PRELIMINARY ASSESSMENT OF STATIC STRESS CHANGES ALONG LOW-ANGLE DETACHMENT FAULTS IN PANAMINT AND SEARLES VALLEYS

The location and style of the Ridgecrest earthquake sequence imply it occurred as a consequence of distributed shear along the Pacific-North America plate boundary system through California. At this latitude, the Eastern California Shear Zone (ECSZ) overlaps with the western edge of the Basin and Range extensional province. How these two deformational systems interact - does activity on one trigger or dampen activity on the other - remains an open question. The Ridgecrest sequence is an opportunity to evaluate this interaction along the ECSZ. In the SW Basin and Range of North America, large magnitude extension during Miocene – Pliocene time was accommodated on a system of low-angle detachment faults. In Panamint Valley, the active range-front fault system exploits a low-angle (15-30°), curviplanar detachment fault that connects to strike-slip faults at its southern and northern ends. Structural and kinematic relationships along the active fault system imply that extension is accommodated at depth along the low-angle detachment system. In Searles Valley, direct observation of high-angle faults that displace Late Pleistocene lacustrine deposits (<20 ka) but root into this detachment require that extension remains active (Numelin et al., 2007).

We have assessed the impact of the Ridgecrest earthquake sequence on the stress conditions on a generalized representations of these low-angle fault systems (some of which may extend to or beneath the shallow strike-slip system that ruptured during the Ridgecrest events). Models of Coulomb stress change indicate that the effects of the Mw 7.1 main shock would increase the potential for normal faulting activity on west-dipping low-angle structures in the Panamint, Searles, and western Death Valley region, consistent with the occurrence of aftershocks in that region. These results imply that stress changes associated with moderate-to-large earthquakes in the ECSZ can potentially trigger activity in the westernmost Basin and Range along low-angle structures. Additionally the timing of seismic activity elsewhere along this N-S corridor of the ECSZ may induce sympathetic activity along the low-angle structures of the adjacent extensional domains.