Signature of transition to supershear rupture speed in coseismic off-fault damage zone

TL;DR

This study combines theoretical, numerical, and observational methods to identify the specific location of the transition from subshear to supershear rupture speeds in earthquakes, marked by a decrease in off-fault damage zone width.

Contribution

It provides the first clear identification of the supershear transition location in natural earthquakes using combined modeling and high-resolution observations.

Findings

Supershear transition correlates with a decrease in coseismic off-fault damage zone width.

Numerical models and observations agree on the transition signature.

Refines understanding of supershear rupture mechanics in natural settings.

Abstract

Most earthquake ruptures propagate at speeds below the shear wave velocity within the crust, but in some rare cases, ruptures reach supershear speeds. The physics underlying the transition of natural subshear earthquakes to supershear ones is currently not fully understood. Most observational studies of supershear earthquakes have focused on determining which fault segments sustain fully-grown supershear ruptures. Experimentally cross-validated numerical models have identified some of the key ingredients required to trigger a transition to supershear speed. However, the conditions for such a transition in nature are still unclear, including the precise location of this transition. In this work, we provide theoretical and numerical insights to identify the precise location of such a transition in nature. We use fracture mechanics arguments with multiple numerical models to identify the signature of supershear transition in coseismic off-fault damage. We then cross-validate this signature with high-resolution observations of fault zone width and early aftershock distributions. We confirm that the location of the transition from subshear to supershear speed is characterized by a decrease in the width of the coseismic off-fault damage zone. We thus help refine the precise location of such a transition for natural supershear earthquakes.