NOVEL MODES OF SLIP PARTITIONING IN TRANSTENSIONAL SETTINGS INFERRED FROM DATA ON THE WHITE MOUNTAIN FAULT ZONE, CALIFORNIA

Where regional transport direction is oblique to local fault trends, slip is partitioned between strike-slip and dip-slip faults, a configuration commonly observed at the surface in oblique tectonic domains. Subsurface fault interactions are critical to understanding the mechanics of large magnitude extension, but the nature of these interactions is not well understood. In transtensional settings, subvertical strike-slip faults usually are inferred to carry slip at depth, with normal faults terminating at the intersection. Using 3D modeling of earthquake aftershock clusters from the 1986 Chalfant Valley earthquake sequence, focal solutions, gravity/GPS data, fault scarp analysis, and geomorphic indices, we demonstrate that strike-slip faults terminate into normal faults in the upper crust along a partitioned section of the White Mountains Fault Zone, California. Our models also identify the presence of a cryptic strike-slip fault that terminates upward against a moderate-low-angle normal fault. The resulting fault configuration provides a simple solution for regional discrepancies in geologic and geodetic strain rates and highlights the importance of complex fault intersections for seismic hazard assessments. We suggest that the fault configuration presented here probably occurs in post-orogenic transtensional zones worldwide and can help to explain high regional rates of extension. We also note that analogous structures may play an important role in transtensional regimes.