Time-dependent deformation and seismicity in the Imperial Valley, California

Junle Jiang, & Rowena B. Lohman

Published August 15, 2019, SCEC Contribution #9781, 2019 SCEC Annual Meeting Poster #196

The Imperial Valley region in Southern California straddles the transitional zone from the southern terminus of the San Andreas fault to a series of right-lateral faults and extensional structures that extend to the south of the US-Mexico border. Along with frequent earthquakes and seismic swarms, the region is marked by widespread agricultural activities and geothermal power plant operations that take place to the south of the Salton Sea. In this study, we characterize ground deformation in the Imperial Valley with InSAR time series and investigate its relation with anthropogenic activities and seismicity in the region. We use the Sentinel-1a/b and Envisat satellites to construct surface displacement time series for the periods of 2015–2019 and 2003–2010, respectively. Our goal is to address the challenges associated with agriculture and other noise sources and extract persistent, smaller-scale signals amid low-correlation areas. In our workflow, we identify pixels with high phase stability and perform phase unwrapping after masking and spatial filtering. We then apply the modulo-2pi corrections to the unfiltered data, thereby allowing us to retrieve high-resolution unwrapped line-of-sight (LOS) displacements with minimal impacts from filtering. We apply model-based corrections of tropospheric delay in order to reduce the uncertainty on derived LOS displacement time series. A common source of disagreement between InSAR approaches involves the selection of reference frame, often through a pre-chosen “non-deforming” point or region. We use an approach where we automatically select non-deforming areas and validate with GPS time series. The interseismic deformation associated with the San Andreas-Imperial faults dominate signals over larger scales, whereas anthropogenic signals occur over smaller scales, in some cases complicated by local tectonics. For example, subsidence patterns in the Salton Sea geothermal areas revealed by Sentinel-1a/b span agricultural fields and roads, with variations over smaller (~1 km) and larger (~20 km) spatial scales that are potentially attributable to both tectonic and anthropogenic processes. We also resolve mixed uplift and subsidence at East Mesa, as well as time-dependent changes at Brawley and Heber geothermal fields. We use the surface deformation along with industrial operational data in these fields to test plausible subsurface source models and the evolution of strain changes and seismicity in the region.

Key Words
InSAR time series, ground deformation, seismicity, Imperial Valley, anthropogenic processes

Citation
Jiang, J., & Lohman, R. B. (2019, 08). Time-dependent deformation and seismicity in the Imperial Valley, California. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)