DIP OF THE SIERRA NEVADA FRONTAL FAULT ZONE IN THE VICINITY OF LONE PINE AND INDEPENDENCE, CALIFORNIA: STEEP OR SHALLOW?

The Sierra Nevada Frontal Fault Zone (SNFFZ) includes a series of east-dipping normal faults located at the eastern front of the Sierra Nevada Mountains. According to Byerlee's law, optimal dip for normal faults is 60˚-70˚; therefore, it generally is assumed that SNFFZ normal faults also dip ~60˚. Estimates of late Pleistocene to Holocene horizontal extension rates are 0.2-0.3 mm/yr, but these estimates are based on a 60˚ dipping fault system. Recent studies near Bishop show that many faults of the SNFFZ dip 29˚-46˚. If these shallow dips are correct, then long-term horizontal extension rates based on 60˚ dips should be recalculated because the horizontal component of slip could increase as much as four-fold. This study focuses on faults of the SNFFZ exposed at Tuttle Creek, Bairs/George Creek, and Independence Creek in the vicinity of Lone Pine and Independence. Reconnaissance mapping and fault evaluation suggest that exposed bedrock faults, faults cutting Quaternary alluvial surfaces, and fracture systems dip as low as 29˚ E. New data collected using detailed differential GPS measurements across ~300 m of elevation change, from which 3-D fault orientations will be evaluated, will help constrain the SNFFZ orientation further.