ACTIVE SLIP ON A REGIONAL LOW-ANGLE NORMAL FAULT, DEATH VALLEY, CALIFORNIA

Low-angle normal faults (dips < 30°) have been widely recognized in continental and oceanic settings. However, many workers have used rock-strength data to argue that the faults could not have slipped at their present low dips. Death Valley itself is an iconic example of a continental basin actively extending on a system of normal faults including low-angle normal faults. To investigate whether the low-angle normal faults are active, we deployed 10 portable seismographs, each of which continuously recorded 3-channel short period data at 100 samples per second, for 18 months, from July 2012 through January 2014. We relocated a subset of 313 earthquakes with magnitudes between 0 and 2.5 within the footprint of the portable network using a revised 1D velocity model with individual station corrections. The earthquake hypocenters lie on a well-defined plane dipping ca. 9° to the northwest (azimuth 325°) passing beneath central Death Valley and the bedrock ranges flanking it on the east and west. The calculated coefficient of basal friction of 0.12 indicates the fault is indeed weak. The slip direction on this active, regional low-angle fault is consistent with independent geologic and geodetic evidence for northwest transport of extended continental crust.