Postseismic deformation and viscosity of the Mexicali region following the El-Mayor Cucapah earthquake inferred from GPS observations

Xiaopeng Tong, Alejandro Gonzalez-Ortega, Bridget R. Smith-Konter, & David T. Sandwell

Submitted August 15, 2016, SCEC Contribution #6925, 2016 SCEC Annual Meeting Poster #156

It is important to study the deformation of the lithosphere to understand the thickness, strength, and viscosity of the lithosphere and substrate. Two northwest-southeast trending fault systems connect the San Andreas Fault system to the rift system in Baja California. The 2010 M7.2 El Mayor-Cucapah earthquake ruptured these faults in the Mexicali region and provides a unique observation to better understand the thickness of the lithosphere and viscous substrate. We infer the viscosity structure of the Mexicali region from an analysis of post-seismic GPS time-series observations from 2010-2015, which consists of campaign GPS sites surrounding the Sierra Cucaph and Indiviso faults, and two survey lines covering the Cerro-Prieto fault and the Imperial fault. We compare the post-seismic GPS time-series data with a semi-analytic 3-dimensional viscoelastic model that includes an elastic layer representing upper crust and a viscoelastic substrate representing lower crust and upper mantle. A coseismic slip model is used to generate stress changes caused by the El Mayor-Cucapah earthquake. Here we focus on the viscoelastic response of the postseismic transients to estimate the thickness of the lithosphere and viscosity of the substrate simultaneously. The horizontal component of GPS data captured the large-scale postseismic transients that extend tens to hundreds km from the fault, which provide critical constraints to the viscoelastic model. Postseismic transients observations from 2012-2015, two years after the earthquake, suggests that the viscosity of the lower crust and upper mantle is around 10^18 Pa s and the elastic layer is relatively thin in the Mexicali region.

Citation
Tong, X., Gonzalez-Ortega, A., Smith-Konter, B. R., & Sandwell, D. T. (2016, 08). Postseismic deformation and viscosity of the Mexicali region following the El-Mayor Cucapah earthquake inferred from GPS observations. Poster Presentation at 2016 SCEC Annual Meeting.


Related Projects & Working Groups
Tectonic Geodesy