Graduate Thesis Or Dissertation
 

Structural geology and dislocation modeling of the East Coyote anticline, eastern Los Angles basin

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  • The 1994 Northridge and 1987 Whittier Narrows earthquakes warned Los Angeles residents of the threat of earthquakes due to unmapped, blind reverse faults and emphasized the importance of identifying and characterizing blind reverse faults in assessing the seismic hazard to the region. The East and West Coyote Hills in the eastern Los Angeles basin are the surface expression of uplift accompanying blind reverse faulting. Folded Quaternary strata indicate that the hills are growing and that the faults underlying them are active. We use oil well data from the oil field beneath the East Coyote Hills to characterize the deformation. Detailed subsurface mapping in the East Coyote oil field shows that a previously-mapped, reverse-separation fault that cuts wells in the field is predominantly an inactive strike-slip fault that is not responsible for the uplift of the East Coyote Hills. The fault responsible for folding the East and West Coyote oil fields and the uplift of the Coyote Hills does not cut wells in either oil field. To characterize the geometry of the blind fault responsible for folding, we employ dislocation modeling. The dip and upper fault tip depths obtained from modeling suggest that the thrust fault beneath the Coyote Hills fault may be an extension of the Puente Hills blind thrust fault. The Coyote Hills fault is part of a major crustal structure that underlies much of the northern Los Angeles basin, with important implications for the tectonics and earthquake hazards of the Los Angeles basin. Modeling results suggest that the thrust fault responsible for folding would have 1400 m of reverse displacement over the last 1.2 Ma. This yields an average slip rate of 1.2 +1.4/ o 5 mm/yr for this time interval. Estimated moment magnitude for a reverse displacement earthquake on the Coyote Hills blind fault ranges from 6 to 7 depending on the length of the rupture. The average earthquake recurrence interval is 730 - 4000 years based on slip rates of 1.2 mm/yr and 0.8 mm/yr.
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