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 based on 60˚ fault dips are 0.3-0.2 mm/yr. Studies near Bishop show that many faults of the SNFFZ dip 29˚-46˚. Reconnaissance mapping, fault orientation analysis using detailed differential GPS measurements across ~300 m of elevation change, and bedrock fracture analysis in the vicinity of Lone Pine and Independence were used to evaluate the fault system. Our new data suggest that exposed bedrock faults, faults cutting Quaternary alluvial surfaces, and fracture systems exposed at Tuttle Creek, Bairs/George Creek, and Independence Creek dip as low as 29˚-44˚ E. If these shallow dips are correct, then long-term horizontal extension rates could be as much as 1.9 mm/yr, which is four times greater than previous Pleistocene to Holocene horizontal extension rate estimates for the eastern Sierra Nevada and Owens Valley region.