Distinguishing slip from the M6.4 and M7.1 Ridgecrest earthquakes using
campaign GPS and InSAR data
Abstract
The 2019 Ridgecrest earthquakes pose interesting questions about the
nature of intersecting conjugate ruptures, and also the possibility of
re-rupture of fault segments. Aftershocks of the July 4th M6.4 event
suggest the possibility of a secondary rupture along the fault that
subsequently ruptured in the July 5th M7.1 event. Unfortunately, neither
InSAR nor rupture mapping will be able to resolve this question, as no
SAR acquisitions were made between the two earthquakes, and the critical
‘nexus’ of the two ruptures was located on the China Lake Navy base, and
was not accessible between the events. Campaign GPS data and seismic
data may provide clues to resolving these questions. We reoccupied 5
previously surveyed GPS benchmarks in the hours following the M6.4
event, meaning that we can separately measure the deformation from the
two earthquakes at those locations. We construct a joint inversion of
our campaign GPS data, along with the daily displacements of nearby
continuous GPS stations, and ascending and descending Sentinel-1 InSAR
data, in order to separate the fault geometry and slip of the two
earthquakes, and address the question of re-rupture. This approach also
allows us to precisely estimate the contribution of the early
postseismic deformation to the InSAR data.