  Based on waveform data from a profile of aftershocks following the
north-south trace of the June 28, 1992 Landers rupture across the Mojave
desert, we construct a new velocity model for the Mojave region which features
a thin, slow crust. Using this model, we obtain source parameters, including
depth and duration, for each of the aftershocks in the profile, and in
addition, any significant (M>3.7) Joshua Tree--Landers aftershock between
April, 1992 and October, 1994 for which coherent TERRAscope data were
available. In all, we determine source parameters and stress-drops for 45
significant (M_w > 4) earthquakes associated with the Joshua Tree and Landers
sequences, using a waveform grid-search algorithm. Stress drops for these
earthquakes appear to vary systematically with location, with respect to
previous seismic activity, proximity to previous rupture (i.e., with respect to
the Landers rupture), and with tectonic province. In general, for areas north
of the Pinto Mountain fault, stress-drops of aftershocks located off the faults
involved with the Landers rupture are higher than those located on the fault,
with the exception of aftershocks on the newly recognized Kickapoo (Landers)
fault. Stress drops are moderate south of the Pinto Mountain fault, where there
is a history of seismic swarms but no single through-going fault. In contrast
to aftershocks in the eastern Transverse ranges, and related to the 1992 Big
Bear, California, sequence, Landers events show no clear relationship between
stress-drop and depth. Instead, higher stress-drop aftershocks appear to
correlate with activity on nascent faults, or those which experienced
relatively small slip during mainshock rupture.
