The generation of large earthquakes

Aitaro Kato and Yehuda Ben- Zion(University of Southern California, Los Angeles)

Nature Reviews Earth & Environment,, (2020).


Despite decades of observational, laboratory and theoretical studies, the processes leading to large earthquake generation remain enigmatic. However, recent observations provide new promising perspectives that advance knowledge. Here, we review data on the initiation pro-cesses of large earthquakes and show that they are multiscale and diverse, involving localization of deformation, fault heterogeneities and variable local loading rate effects. Analyses of seismic and geodetic data reveal evidence for regional weakening by earthquake- induced rock damage and progressive localization of deformation around the eventual rupture zones a few years before some large earthquakes. The final phase of deformation localization includes, depending on conditions, a mixture of slow slip transients and foreshocks at multiple spatial and temporal scales. The evolution of slip on large, localized faults shows a step- like increase that might reflect stress loading by previous failures, which can produce larger dynamic slip, in contrast to the smooth acceleration expected for a growing aseismic nucleation phase. We propose an integrated model to explain the diversity of large earthquake generation from progressive volumetric deformation to localized slip, which motivates future near- fault seismic and geodetic studies with dense sensor networks and improved analysis techniques that can resolve multiscale processes.

Schematic illustrations of generation processes of large earthquakes. a | Progressive localization of shear deformation and background seismicity around a large rupture zone. b | Shear localization and several foreshock sequences before the instability leading to the large rupture. c | A space–time diagram of step- like increase in fault slip before a major earthquake associated with combined slow slip and foreshocks. A final rapid local loading by a small foreshock triggers the subsequent major dynamic rupture and circumvents the large nucleation process of a large patch. White and yellow stars denote epicentres of mainshocks and other events, respectively. As an example, two foreshock sequences accompanied with slow slip are displayed.