demolished before time of 

inspection. Data from table 18.

Figure 5. Graph showing loss over deductible versus 

deductible for 1971 San Fernando and 1983 Coalinga 

earthquakes and comparing our data and Insurance Source 

A data (applicable to post-1949 dwellings).

Note 1: Our data, excluding dwellings at sites with faulting, liquefaction, and

other geologic effects. Also excluding one-and-two-story and two-story

dwellings. Data from table 7.

Note 2: Our data, excluding dwellings that had shifted on their foundations or

were posted as hazardous or had been demolished before time of inspection.

Data from table 12.

Note 3: Insurance Source A data, using Insured values and paid claims and

excluding dwellings that had shifted on their foundations or were posted as

hazardous or had been demolished before time of inspection. Data from

table 17.

Note 4: Insurance Source A data, using realtor pre-earthquake market values,

less land values, and excluding dwellings that had shifted on their foundations

or were posted as hazardous or had been demolished before time of

inspection. Data from table 18.

A32 Estimation of Earthquake Losses to Housing in California
Table 19. Comparison of loss over deductible between our data and Insurance Source A data for the 1971 San Fernando 

[1971 San Fernando data: excluding dwellings at or adjacent to sites with observed ground disturbance or other geologic effects and excluding one

1983 Coalinga data: excluding dwellings that had shifted on their foundations or were posted as hazardous or had been demolished before tim

[Insurance Source A data: insured values are from their records, losses are from their paid claims. Market values are pre-earthquake values, l

ff No Age Restrictions

i Authors' Data

§

o

r-

£ 

2

3"

w

«n

9

3

V

*

Ded.

0

1

2

3

1

5

6

7

8

9

10

1971 San

Fernando

Market

Value

8.0

7.2

6.1

5.7

1.9

1.1

3.1

2.7

2.0

1.3

1.1

1983

Coalinga

Market

Value

8.6

7.7

6.9

6.1

5.3

1.6

3.9

3.2

2.6

2.0

1.6

Insurance Co. A

1983

Coalinga

Insured

Value

5.3

1.5

3-9

3.3

2.8

2.1

2.0

1.8

1.5

1.1

1.3

Market

Value

8.1

7.6

6.9

6.2

5.6

5.0

1.5

1.1

3.7

3.1

3.1

Post- 1019 Dwellings

Authors' Data

1971 San

Fernando

Market

Value

7.8

7.0

6.2

5.1

1.7

3.9

3.1

2.1

1.7

0.9

0.7

1983

Coalinga

Market

Value

8.8

7.9

7.0

6.1

5.1

1.6

3.9

3.2

2.5

1.8

1.1

Insurance Co. A

1983

Coalinga

Insured

Value

1.3

3.5

2.8

2.1

1.6

1.2

1.0

0.8

0.6

0.5

0.1

Market

Value

6.6

5.8

5.0

1.3

3.6

3.0

2.5

2.1

1.8

1.6

1.1

1910-19 Dwellings

Authors' Data

1971 San

Fernando

Market

Value

8.0

7.2

6.1

5.6

1.9

1.1

3.3

2.7

2.0

1.1

1.2

1983

Coalinga

Market

Value

8.1

7.6

6.8

6.1

5.3

1.6

3.9

3-3

2.7

2.1

1.8

Insurance Co. 

1983

Coalinga

Insured

Value

5.1

1.6

1.0

3.1

2.8

2.3

!-9

1.6

1.2

1.0

0.9

Marke

Value

8.5

7.6

6.8

6.2

5.6

5.0

1.5

1.0

3.1

3.0

2.5

<O 

»

Number of dwellings: 

10,237 873

Reference tables: 

7 12

178

17

178

18

5,353 530

12

102

17

102

18

1,097 151

12

11

17

11

18
Quite evidently, computation on an insured-value basis 

will generally produce losses over deductible that are less 

than those produced by computation on a market-value 

basis.

Turning next to San Fernando, 94 percent of the 

data in table 19 were for the post-1949 and 1940-49 age 

groups. From our experience in 1971, market values and 

insured values were close to being the same because, in 

part, most of the 1940-49 houses appeared to be of late 

1940's construction.

The amount of insurance to replacement value was 

known for each Insurance Source A dwelling, and 

replacement values were used in the calculations. Some 

dwellings had no damage, and consequently the owners 

did not submit claims. These structures were included in 

the dwelling inventory along with those having claims.

It must be remembered from the "Data sources 

and loss-over-deductible compilation" section that the 

insurance company losses discussed here were at 

essentially zero earthquake deductible for legal reasons. 

Their losses-over-deductible percentages were based 

upon the application of the deductible percentage against 

the amount of insurance that was determined to be 

replacement cost. Losses over deductible for insured 

value can vary depending upon whether the amount of 

dwelling insurance equals replacement cost, actual cash 

value, or some other value, and to what value the percent 

deductible applies.

In summary, data in the columns of table 19 that 

are headed "market value" are consistent for each age 

group, except for "pre-1940 dwellings," which show 

slightly less consistency. The values in the "insured 

value" column are less than those in the "market value" 

column for all categories, except for our "market value" 

column under "pre-1940 dwellings."

Lastly, insurance company data are considered to 

be more reliable than our data in the range of 0-20 

percent deductible. However, our methods are 

satisfactory for approximate aggregate loss estimation 

immediately after the earthquake and in regions where 

no earthquake-loss experience exists.

LOSS DISTRIBUTION AND 

PROBABLE MAXIMUM LOSS (PML)

Our data and the insurance companies' data were 

examined for loss distribution and PML's. A discussion 

of the full definition of PML and its origins is included in 

the appendix.

Table 8 shows our loss distribution of the 1971 San 

Fernando earthquake for the same data as in table 7. 

Table 13 is our loss distribution of the 1983 Coalinga 

earthquake for the same data as in table 12. Table 20 

shows Insurance Source A loss distributions for the 1983

Coalinga earthquake. The number of dwellings for each 

"percent loss" is shown to indicate data quality.

Headings on tables 3, 4, 8,10,11,13, and 20 have 

these meanings:

WOOD-PRE40 refers to dwellings having a wood first 

story floor and constructed prior to 1940. WOOD4049 also is for wood floors, but for construction 

between 1940 and 1949. WOOD-POST49 is for 

subsequent construction. WOOD-ALL groups 

together all wood floors, regardless of date of 

construction.

CONC refers to concrete first floor laid directly on soil. 

(By and large there are no basements in California.) 

The CONC variants are the same as those for wood.

BOTH includes both wood and concrete floors. The 

variants are the same as those for wood. For one 

instance, BOTH-ALL refers to both wood and 

concrete floors regardless of age group.

% LOSS is the percent total loss per dwelling. For our 

data, it was determined on a market value basis using 

the information from the forms submitted by the field 

inspectors. For insurance source data, it was 

determined on a replacement cost basis using paid 

claim information.

NO. DWELL, is the number of dwellings having the 

indicated % LOSS. For our data, dwellings having 2/3 

or greater loss were considered to be constructive total 

losses, and therefore the tabulations lump together all 

losses over 65 percent.

% DWELL, has the same meaning as NO. DWELL., 

except that the number of dwellings is expressed in 

percentage of the total number of dwellings.

SUM PCT is the equivalent of the area under a 

distribution curve from 0 percent to the % LOSS. For 

example, in table 3 under BOTH-ALL (last column) 

at 12 % LOSS is found 88.8 percent. This means that 

88.8 percent of all wood-frame dwellings had 12 percent 

loss or less.

Applying the PML definition of "9 out of 10" (see 

appendix) to tables 8 and 13 develops the PML values for 

the 1971 San Fernando and 1983 Coalinga earthquakes 

in table 21. For example, using BOTH-ALL from the last 

column of table 8, the PML is 11 percent at 90 percent 

cumulative loss (SUM PCT). It is to be recalled that this 

information is on a market-value basis.

Tables 8 and 13, and all similar tables, are based on 

a 0 percent deductible. See the appendix under 

"Sensitivity: Loss over deductible versus dwelling PML 

changes" for changes in PML that result from non-zero 

deductibles.

A34 Estimation of Earthquake Losses to Housing in California
Distribution Curve

Consider a distribution curve drawn from table 8 or 

from any of the other tables using our data. The curve 

would be skewed toward the low end of the percent loss, 

with the peak at about 9 percent loss. The curve rapidly 

flattens to the right of this peak. There is another peak at 

losses equal to or exceeding 65 percent because general 

practice often finds a structure to be a constructive total 

loss at or exceeding two-thirds of its value. Changes in 

damage patterns to a few houses can result in significant 

changes to some PML's. For one such example in table 8 

applied to WOOD-PRE40, the PML is 26 percent at 90 

percent cumulative loss; slight changes in damage 

estimates to a very few houses can radically change the 

PML's. Most other dwelling categories in table 8 are less 

sensitive.

The loss distribution data in tables 8 and 13 do not 

provide for a smooth curve. There are a number of peaks 

and valleys, with a particularly large peak at 9 percent 

loss. This unevenness is inherent in the loss-estimation 

model. The field inspector was required to make a choice 

among degrees of damage to an interior finish: none, 

slight, moderate, or severe. There were similar choices 

for other construction components. Loss to each 

construction component was determined from the 

contractor repair data to the nearest percent of the 

dwelling's pre-earthquake market value, less land value. 

For example, damage to interior gypsumboard finishes, 

cabinets, plumbing, and other interior components, was 

determined on the average to be as follows:

Degree of damage Percent loss

None 

Slight 

Moderate 

Severe

0

6

14

26

Degrees of damage and percentages often exist in the 

context of other damage. Severe interior finish damage 

normally did not occur unless the dwelling also fell from 

its cripple studs or slid off its foundation. Severe damage 

to the interior finish might be accompanied by more 

damage if the exterior finish was plaster rather than wood 

siding. However, the partial failure of an exterior, unreinforced brick chimney might not be accompanied by 

other damage if it fell away from the dwelling. Jumps in 

percent loss to interior finish from 0 percent (none) to 6 

percent (slight) to 14 percent (moderate) to 26 percent 

(severe), as well as other increments for other 

construction components, lead to the peaks and valleys in 

the loss distribution.

Uncertainties Concerning 

Degrees of Damage

Certain degrees of damage are dominant in the 

computational process. Possibly the most important is 

the distribution of the degrees of damage to gypsumboard interior finishes:

Degree of

Damage

None

Slight

Moderate

Severe

Percent loss

San Fernando^

4.2

78.4

11.1

6.3

100.0

Coalings*

19.8

69.3

9.7

1.2

100.0

iSteinbrugge and others (1971), table 8.

8Steinbrugge and others (1990), tables 20.6, 20.7, and 20.8.

In this table "Slight" is predominant and, from the 

previous table, represents 6 percent of the total loss to 

the dwelling. It is not unreasonable that this might 

become an 8 percent loss using different' contractors, 

different loss-estimation criteria, or different acceptable 

repair practices. Our calculations using other than 6 

percent total loss for "slight" show that the 9 percent 

peak changes about 1 percent for each 1 percent change 

in the percent loss assigned to "slight."

Changing the percent loss from 6 to 8 percent for 

"slight" also impacts on the loss over deductible. For 

wood or concrete floors of all ages, the losses over 

deductible are:

Interior finish 

damage Deductible, in percent

6 8 10 Source

"Slight" at 20.2 183 16.5 15.7 14.8 13.3 11.9 Table 9.

6 percent 

"Slight" at 21.2 19.4 17.6 16.7 15.9 14.2 12.7 Unpublished

8 percent______________________________table.____

At a 10 percent deductible, the 2 percent difference 

between 6 and 8 percent for "slight" amounts to a 7 

percent increase in the loss over deductible. Reasonable 

combinations of other damage gradings can show larger 

increases or decreases.

Other Uncertainties

Field data were acquired under strong time 

constraints, and recording errors no doubt occurred. 

Repairs in progress during the inspections made damage 

observations suspect in some cases.

Field inspectors undoubtedly were not always 

accurate in their estimates of dwelling age. Age

Earthquake Losses to Single-Family Dwellings: California Experience A35
determined from insurance files did not agree with the 

inspector's determination in some cases.

It is likely that the field inspectors did not find all 

the San Fernando sites with or adjacent to observable 

ground disturbances.

Contractor records on repair costs and adjuster 

claim information were not distorted by labor and 

material scarcities which would probably develop after a 

great earthquake.

Despite these uncertainties, the fact that aggregate 

losses computed from insurance claims reasonably 

agreed with those computed by our methods provides a 

certain amount of confidence.

Insurance Company Data on 

Probable Maximum Loss (PML) and 

Loss Distribution

Applying the PML definition of "9 out of 10" to 

table 20 does not result in meaningful answers in most 

cases, and the remaining answers are not of the desired 

quality. Table 21 under the subheading Insurance 

Company A lists the PML percentages from table 20 for 

categories that contain 50 or more dwellings. Note that 

WOOD-ALL has a range of 13-16 percent in tables 20 

and 21.

Figure 6 shows the loss distribution from 0 percent 

loss to 15 percent loss, at 0 percent deductible, as a 

function of the percent of dwellings. The reasons for the 

9 percent peak in our data have been discussed in the 

"Distribution curve" section. The Insurance Source A 

data in figure 6 is more orderly than our data and shows 

no large peak at 9 percent.

Figure 7 is another viewpoint on the data shown in 

figure 6. As in figure 6, there are fewer irregularities in 

the Insurance Source A data than in our data. The 

Insurance Source A data are the more realistic of the two 

data bases.

JUDGMENTAL CONSIDERATIONS

Probable Maximum Loss (PML) For 

Magnitude 6.5 Earthquakes

A percent PML that is applicable to all California 

dwellings requires judgmental decisions founded on all 

the foregoing diverse data. "Judgment PML" in column 5 

of table 21 is based on the following considerations.

Construction anomalies are excluded in order to 

have better commonality of data. San Fernando geologic 

anomalies are also excluded. Increased damage in 

Coalinga due to apparent soil amplification, however, is 

considered in the "Judgment PML." All these factors are 

consistent with the definition of the PML.

Many San Fernando dwellings in the post-1949 age 

group were newly built at the time of the 1971 San 

Fernando earthquake and should have had better than 

average building code supervision; the reverse was 

partially true for Coalinga dwellings at the time of the 

1983 Coalinga earthquake. Therefore, for average post1949 housing, PML's are probably slightly understated 

for San Fernando and probably overstated for Coalinga. 

Judgment PML is 12 percent for the post-1949 age group 

for floors of all types.

Dwellings in the 1940-49 age group were 

somewhat difficult to date in the field, and consequently 

the quality of the data probably suffered. This time 

period includes the World War II years with the 

restrictions on construction and the transitions in 

architectural styles. An increase in the PML for the 

1940-49 group is more likely than a decrease when 

compared with the post-1949 group; therefore, the PML 

for San Fernando wood-floor 1940-49 age group appears 

to be anomalously low. Judgment PML is 14 percent for 

the 1940-49 age group for all types of floors.

San Fernando PML values for the pre-1940 age 

group are substantially higher than those for other San 

Fernando age groups. PML's are also markedly different 

between San Fernando and Coalinga for wood floors 

within this age group. The PML for the pre-1940 

Coalinga dwellings is substantially too low due to the 

number of excluded houses being off on their 

foundations. If these had not been excluded, then the 

PML's would have exceeded 65 percent (table 10, 

BOTH-PRE40), which would have been excessive. A 

wide divergence between San Fernando and Coalinga 

PML's can be partially attributed to difficulties in 

consistently dating construction to a single decade. 

Judgment PML's for the pre-1940 age group differed by 

floor type and are of poorer quality than those for other 

age groups.

As the inventory of older dwellings decreases due 

to demolition and as the post-1949 inventory increases 

due to new construction, the post-1949 and "all ages" 

groups are becoming increasingly important. We may use 

changes in California census population (data from 

California Department of Finance) as an index to 

changes in the dwelling inventory:

1940 population 

1940-1950 population growth 

1950-1988 population growth 

January 1, 1989 population

6,907.387 

3,678,836 

18,075,777 

28,662,000

Assuming a direct relationship between the 

number of dwellings and population, more than twothirds of the present dwellings probably are post-1949, 

whereas less than probably one-fifth of the present 

dwellings are pre-1940. The PML for the "all ages"

A36 Estimation of Earthquake Losses to Housing in California
ages" group must be slightly higher than that for the 

post-1949 group because the "all ages" group includes 

older, deficient structures; therefore the judgment PML 

for the "all ages" group is 13 percent.

In regard to the 1933 Long Beach earthquake, 

Martel (1936, p. 161) stated, "The extent of damage for 

wood frame residences *** is very low; in fact in 95 

percent of these buildings the damage was less than 5 

percent ***." The Long Beach analysis relied heavily on 

information from the assessor's office and on 

information for values and losses from the building 

department. Assessors' valuations in California have not 

always represented market values, but have been closer 

to market than insured values. In consideration of this 

uncertainty, we have given preference to the San 

Fernando and Coalinga PML's for calculation of the 

Judgment PML's in table 21. The validity of commingling 

insured values with market values in table 21 to obtain 

Judgment PML values is somewhat questionable.

Judgment PML values in table 21 indicate that no 

distinctions should be made between floor types for 

practical applications and that age groups should be 

limited to pre-1940 and post-1939.

Loss Over Deductible For 

Magnitude 6.5 Earthquakes

The Coalinga and San Fernando lossover-deductible experiences differ from each other. 

There is a judgmental basis for using these for general 

California application. We assume that the curves in 

figures 1,3,4, and 5 can be shifted up or down as a direct 

function of a "state factor" from table 21:

State factor = (Judgment PML)/(1971 San Fernando

PML)

Multiplication of loss-over-deductible values from 

tables such as table 2 by the state factor from table 21 

results in approximate generalized loss-over-deductible 

values for all California wood-frame dwellings near the 

fault in a magnitude 6.5 earthquake if no geologic 

anomalies are present.

TRANSFERABILITY TO 

OTHER EARTHQUAKES

Different earthquakes at different locations will 

show different damage patterns as a result of variations

in:

(1) Wood-frame dwelling construction,

(2) Geologic environment (faulting, landslide, 

"poor ground"),

(3) Distances to faulting (energy release), and

(4) Earthquake magnitude.

Transferability of the results of this analysis to 

other earthquakes requires commonality of data for each 

category of construction characteristics, geologic 

conditions, and earthquake magnitude. With 

commonality, a transfer function can be used to apply 

these parameters to other conditions and locations. 

Variants in wood-frame dwelling construction have been 

identified and quantified so that reasonable commonality 

exists.

Dwellings with damage caused by unusual geologic 

conditions have been identified and removed from the 

data bases. Unusual geologic conditions must be 

reentered in the loss algorithm on a site- or area-specific 

basis.

In our model, the area within 10 kilometers (6 

miles) on either side of the faulting is presumed to be 

within a zone of equal shaking damage for dwellings on 

consolidated alluvium; this area is defined as the PML 

zone. This generalization does not include site 

displacement due to faulting. As an example of 

displacement, strike-slip faulting moves structures 

horizontally near the faulting by about half of the amount 

of the fault offset. The 10-kilometer (6 mile) distance 

approximates the usual focal depth of many California 

earthquakes. This PML zone criterion is met by the 1933 

Long Beach, 1971 San Fernando, 1983 Coalinga, and 

most likely the 1906 San Francisco earthquakes. The 

1987 Whiltier Narrows earthquake was deeper than 

normal [focal depth of 14 kilometers (9 miles)], and no 

surface faulting is known. The 1989 Loma Prieta 

earthquake also was abnormally deep [focal depth of 18 

kilometers (11 miles)], and no surface faulting is known. 

Damage attenuation for distances greater than 10 

kilometers (6 miles) from the fault rupture is not part of 

this study.

Earthquakes of Magnitudes 

Other Than 6.5

The magnitude of the 1971 San Fernando 

earthquake was 6.4, that of the 1983 Coalinga 

earthquake was 6.7, and that of the 1933 Long Beach 

earthquake was 6.3. These magnitudes are sufficiently 

similar to be considered the same for lossover-deductible purposes. A 6.5 magnitude has been 

considered representative for all three events. The 

magnitude of the 1987 Whitter Narrows earthquake was 

5.9, which is less than that of the other three events.

Only the 1906 San Francisco earthquake has useable loss experience for wood-frame dwellings on firm 

soil in the near vicinity of a great earthquake. More than 

1,000 dwellings were examined immediately after that

Earthquake Losses to Single-Family Dwellings: California Experience A37
Table 20. Dwelling loss experience for the 1983 Coalinga earthquake: Loss distribution by number of dwellings, Insuran

shifted on their foundations or were posted as hazardous or had been demolished before time of inspection or were highe

WOOD-PRE40 WOOD-4049 -POST49 WOOD-ALL CONC-PRE40 CONC-ALL BOTH-PRE4

' % NO. SUM NO. SUM NO. SUM NO. SUM NO. SUM NO. SUM NO. SUM NO. SUM NO. SU

,LOSS DWELL. PCT DWELL. PCT DWELL. PCT DWELL. PCT DWELL. PCT DWELL. PCT DWELL. PCT DWELL. PCT DWELL. PC

d

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tt

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

7

5

2

0

2

2

2

1

3

1

0

0

0

0

0

0

0

0

1

0

0

1

0

0

0

0

0

0

0

0

0

1

0

0

0

1

0

0

0

1

0

0

0

0

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22.6

38.7

45.2

45.2

51.6

58.1

64.5

67.7

77.4

80.6

80.6

80.6

80.6

80.6

80.6

80.6

80.6

80.6

83.9

83.9

83.9

87.1

87.

87.

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87.

87.

87.1

87.1

87.1

90.3

90.3

90.3

90.3

93.5

93.5

93.5

93.5

96.8

96.8

96.8

96.8

96.8

96.8

96.8

6

8

1

0

1

4

1

0

4

2

2

1

0

1

0

0

0

0

1

0

0

0

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

18.2

42.4

45.5

45.5

48.5

60.6

63.6

63.6

75.8

81.8

87.9

90.9

90.9

93.9

93.9

93.9

93.9

93.9

97.0

97.0

97.0

97.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

3

2

6

6

8

5

1

3

3

0

1

0

1

1

0

0

0

1

0

0

0

0

0

0

0

0

0

0

0

0

0

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

7.1

11.9

26.2

40.5

59.5

71.4

73-8

81.0

88.1

88.1

90.5

90.5

92.9

95.2

95.2

95.2

95.2

97.6

97.6

97.6

97.6

97.6

97.6

97.6

97.6

97.6

97.6

97.6

97.6

97.6

97.6

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

19

15

9

6

11

11

4

4

10

3

3

1

1

2

0

0

0

1

2

0

0

1

1

0

0

0

0

0

0

0

0

2

0

0

0

1

0

0

0

1

0

0

0

0

0

0

17.4

31.2

39.4

45.0

55.0

65.1

68.8

72.5

81.7

84.4

87.2

88.1

89.0

90.8

90.8

90.8

90.8

91.7

93.6

93.6

93.6

94.5

95.4

95.4

95.4

95.4

95.4

95.4

95.4

95.4

95.4

97.2

97.2

97.2

97.2

98.2

98.2

98.2

98.2

99.1

99.1

99.1

99.1

99.1

99.1

99.1

0 0.0

1 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

0 100.0

1

1

0

2

0

1

1

0

1

0

0

0

0

0

0

0

0

0

0

0

0

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

12.5

25.0

25.0

50.0

50.0

62.5

75.0

75.0

87.5

87.5

87.5

87.5

87.5

87.5

87.5

87.5

87.5

87.5

87.5

87.5

87.5

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

15

9

1

9

4

7

4

3

5

1

0

0

0

0

1

0

0

0

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

25.0

40.0

41.7

56.7

63.3

75.0

81.7

86.7

95.0

96.7

96.7

96.7

96.7

96.7

98.3

Q8.3

98.3

98.3

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

16

11

1

11

4

8

5

3

6

1

0

0

0

0

1

0

0

0

1

0

0

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

23.2

39.1

40.6

56.5

62.3

73.9

81.2

85.5

94.2

95.7

95.7

95.7

95.7

95.7

97.1

97.1

97.1

97.1

98.6

98.6

98.6

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

7

6

2

0

2

2

2

1

3

1

0

0

0

0

0

0

0

0

1

0

0

1

0

0

0

0

0

0

0

0

0

1

0

0

0

1

0

0

0

1

0

0

0

0

0

0

21.

40.

46.

46.

53.

59.

65.

68.

78.1

81.

81.3

81.3

81.3

81.3

81.3

81.3

81.3

81.3

84.4

84.4

84.4

87.

87.

87.

87.

87.

87.5

87.5

87.

87.5

87.

90.

90.

90.

90.

93.

93.

93.

93.

96.9

96.

96.

96.

96.9

96.

96.
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Earthquake Losses to Single-Family Dwellings: California Experience A39
Table 21. Probable Maximum Loss of wood-frame dwellings in magnitude 6.5 

earthquakes

[Excluding geologic effects and construction anomalies]

Probable Maximum Loss (PML) At Zero Deductible

Authors Data

1971

San Fernando

 Value

(Table 8)

Wood floors: 

Age Group:

Pre-1940 26% 

1940-49 10% 

Post-49 11% 

All ages 11%

Concrete floors: 

Age Group:

Pre-1940 14? 

1940-49 13% 

Post-49 11% 

All ages 11%

Wood or concrete floors: 

Age Group:

Pre-1940 22% 

19*10-49 11? 

Post-49 11% 

All ages 11%

1983

Coalinga 

Market Val. 

(Table 13)

19% 

17% 

16% 

17%

12?

Ins. Co. A 

1983

Coalinga 

Insured Val,

(Table 20)

tt 

tt 

 i

13% to 16%

*» 

tt

7% 

8%

 t

8% 

10?

Judgaent

PML

28% 

141 

12%

13%

18% 

141 

12%

13%

22%

14% 

12% 

13?

State 

Factor""

1.08

1.40

1.09

1.18

1 .25

1.08

1.09

1.18

1.00

1.27

1.09

1.18

 Not meaningful. 

 Less than 50 dwellings. 

 Authors' data are market values, but are sase as insured values

for new construction. 

 (State Factor) : (Judgaent PMD/O971 San Fernando)

1-25 -z. r

UJ

o

cr

Ul

00

Ul

1

u.10

O

O

DISTRIBUT

01

_ :

1-

- !

~ ;

 :

 j

_ |

_ I

- i

- |

Insurance Source A data

Our data

\l

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; £

; jj

f

 $

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^

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/ ^

 2 t a

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; m^^m^A^

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 

LOSS AT 0 PERCENT DEDUCTIBLE, IN PERCENT

Figure 6. Graph showing distribution of dwellings versus 

loss at 0 percent deductible for the 1983 Coalinga 

earthquake and comparing our data and Insurance Source A 

data. Dwellings that had shifted on their foundations or were 

posted as hazardous or had been demolished before time of 

inspection or were higher than one story are excluded.

DISTRIBUTION OFDWELLINGS, 

IN CUMULATIVE PERCENT

18 3 

1 1 1 1 

_O Insurance Sou 

 Our data

"~ C

O

 o

 e 

o

~~ * *

i *

i i i i

i i i i

ce A data / 

0 °

0 

O

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1

I 1 1 1

1 I I 1

> o o ° o_s

> ~~

-

1 1 1 1

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 

LOSS AT 0 PERCENT DEDUCTIBLE, IN PERCENT

Figure 7. Graph showing distribution of dwellings versus 

loss at 0 percent deductible for the 1983 Coalinga 

earthquake and comparing our data and Insurance Source A 

data. This figure is similar to figure 6, except that the 

distribution of dwellings is in cumulative percent. Dwellings 

that had shifted on their foundations or were posted as 

hazardous or had been demolished before time of inspection 

or were higher than one story are excluded.

A40 Estimation of Earthquake Losses to Housing in California
Table 22. Loss over deductible for conventional wood-frame dwellings

[First-story floor of any material. Uncertainty factor = 1.50]

Percent Loss Over Deductible for Deductibles of

All ages:

Mag. = 5.0

Mag. = 5.5

Mag. = 6.0

Mag. = 6.5

Mag. s 7.0

Mag. = 7.5

Mag. s 8.0

Mag. s 8.25

Post- 1939:

Mag. =5.0

Mag. = 5.5

Mag. = 6.0

Mag. = 6.5

Mag. = 7.0

Mag. s 7.5

Mag. = 8.0

Mag. = 8.25

Pre-1910:

Mag. =5.0

Mag. = 5.5

Mag. = 6.0

Mag. = 6.5

Mag. = 7.0

Mag. =7.5

Mag. = 8.0

Mag. = 8.25

0%

6.2

6.7

7.1

7.5

8.0

8.11

8.8

9.0

1.5

M. 8

5.1

5.1

5.7

6.0

6.3

6.5

10.1

11.1

11.8

12.5

13.2

11.0

11.7

15.0

1*

5.6

6.0

6.1

6.8

7.2

7.5

7.9

8.1

3-7

1.0

1.2

1.5

M. 8

5.0

5.3

5.1

9.8

10.5

11.2

11.9

12.6

13.2

13.9

11.2

2%

5.1

5.1

5.7

6.1

6.1

6.8

7.1

7.3

3.1

3.3

3.5

3.7

1.0

1.2

1.1

1.5

9.3

10.0

10.6

11.3

11.9

12.5

13.2

13.5

3*

1.5

1.9

5.2

5.5

5.8

6.1

6.1

6.6

2.6

2.8

2.9

3.1

3.3

3.5

3.6

3.7

8.8

9.1

10.1

10.7

11.3

11.9

12.5

12.8

1*

1.1

1.1

1.7

1.9

5.2

5.5

5.8

5.9

2.1

2.3

2.1

2.6

2.7

2.9

3-0

3.1

8.1

8.9

9.5

10.1

10.7

11.3

11.8

12.1

5*

3.7

3.9

1.2

1.1

1.7

5.0

5.2

5.3

1.8

1.9

2.0

2.2

2.3

2.1

2.5

2.6

7.9

8.5

9.0

9.6

10.1

10.7

11.2

11.5

6*

3.3

3.5

3.8

1.0

1.2

1.5

1.7

1.8

1.5

1.6

1.7

1.8

1.9

2.0

2.1

2.1

7.5

8.0

8.6

9.1

9.6

10.1

10.6

10.9

7%

3-0

3.2

3.1

3.6

3.8

1.0

1.2

1.3

1.2

1.3

1.1

1.5

1.6

1.7

1.7

1.8

7.1

7.6

8.1

8.6

9.1

9.6

10.1

10.3

8*

2.7

2.9

3.1

3.2

3.1

3.6

3.8

3.9

1.0

.1

.2

.2

.3

.1

.1

.5

6.8

7.2

7.7

8.1

8.6

9.1

9.5

9.8

9*

2.1

2.6

2.8

2.9

3.1

3.2

3.1

3.5

0.9

0.9

.0

.0

.1

.1

.2

.2

6.1

6.8

7.3

7.7

8.2

8.6

9.0

9.3

10*

2.2

2.3

2.5

2.6

2.8

2.9

3.1

3.1

0.7

0.8

0.8

0.9

0.9

1.0

1.0

1.0

6.1

6.5

6.9

7.3

7.7

8.1

8.6

8.8

lit

2.0

2.1

2.2

2.1

2.5

2.6

2.8

2.8

0.6

0.6

0.7

0.7

0.8

0.8

0.8

0.9

5.7

6.1

6.5

6.9

7.3

7.7

8.1

8.3

12*

1.8

1.9

2.0

2.1

2.2

2.1

2.5

2.6

0.5

0.5

0.6

0.6

0.6

0.7

0.7

0.7

5-1

5.8

6.2

6.6

6.9

7.3

7.7

7.9

13*

1.6

1.7

1.8

1.9

2.0

2.1

2.2

2.3

0.1

0.1

0.5

0.5

0.5

0.5

0.6

0.6

5.2

5.5

5.9

6.2

6.6

6.9

7.3

7.5

1

2

2

0

0

0

0

0

0

0

0

1

5

5

5

6

6

6

7
earthquake in the cities from Belmont to Redwood City. 

All dwellings were within 1-4 miles of the San Andreas 

fault. Damage information is from Lawson (1908), 

beginning on page 354 of volume I, part 2.

Some comparisons between San Francisco in 1906 

and Coalinga in 1983 are of interest. In San Francisco in 

1906, the dwelling foundations were unreinforced brick, 

unreinforced concrete, or wood. Foundation anchorage 

generally did not exist by today's standards. Of 842 

dwellings, 190 (23 percent) shifted on their foundations. 

In Coalinga in 1983, 11 percent of all dwellings shifted a 

measurable amount; 24 percent of pre-1940 dwellings 

shifted a measurable amount (Steinbrugge and others, 

1990). Interestingly, the percentage of older Coalinga 

dwellings that shifted was about the same (24 versus 23 

percent) as that of the dwellings that shifted in San 

Francisco. Admittedly, wood-frame dwelling 

constructions, including foundations, were different in 

the two cities.

Brick chimneys were not reinforced in 1906. Of 

1,097 brick chimneys from Belmont to Redwood City 

that were examined, 88 percent had fallen. In Coalinga, 

130 of 158 (82 percent) pre-1949 chimneys had at least 

moderate damage. Again, the comparison is of interest 

because damage percentages are similar.

It is estimated that 20 percent represents the 

increased dwelling damage from magnitude 6.5 to 8.25, 

with all other conditions being equal. From this, a linear 

expression between magnitude and increase in loss 

(magnitude factor) is:

Magnitude factor = (0.114 x Magnitude) + 0.259

This is based on a magnitude of 6.5. The three significant 

figures exceed the data quality.

Probable Maximum Loss (PML)

The Judgment PML at magnitude 6.5 from table 

21 is modified by a magnitude factor to obtain PML's for 

other magnitudes. There is no need to include an 

uncertainty factor to compensate for the already 

discussed limitations because the uncertainty is covered 

by the "9 out of 10" definition for PML. The resultant 

PML's at 0 percent deductible for floors of all kinds after 

applying the magnitude factor for selected magnitudes 

are:

It is practical to combine the 1940-49 age group with the 

post-1949 age group. Dwelling-population relationships 

examined under "Probable maximum loss (PML) for 

magnitude 6.5 earthquakes" showed that post-1949 

dwellings outnumber 1940-49 dwellings by five-fold. 

For practical purposes, the post-1949 PML's can be 

used for both age groups, as follows:

Magnitude

Age group

Pre-1940, in percent

post-1939, in percent

All ages, in percent

6.5

22.0

12.0

13.0

7.0

23.3

12.7

13.7

7.5

24.5

13.4

14.5

8.0

25.7

14.1

15.2

8.25

26.4

14.4

15.6

Magnitude

Age group

Pre-1940, in percent

1940-49, in percent

Post-1949, in percent

All ages, in percent

6.5

22.0

14.0

12.0

13.0

7.0

233

14.8

12.7

13.7

7.5

24.5

15.6

13.4

143

8.0

25.7

16.4

14.1

15.2

8.25

26.4

16.8

14.4

15.6

The above PML compilations are to three 

significant figures for display purposes. The PML's in 

table 21 are to two significant figures, and the above 

tabulation is reasonable only to two significant figures, at 

most.

Loss over Deductible

Curve 3 in figure 4 is considered to be the most 

useful for loss-over-deductible applications. The 

explanations that accompany figures 6 and 7 provide 

supportive reasoning for curve 3 in the range of 0-9 

percent deductible. Beyond 9 percent deductible, 

insurance data showed a seemingly large number of total 

losses that were not borne out by our inspections the 

insurance total losses may possibly have been influenced 

by the then-current legal considerations. However, losses 

over deductible are low beyond the 10 percent deductible 

for curves 1, 2, and 3, and supporting data for these 

curves are sparse. Curve 3 is the most conservative of 

these three curves and is accordingly considered to be the 

best fit. Calculation methods for loss-over-deductible 

curves and tables were such that constructive total losses 

were included; thus the peak for losses that exceed 65 

percent was included.

Unlike the PML definition, the lossover-deductible tables, such as table 2, do not include an 

uncertainty factor. However, it is appropriate to include 

such a factor. We judge that a 50 percent uncertainty 

factor is reasonable compensation for the many 

identified limitations involved with loss-over-deductible 

data. This uncertainty factor also allows the inclusion of 

one-and-two-story, split-level, and two-story dwellings. 

The term "conventional dwellings" will include these 

height variants in the subsequent discussions. 

Conventional dwellings do not include houses on steeply 

sloping sites where the downside is supported by tall 

columns or walls. Also not included are houses with 

basements and those with minimal first-story crosswalls 

found in the western sections of San Francisco. Geologic 

effects are not included, but must be included in the lossestimation algorithm on a site- or area-specific basis.

A42 Estimation of Earthquake Losses to Housing in California
Regression equations were developed for curve 3 

data. These equations were then multiplied by:

(1) State factor from table 21 (for general 

application in California),

(2) Uncertainty factor which increases values by 

50 percent (or user-modified), and

(3) Magnitude factor (transfer function for 

different magnitudes).

Mathematical equations are presented in the 

"Overview, findings, and recommendations" section at 

the end of this report, as are tabular (table 22) and 

graphical alternatives (fig. 15).

1987 WHITTIER NARROWS 

EARTHQUAKE

Reconnaissance surveys of dwellings immediately 

after the 1987 Whittier Narrows earthquake found few 

damaged structures and few fallen masonry chimneys in 

the epicentral area and elsewhere, except 6 or more miles 

away in sections of the city of Whittier. This is in some 

contrast to the experience from the previously discussed 

earthquakes.

Dwelling deductibles for earthquake insurance in 

California were commonly 5 percent of insured values 

until a few years before the 1987 Whittier Narrows 

earthquake. The 1983 Coalinga earthquake was an 

anomaly in the history of the deductible due to previously 

mentioned legal reasons, and essentially 0 percent 

deductibles were commonly applied to Coalinga losses. 

Deductibles generally had risen to 10 percent by the time 

of the 1987 Whittier Narrows earthquake. However, 

there were a few important exceptions in the amount of 

earthquake insurance written in the context of the 

amount of the accompanying homeowner policy.

Two data sources were investigated. Insurance 

Source C used a variable deductible, and almost all the 

policies had deductibles within a range of 3-9 percent. 

Insurance Source D had a minimal deductible of $250. 

Both types of deductible provided opportunities for 

examination of a greater number of losses than would be 

possible with a 10 percent deductible.

The context of this discussion of the Whittier 

Narrows earthquake indicates whether "dwelling" refers 

to the structure and (or) its contents. However, to 

minimize possible misunderstandings, "building" refers 

to the structure, whereas "dwelling" refers to the 

structure plus its contents.

ZIP distance is the distance in miles between a 

population-weighted ZIP-centroid and the nearest point 

on the computed below-surface fault rupture plane 

(source of energy release). One model estimates the 

below-surface rupture length to be 5 mi for this

magnitude 5.9 earthquake on a thrust fault at a depth of 

10 mi. These were used in the distance-to-ZIP- centroid 

calculations (Steinbrugge and others, 1984).

Insurance Source C

Insurance Source C provided information on 

homeowner dwellings for 63 ZIP's that had earthquake 

claims on record. Of these claims, 398 were paid 

earthquake claims, out of 19,870 policies with 

earthquake, as well as homeowner, coverage. Forty of the 

63 ZIP's had two or fewer paid claims out of usually 

many hundreds of earthquake policies in each ZIP. ZIP's 

with a minimal number of paid claims were in some cases 

located 10 or more miles from the earthquake's energy 

release; one ZIP was 37 miles away.

Insurance Source C is a very large writer of 

dwelling insurance, possibly the largest in the 

earthquake-affected area. Their underwriting and 

marketing practices tended to give uniform market 

penetration throughout the area. There was no 

marketing selectivity by dwelling age, soil condition, or 

hillside location. As a result, their loss data do not 

include these kinds of biases and the findings are 

considered to be representative of the affected area.

Available data for each policy included location, 

year built, building value, contents value, loss to building, 

loss to contents, loss due to additional living expense, 

amount of homeowner building insurance, amount of 

homeowner contents insurance, amount of insurance to 

replacement value, amount of earthquake coverage, and 

amount of a variable earthquake-insurance deductible. 

There was no information on masonry veneer, if any, nor 

on the number of stories. Normally the dwellings were 

one story. All buildings were wood frame.

Geographic Distribution of Losses

Region With Paid Earthquake Claims

The open triangles in figure 8 show the locations of 

each population-weighted ZIP centroid. Distance to the 

earthquake epicenter may be scaled. The figures next to 

each ZIP centroid are, for one example: 90601 which is 

the ZIP number (in Whittier in this instance); 

280/79/28.21 mean, respectively, the number of 

earthquake policies in the ZIP, the number of paid 

claims, and the paid claims as a percentage of the number 

of policies.

A total of 95 percent of the paid claims were 

located in the ZIP's shown in figure 8; the remainder 

were scattered beyond the map's boundaries. Although 

the exact location of each earthquake policy was

Earthquake Losses to Single-Family Dwellings: California Experience A43
91202

A

91207 

A Glendale

91103

A

91203 91206

A A

A 91001 

332/5/1.51

o Altadena 

o 91104

o A 0 l66/4/2.41 

o Pasadena

Sierra Madre 

91024

A 157/1/0.64

91101

91205

A

90039

A

0 oooOooooo 0o 

o° 90041 91105

o 32A1/3.13 107/2/1.87 ^.

0 o oo o . 

90042° 

A .91030

90065 ° A 

A ° 166/16/9.64 

°_ 'South Pasadena 

o 91801

78/6/7.69

91107

A

~ 334/2/0.60

Monrovia 

91016

A

288/1/0.35

Duarte 

91010

A 318/1/0.31

Los Angeles

90026

A

90012

A

90017

A 90013 

90015 A

A

90021

A

90031

A

90033

A

0 A 91776

0 . 166/8/4.82. ^

0 ^90032 Alhambra . 11(2/3/2.11

°/ A 91803 

°.19/2/10.53 A *

o 149/18/12.08 * 91770

 91108 91006

A A

183/2/1.09 91775 726/7/0.96

A

. 214/6/2.80

91780

San Gabriel A

317/8/2.52 c

91702

A

o 91731

o A

Baldwin Park 

91706

A

91722

A 91723

91732

A

90063 o

A o

Monterey Park ( 

91754

A

. 312/18/5.77

Rosemead 91746

A

Los Angeles

90023

A

O 90022

o A _ 42/1/2.38

o o o o o

91790

A

o 9171111

A

283/1/0.35

o "91791

A

312/1/0.32

91792

A

90011 90058

A A

Los Angeles

90640

A

193/3/1.55 91745

A

753/2/0.27

o o o o o

90270

A

~*

<*

90001

A

Los Angeles

90002

A

90059

A

90222

A

Compton 

90220

A

90255

A 90201

A

90280

A

Downey

90240

296/3/1.01

A

294/4/1.36

90241

90601. . 

A .

280/79/28.21 >

24l/5/2"o7;~ 9 A06

 150/11/7.33 90602 *.

A

. 132/35/26.52

Whittier

90605

' 329/39/11.85 90603

 90604. ,,cn 7Tn . A 

432/5/1.16

91748

A

316/1/0.32

Santa Fe Springs 

90670

A

90631 .

A 854/45/5.27

90262

A

0 90221 

0 A

O 37/1/2.70 °

90242 A

215/2/0.93

92621 

534/2/0.37

90723 

A

90650

A 468/2/0.43

90706 

A

La Mirada 

90638

A

632/4/0.63

o o o o o

90805

A

90701

A 603/1/0.17

90621

A

o o o o o 

92633

A

92635

A

384/1/0.26 

o o o o

o o o o 

92631

A

92632

A

Figure 8. Map showing the epicenter of the 1987 Whittier Narrows earthquake and the location of the population-weighted 

ZIP centroids (open triangles). The ZIP number is shown above each triangle. Other numbers, such as 280/79/28.21, refer to 

loss data for Insurance Source C; see text for explanation. Lines of open circles separate the ZIP'S with no paid claims from 

those with paid claims. Lines of solid circles enclose areas of higher than usual losses.

A44 Estimation of Earthquake Losses to Housing in California
available, data were grouped by ZIP's rather than by 

smaller areas due to the small number of paid claims in 

most ZIP's.

The percentage of paid claims to number of 

earthquake policies in each ZIP was used as an index to 

the comparative losses among ZIP's. Other indexes that 

use the variable deductible and other parameters created 

difficulties and were discarded.

The lines formed by the open circles in figure 8 

separate the ZIP's with no paid claims from those with 

paid claims. The shape of the enclosed area is irregular; 

the widest parts of the enclosed area are to the north and 

the southeast of the epicenter. Losses over deductible 

drop off rapidly to the west of the epicenter. There also 

are a larger number of losses to the north and to the 

southeast of the epicenter than elsewhere. The boundary 

line to the east is unusual in that it approaches the 

epicenter. Indeed, if ZIP 91770 adjacent to the epicenter 

had one fewer paid claim, then the epicenter would have 

been in an area with no paid claims!

The locations of the lines formed by the open 

circles are of poor quality; they are predominately 

determined by ZIP's that have only one paid claim rather 

than by those that have none. In its favor, this method 

provided a contiguous paid-claim pattern except for ZIP 

90670 at Santa Fe Springs. However, it must be 

remembered the deductible was a variable, and therefore 

percentage-compared paid claims are not necessarily on 

the same basis particularly so if single paid claims are 

the determinant for locations of the dividing lines. The 

number of earthquake policies in those ZIP's that have a 

single paid claim was also a variable and ranged from a 

few tens to more commonly a few hundreds. Local 

surficial geology and dwelling construction characteristics undoubtedly were variability factors.

Areas With Highest Number of Paid Claims

The loss index (percentage of paid claims to 

earthquake policies) identified two zones of higher than 

usual losses (delineated by lines of solid circles). One 

zone extends northward from Monterey Park to 

Pasadena; its highest index number is 12 percent.

The more important zone is that containing the 

cities of Whittier and La Habra where the index rose to 

28 for one ZIP and over 26 for a second ZIP. La Habra 

is contiguous to the southeast of Whittier and also has a 

high index. It should be noted that all these ZIPs are at or 

near the southern base of the Puente Hills and near the 

Whittier fault (the earthquake did not occur on this 

fault). Field observations indicated that the highest 

concentrations of damage were often found along the 

base of these hills. It is possible that mapping for geologic 

microzonation studies can be identified with locations of 

insured dwellings, but this is beyond the scope of this 

examination.

Although sections of the boundaries are imprecise 

and could be in error by miles, the general delineation of 

the geographic distribution of losses shown in figure 8 is 

reasonable.

The concentration of damage in Whittier has been 

examined from a seismological standpoint by Kawase 

and Aki (1990). They stated in the abstract to their 

paper:

The results show that the amplification due to 

the hill relative to the flat surface is more than 

1.5 for all the source models. Since this amplification is nearly independent of the source type 

and spectrum, we conclude that the combined 

effect of the topographic irregularity and critically 

incident SV waves might be responsible for the 

concentration of damage observed during the 

Whittier Narrows earthquake.

Deductibles and Losses Over Deductible

The deductible was unusual in that it was a 

variable. The amount of earthquake coverage was 

selectable by the assured but could not be less than 

$100,000 and could differ from the amount of the homeowner policy. The homeowner policy was close to or at 

the replacement value, but the earthquake policy was tied 

to neither the homeowner policy nor the replacement 

value. The deductible was 10 percent of the amount of 

the earthquake policy and was applicable to the sum of 

the building, contents, and additional living expense.

Dollar deductibles were converted into percent 

deductibles using building replacement values plus 

contents values. The distribution of dwellings as a 

function of the deductible for 19,862 dwellings (out of 

19,870) is shown in figure 9. This distribution included all 

earthquake-insured dwellings, whether there were paid 

claims or not. Distributions for paid claims in (1) the 

Whittier-La Habra zone, (2) the Pasadena-Monterey 

Park zone, and (3) all ZIP's that had paid claims, were 

very similar to that shown in figure 9. All distributions 

tended to be similarly skewed. A distribution peak at 5-6 

percent was found in all cases. The average deductible 

applied to 19,857 earthquake-insured dwellings was 5.8 

percent. This deductible was about the same for the 

Whittier-La Habra zone, the Pasadena-Monterey Park 

zone, and elsewhere.

The losses over deductible were generally less than 

10 percent and rarely greater than 20 percent. Less than 

2 percent of the dwellings in the severely shaken cities of 

Whittier and La Habra had losses over deductible 

greater than 60 percent. About 1 percent had losses over 

deductible greater than 60 percent for all ZIP's that had 

paid claims. These low percentages should be used with 

caution because the number of dwellings were quite 

small compared to the entire inventory of dwellings with 

paid claims.

Earthquake Losses to Single-Family Dwellings: California Experience A45
40

W

30

I 20

10

CO

oc 

to

Q

Distribution peak

4 6 8 10 

DEDUCTIBLE, IN PERCENT

12 14

Figure 9. Graph showing distribution of dwellings versus 

deductible, based on replacement cost of all earthquakeinsured dwellings.

An examination of the distribution of losses over 

deductible as a function of deductible shows wide 

variations and very few dwellings in each category (see 

table 23 for one such example). More than 7,200 

dwellings in the total dwelling inventory of more than 

19,000 dwellings had deductibles that ranged from 5 to 6 

percent, but only 24 dwellings had losses over deductible 

of 0-1 percent.

The average deductible of 5.8 percent provided 

more loss data than could have come from a more 

conventional 10 percent deductible. It was hoped that the 

variable deductible would produce a range of deductibles 

that had useful losses over deductible. Table 24 

summarizes the most important loss-over-deductible 

data. The listings are limited to the zones and regions 

that had 100 or more paid claims. The third through 

seventh columns are the losses over deductible for 

deductible ranges 2-3 percent through 6-7 percent. 

Other deductible ranges fell on the lower portions of the 

distribution, and each contained less than 5 percent of 

the total number of paid claims. There is an evident trend 

in the third through seventh columns in table 24 toward 

lower losses over deductible as the deductible increases, 

but the data scatter is significant. Slopes of straight lines 

through these data using linear-regression methods were 

(in descending order of zones/regions): -0.188, -0.216, 

-0.392, and -0.014. The choice of a straight-line slope is 

based on figures 4 and 5 where small sections of the 

curves can be approximated by straight lines. These 

straight-line slopes may be compared with that obtained 

from equation 6 (discussed in the "Loss over deductible 

approach" section later in this report), which is the

generic loss-over-deductible equation for the "all ages" 

group. Differentiating this equation and substituting 5 

for X obtains a slope of-0.591, which is at some variance 

with the other slopes.

An alternate and approximate approach seems 

warranted. The last column in table 24 is the average of 

all losses over deductible for deductible of 0-100 percent. 

The values in this column closely approximate the 

weighted averages of the percentages for deductible of 

2-3 percent through 6-7 percent in this table. Another 

view of these data is the average loss over deductible for 

deductibles in the range of 0-100 percent (see, for 

example, the value of 1.01 at the bottom of the next to 

last column in table 23). These two views are compared 

in table 25. The first view is biased toward the 

distribution peak, whereas the second view is biased 

toward the average of the skewed distribution. The 

average of these two views is shown in the second column 

of table 26 and will be used in the following discussions.

Adjustment For Magnitude 8.25 Earthquake and 

Uncertainty Factor of 1.5

Loss-over-deductible relationships for the 

previously discussed 1933 Long Beach, 1971 San 

Fernando, and 1983 Coalinga earthquakes were based on 

magnitudes about 6.5. A 20 percent increase in the loss 

over deductible for these events was considered 

appropriate for a magnitude 8.25 event (see magnitude 

factor in the "Earthquakes of magnitudes other than 6.5" 

section). Assuming a linear relationship, then the 

magnitude factor that is necessary to obtain a loss over 

deductible for a magnitude 8.25 rather than a magnitude 

5.9 earthquake is a 30 percent rather than a 20 percent 

increase.

Table 26 shows the results of applying these 

factors. The second column of table 26, which is a 

compromise between two different views of the data, is 

the average of the second and third columns of table 25. 

The third column of table 26 includes the user-selectable 

uncertainty factor of 1.50. The fourth column includes 

both the magnitude and uncertainty factors. "Adjusted 

loss" in the column headings refers to the inclusion of 

these factors. The 5 percent deductible was judgmentally 

selected as being between the average deductible (5.8 

percent) and the peak of the loss-over-deductible 

distribution.

Commentary on Loss-Over-Deductible Results

The last two columns of table 26 show expected 

values based on the previously discussed three 

earthquakes. These expected values, which are from 

table 22, are applicable only to those zones/regions where 

there are no increases in losses due to geologic effects or 

unknown reasons.

A46 Estimation of Earthquake Losses to Housing in California
Table 23. Number of dwellings with losses over deductible in Whrttier and La Habra, on the basis of percent deductible 

[Percent losses are based on replacement cost]

m

0)

£L

0)* 

o

o«

8w8*

to

<§

9

21

V

,=*

P

$

a5*

(0

PERCENT

DEDUCTIBLE

ZERO

> 0 - 1

> 1 - 2

> 2 - 3

> 3 - 1

> 1 - 5

> 5 - 6

> 6 - 7

> 7 - 8

> 8 - 9

> 9 - 10

> 10 - 11

> 11 - 12

> 12 - 13

> 13 - 11

> 11 - 15

> 15 - 16

> 16 - 17

> 17 - 18

> 18 - 19

> 19 - 20

ZERO

0

7

12

103

211

763

191

366

197

130

18

21

8

3

0

1

0

0

0

0

0

> 0

TO 1

0

0

0

1

9

11

1

1

1

1

0

0

0

0

0

0

0

0

0

0

0

> 1

TO 2

0

1

0

2

3

9

0

3

1

0

0

0

0

0

0

0

0

0

0

0

0

> 2

TO 3

0

1

2

1

6

6

5

2

0

1

0

1

0

0

0

0

0

0

0

0

0

.______________Dclorlci uT i ivjc AII CD iwniinTTni c-_____________

> 3

TO 1

0

0

1

0

2

3

1

1

1

1

1

0

0

0

0

0

0

0

0

0

0

> 1

TO 5

0

0

0

1

1

6

3

6

0

1

0

0

0

0

0

0

0

0

0

0

0

>5 >6 >7 >8 >9

TO 6

0

0

0

2

2

1|

3

0

1

1

0

0

0

0

0

0

0

0

0

0

0

TO 7

0

0

0

1

3

5

0

0

1

0

0

0

0

0

0

0

0

0

0

0

0

TO 8

0

0

0

1

1

5

1

0

2

0

0

0

0

0

0

0

0

0

0

0

0

TO 9

0

0

0

0

2

1

1

1

1

0

0

0

0

0

0

0

0

0

0

0

0

TO 10

0

0

0

1

1

1

0

0

0

1

0

0

0

0

0

0

0

0

0

0

0

> 10

TO 11

0

0

0

0

1

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

> 11

TO 12

0

1

1

0

2

2

3

1

0

0

0

1

0

0

0

0

0

0

0

0

0

> 12

TO 13

0

0

0

0

0

5

0

1

0

0

0

0

0

0

0

0

0

0

0

0

0

> 

T

 Excludes dwellings with no paid claims.
Table 24. Comparison of loss over deductible and percent deductible, Insurance Source C

[Percent deductibles less than 2-3 percent and greater than 6-7 percent contain fewer than 5 percent of 

the paid claims in each category]

Zone/Region*

Whittier - La Habra:

All ages

Post-1939 cor.str.

ZI?s 90601/90602 

All ZIPs with paid claims

No. of

Paid 

Claims

233

200

111

398

Average

Loss Over Deductible 

For * Deductible of;_________

1*-5* 5*-6* 61-7*

1.264 1.09?

1.13* 1.07*

3-93* 2.83*

0.22* 0.15*

1.21* 

1.06* 

14.20* 

0.19*

0.83* 0.15*

0.13* 0.37*

3.63* 1.57*

0.19* 0.13*

* Loss/ 

Deduct. 

For

Deduct. 

>0t-100*

1.21* 

1.06* 

1.20* 

0.19*

 Limited to zones/regions having 100 or more paid claims.

Table 25. Summary of losses over deductible, Insurance Source C 

[All values in percent]

Zone/Region

Average * Loss

Over * Deductible

At 1*-5* Deductible

Whittier - La Habra:

All ages 1.21*

Post-1939 constr. 1.06*

 Pre-1910 constr. 9.50*

ZIPS 90601/90602 1.20*

 Pasadena to Monterey Park 0.27* 

All ZIPs with paid claims 0.19*

 All ZIPs with paid claims, other 

than Whittier - La Habra and 

Pasadena to Monterey Park 0.01*

 Average * Loss

Over * Deductible 

For Entire Range 

Of * Deductibles

1.01* 

0.76* 

10.23* 

3.77* 

0.17* 

0.19*

0.01*

 Fewer than 100 paid claims. 

 Entire range is 0* deductible through 100* deductible.

Except for the Whittier-La Habra zone, the losses 

over deductible for the 1987 Whittier Narrows 

earthquake are remarkably low compared with those for 

1933 Long Beach, 1971 San Fernando, and 1983 

Coalinga earthquakes. One may validly question whether 

loss information for a magnitude 5.9 earthquake can be 

extrapolated to magnitude 8.25 earthquakes despite 

this, the data are valid for the Whittier Narrows and 

similar earthquakes. One may also challenge the transfer 

of these data to other California magnitude 5.9 

earthquakes because the focal depth of the Whittier 

Narrows earthquake was 14 kilometers (9 miles), 

whereas those for Coalinga and San Fernando were 8 

kilometers (5 miles). Lastly, there is no proof that the 

mechanism of energy release and energy spatial 

distributions are the same for all events.

The loss relationship between post-1939 and pre1940 construction in the Whittier-La Habra zone is 

about ten-fold greater for the older construction, which is

much higher than expected. It may be that the actual 

geographic distribution of dwellings by age and by area 

resulted in some bias. However, reconnaissance surveys 

shortly after the event clearly showed that older dwellings 

were much more vulnerable than were newer ones.

The great sensitivity to loss is also surprising for 

what appears to have been geophysically related 

conditions in the Whittier ZIP'S 90601 and 90602. This 

area had not previously been mapped as vulnerable.

Insurance Source D

Insurance Source D is the State of California's 

Department of Veterans Affairs. Their enabling 

legislation (Article 3.8, Disaster Indemnity, Section 

989.4, of State Benefits for Veterans, Division 4) states:

The department shall maintain an Indemnity 

Fund, which is hereby created in the State Treasury, for the purpose of indemnifying eligible

A48 Estimation of Earthquake Losses to Housing in California
Table 26. Adjusted percent loss over 5 percent deductible for magnitude 5.9 and 8.25 earthquakes, 

Insurance Source C

[All values in percent]

Whlttier Narrows EQ

Average of 

Cols. 243 

______Zone/Region___ Of Table 25

 Whittier - La Habra:

All ages 1.13*

Post-1939 conatr. 0.91*

 Pre-igMO conatr. 9.87$

ZIPs 90601/90602 3.99*

 Pasadena to Monterey Park 0.37* 

All ZIP3 with paid claims 0.19*

 All ZIPs with paid claims, other 

than Whittier - La Habra and 

Pasadena to Monterey Park 0.01*

Adjusted Loss Over 

5* Deductible

1.70*

1.37*

T4.81*

5.99* 

0.56* 

0.29*

0.06*

2.20* 

1.77* 

19.25* 

7.78* 

0.72* 

0.37*

0.08*

 Other 3 EQ

Adjusted Loss Over

5* Deductible

M.2* 5.3*

 Fewer than 100 paid claims. 

 1933 Long Beach, 1971 San Fernando, and 1983 Coalinga earthquakes.

purchasers, for the cost of repairing damage in 

excess of two hundred fifty dollars ($250) 

caused by flood, earthquake or other perils not 

otherwise covered by insurance required of purchasers pursuant to Section 987.2. Money accruing to the Indemnity Fund is hereby appropriated for carrying out the purposes of this article.

The foregoing applies to all loans made by the 

Department of Veterans Affairs for the purchase of 

dwellings by qualified veterans.

Insurance Source D provided data on 480 paid 

claims located in 146 ZIPs. These ZIP's contained 9,230 

earthquake policies in force as of June 21, 1988. The 

earthquake occurred on October 1, 1987, almost 9 

months prior. It is quite probable that the foregoing 

count of earthquake policies reasonably reflected 

conditions at the time of the earthquake because this 

coverage was mandated and thereby would not have been 

influenced by pre- and post-earthquake owner views on 

the need for such coverage. One hundred out of the 146 

ZIP's had two or fewer paid claims, which reduced the 

number of ZIP's that had good loss data on a ZIP basis. 

Only 12 ZIP's had 10 or more paid claims.

The low deductible is advantageous because it 

provides an opportunity to examine a range of losses over 

deductible beginning at essentially 0 percent deductible. 

Paid-claim information on each dwelling consisted of 

ZIP Code, street name but no address (only an 

identifying block number), city, year built, number of 

stories, whether first floor was concrete slab on grade or 

supported wood floor, insured amount, and amount of 

paid claim. Other information on ZIP's that had paid 

claims was on an aggregate basis for each ZIP and not 

on an individual dwelling basis; it consisted of the number 

of policies in force and their aggregate insured value as

of June 21, 1988. These insurance policies did not cover 

dwelling contents, medical expenses, or additional living 

expense, as did the more conventional policies.

Distribution of Losses

By Type of First Floor

Loss distribution by type of first floor with the $250 

deductible was:

Floor type

Number of dwellings Percent 

with paid claims loss

Supported wood 238

Concrete slab on grade 85

Unknown 157

6.6

4.7 

4.4

Dwellings with supported wood floors did not 

perform as well as did those with concrete slabs laid 

directly on the ground. The difference is significant 

because the increase in loss amounted to about 40 

percent. This may be approximately compared with 1971 

San Fernando experience where, in table 6, is shown in the 

"all ages" group at 0 percent deductible:

Floor type Percent loss

Supported wood (wood floors, in table 6) 8.87 

Concrete slab on grade (concrete floors, 7.61 

in table 6)._______________________

The increase in loss amounted to 17 percent. The 

Whittier Narrows loss experience is considered to be 

more representative of California because, in the San 

Fernando event, the supported-wood-floor dwellings 

were mostly very new and rot, as well as, other

Earthquake Losses to Single-Family Dwellings: California Experience A49
deterioration, had not yet occurred. This view is 

supported by a comparison of the "pre-1940" age groups 

in table 6. Other kinds of comparisons can be made using 

table 15.

By Number of Stories

Loss distribution by number of stories with the 

$250 deductible was:

Number of dwellings Percent 

Number of stories with paid claims loss

One

One and two

Two or more

Unknown

418

15

40

7

5.8

2.4

5.1

3.7

The data on the one-and-two-story dwellings are 

too few in number to be more than somewhat suggestive. 

Comparisons with the 1971 San Fernando earthquake 

are not very useful because, in the 1971 event, only 3 

percent of the dwellings were in this height category 

(Steinbrugge and others, 1971, table 7). These comments 

are also true to a lesser extent for the two-story dwellings.

By Age Group

Loss distribution by age group with the $250 

deductible was:

Number of dwellings Percent 

Age group with paid claims loss

Pre-1940

Post-1939

Unknown

81

392

7

10.1

4.7

3.7

As for all previous earthquakes, older dwellings 

suffered more extensively than did more recent ones. The 

reasons for this have been previously discussed.

Comparisons may also be made with 1971 San 

Fernando experience using information from table 6. 

Comparisons should not be taken too literally because 

the post-1949 dwellings in table 6 would, at this writing 

(1990), be almost 20 years older and some deterioration 

would increase the 1971 losses should the identical 

earthquake reoccur today.

By Geographic Distribution

Table 27 is a listing of the loss information for each 

ZIP in ascending order of distance from the fault-rupture 

model that was discussed previously. "NA" means that 

the information was not available. The fifth column is the 

percentage of paid claims, based on information from the

third and fourth columns; the eighth column is the 

percent loss based on information from the sixth and 

seventh columns. The percent loss (eighth column) uses 

the aggregate of dwelling insurance of all policies, 

whether claims were paid or not. This, of course, is the 

preferred percentage because percent losses must be on 

the basis of all dwelling values at risk in a ZIP and not 

just those that have losses.

A total of 359 paid claims out of 480 policies (75 

percent) are summarized by ZIP in figure 10. The 

remainder of the paid claims are scattered among 84 

ZIP's that are located outside the map area; one ZIP has 

five paid claims, one has four paid claims, and the other 

81 ZIP's have three or fewer paid claims. Figure 10 

contains most of the meaningful data; the rest of the 

data are scattered over a wide area three paid claims 

were located more than 100 miles from the epicenter.

The numbers adjacent to the population-weighted 

ZIP centroids, which are marked by the open triangles, 

have a different meaning from those on figure 8, due 

principally to the differences in deductibles; Insurance 

Source C had a variable deductible, whereas Insurance 

Source D had a fixed $250 deductible. The average 

percent loss at 0 percent deductible for Insurance Source 

D can be closely approximated by adding the deductible 

to the paid claim shown in the eighth column of table 27. 

Losses less than $250 obviously would not have been 

included with the paid-claim information. The figures 

next to each ZIP centroid are, for one example: 90601 

which is the ZIP number (Whittier in this case); the 

79/26/5.62 mean, respectively, the number of policies in 

force, the number of paid claims, and the average percent 

loss at the approximate zero deductible for all insured 

dwellings. The latter information was limited to ZIP's 

with paid claims.

One may locate the high-loss areas in a manner 

somewhat similar to that used for figure 8. ZIP's that had 

fewer than 20 policies were excluded, thereby eliminating 

9 out of 62 ZIP's. Not to have done so would have 

included ZIP 90002 with two policies and one loss and 

ZIP 90015 with one policy and one loss. With this data 

restriction and also the limitation of losses to those 

greater than 0.50 percent, areas of higher than average 

losses are bounded by the lines formed by open circles. 

As in the case for Insurance Source C, the highest 

percent losses were in Whittier ZIP's 90601 (5.62 

percent) and 90602 (6.14 percent). These high-loss areas 

are similar to those shown in figure 8. The reader can 

replot the loss contours to suit alternate viewpoints with 

the information shown in figure 10. Alternate valid 

limiting criteria will give somewhat different results, but 

the general locations of areas of highest losses will be the 

same. The extended north-south distribution of losses 

compared with its east-west distribution is not as evident 

in figure 10 as it is in figure 8. ZIP 91770, near the

A50 Estimation of Earthquake Losses to Housing in California
Table 27. Dwelling loss experience for the 1987 Whinier Narrows earthquake: Insurance 

Source D

[Sorted in order of distance from the modeled energy release]

ZIP TO 

FAULT 

RUPTURE

DIST.

ZIP

91733

91754

91770

91771

91732

91803

91731

91776

91801

90640

91780

91746

90022

90032

91030

90063

90601

91775

90660

91006

91790

90042

91745

90606

91106

91744

91016

90602

91107

91010

90041

90065

90240

90609

91791

90255

90026

90670

91024

91104

91792

90015

90039

90241

90605

90280

90603

91723

91206

90604

91001

91748

90027

90242

91724

90037

90631

90002

90650

90262

mi.

0.6

0.7

0.7

0.7

0.9

0.9

1.4

2.1

2.1

2.8

2.8

2.9

3.2

3.2

3.6

3.7

4.1

4.1

4.8

4.8

5.2

5.4

5.4

5.5

5.5

5.5

5.8

6.2

6.2

6.5

6.6

6.7

6.9

6.9

7.4

7.5

7.6

7.6

7.6

7.6

7.9

8.1

8.2

8.3

8.3

8.6

8.6

8.8

8.9

9.0

9.0

9.3

9.6

9.7

9.9

10.0

10.1

10.2

10.3

10.4

NUMBER OF 

DWELLINGS 

WITH:

EQ

INS.

34

91

85

NA

53

32

28

28

37

81

99

38

22

45

18

9

79

54

177

103

152

41

145

115

7

102

78

36

40

53

27

38

56

NA

68

19

5

45

19

34

30

1

16

68

127

89

103

65

16

160

43

93

4

69

65

4

137

2

201

33

PAID

CLAIM

2

16

2

1

1

8

1

2

10

6

11

3

2

9

3

4

26

3

22

7

3

5

5

26

2

1

2

12

3

1

4

1

3

2

3

1

3

6

1

4

2

1

3

5

30

i

17

1

1

15

2

6

1

2

1

1

10

1

6

2

PCT.

PAID

CLAIMS

5.88

17.58

2.35

NA

1.89

25.00

3.57

7.14

27.03

7.41

11.11

7.89

9.09

20.00

16.67

44.44

32.91

5.56

12.43

6.80

1.97

12.20

3.45

22.61

28.57

0.98

2.56

33.33

7.50

1.89

14.81

2.63

5.36

NA

4.41

5.26

60.00

13.33

5.26

11.76

6.67

100.00

18.75

7.35

23.62

1.12

16.50

1.54

6.25

9.38

4.65

6.45

25.00

2.90

1.54

25.00

7.30

50.00

2.99

6.06

 AGGREGATE 

DWELLING

INSURANCE

(dollars)

2,187,000

6,788,000

6,174,000

NA

3,232,000

2,351,000

1,878,000

2,083,000

2,892,000

7,333,000

7,897,000

2,397,000

1,708,000

3,256,000

2,106,000

648,000

6,241,000

4,500,000

12,308,000

10,119,000

11,800,000

3,195,000

13,277,000

8,039,000

672,000

6,872,000

5,484,000

2,851,000

3,275,000

3,540,000

2,730,000

3,601,000

5,397,000

NA

6,179,000

1,277,000

623,000

2,961,000

1,738,000

2,494,000

1,, 899, 000

76,000

2,041,000

6,162,000

10,796,000

6,077,000

8,944,000

5,327,000

1,792,000

13,968,000

4,H62,000

7,850,000

319,000

5,619,000

5,561,000

340,000

13,008,000

149,000

13,092,000

2,267,000

AGGREGATE

PAID

CLAIMS

(dollars)

1,660

115,610

7,830

9,650

500

56,877

8,041

10,996

49,819

12,460

60,973

2,464

6,961

39,590

30,109

27,050

344,121

7,971

92,889

24,449

13,933

69,005

23,853

130,171

2,787

50

18,120

172,071

10,495

1,150

23,198

849

5,758

5,545

11,880

9,414

17,855

16,904

4,180

54,757

2,035

2,222

6,502

13,640

123,558

850

68,573

12,432

600

50,711

5,460

27,269

1,950

2,378

3,730

2,720

20,445

3,550

14,295

2,600

 PCT.

LOSS

0.10

1.76

0.13

NA

0.02

2.50

0.44

0.55

1.81

0.19

0.81

0.13

0.44

1.29

1.47

4.33

5.62

0.19

0.80

0.26

0.12

2.20

0.19

1.70

0.49

0.00

0.34

6.14

0.34

0.04

0.89

0.03

0.12

NA

0.20

0.76

2.99

0.62

0.25

2.24

0.13

3.25

0.36

0.24

1.21

0.02

0.81

0.24

0.05

0.39

0.13

0.37

0.69

0.05

0.07

0.87

0.18

2.55

0.12

0.14

AGGREGATE 

INS. AKT. 

HAVING

PAID CLAIMS

(DOLLARS)

100,000

1,498,000

116,000

48,000

75,000

723,000

104,000

126,000

973,000

559,000

890,000

265,000

133,000

721,000

289,000

337,000

2,094,000

232,000

1,859,000

821,000

209,000

446,000

449,000

1,940,000

247,000

39,000

151,000

1,052,000

313,000

126,000

502,000

88,000

341,000

178,000

305,000

72,000

321,000

520,000

155,000

411,000

217,000

75,000

392,000

468,000

2,837,000

56,000

1,714,000

87,000

147,000

1,360,000

333,000

485,000

75,000

202,000

85,000

82,000

1,281,000

89,000

463,000

167,000

Earthquake Losses to Single-Family Dwellings: California Experience A51
Table 27. Dwelling loss experience for the 1987 Whittier Narrows earthquake: Insurance 

Source D Continued

[Sorted in order of distance from the modeled energy release]

ZIP TO

FAULT 

RUPTURE 

DIST.

ZIP

90638

90003

90062

90221

90706

90044

90068

900143

90047

90008

90036

91765

90016

91773

92635

90220

90621

90305

9121*4

90805

91505

90712

90713

90301

91602

90620

90715

90249

90031

90230

90807

91766

90251

90630

90808

910*42

91767

90260

92686

90504

92806

90066

90806

90720

90815

91763

92610

90405

90503

91151

91762

90803

90277

91786

92683

91106

91761

92617

91312

90732

mi.

10. 4

10.6

11.1

11.7

11.7

11.9

12.2

12.1

12.4

12.5

12.6

12.7

12.8

12.9

13.0

13.3

13.3

13-1

13.6

11.1

11.2

11.5

11.5

11.9

15.1

15.2

15.2

15.5

15.6

16.0

16.1

16.1

16.3

16.5

16.5

16.5

16.7

17.2

17.2

17.1

17.1

17.7

18.2

18.6

18.6

18.9

19.5

19.8

20.1

20.6

20.6

20.7

21.1

21.5

21.5

22.8

23.0

23.5

23.8

21.3

NUMBER OF 

DWELLINGS 

WITH: 

EQ PAID

INS.

187

1

3

20

125

11

11

18

15

9

1

68

17

97

21

13

12

5

95

102

55

117

121

15

7

105

36

33

10

27

52

80

2

91

150

55

105

18

19

16

26

36

10

56

131

71

17

7

30

NA

91

21

7

177

103

46

116

97

126

32

CLAIM

13

1

2

1

6

1

2

3

1

1

1

1

1

2

2

3

1

1

1

1

1

2

5

1

1

1

1

1

2

3

1

1

1

i

3

1

3

1

1

1

1

1

2

2

2

1

1

1

1

1

1

2

1

3

1

1

1

1

2

1

PCT. 

PAID

CLAIMS

6.95

25.00

66.67

5.00

1.80

9.09

18.18

16.67

6.67

11.11

25.00

1.17

5.88

2.06

8.33

23.08

8.33

20.00

1.05

3-92

1.82

1.71

1.03

6.67

11.29

0.95

2.78

3.03

20.00

11.11

7.69

1.25

50.00

1.06

2.00

1.82

2.86

5.56

2.04

8.70

3.85

2.78

5.00

3.57

1.53

1.41

2.13

11.29

3.33

NA

1.10

8.33

14.29

1.69

0.97

2.17

0.86

1.03

1.59

3.13

 AGGREGATE AGGREGATE 

DWELLING PAID 

INSURANCE CLAIMS

(dollars) (dollars)

15,530,

241,

256,

1,507,

9,871,

871,

1,494,

1,817,

1,127,

803,

681,

5,394,

1,189,

8,864,

1,950,

847,

594,

370,

8,666,

6,435,

1,391,

9,007,

10,133,

971,

773,

8,451,

2,846,

2,287,

806,

2,264,

1,156,

5,703,

129,

8,081,

13,462,

4,316,

7,584,

1,112,

5,631,

1,319,

2,618,

3,973,

2,662,

6,059,

12,132,

5,119,

3,618,

585,

3,012,

6,755,

1,486,

652,

15,405,

8,120,

3,667,

8,662,

9,621,

9,969,

2,338,

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

NA

000

000

000

000

000

000

000

000

000

000

76,

10,

4,

3,

27,

4,

5,

23,

7,

3,1,

2,

7,

3,

4,

12,

9,

5,

30,

26,

10,

5,

4,

2,

6,

4,

9,

9,

1,

15,

1,

5,

4,

5,

25,

1,

3,

12,

2,

3,

1,

3,

22,

2,

5,

6,

10,

1,

1,

2,

6,

284

450

275

170

721

218

628

612

350

550

050

825

550

007

778

536

592

800

615

526

650

844

254

570

275

035

236

660

860

241

610

534

150

281

525

020

019

450

309

382

225

950

869

780

732

514

531

125

582

398

325

925

700

198

500

125

106

000

700

725

 PCT.

LOSS

0.51

4.39

1.87

0.23

0.30

0.51

0.41

1.34

0.67

0.47

0.19

0.06

0.66

0.04

0.27

1.57

1.66

1.64

0.01

0.49

0.61

0.13

0.06

0.08

0.07

0.05

0.02

0.13

0.91

0.22

0.26

0.01

7.29

0.02

0.12

0.03

0.08

0.42

0.10

0.61

0.06

0.11

0.50

0.05

0.03

0.01

0.05

0.58

0.03

NA

0.04

0.43

1.07

0.07

0.01 o.oi

0.02

0.02

0.07

0.01

AGGREGATE 

INS. AMT.

HAVING 

PAID CLAIMS

(DOLLARS)

1,255

70

168

89

546

66

346

269

79

73

180

94

106

169

260

243

50

93

108

255

125

183

518

112

121

77

65

50

136

269

341

89

53

62

285

48

219

62

105

423

116

222

128

232

301

125

85

58

86

182

74

221

149

225

69

128

51

116

208

101

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

A52 Estimation of Earthquake Losses to Housing in California
Table 27. Dwelling loss experience for the 1987 Whittier Narrows earthquake: Insurance 

Source D Continued

ZIP TO 

FAULT 

RUPTURE 

DIST.

ZIP

92705

91701

92680

91335

91344

92626

91306

91307

91321

91351

93550

93065

92371

93536

92629

92404

92346

92308

93004

92390

92008

92025

92261

92115

92042

92036

ml.

24.5

25.1

25.1

25.4

26.0

27.1

27.8

30.8

31.4

31.4

35.2

38.9

39.2

42.4

D4.2

44.5

47.2

55.7

61.5

65.2

74.0

85. 4

98.2

105.1

105.8

107.9

NUMBER OF 

DWELLINGS 

WITH: 

EQ PAID

INS. CLAIM

25

166

35

62

11i»

22

57

16

63

100

469

138

27

100

15

252

190

87

56

35

89

139

2

112

44

13

2

2

1

1

3

2

1

1

2

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

PCT. 

PAID

CLAIMS

8.00

1.20

2.86

1.61

2.63

9.09

1.75

6.25

3-17

1.00

0.21

0.72

3.70

1.00

6.67

0.40

0.53

1.15

1.79

2.86

1.12

0.72

50.00

0.89

2.27

7.69

 AGGREGATE AGGREGATE 

DWELLING PAID 

INSURANCE CLAIMS

(dollars) (dollars)

2,786

15,525

2,555

4,562

12,749

2,132

5,105

1,509

5,206

8,510

35,215

12,008

1,735

8,772

1,745

18,821

16,031

7,279

4,502

2,802

7,026

12,100

113

7,924

3,174

972

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

,000

1,

2,1,

15,

15,

2,If1,

27,

1,

2,

3,

1.

6,

5,

2,

21,

956

465

562

775

403

049

223

700

741

135

618

750

500

915

650

250

657

250

366

564

880

165

465

442

318

335

 PCT.

LOSS

0.20

0.02

0.07

0.35

0.13

0.12

0.03

0.33

0.54

0.02

0.00

0.02

0.04

0.01

0.22

0.00

0.01

0.01

0.01

0.24

0.02

0.00

0.63

0.07

0.08

2.22

AGGREGATE 

INS. AMT. 

HAVING 

PAID CLAIMS

(DOLLARS)

276,

232,

81,

91,

427,

257,

94,

92,

293,

"7,

77,

102,

54,

86,

80,

75,

133,

100,

100,

72,

103,

75,

113,

125,

60,

116,

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

000

9,230 480 754,125,000 2,466,399 44,549,000

NOTES: Totals do not include NA entries. NA means not available. 

Total of 146 ZIPS.

Number of pre-1940 dwellings with paid claims: 81 

Number of post-1939 dwellings with paid claims: 392

5. Number of unknown age dwellings with paid claims: 7

 All earthquake policies, with or without paid claims. 

 Aggregate paid claims plus $250 deductible per claim divided by 

aggregate dwelling insurance.

epicenter, has 0.13 percent losses for 85 policies, whereas 

adjacent ZIP's to the west have losses that exceed I 

percent. It should be noted that the low losses in the 

vicinity of the epicenter are common for both Insurance 

Sources C and D. Insurance Source D provides, as did 

Insurance Source C, some data for future microzonation 

studies.

Loss Over Deductible

Percent-loss-over-deductible versus percentdeductible relationships are not presented for Insurance 

Source D data due to the small amount of information in 

the PML zone. See similar discussion on Insurance 

Source C for additional limitations.

Loss Attenuation With Distance From 

Seismic Energy Release

Although an analysis of loss attenuation with 

distance from the source of seismic energy is not a goal of 

this study, this earthquake provided an opportunity to 

examine some of the problems associated with this 

subject. This opportunity was especially true for 

Insurance Source D because its low deductible resulted 

in more widespread losses than did the higher deductible 

that was commonly used by other companies.

A graph of percent loss as a function of distance 

from the fault rupture zone is shown in figure 11. 

Excluded were ZIP's that contained fewer than 20 

earthquake policies. If these ZIP's had not been

Earthquake Losses to Single-Family Dwellings: California Experience A53
. 1202 91207

A Glendale

91203 91206

A A

16/1/0.05

91103

A

A 91001

13/2/0.13 

Altadena

o o o 0

o 91101 o

0 A

03V1/2.21 0

° Pasadena o

91101 ° o o

91205 0 0 0 °°o

A o

0

o 2

90011 ° 0 91105^

7/1/0.89 °0

o

** 91106

A

7/2/0.19

91108 0 . - A 0 90012 o **

0 A o 91030

90039 90065 ° 1 1/5/2. 20 o A 

A A °0 0 18/3/1 

16/3/0.36 38/1/0.03 o South Pa

0 ° °

Los Angeles 

90026

A

5/3/2 '" 90012

A

90017

s* °t \ ? ? f

Sierra Madre G 4 B

91021 *GL

> A ^o//.

19/1/0.25 ^^ItoN S

91107 Monrovia 

« Duarte

10/3/0.31 ^ 91010

78/2/0.31 53/1/0.0*

91006

A

91775 103/7/0.26

A

U7 51/3/0.19 n 0 0 0 0

sade o o o o o o o o o 9178o o 

3 o eo aOq01 o° San Gabriel A o 

91 °01 99/11/0.810

90031 °0 37/10/1.81 9 A76 o o00 ° Baldwin Park 

A 0 90032 Alhambra 28/2/0.55 o ° 9173 i 91706 

** 0 A 91803 o A A

15/9/1.29 A ° . 28/1/0. UU

5 6 MILES

91702

A

91722

* 91723 

65/1/0.21

0 32/8/2.50 0 91770 ---.. gm2 

0 85/2/0. 13 A A 9 I 0 0 ^EPICENTER K ,7T/n * > A 

° Q Monterey Park n W-+^ 91733 53/1/0.02 152/3/0.12 91791

r\

A 90033 , _,, ~o 91751 o 

" 90013 A A 3 o A ° 

90015 A * 9/ft,.33 ° 0 91/16/1.76 ^o

A L

1/1/3-25 90021

A

90011 90058

A A

Los Angeles 

oow 90001 " ?'

& 19/1/0

Los Angeles

90002

A2/1/2.55

90059

A

90222

A

Compton 

90220

A

13/3/1.57

3S Angeles

90022

9 A23 22/£0 .

90010

A

90270 

A

Bell

90201

76 A

90280

89/1/0.02

90262

A

33/2/0. 11

90723 

90221 A 

A Paramount 20/1/0.23

90805 

A 102/1/0. 19

o

0 ^ °

0 o °

11

90610

A

81/6/0.19

o 

o 

o

^^

Rosemead 31/2/0.10 91716 A

38/3/0.13

91711

A 102/1/0.00

_ O O O O 0 n 

n 0 ° ° o 91715

o o A.

o° *(, o 115/5/0.19

o $ o 

o 90601 <v. o

906?0 79/26/5.62 ^°° 0

&A ortAn£ ^ -

A

68/3/0.20

91792

A

30/2/0.13

91718

A

93/6/0.37

0 177/22/0.80 '"""" "</ U n

o /v < , °

o

o 

o

Q

115/26/1.70 90602 <T o

A o

36/12/6.11 o

Whirrier ^

90210 _ Santa Fe Springs , 

Downey A °o 90670 9°6°5 ° , H 56/3/0.12 _ A A o La Habra

68/5/0.21

90212 A

69/2/0.05

90706

A

125/6/0.30

0 *± 127/30/1. 21 m r, yuou3 » 

o Ooooooooooo 15/6/0.62 o o Oonfinu ° ^ °90631 90601 i03/17/o.8i o ^

I60/*10.39o 0137/10/0.18

0 0

0 O 

Norwalk o

0 La Mirada o

T ° 9^38

20^6 /0.12 0187/13/0.51 0 ° 

O o O O

Artesta 92633

90621 A

90701 A

A 12/1/1.66

92621

92635

A21/2/0.27

92631

A

92632

A

Figure 10. Map showing the epicenter of the 1987 Whittier Narrows earthquake and the location of the population-weighted 

ZIP centroids (open triangles). The ZIP number is shown above each triangle. Other numbers, such a 79/26/5.62, refer to loss 

data from Insurance Source D; see text for explanation. Lines of open circles enclose areas of higher than usual losses.

excluded, then even a moderate change in a single loss 

could have significantly affected the loss percentage. Also 

excluded were ZIP's with no paid claims. A straight-line 

equation determined by regression methods, which 

excluded losses greater than 1 percent and ZIP's with

fewer than 20 earthquake policies, was essentially a level 

line. The implication is that damage did not noticeably 

attenuate with distance as far as 15 miles. Losses greater 

than 1 percent are in higher than average loss zones, 

possibly due to geophysical causes. This viewpoint has

A54 Estimation of Earthquake Losses to Housing in California
7

Q- g

X 

O

DC 5 

O 

u.

1* 

0 

DC

IN AVERAGE LOSS, PE

W3 ro - 

918030

91754

*91801

«d

090032

090601

0 

90042

90606

^90602

* 

91104

0

090605

*

1\. » S 1 » s

5 6 7 8 9 10 

DISTANCE FROM FAULT RUPTURE, IN MILES

11 12 13 14 15

Figure 11. Graph showing average loss for each ZIP (dot) versus distance from fault rupture for the 1987 Whittier Narrows 

earthquake. ZIP's with no paid claims (that is, losses, if any, less than $250) are not shown. ZIP's with losses greater than 1 

percent deducible are identified by ZIP.

serious limitations in the light of the east-west geographic 

distribution of damage (figure 10), but there is no 

evidence of a significant reduction in loss with distance in 

the north-south direction.

Figure 12 is another examination of the same data 

except that it is bracketed by ZIP into greater than 

1-mile distances from the source of seismic energy 

release. The values greater than 1 percent show the 

effects of the two zones of high damage in figure 10. The 

graph suggests that attenuation begins at 8 miles.

Neither figure 11 nor figure 12 is definitive but is 

only suggestive at best. It should be recalled that all data 

for the 1987 Whittier Narrows earthquake include the 

effects of a deeper than usual focal depth and a smaller

AVERAGE LOSS, IN PERCEN1

0 -* rs -.

in o wi c

- 

 

 

2 46 8 10 12 14 

DISTANCE FROM FAULT RUPTURE, IN MILES

16

Figure 12. Graph showing average loss for 1-mile interval 

(dot) versus distance from fault rupture for the 1987 Whittier 

Narrows earthquake.

energy release than for the other earthquakes in this 

study. However, the observations are not in significant 

conflict with the assumptions for the PML zone discussed 

in the appendix.

OVERVIEW, FINDINGS, AND 

RECOMMENDATIONS

Overview

The private and public sectors need to know the 

amounts of the losses that will have to be supported by 

each sector, both on an aggregate basis and on an 

individual-dwelling basis. Apportionment of loss among 

the involved parties may be in the the form of (1) an 

insurance deductible, (2) a forgiveness feature in a 

government loan, or (3) other practices that divide the 

loss between involved parties. We explored our available 

data both with and without a deductible. It was evident 

that the amount and consistency of data were not fully 

satisfactory.

Insurance loss experience has been favored over 

that with governmental involvement because insurance 

loss does not include grants, biases to those claiming 

losses for tax-related purposes, incomplete or avoided 

repairs to save money, or improvements beyond repair to 

the original state (Steinbrugge and Schader, 1973).

Earthquake Losses to Single-Family Dwellings: California Experience ASS
Intensity Observations as an 

Alternative Data Source

Intensity observations have been used as the bases 

for loss estimation. In the United States, the Modified 

Mercalli Intensity (MMI) scale of 1931 (Wood and 

Neumann, 1931) is the scale most commonly in use. The 

MMI scale is a descriptive scale of earthquake effects 

with 12 degrees or grades which range from I (not felt) to 

XII (damage nearly total). The grades of intensity of 

most interest in describing damage are VI (minor nonstructural damage) through X (most masonry and frame 

structures destroyed). Intensity maps have been 

prepared for many earthquakes and published in the 

technical literature. Two Federal agencies, the U.S. 

Coast and Geodetic Survey (1928-1973) and the U.S. 

Geological Survey (1974 to the present), have 

undertaken routinely to produce both listings of 

intensities and maps for all significantly felt earthquakes 

in the United States. These studies represent by far the 

largest available data base of descriptions of earthquake 

damage. As has been frequently noted (for examples, 

Steinbrugge and others, 1984; Steinbrugge, 1986), there 

are a number of problems in the use of MMI data in loss 

estimation. For examples:

(1) The descriptions of damage to structures are 

too general.

(2) The descriptions of damage refer to a building 

stock that is not representative of the 

contemporary building stock; that is to say, the 

characteristics of the contemporary building 

stock have changed significantly since the 

publication of the MMI scale in 1931.

(3) Intensity data are generally presented as 

contour maps (isoseismals), and the actual 

observations of intensity may or may not be 

plotted on the map. Because contouring is a 

smoothing process, the actual distribution of 

intensities may be generalized in an 

undesirable way for loss estimation.

(4) The practice in the United States has been, at 

least in the routine intensity investigations of 

the two Federal agencies mentioned above, to 

assign the highest observed intensity to any 

given area, even though this intensity (or 

degree of damage) may not have been widely 

observed. Thus, it is difficult to determine what 

percentage of dwellings in an area assigned a 

particular intensity have actually experienced 

that level of intensity.

The use of intensity data, therefore, poses a 

dilemma. The large data base of intensity observations 

provides only a general guide to the distribution and 

percent damage by class of construction that is required 

for loss assessment. Detailed damage studies as 

presented in this paper are preferable but are usually not

available. Numerous attempts have been made to 

describe damage by class of construction in terms of 

intensity (Algermissen and Steinbrugge, 1978; Applied 

Technology Council, 1985); success has been limited.

Intensity data may possibly be integrated into loss 

studies in another way. Figure 13 shows the distribution 

of intensity with distance (X) from the fault rupture for 

earthquakes in northern California. I is the intensity at 

any distance, and 70 ' is the mean maximum intensity. 

Note that intensities vary around the regression curve by 

several degrees of intensity. Although some of the 

variations in intensity probably reflect errors in 

assignment of intensity, much of the deviation from a 

smooth attenuation curve is related to site response. Site 

response is taken here to mean the modification of 

ground shaking (and hence damage) related to the 

geotechnical properties of the materials beneath the site 

to depths of about 1 kilometer (0.6 mile) or less.

The analysis of these site effects in terms of the 

detailed loss studies in this paper would be a worthwhile 

endeavor as it would provide additional information for 

the estimation of future losses.

Table 28 lists five well-studied earthquakes for 

which intensities shown on the customary isoseismal 

maps can be compared with actual losses. The isoseismal 

map of the 1969 Santa Rosa earthquake (Steinbrugge 

and others, 1970, p. 95) provided the basis for 

reproduction in publications such as "United States 

Earthquakes, 1969" (von Hake and Cloud, 1971). The 

most severely damaged dwelling areas were examined to 

develop a dollar-loss map (Steinbrugge and others, 1970, 

fig. 18). Rinehart and others (1976) then estimated the 

Modified Mercalli Intensities to be V for Zone A, VI for 

Zone B, VII for Zone C, and VIII for Zone D, and 

obtained dwelling values. We computed approximate 

average percent losses for each zone, except Zone D 

where no useable upper bound existed; these 

percentages are listed in table 28.

For the 1971 San Fernando earthquake, Rinehart 

and others (1976, p. 36) refined the Scott (1945) isoseismal map to show zones of MMI VII, VIII, and IX. 

We computed the 13.2 percent loss using the previously 

described individual damage inspections of about 7,890 

houses in the Rinehart and others (1976) MMI IX 

region. Adequate field-inspection data do not exist for 

other intensities.

Table 29 is another viewpoint of the intensity-loss 

correlations of the 1971 San Fernando earthquake. Field 

inspectors were trained for their roles in intensity 

evaluation. A special DAJ intensity scale (Johnsen and 

Duke, 1973) was developed to suit local conditions. In 

general, the DAJ scale was "designed to correspond 

roughly with the Modified Mercalli Scale of 1931" 

(Johnsen and Duke, 1973). The vast majority of the 

observed structures were single-family wood-frame

A56 Estimation of Earthquake Losses to Housing in California
Table 28. Modified Mercalli Intensities and dwelling percent losses: Five California earthquakes

Modified 

Mercalli 

___Earthquake Intensity Percent Loss (and Reference)

1933 Long Beach 

1969 Santa Rosa

1971 San Fernando

1983 Coalinga

1987 Whittier Narrows

VII-IX

VII-VIII

V

VI

VII

X

IX

VIII

VIII

(1)

(2)

(3)

(H)

(5)

Less than 5% (see text under "1933 

Long Beach Earthquake") 

Undetermined 

0.2? 

1.6?

(see text) 

(see text) 

6.8? (see text) 

9.03? (Table 2) 

13.2? (see text) 

20.16? (Table 9); 15.70? (Table 

5.62? (Table 27, ZIP 90601)

11)

Intensities from customary isoseismal maps found in:

(1) Neumann (1935). See Fig. 2 (MMI = VIII) and page 11 (MMI = VII-IX).

(2) Scott (1970) in Steinbrugge and others (1970). See page 95.

(3) Scott (1973). See Fig 2.

(i») Stover (1987). See Fig. 13.

(5) Kawase and Aki (1990). See Figs. 1 and 2.

dwellings; other kinds of construction materials and 

occupancies were commingled. The correlations between 

percent loss and intensity are better than those found in 

table 28 but still not as satisfactory as one might desire 

for loss estimation. MMI X in table 28 probably 

represents maximum rather than average conditions, 

whereas intensities in table 29 probably represent 

average conditions.

Historically, percent loss has been derived from 

intensity. One may view this relationship in the reverse

3

2

i 

o

-i

-2

-3

-4

-5

-6

-7

-8

order by defining intensity in terms of percent loss as 

shown in figure 7 of Rinehart and others (1976). Our 

reexamination of the source data determined that the 

original percent losses were incorrect due to subsequent 

improvements in dwelling component damage ratios and 

also probably due to programming errors in the nolonger-extant original program. Figure 14 shows the 

corrected percent-loss values for all dwellings in each 

tract, regardless of age. Setting these problems aside, the 

general outlines of the intensity areas as a function of

= _ 0.006X 1.196311og[l+(X/10)]

10° 2 468 IQ 1 2 488 1Q Z 2 6 8

10 3

DISTANCE FROM FAULT RUPTURE, IN KILOMETERS

Figure 13. Graph showing intensity versus distance from fault rupture for 

earthquakes in northern California. / is the intensity at distance Xfrom the fault rupture, 

and I0 ' is the mean maximum intensity.

Earthquake Losses to Single-Family Dwellings: California Experience A57
Table 29. Modified Mercalli Intensities and 

dwelling percent losses: 1971 San Fernando 

earthquake

Intensity 

Location

T:13 

T: 14 

T:6

T:5 

T:2

T:3

T:16 

T:10 

T:17 

T:22 

T:12

Percent 

Loss

19.3*

,9$ 

,7* 

.6%

11.6$ 

10.7$ 

 9$

5%

1$ 

9$ 

6$ 

7$

3.7$

Estimated 

DAJ Intensity

8.5

8

8.5

7.5

8

8+

8-

7.5 

6+ or 7

8-

7 

6+ or 7

7

7

Intensity location and percent loss are from unpublished 

data in the flies of K.V. Steinbrugge and S.T. Algermissen.

Intensities from Johnsen and Duke (1973, fig. 1).

percent losses remain similar. The stippling of the tracts 

in figure 14 distinguishes tracts that have losses greater 

than 9 percent from those that have losses less than 9 

percent. One prominent zone of losses greater than 9 

percent is along the base of the San Gabriel Mountains; 

another zone is in an area of ground disturbance on the 

valley floor. These ground disturbances were related to 

surface faulting (plates in Steinbrugge and others, 1971; 

Oakeshott, 1975). A few areas of high percent losses 

extend southwesterly from this zone, which suggests a 

continuation of the ground disturbances. Another small 

zone contains tracts 19 and 31 and may be related to the 

nearby liquified soil area. Had the intensity criteria been 

applied only to new houses, then tracts 16 and 19 would 

have had losses just less than 9 percent, which would not 

have resulted in significant changes to the MMI IX 

zones.

Despite this criticism, isoseismal maps can be 

excellent in a qualitative sense. Consider the 1987 Whittier Narrows earthquake. Figures 8 and 10 compare 

reasonably well with figures 1 and 2 of Kawase and Aki 

(1990).

In summary, isoseismal maps can be used for 

loss-estimation purposes if better data are not available. 

Table 28 exemplifies the problems. Continued 

development of the thinking behind figure 13 is expected 

to produce better results in loss-estimation methods, 

which, in many regions, must rely solely on isoseismal 

maps.

Findings

Insurance-company data are considered to be 

more reliable than our data in the 0-20 percent range 

where such insurance-loss experience exists. Our 

methods are satisfactory for approximate loss 

estimations at 0 percent deductible immediately after the 

earthquake and also for regions where no insurance-loss 

experience exists.

With the presently common 10 percent deductible 

on dwellings in California, it is likely that future 

insurance-loss experience under a 10 percent deductible 

will be limited because most losses are less than 10 

percent. Thus, there is increasing interest and need to 

develop alternate methodologies for estimates of losses 

that might not be covered by insurance.

Somewhat parallel lines of inquiry have been 

followed during the examination of PML and loss over 

deductible, as discussed below.

Probable-Maximum-Loss (PML) Approach

The PML approach is in conventional insurance 

use for all classes of structures. As discussed in the 

appendix, PML has its origin in the commercial and 

industrial insurance markets for which loss estimates are 

commonly made on an individual risk basis. Loss 

estimates for wood-frame dwellings are not commonly 

made on an individual risk basis.

Loss-distribution curves for building classes other 

than wood frame and all metal are approximately

A58 Estimation of Earthquake Losses to Housing in California
S1

(0

5* 

«e

31

(O

«

^""" ^

SAN GABRIEL MOUNTAINS 

A1U14,

x\

\ A<lminls ?l

T:99 Dwelling tract number. 

21* Average loss to dwellings, in percent. 

 « « Average loss not computed (fewer tha 

_____ 25 dwellings).

EMyffxl Tract with 9 percent loss or greate

0 0.5 L

2 MILES

Figure 14. Map showing the city of San Fernando and the Sylmar and Pacoima districts of Los Angeles, which were part of t

Percentages indicate the average losses to dwellings of all ages in the numbered tracts (for example, 14.4 percent in tract 
symmetrical or skewed to the right. As an example of 

skewing to the right, unreinforced-brick masonry 

structures have conventional PML's of 70 percent at 0 

percent deductible. The peak of PML for unreinforcedbrick masonry structures may be about 70 percent, 

whereas the PML for wood-frame dwellings is highest 

from 1 percent to about 9 percent.

The effect of deductibles on aggregate losses for 

high-PML building classes, such as unreinforced-brick 

structures, is much less than that for low-PML dwellings. 

For example, using a 10 percent deductible, a 70 percent 

PML unreinforced-brick structure will have a loss over 

deductible of 60 percent on a simplistic, but realistic, 

analysis basis. Wood-frame dwellings with their low 

PML's must be considered on a more sophisticated basis; 

see appendix under "Sensitivity: Loss over deductible 

versus dwelling PML changes." If the PML and the 

deductible are close, the relationships between them 

must become more complex to preserve accuracy.

The softness in the dwelling PML values is evident 

in all distribution curves. The weaknesses in the PML 

approach when applied to dwellings warrants an 

examination of an alternative approach, such as one 

based on loss-over-deductible experience.

Loss-Over-Deductible Approach

Loss-over-deductible curves and data from various 

sources and earthquakes were adjusted for 

commonalities in construction and geologic conditions 

and also modified for a variable magnitude.

Equations for loss over deductible are given below 

and are applicable for the range of 0-20 percent deductble. These equations apply to one-story, one-and-twostory, split-level, and two-story wood-frame dwellings 

that have floors of any kind with exclusions as previously 

mentioned. The regression equations used data from 

table 17. Arrangement of the terms in the equations is:

(Loss over deductible) = (State factor from table 21) x

(magnitude factor) x 

(regression equation with 

uncertainty factor F )

Equation 1, pre-1940:

y =(1.00) x (0.114 M +0.259) x(8.354 Fe-° « * x )

Equation 2, post-1939:

y =(1.09) x (0.114 M+0.259) x (3.308 F e-° '«« * ) 

Equation 3, all ages:

y = (1.18) x (0.114 M + 0.259) x (4.251 F r°-»°« x )

where Y = loss over deductible, in percent, 

X deductible, in percent 

M = earthquake magnitude, and 

F = uncertainty factor (1.50, but

user-changeable).

Simplifying for general use, with M = 8.25 as the 

maximum credible magnitude:

Equation 4, pre-1940: Y = 15.031 

Equation 5, post-1939: Y = 6.488 e-° -1843 x 

Equation 6, all ages: Y = 9.025 <?-°- 1053 x 

Table 22 is derived from equations 4-6. Values in 

this table include an uncertainty factor of 1.50, and the 

values may be changed to any other factor by direct 

proportion. Figure 15 is a graphical representation of 

equations 4-6.

The loss-over-deductible approach acknowledges 

that dwellings can be treated differently from mercantile 

and commercial structures in both insurance and 

governmental loss-estimation methods. It is a direct 

approach and, although the data remain inadequate, is

5 10 15 

DEDUCTIBLE, IN PERCENT

20

Figure 15. Graph showing recommended loss over 

deductible versus deductible, based on equations 4-6.

A60 Estimation of Earthquake Losses to Housing in California
far better for use with dwellings than the approaches that 

are commonly used with non-dwelling structures. Finally, 

the readily changeable "uncertainty factor" is more easily 

understood and applied than is the "9 out of 10" PML 

definition.

For these reasons, we prefer the lossover-deductible approach.

Applications to Simpler Methods

The California Department of Insurance uses a 

class PML that is applicable to all dwellings in each zone. 

The zones normally have political boundaries, which are 

influenced by major known active faults. The class PML 

does not directly recognize differences in soil conditions 

or distances from potential earthquakes. Exceptions are 

Zones A and B where subzones were established to 

consider partially the distance from potential 

earthquakes (Steinbrugge, 1982, chap. 9).

A better PML for dwellings can be established for 

each zone that has major known faults using a method 

based on an updated census inventory of dwellings and 

values. The maximum aggregate loss for the zone can be 

developed if the inventory data are processed by more 

sophisticated loss-estimation methods. These methods 

include variables such as the magnitude of the maximum 

credible earthquake, damage attenuation with distance, 

and soil factors. This maximum aggregate loss should 

equal the aggregate loss from the Department of 

Insurance's PML methods for each zone. It is possible 

for the Department of Insurance's percent PML for each 

zone to be changed so that the losses computed by each 

method are equal.

For a computational example, assume that the 

more sophisticated methods determined a $10 billion 

aggregate loss in a given zone that has no subzones. The 

aggregate losses are computed by the Department of 

Insurance by multiplying aggregate values in that zone by 

the Department of Insurance-assigned percent PML. 

Equating this $10 billion loss to this method:

$10 billion = (aggregate dwelling values, in billions

of dollars) x (PML, in percent),

with the unknown being the PML. This PML is an 

average value for the zone and includes effects from soils 

and distances from faults. The PML can be applied to any 

other inventory of dwellings that is distributed in a 

manner reasonably consistent with the general housing 

throughout the zone. This is the normal case.

Other Findings

Older dwellings did not perform as well as did 

newer dwellings, with the dividing date being 1940. This 

decision was made in 1971 and has been maintained for 

the purpose of data consistency. The current validity of

this 1940 dividing date was examined on a decadeby-decade basis for the 1987 Whittier Narrows 

earthquake using all the information from Insurance 

Source C:

Number of 

Age Group dwellings Percent loss

Pre-1920

1920-29

1930-39

1940-49

1950-59

1960-69

1970-79

92

382

534

1526

5994

5440

3996

0.74

1.29

0.70

0.24

0.23

0.21

0.07

The percent loss is the average for all dwellings in 

their respective age groups. We judge that the 1940 

dividing date remains appropriate, that is, pre-1940 and 

post-1939 construction.

Structures with supported-wood first floors did not 

perform as well as did those with concrete slabs on grade 

if age was not a factor. However, performance was about 

equal among newer structures.

Recommendations

Overall, the available records of quantified loss 

experience for dwellings remain unsatisfactory. In 

addition, this experience is only from moderate 

earthquakes, and extrapolations to the maximum 

credible earthquake require major judgmental 

considerations for insurance purposes. These judgmental 

considerations need much more study. Isoseismal maps 

are the only recourse in some circumstances.

Appropriate data gathering after all damaging 

events should be conducted on a consistent and unified 

basis. The effort should include the public and private 

sectors. Gathered information should be made available 

in a prompt manner to all interested so that many 

investigators can study the losses. It may best be 

accomplished through an entity having this goal as one of 

their mandates. Funds possibly can come from some type 

of charge to financial institutions and others having a 

need to know. Logical entities can include state, Federal, 

and the insurance industry, among others. Data 

gathering should include much more than dwellings. The 

kinds of gathered information may be based on the 

California Department of Insurance's "Call for Data" for 

loss experience on the 1989 Loma Prieta earthquake 

("San Francisco" earthquake).

Earthquake Losses to Single-Family Dwellings: California Experience A61
REFERENCES CITED

Algermissen, S.T., and Steinbrugge, K.V., 1978, Earthquake 

losses to buildings in the San Francisco Bay area, in 

Proceedings of the Second International Conference on 

Microzonation: v. I, 13 p.

Applied Technology Council, 1985, Earthquake damage 

evaluation data for California, ATC-13: Redwood City, 

Calif., 492 p.

California Department of Insurance, 1981 [and annually 

thereafter], California earthquake zoning and probable 

maximum loss program, 54 p.

Johnsen, K.E., and Duke, CM. 1973, Damage distribution in 

the Sylmar Valley area, in San Fernando, California, 

Earthquake of February 9, 1971: National Oceanic and 

Atmospheric Administration, U.S. Department of 

Commerce, v.l, pt. B, p. 801-813.

Kawase, H., and Aki, K. 1990, Topography effect at the critical 

SV-wave incidence Possible explanation of damage 

pattern by the Whittier Narrows, California, earthquake 

of 1 October 1987: Seismological Society of America 

Bulletin, v. 80, p. 1-22.

Lawson, A.C., ed., 1908, The California earthquake of 1906, 

report of the State Earthquake Investigation 

Commission: Carnegie Institution of Washington, 2 

volumes plus atlas.

Martel, R.R., 1936, Earthquake damage to Type III buildings in 

Long Beach, 1933, in Earthquake investigations in the 

Western United States, 1931-1935: U.S. Department of 

Commerce, p. 143-162, 1 pi. [Reprinted in Earthquake 

investigations in the Western United States, 1931-1964: 

U.S. Department of Commerce, Coast and Geodetic 

Survey publication 41-2, p. 213-222, 1965.]

McClure, F.E., 1973, Performance of single family dwellings in 

the San Fernando earthquake of February 9, 1971: U.S. 

Department of Housing and Urban Affairs and the U.S. 

Department of Commerce, 95 p., plus appendices.

Neumann, Frank, 1935, United States earthquakes 1933: Coast 

and Geodetic Survey, U.S. Department of Commerce, 

Serial 579, 83 p.

Oakeshott, G.B., ed., 1975, San Fernando, California, 

earthquake of 9 February 1971: California Division of 

Mines and Geology, 436 p., plus plates.

Real Estate Research Council of Northern California, 1988, 

Northern California real estate report: San Francisco, 

Calif., v. 40, no. 1.

Real Estate Research Council of Southern California, 1988, 

Real estate and construction report, 2d quarter 1988: 

Pomona, Calif., California State Polytechnical 

University.

Rinehart, W., Algermissen, S.T., and Gibbons, Mary, 1976, 

Estimation of earthquake losses to single family 

dwellings: U.S. Geological Survey Open-File Report 

76-156, 57 p., plus 7 appendices.

Scott, N.H. 1970, Felt area and intensity, Santa Rosa, 

California, earthquakes, October 1,1969, in Steinbrugge, 

K.V., Cloud, W.K., and Scott, N.H., The Santa Rosa, 

California, earthquakes of October 1, 1969: Coast and 

Geodetic Survey, U.S. Department of Commerce, p. 

94-99.

___ 1973, Felt area and intensity of San Fernando 

earthquake, in San Fernando, California, earthquake of 

February 9, 1971: National Oceanic and Atmospheric 

Administration, U.S. Department of Commerce, v. 3, p. 

23-48.

Steinbrugge, K.V., 1982, Earthquakes, volcanoes, and tsunamis An anatomy of hazards: New York, Skandia, 392 p.

___ 1986, Comment on the use and misuse of Modified 

Mercalli Intensities, in Future directions in evaluating 

earthquake hazards of southern California: U.S. 

Geological Survey Open-File Report 86-401, p. 

147-156.

Steinbrugge, K.V., Algermissen, ST., and Lagorio, H.J., 1984, 

Determining monetary losses and casualties for use in 

earthquake mitigation and disaster response planning, in 

Proceedings 8th World Conference on Earthquake 

Engineering, San Francisco, California, July 21-28,1984: 

Prentice-Hall, v. VII, p. 615-622.

Steinbrugge, K.V., Cloud, W.K., and Scott, N.H., 1970, The 

Santa Rosa, California, earthquakes of October 1, 1969: 

Coast and Geodetic Survey, U.S. Department of 

Commerce, 99 p., plus plates.

Steinbrugge, K.V., Fowkes, E.J., Lagorio, H.J., and Algermissen, S.T., 1990, Dwelling monetary losses, Chap. 20, in 

Rymer, MJ., and Ellsworth, W.L., eds., The Coalinga, 

California, earthquake of May 2, 1983: U.S. Geological 

Survey Professional Paper 1487, p. 359-380 [in press].

Steinbrugge, K.V., and Schader, E.E., 1973, Earthquake 

damage and related statistics, in San Fernando, 

California, earthquake of February 9, 1971: National 

Oceanic and Atmospheric Administration, U.S. 

Department of Commerce, v. 1, pt. B, p. 691-724.

Steinbrugge, K.V., Schader, E.E., Bigglestone, H.C., and 

Weers, C.A., 1971 [undated], San Fernando earthquake, 

February 9, 1971: San Francisco, Pacific Fire Rating 

Bureau, 93 p.

Stover, C.W., ed., 1987, United States earthquakes, 1983: U.S. 

Geological Survey Bulletin 1698, 197 p.

___ed., 1988, United States Earthquakes, 1984: U.S. 

Geological Survey Bulletin 1862, 179 p.

von Hake, C.A., and Cloud, W.K., 1971, United States 

earthquakes, 1969: National Oceanic and Atmospheric 

Administration, U.S. Department of Commerce, 80 p.

Wood, H.O., and Neumann, Frank, 1931, Modified Mercalli 

Scale of 1931: Seismological Society of America Bulletin, 

v. 21, p. 277-283.

A62 Estimation of Earthquake Losses to Housing in California
PROBABLE-MAXIMU M-LOSS 

BACKGROUND INFORMATION
APPENDIX

PROBABLE-MAXIMUM-LOSS 

BACKGROUND INFORMATION

Definition of Probable Maximum Loss

Probable maximum loss (PML) is a term 

commonly used in California earthquake-insurance loss 

estimation. The California Department of Insurance 

(1981, p. 6) defined PML in "California earthquake 

zoning and probable maximum loss evaluation program" 

as follows:

The probable maximum loss for an individual 

building is that monetary loss expressed in dollars (or as a percentage of insured value) under 

the following conditions:

(a) Located on firm alluvial ground or on equivalent compacted man-made fills in a probable 

maximum loss zone (defined later), and

(b) Subjected only to the vibratory motion from 

the maximum probable earthquake, that is, not 

astride a fault or in a resulting landslide.

The building class probable maximum loss 

(class PML) is simplistically defined as the expected maximum percentage monetary loss 

which will not be exceeded for 9 out of 10 buildings in a given earthquake building class under 

the conditions stated in the previous paragraph. 

The loss to the tenth building may be quite 

anomalous due to poor design or construction 

peculiarities, or to unusual earthquake motions 

and building response, or geologic hazards. *** 

Henceforth, when PML is stated in this report, 

class PML is the intent unless the context of the 

text is clearly to the contrary.

The California Department of Insurance (1981, 

and annually thereafter) report for 1989 states on page 

24: "PML, for the purposes of this report, is defined as 

the average probable maximum insured loss which will 

be experienced by 9 out of 10 buildings (the atypical loss 

being excluded) in a given earthquake building class in a 

specified earthquake zone."

Further information may be found in Steinbrugge 

(1982, chap. 9). The 1981 PML definition, if applied to 

dwellings, must be considered in the context of its 

commercial/industrial origins, as discussed in the 

following section.

Zones used by the California Department of 

Insurance are practical applications of a geologic model. 

The California geologic PML zone applies to the 

maximum credible earthquake for insurance purposes on

each insurance-important fault. Some insuranceimportant faults are the San Andreas, Hayward, 

Calaveras, Newport-Inglewood, Whittier, Elsinore, Malibu, Raymond, San Fernando, San Jacinto, Imperial, 

Arroyo Parida, and Rose Canyon faults, among others, 

all of which are insurance important due to being in 

heavily populated areas. The geologic zone boundary is 

defined as being 6 miles on either side of a strike-slip 

fault rupture such as found on the San Andreas fault. For 

other types of faults, the surface projection of the seismic 

energy modeled as a line source at depth replaces the 

surface rupture. The maximum credible earthquake on a 

major fault, which is implicit in the definition of PML, 

normally results in rupture of the surface. Where the 

geologic model does not apply, such as the central valleys 

of California, county boundaries are selected on the basis 

of area and population.

Origin of Wood-Frame-Dwelling 

Probable Maximum Loss

PML loss-estimation methods were developed over 

a period of years by the structural engineers of the Pacific 

Fire Rating Bureau. Applications were limited to 

commercial and industrial buildings on an individual risk 

basis. These dollar PML's were used by company 

underwriters to determine their lines and, for several 

companies, to determine their aggregate losses over 

deductible on an individual-risk basis.

Dwellings were included in the building 

classification system of the Pacific Fire Rating Bureau 

and its successor Insurance Services Office. As a 

consequence, a PML for wood-frame dwellings was also 

available; this was a secondary consideration because the 

underwriters of specific risks almost never asked for data 

on such dwellings. Although PML methods were widely 

known and used in California, most of this information 

was not published prior to the beginning of the California 

Department of Insurance's earthquake program in 1981.

The original concept of earthquake PML was 

patterned after fire whereby emphasis was placed on a 

single building or group of buildings at a specific site. 

This is an appropriate basis for a conservative loss 

estimate for a single risk in the event of a severe 

earthquake located in the near vicinity. Clearly, buildings 

situated miles away from the shock will experience lesser 

damage. It follows that 1,000 wood-frame dwellings 

spread over a large area would not experience the PML 

at each site if located on firm soil. Secondly, the "9 out of 

10 dwellings having that PML loss or less," although 

reasonable for a single structure if underwritten on that 

basis, may become quite conservative for 1,000 dwellings 

that are scattered throughout an underwriting zone.

A64 Estimation of Earthquake Losses to Housing in California
A 7 percent PML was established for dwellings on 

the basis of the 1933 Long Beach experience, which was 

the only data available at that time. Subsequent 

discussions in the 1970's asked if an 8 percent PML 

would be more appropriate, but no action was taken to 

apply the 1971 San Fernando experience.

The California Department of Insurance (1981) in 

its first report adopted the commonly used PML values 

for all classes of construction, including 7 percent PML 

for dwellings (at that time the deductible was 5 percent). 

This had the concurrence of the National Committee on 

Property Insurance. It was a reasonable decision for 

dwellings in view of the State budget constraints, time 

requirements for program implementation, companies' 

abilities to respond, and objectives of the program at that 

time. The common deductible has risen from 5 percent to 

10 percent since then, and the latter value is usually given 

emphasis in this study.

Sensitivity: Loss Over Deductible versus 

Dwelling PML Changes

There is frequent confusion when using the term 

"percent PML." The commercial/industrial underwriters 

emphasize individual risks in their loss evaluations, 

whereas the personal lines underwriters emphasize large 

numbers of risks. Commonly stated, the percent PML 

minus the percent deductible is the percent loss over 

deductible. In a mathematical sense:

(percent PML) - ( percent deductible) =

( percent loss over deductible)

These terms may be re-arranged:

(percent PML) = (percent loss over deductible)

+ (percent deductible)

This latter form is used in the following discussion. 

The percent PML for wood-frame dwellings is not a fixed 

value because it is always in the context of a deductible 

plus the loss over deductible. For example, consider a 

damaging earthquake during which 1,000 wood-frame 

dwellings in a small area are subjected to the same severe 

ground motion. First, assume that two dwellings are total 

losses and the others have losses distributed between 0 

percent and 100 percent. With a 10 percent deductible 

and using the current State of California's 1.5 percent 

loss over deductible, the result is a 11.5 percent PML. 

Next assume a highly improbable deductible of 95 

percent. There still would be at least two dwelling losses 

greater than the 95 percent deductible. The percent PML 

for the 1,000 houses would therefore have to be the 95 

percent deductible plus a very small loss over deductible 

to reflect the two total losses plus any other losses 

between 95 percent and 100 percent. In summary, the 

percent PML varies as a function of the percent 

deductible and may never be less than the percent 

deductible.

If the percent PML is close to the percent 

deductible, as in the case of wood-frame dwellings, the 

percent loss over deductible is very sensitive to any 

change in the percent PML. Consider a 10 percent 

deductible with a 11.5 percent PML for wood-frame 

dwellings. For $1 billion in wood-frame-dwelling 

liabilities, the loss over deductible would be 1.5 percent 

of $1 billion, or $15 million. However, should the 

maximum credible earthquake actually produce a 12.5 

percent PML, instead of an 11.5 percent PML, then the 

loss over deductible would be 2.5 percent, or $25 million. 

In this case, a 1 percent increase in the percent PML 

creates a 67 percent increase in the aggregate dollar 

PML.

Earthquake Losses to Single-Family Dwellings: California Experience A65

U.S. GOVERNMENT PRINTING OFFICE:1990 775-564