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Research about Los Angeles basin

Source-linked reports with geographic coverage including Los Angeles basin.

8 recordsLinked to original sources
USGS2018

Revisiting earthquakes in the Los Angeles, California, basin during the early instrumental period: Evidence for an association with oil production

A total of seven independent M L ≥ 4.0 earthquakes occurred in the Los Angeles, California, basin, during the early instrumental period between 1932 and 1952, the largest of which was the 1933 Long Beach earthquake. Revising available macroseismic and instrumental data for a total of 6 4.0 ≤ M L ≤ 5.1 events between 1938 and 1944, we conclude that early instrumental locations can be grossly inconsistent with detailed macroseismic data. We use available macroseismic data to revisit event locations. We further present evidence that most if not all of these moderate earthquakes may have been induced by oil production. We quantify the predicted stress change associated with production from eight oil fields in the southwestern Los Angeles basin and show that frictional failure would have been encouraged beneath and at the periphery of high-volume fields, with stress changes upward of 0.1 MPa at 5-km depth. The results suggest that if earthquakes are induced by stress changes associated with production, the magnitudes of events might tend to be limited by the limited spatial extent of lobes of increased Coulomb failure stress. It further appears that the advent of fluid injection recovery methods ( water-flooding ) around 1960 mitigated induced earthquake risk considerably.

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USGS2011

No: The L.A. array is not ready for prime time

Although much interest will focus upon the temporal behavior of observed deformation, the principal justification for the SCIGN array is that within a 5‐year interval it will provide an accurate and detailed determination of the velocity field in the Los Angeles basin that can be used to identify the active faults and estimate their secular slip rates. Obviously, the accuracy of the measurements will determine the success of the SCIGN array in reaching its objective. Over the past several years, Duncan Agnew, Hadley Johnson, and Frank Wyatt have developed arguments that quantify the accuracy likely to be obtained in the measurements and the accuracy that will be required to resolve slip rates on individual faults. In view of those arguments I do not believe that the SCIGN strategy can accomplish its objective. Instead, a mix of annual and continuous GPS surveys may be a more cost‐effective way to accomplish what actually can be achieved.

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USGS2000

Paleogene strata of the Eastern Los Angeles basin, California: Paleogeography and constraints on neogene structural evolution

Post-Paleogene dextral slip of 8–9 km is demonstrated for the southeastern part of the Whittier fault zone in the eastern Los Angeles basin area of southern California. A linear axis of greatest thickness for the combined upper Paleocene and lower to lower-middle Eocene clastic formations intersects the fault zone and is offset by it to give the new measure. Fragmentary evidence hints that the Whittier structural zone may have exerted control on bathymetric-topographic relief and sedimentation even in latest Paleocene (ca. 54 Ma). A clear topographic influence was exerted by 20–17 Ma. Strike-slip and present deformational style is younger than ca. 8 Ma. Our Paleogene isopach map extends as far west as long 117°58′W and is a foundation for companion zonal maps of predominant lithology and depositional environments. Integration of new palynological data with published biostratigraphic results and both new and published lithologic and sedimentological interpretations support the zonal maps. Reconstruction of marine-nonmarine facies and fragmented basin margins yields a model for the northeastern corner of a Paleogene coastal basin. Palinspastic adjustment for the Neogene–Quaternary Whittier fault offset and a reasoned westerly extension of the northern edge of the basin model yield a reconstruction of Paleogene paleogeography-paleoceanography. Our reconstruction is based partly on the absence of both Paleocene and Eocene deposits beneath the unconformable base of the middle Miocene Topanga Group in a region nowhere less than 15 km wide between the Raymond–Sierra Madre–Cucamonga fault zone and the northern edge of the Paleocene basin. Thus, Paleogene strata of the Santa Monica Mountains could not have been offset from the northern extension of the Santa Ana Mountains by sinistral slip on those boundary faults. Structural rearrangements needed to accommodate the clockwise rotation of the western Transverse Ranges from the early Miocene starting position are thereby fixed.

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USGS2000

A test of various site-effect parameterizations in probabilistic seismic hazard analyses of southern California

We evaluate the implications of several attenuation relationships, including three customized for southern California, in terms of accounting for site effects in probabilistic seismic hazard studies. The analysis is carried out at 43 sites along a profile spanning the Los Angeles basin with respect to peak acceleration, and 0.3-, 1.0-, and 3.0-sec response spectral acceleration values that have a 10% chance of being exceeded in 50 years. The variability among currently viable attenuation relationships (espistemic uncertainty) is an approximate factor of 2. Biases between several commonly used attenuation relationships and southern California strong-motion data imply hazard differences that exceed 10%. However, correcting each relationship for the southern California bias does not necessarily bring hazard estimates into better agreement. A detailed subclassification of site types (beyond rock versus soil) is found to be both justified by data and to make important distinctions in terms of hazard levels. A basin depth effect is also shown to be important, implying a difference of up to a factor of 2 in ground motion between the deepest and shallowest parts of the Los Angeles basin. In fact, for peak acceleration, the basin-depth effect is even more influential than the surface site condition. Questions remain, however, whether basin depth is a proxy for some other site attribute such as distance from the basin edge. The reduction in prediction error (sigma) produced by applying detailed site and/or basin-depth corrections does not have an important influence on the hazard. In fact, the sigma reduction is less than epistemic uncertainties on sigma itself. Due to data limitations, it is impossible to determine which attenuation relationship is best. However, our results do indicate which site conditions seem most influential. This information should prove useful to those developing or updating attenuation relationships and to those attempting to make more refined estimates of hazard in the near future.

California↗
USGS1991

Seismic excitation by the space shuttle Columbia

Seismic stations in southern California recorded the atmospheric shock waves generated by the space shuttle Columbia on its return to the Edwards Air Force base on 13 August 1989 (Fig. 1). In addition to the shock wave, the broad-band IRIS–TERRAscope station at Pasadena recorded a distinct pulse with a period of ~2–3 seconds, which arrived 12.5 seconds before the shock wave (Fig. 2). This pulse was also recorded at the University of Southern California, near downtown Los Angeles, where it arrived 3 seconds after the shock wave. The origin of this pulse could not be readily identified. We show here that it was a seismic P wave excited by the motion of high-rise buildings in downtown Los Angeles, which were hit by the shock wave. The proximity of the natural period of the high-rise buildings to that of the Los Angeles basin enabled efficient energy transfer from shock wave to seismic wave.

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USGS1988

The Whittier Narrows, California earthquake of October 1, 1987: Preliminary assessment of strong ground motion records

More than 250 strong-motion accelerograph stations were triggered by the Whittier Narrows, California, earthquake of 1 October 1987. Considering the number of multichannel structural stations in the area of strong shaking, this set of records is one of the more significant in history. Three networks, operated by the U.S. Geological Survey, the California Division of Mines and Geology, and the University of Southern California produced the majority of the records. The excellent performance of the instruments in these and the smaller arrays is attributable to the quality of the maintenance programs and their funding and personnel requirements. Readiness for a magnitude 8 event is directly related to these maintenance programs. Prior to computer analysis of the analog film records, a number of important structural resonant modes can be identified, and frequencies and simple mode shapes have been scaled. The structural records form a basic performance measurement for comparison with larger earthquake response in the future.

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