Andreas Plesch1, John H. Shaw1
(1) Harvard University, Cambridge, MA
ABSTRACT: 3-D Fault Architecture of the Los Angeles Basin, CA
We use advanced geometric modelling software to integrate geophysical and geologic data in the construction of a three-dimensional structural model of the major fault systems in the Los Angeles basin. The fault model integrates industry seismic reflection profiles, well data, surface geology, earthquake focal mechanisms and hypocenters, published structural cross-sections, and surficial neotectonic data. The model defines an imbricate thrust stack in the northern basin, including the Puente Hills (PHT), Las Cienagas, San Vicente, and Elysian Park faults. The geometries and tectonic histories of each system are evaluated based on the growth strata present in overlying fault-related folds and by the cross-cutting relationships of the faults at depth. Rather than obeying a simple break-forward or break-backward thrusting sequence, faults in the basin exhibit complex Pliocene and Quaternary reactivation histories. Moreover, the model defines areas where coeval thrust, reverse, and strike-slip faults interact at depth. We evaluate the kinematics of these transpressional fault interactions to define permissible fault geometries. The new 3-D fault models links numerous oil fields to their causative faults, and describes trap formation in the context of the basin's faulting history. The models are also used for earthquake hazard assessment and mitigation.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado