Vertical Crustal Movements in 

Southern California, 1974 to 1978 

By Robert 0. Burford and Thomas D. Gilmore 

U.S. GEOLOGICAL SURVEY CIRCULAR 905 

1984 
Department of the Interior 

WILLIAM P. CLARK, Secretary 

U.S. Geological Survey 

Dallas l. Peck, Director 

Library of Congress catalog-card No. 84-601 023 

Free on application to Distribution Branch, Text Products Section, 

U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 
CONTENTS 

Page 

Abstract ----------------------------------------------------------------------------------------------------------------- 1 

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

Acknowledgments ---------------------------------------------------------------------------------------------------- 3 

Vertical movements in southern California during the period 1959 to 1974n6 --------------------- 3 

Evaluation of 1978 leveling ---------------------------------------------------------------------------------------- 5 

Comparison of 1978 leveling with surveys completed between 1972 and 1976 --------------------- 9 

Timing and nature of the reversal in vertical movement suggested by other observations ---- 15 

Cumulative vertical displacements during the period 1959 to 1978 ----------------------------------- 18 

Continued northward tilting after the 1978 leveling ------------------------------------------------------- 21 

Conclusions --------------------------------------------------------------------------------------------------------------- 21 

References cited ------------------------------------------------------------------------------------------------------ 2 2 

ILLUSTRATIONS 

FIGURE 1. Index map of routes leveled during the Southern California Releveling Program (SCRP) between January and 

Page 

May, 1978 ----------------------------------------------------------------------------------------------------------------------------------- 2 

2. Vertical displacements in southern California between 1959 and 1974 measured with respect to bench mark Tidal 

8 adjacent to San Pedro tide station ---------------------------------------------------------------------------------------------- 4 

3. Index map of routes leveled between 1972 and 1976 that are common to the 1978 SCRP network ----------------- 10 

4. Compilation of height changes in millimeters at major junctions for circuits 17 and 18 -------------------------------- 12 

5. Map showing changes in heights in southern California relative to bench mark Tidal 8 adjacent to the San Pedro 

tide station, based on comparisons between the results of 1972/76 and 1978 levelings ---------------------------- 14 

6. Changes in heights in southern California, based on comparisons of 1972176 and 1978 leveling results along the 

routes indicated in figure 3 after removal of estimated nontectonic height decreases in known subsidence 

areas; epicenters of earthquakes recorded from January 1, 1974, through December 31, 1978 ---------------- 16 

7. Pattern of residual height changes (1959-78) relative to bench mark Tidal 8 ----------------------------------------------- 19 

8. Profiles showing heights and height changes since 1973/74 along the route from San Pedro, via Burbank and 

Saugus to the position of the San Andreas fault zone near Lebec ------------------------------------------------------- 20 

TABLES 

Page 

TABLE 1. Lengths and closures of circuits, 1978 SCRP network -------------------------------------------------------------------------- 5 

2. Statistical evaluation of selected parts of the SCRP network ---------------------------------------------------------------- 8 

3. Lengths and closures of circuits, 1972176 network ------------------------------------------------------------------------------- 11 

III 

Vertical Crustal Movements in Southern California, 

1974 to 1978 

By Robert 0. Burford and Thomas D. Gilmore 

ABSTRACT 

An extensive resurvey of most of the first-order leveling 

network in southern California, known as the Southern California Releveling Program (SCRP), was carried out during the 

first 5 months of 1978. The primary scientific purpose of these 

measurements was to rapidly update the vertical control record 

throughout a recently uplifted region of southern California in 

order to more thoroughly document the vertical component of 

tectonic movement and to provide a reliable base for comparison with future levelings. Analyses of historic first-order leveling results have clearly demonstrated that a broad crustal upwarping, largely contained within a region consisting of the 

Transverse Ranges province and an area along the intervening 

section of the San Andreas fault system, had developed between about 1959 and 1974. Unfortunately, there is strong evidence that parts of the 1978 SCRP data are contaminated by 

the effects of intrasurvey tectonic deformation, limited surficial 

failures, and, less certainly, magnetically induced systematic 

error associated with the use of automatic levels. However, any 

distortions in leveling results caused by these or other factors 

are not so serious as to render the SCRP data useless. In fact, 

the bulk of these data can be accepted at face value, and most 

of the remaining data can be incorporated with some caution to 

augment the more reliable parts of the network. The evaluation 

of the 1978 leveling is based on a combination of circuit-misclosures, local timing of the field observations, analysis of profiles 

of apparent height changes derived from comparisons with previous levelings, and an analysis of the position and orientation 

of the various routes in relation to the regional structural grain 

and the gradients of differential vertical motion established by 

previous investigations. Comparisons of the 1978 SCRP results 

with the latest of the previous surveys along each route retained in the analysis show that all but about one-third of the 

uplift established by leveling data from 1959 to the combined 

1974/76 survey period had relaxed by early 1978 through tectonic subsidence. Subsequent limited relevelings along several 

of the 1978 routes show that rapid tectonic subsidence probably 

continued through at least early 1979. Despite the pronounced 

down-to-the-northeast (northeastward) tilt that developed between 1976 and early 1978, the overall shape of the uplift was 

well preserved. Results of repeated trilateration surveys since 

1971 demonstrate that a remarkably uniform and nearly 

1 

monotonic negative dilatational strain-change trend reversed 

abruptly between 1977 and 1979. The change from tectonic uplift to tectonic subsidence is associated with this reversal in 

horizontal strain accumulation. The reversal in strain trend was 

expressed as a cessation of the essentially uniaxial north-south 

contraction, which had been accumulating at about 2 x 10- 7 /yr 

(or 0.2 j.LStrain/yr), accompanied by onset of uniaxial east-west 

extension at about 5 x 10- 7/yr (or 0.5 j.LStrain/yr). Minor earthquakes and occasional swarms of moderate earthquakes were 

particularly abundant during 1978 and 1979 in conspicuously 

mobile regions such as the eastern Transverse Ranges and the 

Salton Trough, areas respectively characterized by nearly complete collapse of the previous maximum uplift and by a dramatic 

enhancement of the previously identified tectonic subsidence. 

INTRODUCTION 

A comprehensive resurvey of most of the primary vertical-control network in southern California (fig. 1), funded through the U.S. Geological 

Survey (USGS) and coordinated by the National 

Geodetic Survey of the National Oceanic and Atmospheric Administration (NGS/NOAA), was 

accomplished during the first 5 months of 1978. 

This multiagency observational effort, known as 

the 1978 Southern California Releveling Program 

(SCRP), was conducted by 18 leveling and five 

gravity teams from NGS and USGS, and by 20 additional leveling teams from Ventura, San Diego, 

San Bernardino, Riverside, Orange, Los Angeles, 

and Imperial Counties, the City of Los Angeles, 

the Los Angeles Water and Power Department, 

and the Metropolitan Water District of Southern 

California. During a period of peak effort, 42 teams 

were simultaneously engaged in SCRP field observations. 

The objective of the 1978 regional leveling was 

to establish a highly precise vertical-control base 
!:..;) 

35° 

34° 

33° 

120° 

EXPLANATION 

___. Leveling route showing 

junction marks 

CD 

.,0 

--1'0~ 7c 

Network circuit number 

119° 

0 20 40 60 80 KILOMETERS I I I I I I I I I 

118° 

0~ 

'--1'4--

117° 116° 115° 

Goffs 

FIGURE I.-Index map of routes leveled during the Southern California Releveling Program (SCRP) between January and May, 1978. Data on circuit lengths and on 

observed and orthometrically corrected circuit misclosures presented in table 1 are keyed to numbers shown for network circuits. Shaded areas indicate SCRP circuits with observed misclosures in excess of allowable limits for first-order, class I leveling. 
within as short a period as possible, thereby 

minimizing the effects of possible contemporaneous 

deformation. Vertical control provided by SCRP 

was intended to serve as a reliable reference for 

comparisons with results of both past and future 

levelings to comprehensively document the vertical component of tectonic movement in southern 

California. The SCRP measurements were 

prompted by the discovery of a broad, regional uplift that developed between 1959 and 1974 (fig. 2), 

as established through comparison and analysis of 

numerous, yet somewhat scattered, vertical control surveys repeated in parts of the region at various times during the past half century (Castle and 

others, 1976; Castle, 1978; Castle and others, 1984; 

National Geodetic Survey, 1978). 

Unfortunately, SCRP operations were seriously hampered by weather-related delays. The 

operation was scheduled for the winter months of 

1978 in the hope that generally cool, moderate 

weather conditions over the entire area would enhance both data quality and the efficiency of its collection. However, from the last few days of January through most of March, southern California 

was subjected to heavy precipitation, including locally heavy snowfall in the mountains, that constituted the single wettest season during this century. Observations along many of the leveling 

routes were consequently disrupted, and in several 

cases leveling was delayed for weeks to months. 

These delays were particularly damaging in light 

of the unusual patterns of deformation apparently 

in progress during the extended field observations 

(Raleigh and others, 1982; Jachens and others, 

1983). It is also possible that errors were introduced by the general destabilizing effect of 

heavy rainfall on certain bench marks, especially 

those set in soils or in outcrops of sedimentary 

rocks either rich in expansive clays or susceptible 

to slope failure. Weather-related destabilizing effects may have been particularly prevalent in the 

coastal areas, where generally more susceptible 

surface materials were subjected to heaviest rainfall. 

Despite some uncertainty concerning the reliability of the SCRP results, the data adequately 

augment and update the documentation of continuing, often rapid vertical movement within the general region of the southern California uplift. This 

report assesses the quality of the 1978 leveling 

data and presents the results of a preliminary analysis of vertical displacements that occurred in 

3 

southern California between about 197 4 and 1978. 

ACKNOWLEDGMENTS 

Suggestions and discussions regarding leveling data and the details and interpretation of features of the southern California uplift shared by 

Bob Castle were especially helpful. Ross Stein provided unpublished 1979 leveling data and offered 

several constructive suggestions for improving the 

manuscript. The manuscript was also improved in 

response to the critical reviews and suggestions of 

Mike Elliott and John Tinsley of the U.S. Geological Survey. Emery Balazs of the National Geodetic 

Survey provided statistical data concerning the 

quality of the 1978 observations and answered 

many routine queries concerning other aspects of 

the leveling data. Several critical questions regarding the field observations were resolved with 

the help of Bob Wilson and other members of the 

Office of the County Engineer, Los Angeles 

County, and Donald Tillman and David Dona of the 

Bureau of Engineering, City of Los Angeles. 

VERTICAL MOVEMENTS IN 

SOUTHERN CALIFORNIA 

DURING THE PERIOD 1959 TO 1974/76 

Critical examination and analysis of historical 

leveling data have established that a broad crustal 

uplift, ranging between a few tenths to almost half 

a meter and encompassing nearly 90,000 km2 of 

southern California, developed between 1959 and 

19741761 (Castle and others, 1976; Castle, 1978; 

Castle and others, 1984). The shape of the uplift 

corresponds in several ways to the regional structural grain: from the vicinity of Point Conception 

west of Santa Barbara, the axis of uplift trends 

eastward along the north side of the western 

Transverse Ranges, swings northward to the crest 

of the Tehachapi Mountains just northwest of the 

Garlock fault near Mojave, turns southeastward 

and follows the northeast margin of the San Andreas fault zone through Palmdale to a point near 

the crest of the San Bernardino Mountains, and 

then trends eastward along the axis of the eastern 

Transverse Ranges north of the Salton Trough region (fig. 2). Maximum tilting occurred along the 

1 Dates separated by slashes refer to surveys performed during the stated 

years. Thus, "1974176" indicates that leveling done from 1974 through 1976 is combined and considered as a single survey line. 
120° 119° 118° 117° 116° 115° 

/--..................... 

~ 

' I San Luis Obispo 

~0 

Avila 

35° r Beach 

I ( \ } / /// ~u,:.-Lebe~~ loJav~w..........._ __ 250----_ "-, 

\ 

\ \ \ \ \ 

\ ------- ~ / .StJO-- \~ \ \ \ \ .._so Altll 

\ '-..... o -=-Santa ""- 0-<le 

'.s: Barbara -- .s: un ,4oo Freda " VenMa _ ", l~ '-' ( <.q.o- -;,.,.._~ ~ Junction! 

~ 34° ~ ....____......- I J J 

EXPLANATION ~~Q ~ / j 

~ ~ I .--too- C ,~ cJ~ I J 

Isobase of equal height change- Dashed '\ I 1 

where estimated or extrapolated; bach ures ~0 indicate closed depressions. Contour interval / 

50 mm ~ 

Q 

------ ~ Fault-Dashed where inferred '-"1'~ 

I 

33° 

0 20 40 60 80 100 KILOMETERS 

FIGURE 2.-Vertical displacements in southern California between 1959 and 1974 measured with respect to bench mark Tidal 8 adjacent to San Pedro tide station (from 

Castle and others, 1984, fig. 64). 
south-southwest flank of the uplift, which generally coincides with steeper terrain along the south 

or southwest slopes of the western Transverse 

Ranges, the San Gabriel Mountains, and the eastern Transverse Ranges. Strong down-to-the-north 

(northward) tilting also developed at least locally 

on the north side of the uplift, especially in the vicinity of Bakersfield, and although not as completely documented, it was generally more subdued than the south-southwest tilting along the 

south flank of the uplift. 

EVALUATION OF 1978 LEVELING 

Misclosures based on observed elevation differences exceeded the acceptable limits for firstorder, class I leveling (defined as 4 mmlkm 112 

x ~ where K is the circuit length in kilometers) in five of the 20 circuits that compose the 

SCRP network. These above-limits misclosures 

are clustered in the south-central and western 

parts of the network (fig. 1), whereas the rest of 

the circuits have misclosures that are remarkably 

low (table 1). It is noteworthy that the mean misTABLE 1.--Lengths and closures of circuits, 1978 SCRP network 

CN--Circui t number as given on map of figure 1., 

K--Circuit length in kilometers. 

S--Circuit-misclosure specifications (allowable limits) for first-order, 

class I leveling, in millimeters (4 mm/km~ x~). 

OM--Observed circuit misclosures in millimeters (clockwise). 

OC--Orthometric corrections for circuit closures in millimeters (clockwise) 

based on observed gravity. 

OCM--Orthometrically corrected clockwise misclosures in millimeters (OCM = OM + OC). 

RM--Refraction-corrected orthometric misclosures in millimeters (Holdahl 

model) (National Geodetic Survey, written commun., Dec. 1981). 

D/I--Deterioration or improvement of refraction-corrected misclosure over 

orthometrically corrected misclosure alone (positive values designate 

improvement, negative values deterioration). 

* Indicates that observed misclosure is in excess of limits specified for 

first-order, class I leveling. 

CN K s OM oc OCM RM D/I 

(fig. 1) (km) (mm) (mm) (mm) (mm) (mm) (mm) 

1 569.0 +95 -231. 7* +75.2 -156.5 -159.3 -2.8 

2 287.9 "+68 88.2* +15.6 103.8 74.3 +29.5 

3 275.4 "+66 2.1 +2.0 4.1 3.4 +0.7 

4 83.5 +37 -2.4 +9.6 7.2 13.6 -6.4 

5 109.0 "+42 5.9 -9.0 -4.9 -13.9 -9.0 

6 148.1 "+49 17.5 -1.2 16.3 32.1 -15.8 

7 263.6 "+65 82.3* +7.1 89.4 82.4 +7.0 

8 374.3 "+77' -72.7 +2.0 -70.7 -96.4 -25.7 

9 295.6 "+69 -38.6 +25.9 -12.7 56.5 -43.8 

10 205.9 "+57 -30.1 +9.8 -20.3 -28.4 -8.1 

11 366.7 "+77 -0.7 -9.6 -10.3 -12.3 -2.0 

12 255.7 "+64 -67.3* +7.2 -60.1 -82.3 -22.2 

13 236.5 "+62 -116.5* +1.3 -115.2 -108.3 +6.9 

14 599.7 "+98 -20.2 -16.2 -36.4 -31.3. +5.1 

15 305.0 "+70 -43.7 +20.5 16.8 35.2 -18.4 

16 424.6 "+82 53.6 -27.5 26.1 16.7 +9.4 

17 252.4 "+64 56.3 -11.3 45.0 9.4 +35.6 

18 407.2 +"81 11.8 -17.1 -5.3 0.4 +4.9 

19 417.7 "+82 26.4 -47.6 -21.2 -20.2 +1.0 

20 74.4 +35 14.1 +0.1 14.2 12.7 +1.5 

Mean values ----- +67 +49.1 +42.0 +44.0 -=5T.O 

(sum) 

5 
closure for all SCRP circuits is only ± 49 mm, in 

comparison with an average tolerance of ± 67 mm, 

and that positive and negative misclosures are approximately balanced throughout the network. 

Since misclosures in observed height differences around leveling circuits serve primarily as a 

field check for the work as it progresses, orthometric corrections based on observed gravity values 

(Vanicek and others, 1980) have been applied to 

each of the SCRP circuits in order to convert pathdependent observed elevation differences into 

uniquely defined true height differences. Orthometric corrections for each of the circuits are 

presented in table 1, along with the residual, orthometrically corrected misclosures. These corrections reduce the misclosures for all but six of the 

circuits, and the reductions are especially significant for circuits 1, 9, 10, and 15 through 18. After 

application of orthometric corrections, the misclosure around circuit 12 is brought to within acceptable limits, and the mean value of the circuit misclosures is reduced to ± 42 mm. 

Although they are important indicators of survey accuracy, circuit misclosures alone are less 

than comprehensive indices of the quality or reliability of leveling data over an entire network. For 

instance, compensating errors in different seg- · 

ments of a circuit might result in an acceptable closure, although such errors occurring on opposite 

sides of a junction with branching routes would 

produce distortions in adjacent circuits. Furthermore, excessive closure errors do not necessarily 

indicate leveling or recording blunders. Instead, 

they may result from systematic accumulation of 

height-, slope-, or azimuth-dependent errors, or, in 

tectonically active regions such as southern 

California, from contamination of leveling results 

due to intrasurvey tectonic deformation. The records of repeated levelings in southern California 

contain a number of well-documented examples of 

the effects of intrasurvey or intersurvey deformation (Castle and Elliott, 1982; Castle and others, 

1983; J achens and others, 1983), whereas clearly 

documented cases of significant systematic error 

are comparatively rare (Mark and others, 1981). 

The potential fo:r contamination of geodetic 

leveling by height- or slope-dependent systematic 

error has been recognized since the 1890's and has 

been explored in depth by a number of investigators (Bomford, 1971; Vanicek and others, 

1980). It is the recognition or suspicion of potential 

systematic errors that has dictated many of the 

rigorous procedural requirements stipulated for 

geodetic leveling and has also encouraged a progressive tightening of these standards through 

time (Department of Commerce, Coast and Geodetic Survey Special Publications Numbers 18, 39, 

and 239; Federal Geodetic Control Committee, 

1974; Vanicek and others, 1980, fig. 2). Rigorous 

analyses show no clear or compelling evidence for 

systematic error in the 1978 data of the magnitude 

necessary to account for the larger misclosures 

(Stein, 1981, fig. 10; Mark and others, 1981), despite various allegations that such errors contaminated certain of the pre-197 4 measurements 

(Jackson and others, 1980; Strange, 1981). 

A potential for serious systematic error unrecognized until very recently arises from an apparent 

interaction between the Earth's magnetic field and 

the pendulum compensators in modern, automatic 

levels. At present the full potential for magnetically induced errors is poorly understood. The 

magnetic response has been demonstrated by laboratory experiments and attempted calibrations of 

certain instruments (National Geodetic Survey, 

· 1982), but it is not yet clearly established that laboratory test results are strictly applicable to the 

results of field surveys. The magnetic response of 

pendulum compensators is not only azimuth dependent, but seemingly also varies with instrument 

design, and it is both instrument specific and time 

dependent. Since there may be significant drift in 

the susceptibility of each instrument, it is doubtful 

that results of a laboratory calibration obtained in 

1982 for a particular instrument should be applied 

to data acquired with that instrument during the 

period from 197 4 through 1978. Given the mix of 

instruments involved, including a wide variety of 

both automatic and spirit levels, the SCRP misclosures are generally so small as to preclude major 

or pervasive contamination by magnetically induced systematic error. A similar conclusion is 

reached when results of levelings partially based 

on suspected instruments are compared with results of independent strain and gravity monitoring 

(J achens and others, 1983, fig. 2). Thus, although 

a number of pendulum-type instruments, doubtless 

having various levels of potential vulnerability, 

were deployed in the SCRP and earlier levelings, 

detailed records of where these instruments were 

used and what their individual susceptibilities 

might have been at the time are not considered in 

this report. 

A more serious problem is the fact that height 

6 
differences determined from the 1978 SCRP leveling along the coastal route show significant discrepancies when matched against height differences established by previous levelings and against 

steric (oceanographic) determinations of mean sea 

level at Avila Beach, San Pedro, Newport Beach, 

and San Diego. Acceptance of the 1978 leveling 

data along the entire coastal route at face value implies extraordinarily rapid changes in an apparently stationary sea slope that probably has persisted for several decades (Castle and Elliott, 

1982). In addition, a sharp break in the 1974 to 

1978 height-change profile along the southwest 

side of the Palos Verdes peninsula west of San 

Pedro probably is attributable to measurement 

error, especially since the associated circuit misclosure is of about the same size. In addition, similar 

uncertainties are raised regarding a succession of 

abrupt steps in the 197 4 to 1978 height-change profile along the coastal route from Newport Beach 

southeastward to San Diego. Possible errors in 

either or both of the two surveys compared could 

have been incorporated because of either misidentification of bench marks, effects of intrasurvey 

surficial movement (for example, soil slump or 

landslide slope failure), or observational blunders. 

The latter source is considered much less likely 

than the others, because gross blunders are rendered all but impossible by current observational 

procedures specifying the use of dual-scale leveling 

rods and programmed recording methods. However, because the coastal leveling was an NGS effort based on automatic levels and almost exclusively (95 percent of the route) on the Zeiss2 Ni 1, 

the instrument now considered most susceptible to 

magnetic error, there is increased likelihood that 

the large misclosures of certain circuits involving 

the coastal route and other described discrepancies 

along the coast may be the product of magnetically 

induced systematic errors. 

The possibilities of contamination of the SCRP 

leveling results by intrasurvey deformation (warping or tilting) in the tectonically active southern 

California region were greatly increased by extended delays in the work, caused by inclement 

weather, during a time of conspicuous change in 

the pattern of strain accumulation (Raleigh and 

others, 1982). Leveling along virtually all routes 

was delayed to some extent. Particularly susceptible to such contamination are the generally northsouth level lines across the Transverse Ranges and 

2 Any use of trade names is for descriptive purposes only and does not imply 

endorsement by the USGS. 

the San Gabriel Mountains, not only because of delays experienced there during the period of heavy 

snow cover at the higher elevations, but also because these routes generally are nearly perpendicular to the axis of the 1959-1974/76 uplift, which 

tends to follow the regional tectonic grain (see figs. 

2 and 4). Presumably, leveling along routes at high 

angles to the structural grain would be more subject to intrasurvey distortions, produced by any 

continuation or reversal of the established pattern 

of deformation, than leveling along routes that follow the regional structure (that is, routes nearly 

parallel to isobases of regional tilting). Possible 

tectonic movement during long delays at several 

places along the coastal route may have contributed to discrepancies between geodetic leveling results and independent mean sea-level determinations, as well as to the excessive circuit misclosures. This possibility is especially critical in areas 

of known high activity such as in the coastal mountains just west of Ventura, where rapid vertical 

deformation is well documented by large signals 

developed between earlier leveling surveys 

(Buchanan-Banks and others, 1975) and by studies 

of uplifted marine terraces that have established 

long-term uplift rates near Ventura as great as 10 

mrnlyr during at least the past 40,000 years (Lajoie 

and others, 1979; Lajoie and others, 1982, p. 47-

48). 

The possibility that the excessive circuit misclosures and other discrepancies may have resulted largely from intrasurvey tectonic deformation is also suggested by comparison of repeated 

leveling within at least two short sections observed 

before and after long delays. Specifically, the leveling across steep, high terrain of the San Gabriel 

Mountains between Azusa and Llano (fig. 1) was 

delayed for 87 days because of heavy snowfall, and 

the subsequent releveling of an 830-m-long section 

showed that the initial elevation difference had increased by nearly 4 mm (a=± 1.4 mm), equivalent 

to a northward tilt of 4.8 ± 1. 7 ..,..radians. Another 

long delay, between January 11 and April 13 (92 

days), hampered the leveling about 15 km north of 

Ozena (fig. 1). Subsequent releveling detected a 

4.5-mm (a=± 1. 7 mm) increase in the elevation 

difference between endpoints of the 1.35-km-long 

section, equivalent to a northward tilt of 3.3 ± 1.3 

J.Lradians. These probable indications of intrasurvey tectonic deformation during the course of the 

SCRP leveling, although conceivably related instead to rainfall-induced instabilities of bench 

7 
marks, are further reinforced by observations of 

continued northward tilting on several of the 

north-south routes that were releveled during 1979 

as part of a regional tilt-monitoring project 

(Jachens and others, 1983). 

Despite excessive closure errors within four of 

the network circuits (table 1) and independent indications of continuing deformation during the 

period of observations, the precision of the 1978 

SCRP leveling was generally good, although somewhat less than the conventionally estimated 

±0.512 mmlkm random error expected on the 

basis of first-order, class I specifications (Federal 

Geodetic Control Committee, 1974). A set of standard-deviation determinations based on comparisons of observed elevation differences obtained for 

forward and backward leveling runs on each section between bench marks, normalized to a 1-km 

section length, averaged ± 0. 71 mm for the network as a whole and ranged from ±0.54 to ± 1.07 

mm for a subset of 15 segments from several of the 

leveling routes separately evaluated (table 2). 

Evidence from other networks has been cited 

to suggest that a systematic (statistically dependent or correlated) error in section misclosures 

may increase circuit misclosures above the tolerance limits by as much as 30 percent, a figure 

based on the predicted accumulation of conventionally estimated random error (Remmer, 1975; Vanicek and others, 1980). However, the large residual 

misclosures for four of the SCRP circuits, which 

after orthometric corrections still range between 

38 percent and 86 percent above the conventionally 

estimated misclosure tolerances (fig. 1, table 1), 

are not readily explained as the product of statistically dependent errors associated with section misclosures. 

The relatively high precision of section closures, as contrasted with the excessive residual 

misclosures of isolated circuits, suggests that the 

circuit misclosure problem is attributable to intrasurvey tectonic deformation. Castle and Elliott 

(1982, p. 6989) conclude, for example, that "Geodetic leveling is the inherently accurate measurement system that it has been thought to be. However, it is flawed in application in one significant 

respect--it is time consumptive." In the case of the 

1978 SCRP data, intrasurvey tectonic deformation 

remains as the most likely cause of otherwise inexplicably large circuit misclosures because the inTABLE 2.--Statistical evaluation of selected parts of SCRP network 

N--Number of sections used in the test. 

S--Standard deviation of double-run sections within the test segment, 

normalized to a 1-km length, in millimeters per kilometer. 

R--Percentage of sections within the test segment initially rejected for 

excessive misclosure (sections partially or wholly reobserved at least 

once). 

Line No. Description of test segment N s R 

All lines Entire SCRP Network--------------- 6484 + .709 5.9 

124301.1 Pismo Beach to Ventura------------ - 272 + .61 3.9 

124301.1 Topanga Beach to San Pedro-------- 165 + .63 4.1 

124301.1 San Pedro to Seal Beach----------- 56 + .54 3.4 

124301.1 Seal Beach to Newport Beach------- 49 + .70 3.9 

124301.1 Newport Beach 269 - to San Diego-------- + .68 4.1 

124301.2 Pismo Beach to McKittrick--------- 191 + .77 9.5 

124301.2 McKittrick to Ozena--------------- 262 -

+ .56 2.8 

124301.2 Ozena to Ojai--------------------- 112 + .90 5.9 

124301.13 Colton to near Cajon Pass--------- 182 + .71 5.0 

124301.16 Colton to Newport Beach----------- 179 + .75 6.0 

124301.24 Yucca Valley to Whitewater-------- 36 + .48 5.3 

124301.28 Mecca to Cottonwood Pass---------- 29 +1.07 13.6 

124301.13 Burbank to Colton----------------- - 200 + .64 5.0 

124301.23 Amboy to Twentynine Palms--------- 86 + .67 9.0 

124301.18 El Centro to Mecca---------------- 153 + .so 15.7 

8 
dividual section closures were rapidly completed 

within hours or days, whereas the large circuits 

were not completed for weeks or months and, as a 

consequence, were much more susceptible to the 

effects of continuing or frequent episodes of vertical deformation. On the basis of strong evidence 

for dramatic, short-term pulses of aseismic deformation in the southern California region (J achens 

and others, 1983) and the data concerning aseismic 

slip on various parts of the San Andreas fault system in other regions (Goulty and others, 1978; 

Schulz and others, 1982), it is not unreasonable to 

expect short-term differential vertical movements 

in southern California on the order of 10 mm due to 

episodes of local to regional aseismic deformation 

lasting from a few days to a few months. 

COMPARISON OF 1978 LEVELING WITH 

SURVEYS COMPLETED BETWEEN 1972 AND 1976 

In light of the reservations concerning possible contamination of the 1978 SCRP data by intrasurvey deformation and possible systematic errors, perhaps the most reliably determined height 

changes are those obtained along the generally 

east-west leveling routes (figs. 1, 3). For the purpose of constructing a framework of connected 

routes to compare the 197 4 and 1978 levelings, 

height changes along the east-west routes were 

tied to height changes along the frequently releveled route from San Pedro through Saugus and 

Palmdale to Mojave (figs. 1, 3). Wherever compatible, the results obtained along other north-south 

routes and parts of the coastal route were incorporated to augment the coverage. The east-west inland routes were combined primarily with connecting routes that form smaller, well-closed circuits to 

provide 1978 coverage that can be compared most 

confidently with the results of earlier surveys to 

obtain a preliminary set of recent height-change 

values. 

The most recent prior surveys along most of 

the 1978 SCRP routes were completed during 1973 

and 1974 (fig. 3). Additional control from observations completed in adjoining parts of the network 

during 1972, 1975, and 1976 generally produce 

satisfactory circuit closures in combination with 

the 1973n 4 levelings, except around the easternmost circuit. With that one exception, the circuit closures based on combinations of 1973/7 4 data 

with results of 1972 and 1976 levelings indicate 

that these selected parts of the region showed no 

9 

significant tilting and thus were relatively stable 

between 1972 and 1976 (table 3; fig. 3). Relative 

height changes for all bench marks that were common to both the 1972/76 and the 1978 surveying 

periods were computed by direct comparison along 

each of the routes shown in figure 3. Bench mark 

Tidal 8, adjacent to the San Pedro tide station, was 

held fixed as the primary reference point for all 

comparisons. 

Results from several of the releveled segments suspected to be contaminated were omitted 

before proceeding with the final analysis. Apparent height changes along the coastal route from 

San Pedro to Topanga Beach were rejected because the height-change value at Topanga Beach 

was inconsistent with the value determined along 

the route passing through Burbank, Saugus, and 

Oxnard (fig. 3). The results of additional 1978n9 

leveling by Los Angeles City and County along 

four ties crossing the area enclosed by circuit 7 

(fig. 1) of the 1978 network isolates an error in the 

coastal segment between San Pedro and Topanga 

Beach comparable to the 1978 misclosure (Robert 

Wilson, written commun., 1979). Results from 

Newport Beach inland to Cajon Junction were set 

aside because of inconsistencies in height-change 

values at Colton and Cajon Junction in comparison 

with results for routes from San Pedro through 

Burbank and Pomona to Colton, and through 

Saugus and Palmdale to Cajon Junction. Thus, the 

framework of comparable, repeated levelings along 

the routes shown in figure 3 (less the three sections omitted) provides the basis for a preliminary 

comparison of 1972/76 and 1978 heights. Although 

the available coverage actually consists of two separate networks connected only by the single line 

between Mojave and Amboy, the validity of the 

connection is supported by the remarkable stability of this segment (absence of significant tilting) 

determined by comparisons with other recent 

levelings; the only exceptions are the apparent 

coseismic effects associated with the 1952 Kern 

County earthquake and the westward tilting along 

the route from Boron to Barstow between 1972 

and 1974 (Castle and others, 1984). 

Several critical assumptions were introduced 

into the analysis of 1972/76 to 1978 height changes 

in order to interpolate or extend the pattern of 

vertical deformation between and beyond the 

areas of directly comparable survey control shown 

in figure 3. Because contanrination of SCRP results 

along the coastal route is suspected as a conse-
...... 

0 

120° 

35° 

34° 

119° 

M 1972 .~field 

cK1ttrick 

EXPLANATION 

Leveling route 

~ 

showing junction 

marks and dates of leveling 

® 

Circuit number -Refer to table 2 

.... --...... _ _.. 

Topangll', 

Beach~\ ~, 

P'l 

33° I- Com pari son with 197 8 omitted 

because of excessive loop or sea-level misclosures (see text) 

0 10 20 30 40 50 60 70 80 KILOMETERS I I I I I I I I I 

118° 117° 

.san Diego 

116° 

" ' 

@ 

115° 

'-..... ?. 

\f.>6' 

" '-,,, 

' Freda 

Junction 

FIGURE 3.-Index map of routes leveled between 1972 and 1976 that are common to the 1978 SCRP network. Circuits that were included in the 1978 SCRP network are 

identified by the same numbers given in table 1 and figure 1. Data on circuit lengths and on observed and orthometrically corrected misclosures for levelings completed 

between 1972 and 1976 are presented in table 3. 
quence of instrumental errors or intrasurvey displacements, a comparison of the 19-year sea-level 

means for the San Pedro, Avila Beach, and San 

Diego tide stations is included in the analysis. This 

comparison independently indicates that these tide 

stations have remained relatively stable with respect to one another, thus providing a reliable 

basis for extending the control for vertical motion 

from San Pedro to the two outlying points (Castle 

and Elliott, 1982). In addition, relative stability or 

a minimal eastward tilt of the northern Peninsular 

Ranges east of San Diego is assumed on the basis 

of a nearly perfect match between the 1956, 1968, 

and 1978 height determinations along the route between San Diego and Julian (Mark and others, 

1981, fig. 12). This assumption, if true, would constrain a zone of steep eastward tilting to within the 

region between Julian and a point near Campo, 

about 65 km east of San Diego, near the end of the 

197 4 and 1978 comparison west of El Centro (see 

figs. 3 and 5). Finally, a partial collapse and westward tilt between 1976 and 1978 of the terrain 

covered by the easternmost circuit of the network 

(circuit 18) is assumed to be well represented by an 

unconstrained height-change profile between Cotton wood Pass and Freda Junction obtained 

through comparison of 1976 and 1978 levelings (fig. 

4). 

Although this final assumption is seemingly 

arbitrary, the basis for it is provided in the following detailed assessment of the complicated nature 

of deformation between 1974 and 1978 in the vicinity of circuit 18. The area within the eastern 

Transverse Ranges north of the Salton Sea has undergone intense, relatively complex deformation in 

recent geologic time that has continued to the present, as indicated by high seismicity, steep and 

rugged terrain, complex patterns of faulting, and 

the distribution of vertical movement that accumulated between 1959 and 1974 (fig. 2). Thus, the 

complexity of deformation (fig. 5) determined by 

comparisons of 197 4, 1976, and 1978 leveling surveys around circuits 17 and 18 (figs. 3, 4) comes as 

no surprise. Unfortunately, the temporal distribution of leveling in the area is insufficient for a complete and unambiguous resolution of the details of 

post-197 4 deformation. 

The only leveling done during 197 4 in the eastern Transverse Ranges was along the route from 

Barstow to Frink, via Amboy, Twentynine Palms, 

TABLE 3.--Lengths and closures of circuits, 1972/1976 network 

CN--Circuit number as given on map of figure 3. 

K--Circuit length in kilometers. 

S--Circuit misclosure specifications in millimeters (allowable limits) 

for first-order, class I leveling (4 mm/km~ x~) • 

OM--Observed circuit misclosures in millimeters (clockwise). 

OC--Orthometric corrections for circuit closures in millimeters 

(clockwise) based on observed gravity. 

OCM--Orthometrically corrected clockwise misclosure in millimeters 

(OCM =OM+ OC). 

* Indicates that observed circuit misclosure is in excess of limits 

specified for first-order, class l leveling 

CN K s OM oc 

(fig. l) (lan) (mm) (mm) (mm) 

4 83.5 +37 -33.0 +9.6 

8 374.3 "+77 20.8 +2.0 

10 205.9 "+57 -12.9 +9.8 

13 236.5 "+62 56.0 +1.3 

17 252.4 +64 29.5 -11.3 

18 407.2 +81 156.8* -17.1 

21 324.1 "+72 -25.7 -3.1 

22 349.1 "+75 19.2 +33.1 

Mean values +66 +44.2 

11 

OCM 

(mm) 

-23.4 

22.8 

-3.1 

57.3 

18.2 

139.7 

-28.8 

52.3 

+43.2 
A 

c 

White 

Water 

(WW) 

340 ww 

+172 

E 

1~?4 to 1978 

1974 to 1976 

OBSERVATIONS 

Freda 

Junction 

(FJ) 

B 

MODELS 

D 

19.?~ to 1978 

-127±34 

1974 to 1978 

+56±29 

INCREMENTAL HEIGHT CHANGES RELATIVE TO TIDAL 8, SAN PEDRO 

F 

1974to 1976 

12 

1976 to 1978 and ( 1974 to 19781 

-270±34 

(-231±291 

(-271±211 

FJ 

-8±12 

FJ 

-151±12 

(-143) 
Cottonwood Pass, and Mecca (figs. 3, 4A). Circuits 

17 and 18 were closed against the north-south 197 4 

route by 1976 levelings to the west through White 

Water and Yucca Valley and to the east through 

Freda Junction (fig. 4B). The route between Cottonwood Pass and Mecca was also releveled during 

1976. Combining the 1974 and 1976 levelings 

around circuit 17 results in an orthometrically corrected misclosure of only + 18 mm (table 3), which 

suggests that the junction marks at Twentynine 

Palms and Mecca were very nearly stable or 

moved uniformly during 1974 to 1976 (fig. 4C). 

Nevertheless, the large, orthometrically corrected 

misclosure of+ 140 mm for circuit 18 (table 3) produced by linking the 1974 survey at Amboy and at 

Cottonwood Pass with the 1976 survey (through 

Freda Junction) indicates that deformation was in 

progress, at least between the two junctions, 

sometime during the same period. Specifically, the 

Cottonwood Pass junction must have been uplifted 

about 140 ± 34 mm with respect to Amboy sometime after the 1974 leveling along the north-south 

route but before completion of the 1976 leveling 

along the route through Freda Junction (fig. 4C). 

The comparison of relative heights at Cottonwood 

Pass with respect to Amboy, as determined by 

separate, unconstrained surveys in 1974 and 1976, 

and by the 1978 network results, suggests an uplift 

of about 153 mm at Cottonwood Pass between 1974 

and 1976. Approximately the same amount of uplift 

relative to Amboy is assumed for the same period 

at Freda Junction. 

The apparent stability between 1974 and 1976 

of the junction marks at Twentynine Palms and 

Mecca (or Cottonwood Pass) indicates that about 

the same amount of relative movement occurred at 

all three junctions with respect to Amboy. The effeet of arbitrarily distributing the 287 -mm collapse 

of Amboy with respect to San Pedro equally between the two periods 197 4-76 and 1976-78 (about 

-143 mm during each 2-year period) suggests that 

a general collapse of the previous uplift in the eastern Transverse Ranges area may have started in 

the north (197 4-76) and then proceeded southward 

(1976-78), perhaps leaving Freda Junction relatively high (fig. 4E, F). Thus by the time of the 1978 

leveling, the maximum rate of collapse may have 

already shifted southward to a center near Yucca 

Valley, the site of previous maximum uplift (fig. 

2). The assumption that Freda Junction moved upward 152 mm during 1974-76 (fig. 4C) to keep pace 

with the upward movement of Cottonwood Pass 

(with respect to Amboy) has the effect of closing 

off the 197 4-78 vertical deformation rapidly toward 

the Colorado River to the east, a feature of the 

general deformational history suggested by several other lines of evidence (Gilmore and Castle, 

1983). 

The pattern of relative height changes from 

197 4176 to 1978 (figs. 5, 6) is dominated by pervasive eastward to northward tilting throughout 

most of the region, modified by local tectonic warping in the Transverse Ranges east of Ventura, in 

the San Joaquin Valley south of Bakersfield (after 

removal of the estimated effects of artificially induced subsidence), in the Imperial Valley area 

from the Salton Sea southeastward, and north of 

the Little San Bernardino Mountains near Yucca 

Valley (between Barstow and Mecca). Height 

changes shown in figure 5 include the effects of 

nontectonic subsidence attributable to removal of 

underground fluids in at least two well-defined regions of extensive pumping, one south of 

Bakersfield and the other in the Antelope Valley 

FIGURE 4.-Compilation of height changes (in millimeters) at major junctions for circuits 17 and 18 in the eastern Transverse Ranges area of southern California, based on discrepancies in leveling results along different routes observed 

(A) between 1974 and 1978 and (B) between 1976 and 1978. (C) Height changes at Cottonwood Pass, Mecca, and 

Twentynine Palms relative to Amboy, indirectly determined by comparison of height values established by 1974 and 

1976 surveys along different routes (except for the common link between Cottonwood Pass and Mecca), are 

augmented by assumed height changes (numbers in italics) at Freda Junction ( + 152 mm), and at White Water and 

Yucca Valley ( + 172 mm). Aside from assumed changes, these values are obtained by subtracting the 1976-78 height 

changes relative to Amboy (as shown in B) from the 1974-78 changes (as shown in parentheses in A). (D) The model 

of 1974-78 height changes relative to Amboy is derived by adding the height changes shown in Band C. Italicized 

numbers indicate values based on the assumed changes shown in C. Incremental changes (1974-76, 1976-78, and 

1974-78) with respect to the prime reference bench mark Tidal8 at San Pedro are based on an assumption that the 

287-mm downward movement at Amboy accumulated at an approximately constant rate between 1974 and 1978: 

about -144 mm (relative changes in C minus 144 mm) from 1974 to 1976 (E), and another -143 mm (relative 

changes in B minus 143 mm) between 1976 and 1978 (F). Values in parentheses in F designate the long-term changes 

between 1974 and 1978 given by the observed and assumed relative changes in D minus 287 mm. 

13 
""""' Jol::o. 

120° 119° 118° 117° 116° 115° 

--.. Bakersfield ~roO ----..._--- o\ \ / roo 

I I I I \ \ I 

I \ I 

1 

I 

\I\\ 

I I I 

1/ f( /,--~-:_4o~ -soo 40::::\'\\\\ ':\\ \ j / ~/\Mojave /:~~0 I \ I \ \ \ \ \ \ \\\ ,\~\:---~'-. :!J;;J; (_/ ~j~ ( ~rsto\V-o- 280 ""'-J / / \ 

Avi":~ \ \ \\ \~~oo '-~-::_;:-~/ _______ ) r-' ~--~, / // / \I\ \.~-..>:-<:::: .. '::::::-:=--~=-__:::-__ / / I ( - // / Amboy 

Beach 

0 

}\ \\\\\\\ ->0: ~:::_~ ""Leb~ ( ((~ rr--.. 

00

\) /------ -<4o--.. __ / / _/'9· I 1 \ 

35' 1- I \ ", (~ 1\ ~ I \' '-.\\ ~Oo)) I / / 0------ \ \ I 

I \ \\"-, -----~---,--' J '_,..,o\"- \. "'-'-~.2'/ / ~-~) / / -~~ \ I 1 I I \\Freda 

1 

I \\ 

1 

\. -'&o, C:::,---~ -0'-", \ ~.we--~-~-~ ( 1 // ___ \ \ \ \ \ \Junction 1'\l - " '" :---~ "-'~~---c _______ :::: // /" \ \ ' 0 

; J 'b \ -- \:~, ~~200 _ --=::_-v~::> /"-----\ I 

1

1 1!~--340~\ \ ) I I I I I 

J / / ~~ ~ '"""'-t•o -=---..:::-_::;:--~-----'- \ 1 

1 

1(1!~_:::-;::::: ~ I 

1 

I 1 1 I I 

10

o 

00 

/ /1 Vent~ " ~-~~I -T2o------;,~:-.\:\. ·~--~Colton'-'~\\\\\\\"--=___ \\\ \~ ...:~~ ;~/ I I I I 1 1 ~ I ~ c 34° 

0 20 40 60 80 100 KILOMETERS 

An:e·~ ~ '-./ -----~~- \'\\. \\\ i ( I I 2 

1 '--------._ ""\ '-':-.\ '\ \\_ \ \\_'-::>----240-\ \_ \_ '--: ---._ I : : \ ~ o 

"'<fc -60 ==:=:::: --.., '-\ \\ \ \."-0 ""-'"'b ~c / I \ 

7

1'/c -._,-= ----.. ..___'- \. \ \ \ \' \~ \ ;I .. ·· 

Tdat 8 '-. \ \ \ \ \\ o I ' f f .· ··%~ '-... 

' \ \ \ \ \ \ ~ \ \ I I I /o_, ~" \ EXPlANATION \ \ '.. \ <g \ \\ \ ,\, II I I / ------

- "'~I I 1111111/ .. /"--. --

120 

e-D .. hed a \ \ \ \ \ \ Iiiii I I ~ ~ i '? .---r--····· ~ b e 

of equal heightxtcr~~~Tated; hachur red r'¢><1/1? \ \ \ \ \ \ \ \\\1/ / ;v I / f / n,CO l•o " · d ore - Contou _. - 1 

where_ e.ttmc~~';.,d depre'"~~!;y 10 m m \ I I \ \ \ \ \1 I I/; I / / _. --- .~ 0 

l~~;!~~:l?h~!"~ ~~P~~~~~ /I! "---- -'6o line. \ \ \ \ \ \ ~~~:1/f'(/~/~e~~y \\ \ \ \ \ 11111![11{ ,~/ ... D1ego ~an \ \ \ ' I\ 1,\. \ 1 

33° 

FIGURE 5.-Map showing changes in heights in southern California relative to bench mark Tidal 8 adjacent to the San Pedro tide station, based on comparisons between 

the results of 1972/76 and 1978 levelings. Closed depressions south of Bakersfield and north of Palmdale represent areas of major subsidence associated with withdrawal 

of underground fluids. 
north of Palmdale. Bench marks in Bakersfield, 

however, appear to be situated in an area free of 

the effects of artificially induced subsidence, as indicated by the nearly stable 197217 4 to 1978 heightchange profile between McKittrick and Mojave 

that passes through Bakersfield. Moreover, comparisons between several earlier surveys demonstrate consistently stable conditions at Bakersfield 

(Castle and others, 1976; Castle, 1978). Although 

downward movement in the vicinity of Ventura occurs in an area of high-volume oil production, the 

breadth of the downwarp and the intervening occurrence of several strong earthquakes in that area 

suggest tectonic deformation. 

Excluding areas of artificially induced subsidence, the maximum north to northeastward tilting occurred within a narrow zone that coincides 

with the southern boundary of the Transverse 

Ranges province, a belt of generally steep terrain 

characterized by strong south to southwestward 

tilting during the 1959-74 uplift. The 1972/76-1978 

pattern of height changes is related to the patterns 

of major faulting and of minor to moderate earthquake occurrences during 1974 through 1978 (fig. 

6B); regions of pronounced tilting or warping are 

also commonly characterized by much more frequent occurrences of minor to moderate earthquakes than the surrounding, relatively quiescent 

regions. For example, the nearly total collapse of 

the previous maximum uplift in the vicinity of · 

Yucca Valley and Twentynine Palms occurred in 

an area of frequent earthquake activity, including 

occasional swarms of moderate shocks. Along the 

south side of the local downwarp, east-west lineations in the pattern of earthquake epicenters and 

similar orientations in the height-change contours 

(fig. 6A) concide with active east-west oriented 

fault traces, as represented by the Pinto Mountain 

and Blue Cut faults (figs. 2, 6B). 

TIMING AND NATURE OF THE REVERSAL 

IN VERTICAL MOVEMENT SUGGESTED 

BY OTHER OBSERVATIONS 

Large, correlated changes in local gravity, 

elevation, and strain values recorded between 1977 

and 1981 near Lebec, Palmdale, and Cajon Junction (fig. 1; Jachens and others, 1983) strongly support the conclusions that aseismic tectonic deformation can occur rapidly and that such changes 

may not always be smooth and progressive. Each 

of the three monitoring sites was subjected to 

15 

short period (1 to 2 yr), high amplitude (100 to 150 

mm) relative elevation changes that were accompanied by local changes in both gravity and horizontal strain (plane dilatation). Changes in each parameter were consistent with the concept that vertical bulging, indicated by increases in elevation 

(8e>O) and corresponding decreases in observed 

gravity (8g<O), is likely associated with negative 

changes in plane dilatational strain (8A<0), and 

vice versa for tectonic subsidence. Stable conversion constants (scale factors) were derived from 

the three correlated data sets. The scale factor relating gravity and elevation changes for these data 

(8g/8e = -0.2 tJ.gal/mm) is the same as that estab- . 

lished by studies of coseismic deformation associated with the 1964 Alaskan and 1971 San Fernando earthquakes (J achens and others, 1983, fig. 

2 and p. 1216). 

The derived scale factor relating changes in 

elevation and horizontal strain for the 1977-81 

southern California data (8e/8.A = - 100 mm/ 

tJ.Strain) seemingly requires that the vertical 

strains associated with elevation changes be distributed through an elastic plate 200 to 300 km 

thick, assuming a Poisson's ratio of 0.25 to 0.30 

(Jachens and others, 1983, p. 1216). Despite some 

uncertainty and skepticism regarding this result, 

this scale factor, in conjunction with the longterm, negative strain-change trend of about 

-1.7 x 10- 7/yr (Savage and others, 1981), predicts a regional average uplift rate in southern 

California of about 17 mm/yr during the strainmonitoring period between 1971172 and 1977/79. 

This period was characterized by a nearly steady, 

regional accumulation of north-south contraction 

at 2 to 3 x 10- 7/yr with little or ... no significant 

east-west extension. 

If we assume that the 1971172 through 1977/79 

negative strain-change trend was actually established in the late 1950's at about the onset time of 

the most recent southern California uplift, then an 

average regional uplift of about 320 mm would 

have been produced at that rate by the late 1970's, 

a close match for the general uplift value based on 

repeated leveling (fig. 2). Thus, the uplift value 

predicted from backward extrapolation of the 

strain trend strongly supports the reliability of the 

leveling results. The apparent onset of the uplift in 

about 1959 came a few years after a period of high 

seismicity (1952-55) that was dominated by the 

1952 Kern County earthquake sequence (main 

shock of ML = 7. 7). The end of high seismicity in 
.... 

0) 

35° 

34° 

33° 

I 

I 

\ 

I 

U\ 

c 

\ 

\ 

\ 

120° 119° 118° 

\ - - U\ c 0 c 

/--

/ ------ \ ( Bakersfield o '\ 

\ '- -300----) 

\ ' ' <so ~oo 

----\ ......... /1> Mojave 

-- \ 

117° 

'U! 

o Barstow00 '-..._ / \ \ 

\ """"' 

oLebec? ...__ _____ _ 

~ ~ ---

116° 115° 

A 

\ 

N 

I ) "" <.. '----- " '.,.., / / 

'?so~ ) oPalmdale ---- / A 6<t> 0 4' Amboy 0 

~~ ------ ~ --------.... ~- _2oo"""' I 

t:l\ 

0 \ 

\"b 

\ 0\ \ .... 1.oo \ \ % 

~ 

~OA 7c 

EXPLANATION 

---100--

lsobase of equal height change-Dashed 

where estimated or extrapolated; hachured 

to indicate closed depressions. Contour 

interval 50 mm 

0 20 40 60 80 100 KILOMETERS 

...___ \ I / -3oo -- \ \ ,,..~ \ / / ~-3so~ Cohon \ 

0 " \ ( ~ ~Tw~ntynine ~ -c!P '% \ \ \ ---~ 

I ~Freda )o 

/ Junction 

I I 

.......... --- \ \ \ "...__ -' \" ", ----- .$'0 \ ~ " 

\ \ "' "\ \ \ \ I 

\ \ \ I I 

\ \ \ I f 

I \ \ I I 

1 \ \ I I 

\ I I \ I I I /J 

\ II/ / 

\ ij/1 

I Iii I 

0 

Oc,e~/j? 

I 

l 

..._ ..... 3oo 

v--...-3fJO 

El Centro 0 ) 

!.., 

-----

FIGURE 6.--(A) Changes in heights in southern California, based on comparisons of 1972!76 and 1978 leveling results along the routes indicated in figure 3 after 

removal of estimated nontectonic height decreases in known subsidence areas. (B) Epicenters of southern California earthquakes recorded from January 1, 

1974, through December 31, 1978. Trends of major faults in the region are also shown. 
....... 

-.;J 

36005'r 121°u(o~o~·--~-----------------------------------------------------------------------------------------------------------

0 0 

0 

0 

0 

0 

a 

0 

0 

0 

0 

~ ,"91-o 

0 0 

',..,~ 

<::>~ «' 

0 

0 

,"'?U' 0..(> 

..,v 

<";-

v~ 

0 

~ 

EXPLANATION 

Magnitude range (Md 

0 3.0-3.9 

8 4.0-4.9 

.2: 5.0 

0 

0 

0 

1-

5 c7o o I 

l.l..f 

5 

o~/ or:e 

0 I 0 

~0~ 

0 

0 

0 

0 

0 B 0 0 ~0 0 0 0 

0 0 0 0 

0 ~cg 0 OJO 

0 

0 

~o- oO 

0 

0 

,N.&Cb 0 oS~ ~~~~ oc~ 

0 

/ ,0 8 0 6~~\; ~ 0 

0 0 

&-· 

@ 0 

0 

0 

0 0 

0 

0 

0 ~~~ '>?<S> .S.q4< 0 ';. 

CD~ .q '(<(_~ o ~D~~ ~ o a{;) ~ '""!!.~.q8 S CD 

C6 o -ooFA ~ ~ 0 ~ 0 -.J:!.!:.L_ _/ 0 Q ._!",.q ((f) 0 Q, 6Q) 0 0 

0 o'd u~.,.§ ~ Q) cf"'<@ rtF 0 

0 

0 

0 

% S 8 6'~ 0 (g) • 0 p\NiO MOUNTAIN 

0 

o o o '- 0 ~o~ FAULT 

<9 o© o ~@Cb 0 ° cP (!!) 0 

0 

~ o s.ID-UEoCUi8FAULi 

CO 0 0 0 O"Q 0 0 0 0----;;--- 0 

g SAN JACINTO~ 0 Oo 

FAULT oo o 

0 0 0 

~ 0 

0 

0 

~ 

~ 'b " @OQ:) 

' c 0 00 00 8~ 

0 0 ° "'-8 

0 

0 

co t 0 \. 

~ ~ 

0 

~ ~~l IMPERIAL 

~ FAULT 0 

0 

0 

e 00~ 0 

0 

0 

0 

0 0 ' 

oO 0 

32°25' 0 

0~ 0

0 

o ~ 

0 20 40 60 80 100 KILOMETERS 

FIGU~E b.-Continued 

_1_14°30' 
about 1955/56 marked the onset of a period of relative quiescence, somewhat interrupted by the 1971 

San Fernando shocks, but more positively terminated by the occurrence of moderate to major 

earthquakes in 1978/79. 

As emphasized by Raleigh and others (1982, 

figs. 7 and 8), the recent increase in seismic activity (1978/81) was associated with a dramatic reversal of the 1971/72 to 1977179 negative strain trend 

(onset of regional east-west extension with little to 

no significant north-south strain). While the reversal occurred as early as late 1977 or early 1978 in 

the Salton Sea and Anza areas, and as late as the 

beginning of 1979 in the Palmdale area, the change 

was essentially coherent over the broad southern 

California region within a 1.2-year time span with 

a mean reversal time of about April 1978. Thus, 

the change in regional deformational pattern from 

tectonic uplift to subsidence, which according to 

results of repeated levelings seems to have had an 

onset sometime after 1976 but before 1978 and a 

definite continuation during 1978 and 1979, is 

closely associated with the change in the pattern of 

horizontal strain accumulation. The average rate of 

positive dilatational strain was about 0.5 ..,._strain/ 

yr during 1978 and 1979, consistent with a rapid 

partial collapse of the previous uplift at a rate of 

about 50 mm/yr. 

CUMULATIVE VERTICAL DISPLACEMENTS 

DURING THE PERIOD 1959 TO 1978 

Preliminary results of the comparison of 1972/ 

76 and 1978 levelings indicate a partial collapse of 

the southern California uplift with little substantial 

change in its shape and relatively modest reduction 

in its areal extent. This result can be most readily 

demonstrated by superimposing values of 1972/76-

1978 height change on the pattern of 1959-74 uplift 

contours to produce a map of 1959-78 cumulative 

(residual) height changes (fig. 7). Despite local 

complexities in the pattern of the more recent 

height changes and the strongly developed north 

to northeastward tilting, the prime features of the 

1959-7 4 uplift clearly persist in the pattern of 

cumulative vertical movement, albeit at substantially lower amplitudes (compare figs. 2, 7). The 

major axis of the residual uplift follows nearly the 

same trend as that developed between 1959 and 

1974. West of Lebec, the axis follows a nearly east18 

west trend, parallel to that of the western Transverse Ranges. The axis turns southeastward at 

Lebec and follows the trend of the San Andreas 

fault zone to the Little San Bernardino Mountains, 

where it turns eastward and continues along the 

trend of the eastern Transverse Ranges. Residual 

height-change values along the primary axis of uplift range from less than 100 to more than 150 mm 

relative to bench mark Tidal 8, roughly one-third 

of the peak values attained by 197 4. 

Several secondary features of local warping 

associated with the 1959-7 4 uplift were sharply accentuated by the continuing deformation. A local 

tectonic depression, between 50 and 100 mm in 

amplitude, centered on the San Andreas fault 

about 20 km southeast of Lebec and clearly defined 

in the pattern of vertical movement between 1959 

and 1974, was enlarged to an elongate, northwesttrending troughlike downwarp. A lobe of the 1959-

7 4 uplift centered just north of Cottonwood Pass, 

which was flanked on the south by a steep gradient 

of southeast tilting and on the north by a slight 

downwarp, subsequently developed into a more 

elongate east-west-oriented residual upwarp with 

steep southeastward tilt on the south and a more 

pronounced east-west elongate depression on the 

north. The center of 1959-74 tectonic subsidence 

near Frink, in the Salton Sea area, had by 1978 apparently shifted about 20 km to the south, and the 

subsidence increased. The initial differential height 

change of 450 to 500 mm between Cottonwood 

Pass and this center of subsidence apparently increased by 50 mm or so, even though a roughly 

250-mm collapse occurred in the Cottonwood Pass 

area during the continuing deformation. In addition to the general decrease in uplift amplitude and 

the almost complete collapse of the previous 

maximum uplift near Yucca Valley and Twentynine Palms, the most significant changes in the 

cumulative (residual) pattern since 1974 were the 

development of an east-west-trending downwarp 

of more than 200 mm along the south flank of the 

uplift which cuts across the coastline just south of 

Ventura and may extend westward into the Santa 

Barbara Channel, a remarkable deepening of the 

tectonic depression in the southeast end of Salton 

Sea, and the enhancement of an east-west-trending residual upwarp running from about 20 km 

north of Mecca eastward along the crest of the 

Eagle Mountains. 
...... 

(C 

35° 

34° 

33° 

0 

120° 119° 118° 

*4.6 

Bakersfiel ------------ -:::::.--=:=-.-=:::_--::::..._--

-- ~--- ---------

-- I ~~- -- -150-=--=--=-- ~---=---

EXPLANATION 

---TooIsobase of equal height changeDashed where estimated or extrapolated; hachured to indicate closed depressions. 

Contour interval 50 mm 

*s.o 

.P 

~Or­~7c 

20 40 60 80 100 KILOMETERS 

0~ ~4--

117° 116° 

El Centro 0 

115° 

/--50 

50-....___ 

--·--------------------

FIGURE 7.-Pattern of residual height changes (1959-78) relative to bench mark Tidal8 at San Pedro obtained by superimposing 1972176-1978 height changes indicated 

in figure 5 on the contours of 1959-74 vertical movement shown in figure 2. Epicenters of earthquakes (ML ~ 4.5) that occurred between July 1, 1974, and August 

31, 1978, are indicated by asterisks. 
~ 

0 

w 

z 

0 

1- 1- 1- N _, _, _, 1- ::> ::> ::> 1- _, <( <( <( _, ::> LL LL LL ::> <( 

e 

"0 

II) 

t:l.. 

c 

"' Ill 

oO 

;; 

"0 

f:::; 

<( 0 <( <( LL 

u c z c LL en z 0 z <( .$2 _, <( 

"0 <( en () w w "' II) 0 c a: z ::> c a: Q) ~ "' a: en ::s m c til) ..><: E ..... <( z c <( c II) w <( "' t) (!) t) <( < 1- "' ~ LL 1- ::s z .&J z z til) ·~ z ·~ z C3 <( a c <( <( ::s "' <( "' <( "' "' .....l en Q:l Ill en en Ill u en u en 

1000 

900 

800 

en 

a: 700 w 

1-

w 600 ~ 

~ 500 

~ 

:r: 400 (!) 

w 

:r: 300 

200 

100 

0 

---------------------------------------------------N.20°W.------------------------------------------------~ ~ 

150 

en 

a: 100 w 

1-

w 50 ~ 

:::::i 

::! 0 ~ 

~ -50 

~ -100 z 

~ -150 u 

1- -200 :r: 

(!) 

w -250 :r: 

-300 0 5 10 15 20 25 KILOMETERS 

FIGURE 8.-Profiles showing heights and height changes since 1973n4 along the route from San Pedro via Burbank and Saugus to the position of the San Andreas fault zone 

near Lebec for 1976, 1978, and 1979 levelings. 
CONTINUED NORTHWARD TILTING AFTER 

THE 1978 LEVELING 

Comparisons of 1976, 1978, and 1979 leveling 

results with a 1973/74 leveling baseline along the 

route from bench mark Tidal 8 at San Pedro northward through Burbank and Saugus to the position 

of the San Andreas fault zone near Lebec (fig. 8) 

demonstrate that a substantial northward tilt developing since 197 4 continued during 1978 and 

1979. Furthermore, the resulting displacement 

profiles suggest that the zone of maximum tilting 

gradually migrated northward, passing through 

the southern section of the route (San Pedro to 

Burbank) between 197317 4 and 1976, through a 

central section (Burbank to Castaic) between 1976 

and 1978, and finally through a 12-km-long section 

north of Castaic from 1978 to 1979. The ends of 

these tilted sections appear to coincide with the 

traces of the Santa Monica, San Fernando (or the 

fault trend defined by the Red Mountain, Oakridge, Santa Susana, and San Fernando faults), 

and San Gabriel faults. Consequently, it appears 

that the major faults may serve as hinge lines, essentially decoupling the tilting induced across 

large, fault-bounded crustal blocks by the passage 

of a deep-seated, northward-sweeping wave of 

down-to-the-north tilting. Preliminary analyses of 

1978-79 height changes along at least two additional north-south routes, from Ventura to just 

south of Maricopa and from Azusa to Islip Saddle, 

25 km north of Azusa in the San Gabriel Mountains, also indicate continuing northward tilting of 

a similar magnitude (J achens and others, 1983). 

CONCLUSIONS 

Two important implications of the 1974-79 

leveling data for the southern California region are 

very clear: (a) the 1978 releveling was carried out 

during an active period of tectonic deformation 

that almost certainly contributed to some distortion of the reference surface during the 5-month 

period of its establishment, and (b) this deformation consisted primarily of north to northeastward 

tectonic tilting over much of the area of the southern California uplift, starting as early as 1976 and 

continuing at least through the period of 1979 monitoring. 

21 

Other conclusions based on the 1972176 and 

1978 data comparison, the continued northward 

tilting during 1978 and 1979, and the results of independent strain and gravity monitoring are: 

(1) The shape and extent of the southern 

California uplift of 1959-7 4 were only slightly altered during the subsequent deformation, despite 

the occurrence of pervasive northward to northeastward tilting that reduced the uplift to about 

one-third its previous maximum value. 

(2) Major modifications of the 1959-74 uplift 

pattern, aside from the general decrease in 

amplitude, include the almost complete collapse of 

the region of maximum uplift in the eastern Transverse Ranges, a substantial increase in the tectonic 

subsidence of the central Salton Trough, and the 

development of a prominent tectonic downwarp 

within the Ventura Basin that may extend westward into the Santa Barbara Channel. 

(3) Deformation in southern California apparently accumulates in distinct pulses perhaps associated with episodic adjustments within crustal 

blocks to deep-seated subcrustal movement. At 

times the shallow deformation seems to be expressed as a rocking motion of large tectonic blocks 

which are separated and mechanically decoupled 

by major faults. 

(4) The last third of the period of tectonic uplift (1971-76) is associated with the welldocumented accumulation of negative plane dilatational strain (north-south contraction) at about 

- 1. 7 x 10- 7 /yr. While tectonic subsidence in isolated areas may have begun as early as 1976, the 

regional collapse is clearly associated in time, 

space, and by mechanism with a conspicuous 

change in the pattern of strain accumulation (aseismic strain release?) marked in 1977179 by the cessation of north-south contraction and the onset of 

east-west extension at a rate of about 5 x 10- 7/yr. 

(5) Numerous minor earthquakes and occasional moderate shocks occurred throughout the 

region of the southern California uplift during its 

partial collapse, but earthquake activity was particularly common in the eastern Transverse 

Ranges area and in the Salton Trough region, 

where crustal downwarping and rapid subsidence 

were accompanied by several swarms of moderate 

earthquakes that dominated the 197 4-77 pattern of 

seismic-energy release (Fuis and others, 1977; 

1978). 
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GPO 787-042/121