A physics-based approach of deep interseismic creep for viscoelastic strike-slip earthquake cycle models

Lucile Bruhat

Published September 24, 2019, SCEC Contribution #9935

Most geodetic inversions of surface deformation rates consider the depth distribution of interseismic fault slip-rate to be time invariant. However, some numerical simulations show down-dip penetration of dynamic rupture into regions with velocity-strengthening friction, with subsequent up-dip propagation of the locked-to-creeping transition. Recently, Bruhat & Segall (2017) developed a new method to characterize interseismic slip rates, that allows slip to penetrate up dip into the locked region. This simple model considered deep interseismic slip as a crack loaded at its down-dip end, and provided analytical expressions for stress drop within the crack, slip, and slip rate along the fault. This study extends this approach to strike-slip fault environments, and includes coupling of creep to viscoelastic flow in the lower crust and upper mantle. I employ this model to investigate interseismic deformation rates along the Carrizo Plain section of the San Andreas fault. This study reviews possible models, elastic and viscoelastic, for fitting horizontal surface rates. Using this updated approach, I develop a physics-based solution for deep interseismic creep which accounts for possible slow vertical propagation, and investigate how it improves the fit of the horizontal deformation rates in the Carrizo Plain region. I found solutions for fitting the surface deformation rates that allow for reasonable estimates or earthquake rupture depth and coseismic displacement and improves the overall fit to the data. Best fitting solutions present half-space relaxation time around 70 years, and very low propagation speeds, less than a meter per year, suggesting a lack of creep propagation.

Bruhat, L. (2019). A physics-based approach of deep interseismic creep for viscoelastic strike-slip earthquake cycle models. Geophysical Journal International,. doi: 10.1093/gji/ggz426.