Damage pattern

Signature of supershear transition seen in damage and aftershock pattern

With Jorge Jara (ENS Paris), Harsha Bhat (ENS Paris), Solène Antoine (IPGP), Kurama Okubo (Harvard), Marion Thomas (ISTeP), Esteban Rougier (LANL), Ares Rosakis (Caltech), Charles Sammis (USC), Yann Klinger (IPGP) and Romain Jolivet (ENS Paris).

Supershear earthquakes are rare but powerful ruptures with devastating consequences. How quickly an earthquake rupture attains this speed, or for that matter decelerates from it, strongly affects high-frequency ground motion and the spatial extent of coseismic off-fault damage. Traditionally, studies of supershear earthquakes have focused on determining which fault segments sustained fully-grown supershear ruptures. But the rarity of such events, combined with the fact that conditions for supershear are still debated, complicates the investigation of supershear transition in real earthquakes. The details of the transition, including its location, are then often overlooked.

Here, we propose a unique signature of the location of a supershear transition. We combine theoretical fracture mechanics, and numerical modeling of off-fault coseismic damage, with high-resolution field observations of fault damage and aftershock distribution, to show that the location of the transition from subshear to supershear speeds can be pinpointed by a localized absence of aftershocks, and a decrease in off-fault damage, due to a transient reduction of the stress intensity at the rupture tip.

Related publication: Jara, J., Bruhat, L., et al. 2021 Signature of transition to supershear rupture speed in the coseismic off-fault damage zone.Proc. R. Soc. A 477: 20210364. https://doi.org/10.1098/rspa.2021.0364