Slip partitioning and deformation cycles close to major faults in southern California: Evidence from small-scale faults

Abstract

Geometry and kinematics of small-scale faults adjacent to large seismically active faults have been analyzed for a large region of southern California. The sampled population of small-scale faults is scattered in orientation and slip but possesses distinct trends. Two important characteristics are, first, the paucity of small-scale faults that mimic orientations and mechanisms of the adjacent master faults, and, second, the large variation in slip mechanisms of fault planes oriented E-W and N-S. In order to test the similarity of the sampled fault population to present-day deformations, data on geometry and slip of the small-scale faults have been used for stress inversions. These results are compared with those derived from focal mechanisms of low-magnitude earthquakes in the same region. Stress orientations derived from small-scale faults are spatially heterogeneous, but horizontal axes of stress maintain N-S and E-W trends over the entire region. The similarities between stress inversions from small faults and seismicity support the conclusion that most of the sampled faults are recent and formed during cyclical events of fracturing in a relatively strong crust adjacent to weak master faults. Copyright 2000 by the American Geophysical Union.