Geodetic Imaging of the Coseismic and Early Postseismic Deformation from
the 2019 Mw 7.1 and Mw 6.4 Ridgecrest
Earthquakes in California with SAR
Abstract
The 4 July 2019 Mw 6.4 Earthquake and 5 July Mw 7.1 Earthquake struck
near Ridgecrest, California. Caltech-Jet Propulsion Laboratory Advanced
Rapid Imaging and Analysis (ARIA) project automatically processed
synthetic aperture radar (SAR) images from Copernicus Sentinel-1A and
-1B satellites operated by the European Space Agency, and products were
delivered to the US and California Geological Surveys to aid field
response. We integrate geodetic measurements for the three-dimensional
vector field of coseismic surface deformation for thee two events and
measure the early postseismic deformation, using SAR data from
Sentinel-1 satellites and the Advanced Land Observation Satellite-2
(ALOS-2) satellite operated by Japanese Aerospace Exploration Agency. We
combine less precise large-scale displacements from SAR images by pixel
offset tracking or matching, including the along-track component, with
the more precise SAR interferometry (InSAR) measurements in the radar
line-of-sight direction and intermediate-precision along-track InSAR to
estimate all three components of the surface displacement for the two
events together. InSAR coherence and coherence change maps the surface
disruptions due to fault ruptures reaching the surface. Large slip in
the Mw 6.4 earthquake was on a NE-striking fault that intersects with
the NW-striking fault that was the main rupture in the Mw 7.1
earthquake. The main fault bifurcates towards the southeast ending 3 km
from the Garlock Fault. The Garlock fault had triggered slip of about 15
mm along a short section directly south of the main rupture. About 3 km
NW of the Mw 7.1 epicenter, the surface fault separates into two strands
that form a pull-apart with about 1 meter of down-drop. Further NW is a
wide zone of complex deformation. We image postseismic deformation with
InSAR data and point measurements from new GPS stations installed by the
USGS. Initial analysis of the first InSAR measurements indicates the
pull-apart started rebounding in the first weeks and the main fault had
substantial afterslip close to the epicenter where the largest coseismic
slip occurred. Slip on a NE-striking fault near the northern end of the
main rupture in the first weeks, in the same zone as large and numerous
aftershocks along NE-striking and NW-striking trends shows complex
deformation.