Late Neogene alluvial-fan geochronology and faulting, southern Death Valley, California.

摘要

The normal-oblique Black Mountain fault zone (BMFZ) is part of the Death Valley fault system. Fault scarps offset late Pleistocene to Holocene alluvial-fan deposits along most of the 80-km length of the BMFZ. However, slip rates, recurrence intervals, and event magnitudes for the BMFZ are poorly constrained due to a lack of age control.; Optically stimulated luminescence (OSL) dating of eolian and fluvial sand lenses within the alluvial-fan deposits suggests the offset alluvial fans range in age from 24 ka to 3.7 ka. The OSL ages are used in the calculation for slip rates and recurrence intervals and used to correlate deposition of the alluvial fans with regional and global climate changes.; Scarp profiles were measured with a total station theodolite. Combining the OSL ages and vertical offset, event ages of 10 -2 ka with a post-late Pleistocene slip rate of 0.2---0.35 mm/yr and recurrence intervals of 9000 years/event can be inferred for the southern BMFZ. Moment magnitudes (Mw) between 6.5 and 7.2 for the BMFZ are estimated from regression equations for the estimated geomorphically constrained rupture length of the southernmost section and surveyed event displacements.