Tsunami earthquakes: Vertical pop-up expulsion at the forefront of subduction megathrust

TitleTsunami earthquakes: Vertical pop-up expulsion at the forefront of subduction megathrust
Publication TypeJournal Article
Year of Publication2020
AuthorsHananto N, Leclerc F, Li L, Etchebes M, Carton H, Tapponnier P, Qin Y, Avianto R, Singh SC, Shengji W
JournalEarth and Planetary Science Letters
Date Published05/2020

Published slip distribution models, based on geodetic, seismological and tsunami data, of the M-w 7.8, 2010 Mentawai tsunami earthquake offshore south-central Sumatra, suggest that the large tsunami wave was generated by a narrow swath of high seafloor uplift along the accretionary wedge front, implying higher vertical throw than that consistent with slip on the shallow-dipping megathrust. Here we present high-resolution seismic reflection profiles across the 2010 rupture zone that image the youngest deformation at the accretionary wedge front. The profiles reveal conjugate, steeply-dipping, active thrust faults that branch upwards from the megathrust and bound triangular pop-ups. The seismologically determined co-seismic slip (>= 10 m) on the 6 degrees-dipping decollement probably caused a comparable amount of upward expulsion of these similar to 3 km-wide, flat-topped pop-ups. Co-seismic throw on the approximate to 60 degrees dipping thrusts that bound the pop-up plateaus maximize the uplift of the seafloor and overlying water-column, providing an additional localised tsunami source. Tsunami simulations show that such combined deformation, i.e. the broad-scale seafloor displacement caused by slip on the megathrust and the localized 8-10 m seafloor uplift across a 6-9 km-wide pop-up belt involving up to three pop-ups, is able to reproduce the 2010 tsunami amplitude measured by a DART buoy, and observed run-up heights in the Mentawai Islands. This simple mechanism, observed in analogue sandbox shortening experiments, may thus efficiently generate the oversize waves that characterize Tsunami-Earthquakes. Systematic mapping of pop-ups along accretionary wedge fronts may help identify trench segments prone to produce the special class of seismic events that spawn exceptionally large tsunamis.