SCEC Award Number 19100 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Towards a Southern California Community Rheology Model
Investigator(s)
Name Organization
Sylvain Barbot University of Southern California
Other Participants Zhen Liu
Walter Landry
Chi-Hsien Tang
SCEC Priorities 1c, 1e, 3b SCEC Groups Geodesy, SDOT, CXM
Report Due Date 03/15/2020 Date Report Submitted 03/11/2020
Project Abstract
 The rheology of the lower crust controls the stress interaction in the fault zones and stress states in the lithosphere over seismic cycles. However, the spatial and temporal features of these rheological properties are often ambiguous. Here, we access the lower-crustal rheology of the Salton Trough by exploiting the eight-year of GPS postseismic deformation following the 2010 El Mayor-Cucapah earthquake. We examine the transient lower-crustal flow and the lateral variation of rheology following the earthquake. We demonstrate that a nonlinear Burgers rheology can approximate the temporal evolution of stress and strain-rate, indicating the role of nonlinear transient creep and steady-state dislocation creep. Our results indicate that the transient and background viscosities in the lower crust are on the order of ~1019 and ~1020 Pa s, respectively, while the viscosities beneath the Salton Trough are about an order lower than its surrounding region. We argue the need of transient rheology and its lateral variation to capture the entire history of postseismic relaxation following the El Mayor-Cucapah earthquake. This work was funded by SCEC awards number 18108 and 19100.
Intellectual Merit The project contributes directly to establishing and refining the Community Rheology Model and helps decipher crustal dynamics in Southern California due to postseismic deformation following large earthquakes. Conceptual take aways are the non-linear rheology of the lower-crust and mantle in the Salton Trough and the importance of non-linear transient creep during the early phase of deformation. More practical outcomes are the distribution of effective viscosity in space and time in the Salton Trough after the El Mayor-Cucapah earthquake.
Broader Impacts The project was conducted by a young investigator, part of his Ph.D training. A manuscript has been submitted at the Journal of Geophysical Research, currently under evaluation.
Exemplary Figure Figure 7. Estimated transient viscosity over the first month in the lower crust with a unified steady-state viscosity of 5×1019 Pa s and a background strain-rate of ~5×10-15 s-1. The purple box marks the volume element represents for the Salton Trough. Black lines enclose the geologic units and colored crosses mark the observed surface heat flow, as shown in Figure 2.