Geology Reports⌕ Search

Geology topics

Robert O. Castle

Publications and source records attributed to Robert O. Castle.

At least 19 recordsLinked to original sources
USGS2012

Estimation of rod scale errors in geodetic leveling

Comparisons among repeated geodetic levelings have often been used for detecting and estimating residual rod scale errors in leveled heights. Individual rod-pair scale errors are estimated by a two-step procedure using a model based on either differences in heights, differences in section height differences, or differences in section tilts. It is shown that the estimated rod-pair scale errors derived from each model are identical only when the data are correctly weighted, and the mathematical correlations are accounted for in the model based on heights. Analyses based on simple regressions of changes in height versus height can easily lead to incorrect conclusions. We also show that the statistically estimated scale errors are not a simple function of height, height difference, or tilt. The models are valid only when terrain slope is constant over adjacent pairs of setups (i.e., smoothly varying terrain). In order to discriminate between rod scale errors and vertical displacements due to crustal motion, the individual rod-pairs should be used in more than one leveling, preferably in areas of contrasting tectonic activity. From an analysis of 37 separately calibrated rod-pairs used in 55 levelings in southern California, we found eight statistically significant coefficients that could be reasonably attributed to rod scale errors, only one of which was larger than the expected random error in the applied calibration-based scale correction. However, significant differences with other independent checks indicate that caution should be exercised before accepting these results as evidence of scale error. Further refinements of the technique are clearly needed if the results are to be routinely applied in practice.

Journal of Geophysical Research B: Solid Earth↗
USGS2012

The sea slope problem revisited

Discrepancies in sea surface topography based on comparisons between the results of steric leveling and repeated geodetic levelings have identified what is known as the ‘sea slope problem.’ This problem is actually twofold: (1) the sea surface relief based on steric leveling differs significantly from that based on geodetic leveling along several generally north-south coasts, and (2) successively propagated levelings between several widely separated tide stations indicate that the stationary sea slope seemingly has been changing with time, whereas differenced sea level means between these stations indicate that the sea surface relief has remained virtually invariant during the same intervals. Reexamination of the three reported discrepancies between geodetically and sterically determined sea slopes indicates that the Australian example is based on leveling of a quality inappropriate to the comparison. The discrepancy developed along the Atlantic coast of the United States is limited to the reach between Portsmouth–Hampton Roads, Virginia, and Key West, Florida, where the accuracy of steric leveling may be especially vulnerable owing to the dynamic effects of the Gulf Stream. Reconsideration of the example along the Pacific coast of the United States indicates that the various discrepancies are due chiefly to intrasurvey movement and resultant distortion of geodetically defined height differences between tide stations. Agreement between the results of steric and geodetic leveling along tectonically inactive north-south coasts devoid of strong boundary currents is generally good. This observation supports the conclusions (1) that any directionally dependent systematic error in geodetic leveling is measurably insignificant and (2) that where allowance is made for the possible effects of major boundary currents or intrasurvey movement during levelings between tide stations, the sea slope problem tends to vanish.

Journal of Geophysical Research B: Solid Earth↗
USGS2005

Height changes along selected lines through the Death Valley region, California and Nevada, 1905-1984

Comparisons among repeated levelings along selected lines through the Death Valley region of California and adjacent parts of Nevada have disclosed surprisingly large vertical displacements. The vertical control data in this lightly populated area is sparse; moreover, as much as a third of the recovered data is so thoroughly contaminated by systematic error and survey blunders that no attempt was made to correct these data and they were simply discarded. In spite of these limitations, generally episodic, commonly large vertical displacements are disclosed along a number of lines. Displacements in excess of 0.4 m, with respect to our selected control point at Beatty, Nevada, and differential displacements of about 0.7 m apparently occurred during the earlier years of the 20th century and continued episodically through at least 1943. While this area contains abundant evidence of continuing tectonic activity through latest Quaternary time, it is virtually devoid of historic seismicity. We have detected no clear connection between the described vertical displacements and fault zones reportedly active during Holocene time, although we sense some association with several more broadly defined tectonic features.

Open-File Report↗
USGS2000

Height changes in the epicentral region preceding the January 17, 1994 Northridge earthquake

Analysis of the results of repeated levelings through the epicentral region of the M w 6.7, 1994 Northridge earthquake has disclosed the occurrence of differential uplift in this area that preceded the earthquake. Although the distribution of the relevant vertical-control data is somewhat sparse, in both space and time, those data that we have recovered indicate that this uplift exceeded 0.10 m and peaked 20-25 km west of the 1994 epicenter. While our data also indicate that this deformational event must have occurred during the period 1978-1989, evidence based on the character and magnitude of misclosures developed from 1987 and 1989 surveys argue that the deformation occurred largely during the period 1987-1989. The preseismic vertical-displacement field that preceded the Northridge earthquake is similar in form and, less certainly, magnitude to that which preceded the M w 6.7, 1971 San Fernando earthquake; other possible, but less significant southern California analogues include the deformational events that preceded the M w 5.3, 1973 Point Mugu and M w 5.9, 1987 Whittier Narrows earthquakes. The small but growing number of recognized aseismic deformational episodes that preceded small to moderate magnitude earthquakes in southern California suggests that the deployment of the dense array of continuously recording GPS receivers planned for southern California can be expected to detect and more accurately describe such events than was heretofore possible. Moreover, if the relation between the duration of these deformational anomalies and the magnitudes of any ensuing earthquakes can be much more clearly established, the near perfect temporal control on position afforded by GPS suggests that we may be on the threshold of a realistic earthquake warning system.

California↗
USGS1989

Vertical surface displacements along a part of the Newport-Inglewood zone of folds and faults, Los Angeles and Orange Counties, California

During the past half century, the onshore section of the Newport- Inglewood zone of folds and faults between the Dominguez oil field and Corona del Mar (fig. 1) has been repeatedly leveled to geodetic standards. These essentially fortuitous surveys are unrelated to either the tectonic framework or the urbanization of the Los Angeles basin, but were established instead because the Newport-Inglewood zone southward from the Long Beach area is roughly coincident with the coastline--and, hence, is roughly coincident with a naturally defined leveling route. Although these have been several relevelings athwart this zone north of the long Beach area, notably in the Baldwin Hills area (Castle and Yerkes, 1976), about 25 km to the northwest, the survey density, in both space and time, diminishes markedly northward. Thus, the results of the indicated relevelings along the Los Angeles-Orange County coast have permitted the relatively detailed appraisal of historic vertical surface movements described in this report. The Newport-Inglewood zone of folds and faults forms the surface expression of a major crustal boundary separating the Peninsular Ranges province on the east from the Continental Borderland province on the west (Castle and others, 1984, p. 8-9, pl. 1). Transcurrent fault movement along this boundary has produced not only continuing seismic activity, for which this zone is justly famous, but also folds and other structural features within the sedimentary veneer that have entrapped the petroleum deposits for which the Newport-Inglewood zone is even more famous. Although the northeast boundary of the exceptionally prolific Wilmington oil field is roughly coincident with the southeast edge of the Newport-Inglewood zone, we have deliberately excluded this area from consideration--in other than a peripheral way--simply because compaction-induced subsidence centering on the Wilmington field is viewed as a singularly spectacular example of this phenomenon and, hence, has been the subject of a series of detailed investigation (Harris and Harlow, 1947; Gilluly and Grant, 1949; Hudson, 1956; Miller, 1966; Poland and Davis, 1969; Allen and Mayuga, 1970; Castle and Yerkes, 1976).

California↗
USGS1984

The evolution of the southern California uplift, 1955 through 1976

The southern California uplift culminated in 1974 as a 150- km-wide crustal swell that extended about 600 km eastward and east-southeastward from Point Arguello to the Colorado River and Salton Sea, respectively; it was characterized by remarkably uniform height changes between 1959 and 1974 of 0.30-0.35 m over at least half of its 60,000-70,000 km 2 area. At its zenith, the uplift included virtually the entire Transverse Ranges geologic province and parts of the Coast Ranges, San Joaquin Valley, Sierra Nevada, Basin and Range, Mojave Desert, Peninsular Ranges, and Salton Trough provinces. The alinement of the western part of the uplift closely paralleled the east-trending Transverse Ranges, whereas the southern flank of the eastern lobe roughly coincided with the west-northwest-trending San Andreas fault. The position and configuration of the uplift associate it with a singularly complex section of the boundary between the North American and Pacific plates that has certainly sustained major modification during the past 5 million years and probably during the past 1 million years. Surface deformation can be categorized as tectonic or nontectonic. Nontectonic vertical displacements associated with the activities of man have overwhelmed natural compaction and areally significant soil expansion in the southern California area. Because tectonic displacements are implicitly defined as those that cannot be otherwise explained, those vertical movements that can be reasonably attributed to artificial processes have been subtracted from our reconstructed configurations of the uplift. Hence this reconstruction has necessarily included the assembly and evaluation of an enormous volume of data on oil-field operations, changes in ground-water levels, and measured subsidence (or rebound) associated with changes in the underground fluid regimen. Measured changes in height at various stages in the evolution of the uplift have been based chiefly on first-order levelings carried out between 1953 and 1976. Exceptions to this generalization consist largely of the results of pre-1953 surveys through the western Transverse Ranges and the eastern Mojave Desert. Errors in measured height differences derive from blunders, systematic survey errors, random survey errors, improperly formulated orthometric corrections, and intrasurvey movement; the last of these has created the most serious problems encountered in our reconstruction of the basic data. A variety of independent tests indicate that survey error associated with the utilized levelings was generally small and fell largely within the predicted random-error range. Moreover, the redundancy and coherence displayed by the entire data set provide convincing evidence of survey accuracy and the virtual absence of height- and slope-dependent error in particular. Our reconstructions of the changing configuration of the uplift derive chiefly from comparisons among sequentially developed observed elevations along the same route. Most of the observed elevations from which the vertical displacements were computed have been reconstructed with respect to bench mark Tidal 8, San Pedro, as invariant in height. Because the San Pedro tide station has been characterized by a history of modest relative uplift, vertical displacements referred to this station are biased slightly toward the appearance of subsidence. Where the observed elevations cannot be conveniently tied to Tidal 8, they have been referred to secondary control points whose history with respect to Tidal 8 can be independently established. Each of the lines of observed elevation changes provides, accordingly, a section athwart or along the axis of the uplift from which the changes in the configuration of the uplift can be roughly generalized. Because relatively few surveys were run in 1955, which we choose as a representative temporal datum, we have commonly incorporated the results of earlier or of somewhat later levelings as the equivalents of 1955 surveys. Although this procedure introduces a certain subjectivity, the probable equivalence between the results of these earlier or later surveys with those that would have been obtained had this leveling been carried out in 1955, usually can be independently tested. Wherever the calculated vertical displacements are based on comparisons between the results of levelings over different routes, the observed elevations have been orthometrically corrected to agree with those that would have been produced had each of these surveys been along the same route. The growth of the southern California uplift consisted of two well-defined spasms of positive movement, the second of which was closely followed by partial collapse. Our reconstruction, although it clearly errs in detail, indicates that the uplift, together with marginal and apparently ephemeral tectonic subsidence, nucleated in the west-central Transverse Ranges near Ozena, sometime between the spring of 1959 and the spring of 1960. The uplift expanded rapidly eastward (and probably westward as well), and by the fall of 1961 much of the Transverse Ranges and the Mojave Desert at least as far east as Twentynine Palms had risen by as much as 0.25 m. Between 1962 and 1972 the area included by the initially developed (1959-61) uplift sustained additional but clearly decelerating uplift accompanied locally by oscillatory displacements. Between 1972/ 73 and 1974 a second crustal spasm extended the uplift eastward to the Colorado River and elevated much of the eastern Mojave Desert by values that equaled or exceeded those developed within the western lobe. Between 1974 and 1976, at least the central part of the uplift sustained partial collapse that nowhere amounted to less than 50 percent of the cumulative uplift since 1959. Whether this collapse affected the entire uplift is conjectural, but we now recognize well-defined evidence of major down-to-the-north tilting that must have occurred within the eastern part of the uplift at some time between 1974 and 1976. Accumulating evidence indicates that nearly all the area included with the southern California uplift underwent similar uplift and partial collapse during the early part of the 20th century. Thus we infer that the recent uplift represents but a single event in an ongoing, more or less cyclic deformational process characterized by a period of about 50 years. Even though less than two full cycles are expressed in the geodetic record, the cumulative rate of uplift near the center of the recent uplift probably has averaged about 5 mm/yr, a value that is roughly consistent with the uplift rates that have been deduced for the late Quaternary emergent marine terraces along the south flank of the Transverse Ranges. Although the evolution of the recent uplift is relatively well defined, its correlation with the regional seismicity is poorly defined. A comparison between the occurrence of southern California earthquakes of magnitude ≥4 during the period 1932 to 1976 with the 1974 configuration of the uplift demonstrates the existence of (1) relatively aseismic areas within the western lobe of the uplift (in the western Transverse Ranges), in the central part of the uplift (in the western Mojave Desert), and along an east-trending zone that extends into the eastern Mojave athwart the south flank of the uplift (north of the Salton Sea) and (2) localized concentrations of seismic activity along the flanks of the uplift. Moreover, 9 of the 10 largest earthquakes recorded within or around the area of the southern California uplift during the period 1932 to 1976 (the 1933 Long Beach, the 1941 Santa Barbara, the 1946 Walker Pass, the 1947 Manix, the 1948 Desert Hot Springs, and the four major 1952 Kern County shocks) occurred before the inception of the uplift in 1959 or 1960. The area embraced by the southern California uplift has been identified with geodetically defined horizontal strain, part of which may have accumulated as a major north-south contractional event that roughly coincided with the first spasm of uplift. Nonetheless, continuing contractional strain associated with regionally developed partial collapse argues that the uplift cannot be fully explained simply as the vertical expression of continuing north-south compression. Consideration of the two well-defined historical episodes of uplift and partial collapse indicate that the southern California uplift may be the product of decoupling and viscous flow beneath the seismogenic zone, presumably driven by continuing motion between the irregularly margined plates south of the great bend of the San Andreas fault. Because the magnitude of the maximum uplift associated with each episode was approximately the same, there may be some threshold value above which collapse (viscous flow) may ensue; the absence of total collapse may be a function of precollapse strain hardening within the postulated subseismogenic viscoelastic layer.

California↗
USGS1979

Four-dimensional modeling of recent vertical movements in the area of the southern California uplift

This paper describes an analytical technique that utilizes scattered geodetic relevelings and tide-gauge records to portray Recent vertical crustal movements that may have been characterized by spasmodic changes in velocity. The technique is based on the fitting of a time-varying algebraic surface of prescribed degree to the geodetic data treated as tilt elements and to tide-gauge readings treated as point movements. Desired variations in time can be selected as any combination of powers of vertical movement velocity and episodic events. The state of the modeled vertical displacement can be shown for any number of dates for visual display. Statistical confidence limits of the modeled displacements, derived from the density of measurements in both space and time, line length, and accuracy of input data, are also provided. The capabilities of the technique are demonstrated on selected data from the region of the southern California uplift.

California↗
USGS1975

Vertical crustal movements preceding and accompanying the San Fernando earthquake of February 9, 1971: A summary

Comparative elevations referred chiefly to a tidal bench mark with a history of relatively positive movement show that much of the Transverse Ranges of southern California sustained major changes in elevation both before and in association with the M L 6.4 San Fernando earthquake of February 9, 1971. Preseismic changes in elevation in the southern Transverse Ranges were almost uniformly positive and generally episodic. Maximum uplift measured between 1960/61 and 1968/69 was 0.205 m (observed) or 0.200 m (adjusted); it occurred about 30 km northeast of the 1971 epicenter. As much as 0.129 m (observed) of preseismic uplift was also measured about 30 km northwest of the epicenter between 1964 and 1968. A comparison between 1968 and 1969 elevation data revealed 0.078 m (observed) of differential uplift centered about 10 km west of the epicenter; earlier leveling indicates that this uplift began between February 1967 and May 1968. Changes in elevation measured during the interval 1968/69-71 (postearthquake) are interpreted as chiefly coseismic and were concentrated along a 15-km ruptured segment of the east-trending, north-dipping San Fernando fault. These changes were characterized by subsidence of as much as 0.111 m (observed) or 0.092 m (adjusted) south of the fault and a ridge of uplift of up to at least 2.195 m (observed) or 2.196 m (adjusted) immediately north of the fault. The more episodic preseismic movements are interpretable as deep-seated creep events on the San Fernando fault. Alternatively, these episodic movements may be due partly to the operation of dilatancy; the onset of the 196849 epicentral uplift accords closely with the initiation of a V p / V s anomaly recognized in this same area. The 1968/69-71 elevation changes can be attributed almost entirely to slip on the San Fernando fault.

California↗
USGS1975

Elevation changes in the central Transverse Ranges near Ventura, California

Profiles of elevation changes developed from repeated levelings in the east-trending Transverse Ranges near Ventura, California, reveal three general types of vertical movements: 1. (1) broadly defined regional tilting; 2. (2) sharply defined differential movements across recently active faults; and 3. (3) differential subsidence centering on producing oil fields. Down-to-the-southeast tilting is evident in profiles along the coast this sense of movement, however, is the inverse of that that may have prevailed during late Pleistocene time. Profiles along lines extending north and northwest from Ventura show prominent inflections formed by up-to-the-north differential movements that coincide roughly with the Red Mountain fault; this fault is a north-dipping reverse fault that displaces a Holocene(?) soil zone and along which scarps and sag ponds are preserved. A similar inflection coincides with the Padre Juan fault; post-Pleistocene activity on the Padre Juan, however, is uniquely indicated by the geodetic data. Contemporary integrity of the structural block extending northward from the Red Mountain fault is suggested by the apparent absence of differential movements across the Munson Creek, Tule Creek, Santa Ynez, and Arroyo Parida faults since at least 1934. Subsidence is recognized over both the Ventura and Rincon oil fields; although maximum subsidence has not been recorded in either case, 277 mm of differential subsidence was measured within the Ventura field between 1934 and 1968.

California↗
USGS1969

Recent surface movements in the Baldwin Hills, Los Angeles County, California

The Baldwin Hills are located in the northwest part of the densely populated Los Angeles basin. They comprise one of several groups of isolated hills that extend along the northwest-trending Newport-Inglewood zone of folds and faults, a structural lineament identified with a series of very productive oil fields. In addition to being the site of the Inglewood oil field, these hills are the site of surface deformation that has been monitored for over 35 years. This record of deformation, which includes differential subsidence, horizontal displacements, and surface rupturing, forms one of the best documented examples of oilfield-associated surface deformation yet recognized. The deformation is described in detail, analyzed as to cause(s), and finally attributed largely or essentially entirely to the exploitation of the spatially-associated Inglewood oil field. The Baldwin Hills are underlain by gently to moderately arched and conspicuously faulted Cenozoic sedimentary and volcanic rocks that overlie crystalline basement rocks at a depth of more than 10,000 feet. The Inglewood fault, a part of the northwest-trending Newport-Inglewood zone, diagonally transects the hills. Right-lateral displacements of 3,000-4,000 feet since middle or late Pliocene time and 1,500-2,000 feet during Quaternary time are indicated by offset structural and physio-graphic features; indications of vertical separations of up to about 200 feet during late Quaternary time occur locally. Evidence of continuing deformation includes recognized seismicity and regional elevation changes. The M5-5 1/2 Inglewood earthquake of 1920, the largest local earthquake of record, is believed to have originated immediately southeast of the Baldwin Hills; it was apparently unassociated with surficial fault displacements. Leveling in and around the west and central Los Angeles basin has shown that lowland stations have been consistently subsiding, whereas foothill stations commonly have been rising. Several seemingly persistent basins of differential subsidence and a zone of positive movement, roughly coincident with the Newport-Inglewood zone, have also been identified in the northwest part of the basin. A prominent, elliptically-shaped, northwest-trending subsidence bowl encompassing the northwest part of the Baldwin Hills, has been defined by repeated level circuits. Partial reconstruction of selected level circuits with respect to a common, relatively stable control point (Hollywood E-11), located on the edge of the subsidence bowl, has permitted evaluation of the subsidence since 1910 and 1911 at two points near the center of the bowl. Thus bench mark PBM 67 is estimated to have subsided approximately 4.324 feet between June 1910 and February 1963; and bench mark PBM 68 (the only bench mark within the subsidence bowl that was leveled prior to 1926 and has been repeatedly leveled since) subsided 3.846 feet between November 1911 and June 1962. Analysis of the available data indicates little if any elevation change at PBM 68 (or elsewhere throughout the Baldwin Hills-Inglewood area) associated with the Inglewood earthquake of 1920. Maximum subsidence of PBM 122 (which has remained very close to the center of subsidence since at . least 1950) between 1911 and 1963 is calculated to have been 5.67 feet. Horizontal displacements (with respect to a north-south base line about 3 miles east of the hills) of six triangulation points within the subsidence bowl have been measured for various periods between 1934 and 1963. Displacements have been generally toward the center of subsidence and almost precisely perpendicular to the immediately adjacent isobases of equal elevation change. Maximum movement has been recorded at triangulation point Baldwin Aux, which was displaced 2.21 feet between 1934 and 1961; horizontal displacements of three additional points ranged from 0.95 foot to 1.85 feet between 1936 and 1961. Displacements of 0.10-0.29 foot were recorded at all six monuments during the period 1961-1963. "Earth cracks" and surficial fault displacements were recognized in the Baldwin Hills at least as early as 1957. The cracks are relatively straight, generally continuous fractures confined to the structural block east of the Inglewood fault; they are concentrated in two areas centering on (1) the Baldwin Hills Reservoir and (2) the Stocker Street-LaBrea Avenue-Overhill Drive intersection. The cracks trend north to north-northeast and are nearly everywhere parallel to or coincident with minor faults and joints, and are generally orthogonal to radii emanating from the center of subsidence. Differential movement along the cracks has been almost entirely dip slip along steep to nearly vertical surfaces, and generally down-dropped toward the center of subsidence. Cumulative displacements have been as much as 6 or 7 inches. Rates of displacement have ranged widely, and the movement has generally occurred as creep or very small discrete jumps. A probable exception is the several inches of differential movement that is believed to have occurred along a crack through the floor of the Baldwin Hills Reservoir on or about December 14, 1963. The contemporary surface movements are attributable to one or more of the following phenomena: (1). exploitation of the Inglewood oil field; (2) changes in the ground-water regimen; (3) compaction of sedimentary materials in response to surface loading; (4) tectonic activity. The following considerations indicate that the differential subsidence is attributable largely or entirely to exploitation of the underlying Inglewood oil field: (1) the coincidence of the centers of the oil field, the producing structure, and the subsidence bowl; (2) the general correspondence between the pattern of subsidence and the outlines of the oil field; (3) the approximate coincidence between the initiation of production and the initiation of subsidence; (4) the generally linear relations between various measures of subsidence and liquid production from both the field as a whole and the exceptionally prolific Vickers zone in particular; (5) the sharp deceleration of subsidence in the eastern block of the field coincident with the initiation of full-scale water flooding there; (6) the many examples of oil fields In which both spatial and temporal associations between production and subsidence are recognized; (7) the many similarities of the subsidence-production relations in the Inglewood field to those in the Wilmington field, where the subsidence has been authoritatively attributed to oilfield operations; (8) the theoretical relation between subsidence or a tendency toward subsidence and increased effective pressure associated with underground fluid extraction. Consideration of six possible explanations for the increasing rather than decreasing or constant rate of subsidence with respect to reservoir fluid pressure decline suggests that measured or calculated down-hole reservoir fluid pressure decline is non-representative of average or real fluid pressure decline away from producing wells. The near-linear relations between net-liquid production and subsidence are explained through analogy with a tightly confined artesian system of infinite areal extent, where production must derive from liquid expansion and/or reservoir compaction. Test data from compaction studies in two other oil fields yield estimates of ultimate compaction of the Vickers zone resulting from a total loss of fluid pressure; these estimates range over an order of magnitude. The best estimate, based on these data and considerations of late Cenozoic history in the Baldwin Hills area, is about 10 feet. The centripetally-directed horizontal movements are considered attributable to exploitation of the Inglewood oil field on the basis of: (1) their well-defined symmetrical and geometrical association with the differential subsidence; (2) the similarities between these associations and those developed in and around other subsiding oil fields; and (3) the mechanical compatibility of these movements with subsidence induced by the extraction of subsurface materials. The earth cracks and surficial fault displacements are considered largely or entirely attributable to the exploitation of the Inglewood oil field on the basis of: (1) their spatial and temporal relations to both oil-field operations and the differential subsidence; (2) the similarities of these cracks and displacements to those generated in and around other oil fields and areas of subsurface materials extraction; and (3) surface strain patterns predicted from the measured vertical and horizontal surface movements. The cracks and displacements can i)e explained by an exploitation-based, elastic-rebound model which requires elastic compression of the sedimentary section in response to compaction-induced downdrag within those blocks around the periphery of the subsidence bowl. The measured displacements have been about one-quarter to one-half those predicted for a purely elastic system. Analysis of: (1) the history of ground-water extraction within and around the Baldwin Hills; and (2) subsidence associated with water-level declines in sediments comparable with those in the Baldwin Hills, indicate that the surface movements can be no more than incidentally attributed to changes in ground-water conditions. Similarly, analysis of the history of natural and artificial changes in surface loading indicate that these movements are generally unassociated with changes in surface loading conditions. Considerations of local geologic history and various tectonic associations indicate that it is very unlikely that the differential subsidence and horizontal movements are due to tectonic downwarping. There exists a far stronger prima facie argument for tectonic involvement in the earth cracking and associated fault displacements. This argument is disputed by; (1) the spatial and temporal relations of the earth cracks to, and their mechanical compatibility with, the nontectonic differential subsidence; (2) the absence of displacements on the Inglewood fault in conjunction with those along the conjugate earth cracks; (3) the probability that purely tectonic displaceMents would be characterized by oblique or strike slip; and (4) the absence of any clear temporal relation between crack growth and local seismicity, However, because as much as 10 percent of the local isobase gradient may be unexplained' by oil-field exploitation, a small fraction of this gradient, and thus the displacements among the southern group of cracks, may be attributable to tectonic activity. This fraction should have been insignificant in the presence of the strain pattern produced by nontectonic compaction of the underlying oil measures. Because nearly all of the observed and measured surface movements can be fully explained as the products of oil-field operations, yet can be no more than incidentally attributed to changes in ground-water conditions, surface loading, or tectonic activity, we conclude that these movements are attributable largely or essentially entirely to the exploitation of the Inglewood oil field.

California↗
USGS1954

Geologic interpretation of seismic data along the proposed relocation of Route 138; stations 59+00 to 83+00 in Brockton, Mass.

This investigation was made to determine the surface and subsurface geological conditions along the proposed relocation of Route 138 in the vicinity of the Torrey Street crossing in Brockton, Mass. The field work was done in April 1952 as part of cooperative program of the Commonwealth of Massachusetts, Department of Public Works, and the United States Department of the Interior, Geological Survey.

Massachusetts↗