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

Earthquakes abruptly release tectonic stress that builds slowly over time through the coupled evolution of faults and the surrounding crust. Seismic wavespeeds track crustal deformation and stress changes, but typical monitoring methods are most sensitive to shallow depths. Using receiver functions, we tracked rupture-zone wavespeed and anisotropy changes throughout the crust during the 2019 Ridgecrest earthquake sequence. Shallow coseismic wavespeed reductions recovered within months, whereas a deeper postseismic wavespeed drop persisted without measurable recovery over several years. The deep, persistent wavespeed drop likely reflects accumulating damage driven by postseismic deformation, suggesting two possible scenarios: (i) a slow interseismic recovery where wavespeed and anisotropy track long-term stress evolution; or (ii) permanent deformation of an immature fault zone. Both scenarios affect the dynamics and energy budget of the seismic cycle. Editor's summary: When faults rupture, the sudden release of energy alters the properties of the surrounding crust, affecting its response to future stress. Seismic monitoring of these changes has been limited to shallow depths, leaving an incomplete picture of the response-recovery cycles of fault zones. To look deeper into this, Bryan et al. applied optimal transport to receiver functions at broadband seismic stations for several years before and after the 2019 Ridgecrest earthquakes in California (see the Perspective by Rodriguez Padilla). After the events, seismic waves slowed throughout the crustal column, a sign of both shallow and deep damage. Recovery at shallow depths occurred within months, whereas deep damage persisted for at least several years after rupture. —Angela Hessler [ABSTRACT FROM AUTHOR]