Interseismic coupling at the Mentawai seismic gap, Sumatra

Abstract

Following the 2004 Mw 9.1–9.3 Sumatra-Andaman earthquake, the Sunda megathrust offshore Sumatra has ruptured in a series of large magnitude events with significant related afterslip, with the exception of the ∼ 200 km Mentawai seismic gap extending from the Batu Islands to Sipora. Paleogeodetic records indicate this region last ruptured in 1797, while an adjacent patch ruptured in 1833 and more recently in 2007. Although several M>7 events have occurred within and on the edge of the greater Mentawai segment since 2007, their slip distributions show limited propagation into the seismic gap, indicating that earthquake and tsunami hazards persist. We present a new interseismic coupling model, wherein we account for updated slip rates of the Sumatran Fault, large-scale deformation across the Wharton Basin oceanic lithosphere, and stress constraints on the megathrust. Our results reveal a strongly coupled region that extends from Siberut to the Pagai Islands, with coupling extending to the trench updip of Siberut, and updip of the 2007 Mw 8.4 rupture. While the region updip of the 2007 rupture has experienced both afterslip and seismic rupture, the region updip of Siberut has not and appears to have accumulated >11 m of slip deficit since the 1797 rupture. We estimate that despite significant modern slip deficit release, the greater Mentawai segment retains a significant amount of moment accumulation, equivalent to a Mw ∼ 8.8–8.9 event, that is liable to be released in some combination of future seismic ruptures and aseismic slip.

The authors' abstract, as published at the source. Earth and Planetary Science Letters, 2026 · DOI ↗