SURFACE-WAVE PROFILING OF THE LITHOSPHERE BENEATH THE MOJAVE DESERT USING TERRASCOPE DATA

We have applied surface wave analysis to the Mojave Desert in southern California to extract the regional lithosphere velocity structure. Se ismograms from teleseismic sources recorded by the TERRAscope stations , a recently established network of broadband instruments, were used t o determine the phase velocity dispersion data of Rayleigh waves for w ave paths crossing the Mojave Desert. An inversion analysis on the dis persion data for each path gave the shear wave velocity structure bene ath the path. Inversion results show that there is a low-velocity laye r at the middle and lower crust, which is particularly pronounced for paths traversing the western part of the Mojave Desert. This low-veloc ity layer at the midcrust may reflect the existence of a transition zo ne from the brittle to the ductile regimes, where there is an absence of earthquake occurrence.