EPS Colloquium – Camilla Cattania, MIT

Fracture mechanics insights into fault coupling and earthquake nucleation

The occurrence of precursory activity prior to large earthquakes, and its physical origin, remain outstanding questions in earthquake physics. A discrepancy exists between laboratory experiments, characterized by vigorous precursory activity enabling prediction of frictional failure; and natural fault systems, where seismic and aseismic precursors are rarely observed. Here I will present recent progress in these areas from numerical simulations and theoretical models based on fracture mechanics, focusing on two complementary aspects: 1) the seismic behavior of geometrically complex faults; 2) fault coupling and earthquake nucleation on faults subject to gradients in stressing rate (such as those due to adjacent creep). In the first part of the talk, I will explore the hypothesis that spatial heterogeneity can give rise to interseismic fault unlocking, aseismic transients, and an increase in seismicity rate not captured by classical nucleation models. Spatially variable strength or stressing rate cause neighboring fault patches to reach failure at different times, producing a gradual expansion of creeping patches. The evolution of fault coupling can be explained by a fracture mechanics criterion, which successfully predicts the evolution of acoustic emission measured in laboratory experiments on rough vs. smooth faults. The model predicts a transition to dynamic rupture once creep fronts reach a critical dimension, consistent with earlier studies; additionally, under certain loading conditions, dynamic rupture is preceded by a sequence of aseismic transients. Numerical simulations confirm this behavior for specific realizations of heterogeneity, including faults loaded by deep creep and fault strength modulated by subducted seamounts. Taken together, these studies indicate that heterogeneity in fault strength and loading rate can produce a broad range of fault slip behaviors, including stable creep, slow transients, and earthquakes. Different slip modes can overlap spatially, but they evolve in predictable and diagnostic ways throughout the seismic cycle, consistent with laboratory observations. I will conclude by discussing possible implications for natural faults and the conditions under which these processes may or may not be observable.

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Camilla Cattania is a seismologist with experience in numerical modeling, earthquake physics, and statistical seismology. She has developed new models of aftershock triggering based on static stress changes and studied swarms drive by magmatic intrusions and dynamic triggering. A separate but complementary aspect of her research consists of analytical and numerical modeling of slip on a single fault. Cattania has applied ideas from fracture mechanics to investigate the interaction between seismic and aseismic slip on isolated asperities, a topic she is now exploring in a wider range of tectonic settings and including additional physical processes.