Project Abstract
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Recent structural models for the Los Angeles (LA) Basin attribute deformation along the Compton-Los Alamitos fault (CLA) to fault-bend folding above a NE-dipping ramp rather, than to a shallow fault propogation fold. Our discovery last year of repeated stratigraphic sections on oil well logs across the northwestern CLA, however, support the latter interpretation. To test whether the fault we observe represents a significant structure, rather than localized fold-related faulting, we focused our efforts this year on confirming our earlier work, and extending our study to the southeastern CLA. Analysis of new exploratory well data, petroleum industry seismic lines, and cross-sections of seismicity across the southeastern CLA reveal a complex fault that cannot be explained by folding. Newly relocated seismicity by Yang and Hauksson reveal primarily reverse focal solutions below this section of the CLA. South of the LA River, seismic lines and well data reveal truncated reflectors up to depths of 5-1.5 km and gently warped basinal stratigraphy, exhibiting less apparent vertical separation than observed on the northwestern section of CLA. This southeastern section of the CLA also corresponds to the easternmost extent of uplift measured by Gilluly and Grant after the 1933 Long Beach earthquake. Its proximity to the eastern boundary of this coseismic uplift and the oblique strike-slip focal mechanisms calculated by Yang and Hauksson suggest a structural connection between the southeastern extent of the CLA and NIFZ, implying a strain-partitioning relationship between the two faults. |
