The sharp turn: backward rupture branching during the 2023 Mw 7.8 Turkey earthquake

TL;DR

This study uses dynamic rupture simulations to investigate the complex backward rupture branching observed in the 2023 Turkey earthquake, revealing how multi-segment ruptures can be triggered and propagated.

Contribution

It introduces a novel simulation approach to explain backward rupture branching, enhancing understanding of multi-segment earthquake rupture mechanisms.

Findings

Both subshear and supershear ruptures can trigger bilateral EAF ruptures.

SW EAF rupture often follows NE rupture, triggered by it.

Direct triggering of SW EAF by the splay fault occurs only under near-failure stress conditions.

Abstract

Multiple lines of evidence indicate that the 2023 Mw 7.8 Turkey earthquake started on a splay fault, then branched bilaterally onto the nearby East Anatolian Fault (EAF). This rupture pattern includes one feature deemed implausible, called backward rupture branching: rupture propagating from the splay fault onto the SW EAF segment through a sharp corner (with an acute angle between the two faults). To understand this feature, we perform 2.5-D dynamic rupture simulations considering a large set of possible scenarios. We find that both subshear and supershear ruptures on the splay fault can trigger bilateral ruptures on the EAF, which themselves can be either subshear, supershear, or a mixture of the two. In most cases, rupture on the SW segment of the EAF starts after rupture onset on its NE segment: the SW rupture is triggered by the NE rupture. Only when the EAF has initial stresses very close to failure, its SW segment can be directly triggered by the initial splay-fault rupture, earlier than the activation of the NE segment. These results advance our understanding of the mechanisms of multi-segment rupture and the complexity of rupture processes, paving the way for a more accurate assessment of earthquake hazards.