11 October, 2020
Postseismic deformation field following the 1992 Mw 7.3 Landers and 1999 Mw 7.1 Hector Mine earthquakes have been intensively studied and previous studies favored a rheological structure with a strong lower crust overlying a weak the mantle asthenosphere. However, we found that postseismic transients are more active and enduring than previously determined. Based on this new data constraints, we found (1) that the lower crustal steady-state viscosity is ~2e20 Pa s (the transient viscosity is ~2e19 Pa s), only 5 times that of the upper mantle, and (2) that the transient viscosity increases with time, showing geodetic evidence for frequency-dependent rheology. Our modeling results support a thin crème brûlée model for the Eastern California Shear Zone in which both the lower crust and the upper mantle exhibit ductility at decadal time scales.
Link to the paper: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G47729.1/591720/Thin-creme-brulee-rheological-structure-for-the