Predicting timescales of relaxation in the shallow Earth’s subsurface

Abstract

Earthquakes introduce long-lasting transient mechanical damage in the subsurface, which cause postseismic hazards such as enhanced landsliding and can take years to recover to steady-state values. This observation has been linked to relaxation, a phenomenon observed in a wide class of materials after straining perturbations. In this presentation, I analyze the successive effect of two large earthquakes on ground properties through the monitoring of seismic velocity from ambient noise interferometry in the Atacama desert in Chile. The absence of rainfall in this area allows study of the mechanical state of the subsurface by limiting the potential effect of variable groundwater content. I show that relaxation timescales are a function of the current state of the subsurface when perturbed by earthquakes, rather than ground shaking intensity. Our study highlights the predictability of earthquake damage dynamics in the Earth's near-surface and potentially other materials. I propose to reconcile this paradigm with existing physical frameworks by considering the superposition of different populations of damaged contacts.