Post-seismic deformation following large earthquakes offers insights
into the rheology of the lithosphere and upper asthenosphere. The
Mojave, in southern California, is one of the best studied regions on
Earth, yet key questions, about fault slip rates and rheological
heterogeneity, remain unanswered. Unprecedented geodetic coverage of the
2019 Ridgecrest earthquakes provides an opportunity to test whether
rheological models developed for the Mojave, from the Landers, Hector
Mine and El Major Cucapah earthquakes, are applicable north of the
Garlock fault, and to place bounds on the effects of local rheological
heterogeneties associated with the Coso volcanic field. This volcanic
field, which is located to the NW of the Mw7.1 rupture trace, is a
region of high heat flow and geothermal activity. The locally high
temperatures in the Coso volcanic field are likely to be associated with
low viscosities compared to the surrounding regions, and high pore
pressures due to the hydrothermal activity. The aftershock sequence
associated with the Ridgecrest earthquakes shows a notable absence of
large magnitude earthquakes in this region. We use variational Bayesian
independent component analysis to isolate postseismic deformation in GPS
time series around the earthquakes. We present models of the possible
poroelastic, afterslip and viscoelastic response driven by coseismic
stress changes in the July 2019 Ridgecrest earthquakes and investigate
the possible effect of the Coso volcanic field. By modelling a series of
different afterslip geometries, and viscoelastic rheologies we identify
features of the GPS- and InSAR-derived surface deformation which are
diagnostic of different post-seismic mechanisms and rheological
heterogeneities.