ANALYSIS OF FOOTWALL FRACTURES ALONG THE SOUTHERN SIERRA NEVADA FRONTAL FAULT ZONE

In this study we investigate footwall fractures coincident with a left-step along the Sierra Nevada Frontal Fault Zone (SNFFZ) located near Lone Pine California. Fracture measurements along the range front reveal a dominant orientation that is generally North-Northwest striking (320°- 350°). This fracture set is observed in footwall rocks throughout the study area. Principle stress orientations associated with this set are consistent with expected East-West extension along the SNFFZ. A second set of fractures is observed in the vicinities of Whitney Portal and Cottonwood Canyon. These high-angle fractures are predominantly west striking (260°- 280°) and are not observed throughout the rest of the study area. These fractures are interpreted to have formed at the tips of laterally propagating normal faults within the SNFFZ fault array that delineate the north and south extents of a relay zone. Pervasiveness of the North-Northwest trending fracture set, as well as the consistency of footwall topography throughout the entire study area, suggests full mechanical linkage of faults within the relay zone. Further study will incorporate new low-temperature thermochronometric data ((U-Th)/He and apatite fission track) collected along fault-parallel and vertical transects to elucidate the extent of mechanical linkage, determine the pattern of footwall denudation, and constrain the long-tem evolution of the SNFFZ.