Surface Slip Variations And Off-Fault Deformation Patterns In Complex Cross-Fault Systems Revealed From 3D High-Resolution Satellite Optical Image Correlation: The 2019 Ridgecrest Earthquakes

Abstract:

The Ridgecrest sequence (M_w6.4 and M_w7.1, July 2019, California) is a cross-fault earthquake that has been observed using a wide range of geophysical and geological methods. This earthquake constitutes a real-scale laboratory to study shallow rupture physics (0-15 km). The sequence ruptured consecutively two orthogonal cross-faults within 34 hours, which raised the question of how is the surface deformation pattern influenced by the interaction of the two earthquakes? To answer this question, we used high-resolution (50 cm) satellite optical image correlation to measure the full 3D surface displacement field and associated deformation field for the two earthquakes. Because our images bracket the whole sequence - no images at 50-centimeters ground resolution were acquired between the foreshock (M_w6.4) and the mainshock (M_w7.1) - our displacement and deformation maps include both earthquakes. Our data allow for measuring series of slip profiles in the components parallel and perpendicular to the rupture to look at the correlation between slip distribution and rupture complexity at the surface. The amount of off-fault deformation is also quantified. We point out significant differences with previous geodetic and geological-based measurements and show the essential role of distributed deformation in the comprehension of surface displacement and deformation patterns. We discuss the locations of distributed deformation areas, epicenters and aftershocks regarding to the surface rupture geometry. Finally, we compare our surface displacement results to various fault slip models and we try to highlight the important parameters that control surface deformation.