Title: Crustal stresses and damage evolve throughout the seismic cycle of the Ridgecrest fault zone

Speaker: Dr. William Frank, Assistant Professor, MIT 

Abstract: Earthquakes release tectonic stress abruptly, but this stress builds slowly with time through the coupled evolution of faults and the surrounding crust. Rheology governs this interplay, controlling how stress accumulates, deforms the crust, and relaxes. Seismic velocity changes track these processes, but typical methods are limited to shallow depths. Using receiver functions, we monitor seismic velocity and anisotropy changes throughout the crust during the 2019 Ridgecrest earthquake sequence. Shallow co-seismic changes recover within months, while deeper changes accumulate post-seismically and persist, revealing a depth-dependent rheology. This contrast defines a strength boundary, with a weak upper crust and strong lower crust, aligning with co-seismic and post-seismic slip concentrations. Lasting deep changes suggest both the fault zone and the crust prepare for future earthquakes over inter-seismic time scales.