Geology of the Los Angeles Basin, California — An introduction

Yerkes, R.F.; McCulloh, Thane H.; Schoellhamer, J.E.; Vedder, J.G.

doi:10.3133/pp420a

Cited by 138 publications

(66 citation statements)

References 13 publications

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“…it is best exposed in the Puente Hills, the Whittier fault is dominantly a steeply northeast dipping, strike-slip fault with a small reverse component [Yerkes et al, 1965]. The Whittier Narrows earthquake was caused by rupture on a gently north dipping, west striking thrust fault.…”

Section: Son Gobritji Mountainsmentioning

confidence: 99%

“…It was also located well south of the mapped reverse and thrust faults of the Transverse Ranges and thus occurred on a structure not expressed at the surface. As a thrust faulting earthquake in what previously has been thought to be a strike-slip to oblique-reverse regime, the occurrence of the Whittier Narrows earthquake requires that existing interpretations of the neotectonics of the Los Angeles basin and the southern margin of the central Transverse Ranges [e.g., Yerkes et al, 1965;Morton and Yerkes, 1987] be modified.…”

Section: Son Gobritji Mountainsmentioning

confidence: 99%

See 1 more Smart Citation

The 1987 Whittier Narrows earthquake sequence in Los Angeles, southern California: Seismological and tectonic analysis

Hauksson¹,

Jones²

1989

J. Geophys. Res.

108

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The October 1, 1987, Whittier Narrows earthquake (ML=5.9) was located at 34°2.96'N, 118°4.8_6'W, at a depth of 14.6 ±0.5 km in the northeastern Los Angeles basin. The focal mecharusm of the mainshock derived from first motion polarities shows pure thrust motion on west striking nodal planes with dips of 25°±5° and 65°±5°, respectively. The aftershocks defme an approximately circular surface that dips gently to the north, centered at the h~center of the mainshock with a diameter of 4-6 km. Hence the spatial distribution of the mamshock and aftershocks as well as the focal mechanisms of the mainshock indicate that the causative fault was a 25° north dipping thrust fault striking west and is confmed to depths from 10 to 16 km. Although most of the 59 aftershock focal mechanisms presented here document a complex sequence of faulting, they are consistent with deformation of the hanging wall caused by.~e thrust faulting obs~~ in the mainshock. A cluster of reverse faulting events on north strikmg planes occurred wtthin hours after the mainshock, 2 km to the west of the mainshock. The _largest aftershock (ML=5.3) occurred on October 4 and showed mostly right-lateral faulting on the same north-northwest striking plane within the hanging wall. Similarly, several left-lateral focal mechanisms are observed near the eastern edge of the mainshock rupture. The earthquake and calibration blast arrival time data were inverted to obtain two refined crustal velocity models and a set of station delays. When relocating the blast using the ne~ models and delays, the absolute hypocentral location bias is less than 0.5 km. The mamshock was followed by nearly 500 locatable aftershocks, which is a small number of aftershocks for this magnitude mainshock. The decay rate of aftershock occurrences with time was fast, while the b value was low (0.67±0.05) for a Los Angeles basin sequence. INrR.onucnoNThe moderate-sized (ML=5.9) Whittier Narrows earthquake occurred in the east Los Angeles metropolitan area in ~outhern California at 1442 (UT) on October 1, 1987 (Ftgure 1), and caused three direct fatalities and substantial damage to structures in many communities in Los Angeles and Orange counties .The data analyses carried out in this paper are more detailed than those from Hauksson et al. [1988]. The blast arrival time data [Perkins, 1988] that were not available in the previous study are used here to constrain new velocity models. The new velocity models and station delays provide 0.5-1.0 km shallower focal depths for most of the aftershocks, while the epicenters are almost identical within 0.5 km. Detailed aftershock statistics are also derived to facilitate comparison with other sequences, although such a comparison is not the subject of this paper. To analyze the deformation caused by this sequence, 57 new single-event focal mechanisms are determined. The results of this more detailed study mostly confirm the conclusions reached by Hauksson et al. [1988] with three exceptions. First, Hauksson et al.

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Section: Son Gobritji Mountainsmentioning

confidence: 99%

Section: Son Gobritji Mountainsmentioning

confidence: 99%

The 1987 Whittier Narrows earthquake sequence in Los Angeles, southern California: Seismological and tectonic analysis

Hauksson¹,

Jones²

1989

J. Geophys. Res.

108

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“…Wright (1991) also presents a contour map of the amount of uplift during the Pasadenan deformation (3.5 Ma to present); we use this information to correct current sediment depths to depth of maximum burial. McCulloh (1960) and Yerkes et al (1965) show a structurecontour map of the top of crystalline basement rocks inferred mainly from gravity data. The age we use for this horizon is not the rock age, but rather an early Miocene age (20 Ma) that just predates the development of major basement relief and so dates the base of the sediment fill.…”

Section: Model Construction Reference Surfaces and Rule Definitionmentioning

confidence: 99%

The SCEC Southern California Reference Three-Dimensional Seismic Velocity Model Version 2

Magistrale¹,

Day²,

Clayton³

et al. 2000

Bulletin of the Seismological Society of America

259

265

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We describe Version 2 of the three-dimensional (3D) seismic velocity model of southern California developed by the Southern California Earthquake Center and designed to serve as a reference model for multidisciplinary research activities in the area. The model consists of detailed, rule-based representations of the major southern California basins (Los Angeles basin, Ventura basin, San Gabriel Valley, San Fernando Valley, Chino basin, San Bernardino Valley, and the Salton Trough), embedded in a 3D crust over a variable depth Moho. Outside of the basins, the model crust is based on regional tomographic results. The model Moho is represented by a surface with the depths determined by the receiver function technique. Shallow basin sediment velocities are constrained by geotechnical data. The model is implemented in a computer code that generates any specified 3D mesh of seismic velocity and density values. This parameterization is convenient to store, transfer, and update as new information and verification results become available.

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“…In general, exposed Late Pleistocene alluvial deposits cover large parts of the coastal plain except close to the Los Angeles River, where as much as ~10 m of Holocene-aged fluvial and marine sediment has filled in parts of the paleo-river channel of the Los Angeles River during a lower sea level stand. The hydrogeology of the Dominguez Gap region has been well studied [26,27,32] and is summarized in a shore-perpendicular cross-section ( Figure 2). Injection of fresh water in the West Coast Basin and Dominguez Gap Barrier Projects is a significant source of recharge to the West Coast Groundwater Basin [6].…”

Section: Geographic Settingmentioning

confidence: 99%

“…The study area is tectonically active [26][27][28][29], and as a result, uplift and erosion have winnowed many of the fine-grained confining units that serve to protect the underlying aquifers from seawater intrusion. As a consequence, there exists the potential for enhanced vertical and horizontal migration of seawater into the producing aquifers and subsequent landward migration of intruded waters beneath the Dominguez Gap Barrier Project [4,30,31].…”

Section: Introductionmentioning

confidence: 99%

A Combined Radio- and Stable-Isotopic Study of a California Coastal Aquifer System

Swarzenski

Baskaran

Rosenbauer

et al. 2013

Water

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Stable and radioactive tracers were utilized in concert to characterize geochemical processes in a complex coastal groundwater system and to provide constraints on the kinetics of rock/water interactions. Groundwater samples from wells within the Dominguez Gap region of Los Angeles County, California were analyzed for a suite of major cations (Na Rn and 223,224,226,228 Ra). In the study area, groundwater may consist of a complex mixture of native groundwater, intruded seawater, non-native injected water, and oil-field brine water. In some wells, Cl in host matrices, strong isotopic fractionation in these groundwater samples can be used to obtain information of adsorption/desorption kinetics. Calculated Ra residence times are short, and the associated desorption rate constant is about three orders of magnitude slower than that of the adsorption rate constant. Combined stable-and radio-isotopic results provide unique insights into aquifer characteristics, such as geochemical cycling, rock/water interactions, and subsurface transport and mixing.

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Geology of the Los Angeles Basin, California — An introduction

Cited by 138 publications

References 13 publications

The 1987 Whittier Narrows earthquake sequence in Los Angeles, southern California: Seismological and tectonic analysis

The 1987 Whittier Narrows earthquake sequence in Los Angeles, southern California: Seismological and tectonic analysis

The SCEC Southern California Reference Three-Dimensional Seismic Velocity Model Version 2

A Combined Radio- and Stable-Isotopic Study of a California Coastal Aquifer System

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