Constraining Subsurface Slip of Shallow MW 4.8-6.0 Earthquakes Across California Using InSAR Stacking Methods

Katherine A. Guns

Published September 8, 2024, SCEC Contribution #13930, 2024 SCEC Annual Meeting Poster #076

Characterizing subsurface coseismic and aseismic fault slip is a critical goal in understanding earthquake processes. Moderate magnitude earthquakes present a valuable source of additional earthquake-slip measurements, the distribution of which is vital to investigate earthquake rupture depths, learn which factors determine rupture extent, assess the seismic hazard associated with a given fault, and determine how these earthquakes affect the stress field around them. The challenge, however, is that many of these smaller events have occurred off primary fault systems and in areas of sparser geophysical station coverage, thereby limiting our investigative capabilities. Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) data have the potential to serve as an additional source of coseismic observations in areas where other data are limited, given that they comprise continuous spatial coverage with a 6-12-day repeat time. Here, I leverage this substantial dataset to better constrain the source characteristics and slip of MW 4.8-6.0 earthquakes across the state of California (3 in the Imperial Valley, 3 in eastern CA, and 1 in northern CA). I apply two different stacking methods to earthquakes in the Sentinel-1 satellite era (~2015-present): a time-series-based method (which has been shown to increase signal-to-noise for smaller magnitude events) and a more routinely used no-common-scene stacking method. 7 of these events (at ANSS Comprehensive Earthquake catalog (ComCat) depths 1.5 – 14.2 km) display coherent observed surface displacements. For each of these events, I calculate a set of different stacks of line-of-sight earthquake deformation, and a displacement uncertainty. To validate these estimates, I forward model ComCat-based point and plane sources in an elastic half space and iterate to determine best-fit depths, which agree well with available prior independent estimates. This analysis will provide prior constraints for Bayesian inversions for subsurface coseismic and possible aseismic slip across these events with the benefit of displacement uncertainty estimates from an ensemble of InSAR stacks.

Key Words
InSAR, Sentinel-1, moderate magnitude earthquakes, subsurface slip

Citation
Guns, K. A. (2024, 09). Constraining Subsurface Slip of Shallow MW 4.8-6.0 Earthquakes Across California Using InSAR Stacking Methods. Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy