Megathrust Slip Behavior for Great Earthquakes Along the Sumatra-Andaman Subduction Zone Mapped From Satellite GOCE Gravity Field Derivatives

ÁLVAREZ, ORLANDO; PECHUAN CANET, STEFANIE; GIMENEZ, MARIO; FOLGUERA, ANDRÉS

Frontiers in Earth Science

Frontiers Media S.A.

Lugar: Lausanne; Año: 2021 vol. 8 p. 1 - 22

During the last two decades, space geodesy allowed mapping accurately rupture areas, slipdistribution, and seismic coupling by obtaining refined inversion models and greatly improvingthe study of great megathrust earthquakes. A better understanding of these phenomenainvolving large areas of hundreds of square kilometers came from the last gravity satellitemission that allowed detecting mass transfer through the Earth interior. In this work, weperformed direct modeling of satellite GOCE (Gravity Field and Steady-StateOcean CirculationExplorer) derived gravity gradients up to degree/order N 200 of the harmonic expansion andthen corrected this by the effect of topography. Cutting off the model up to this degree/orderallows inferringmass heterogeneities located at an approximate depth of 31 km, just along theplate interface where most (but not all) significant slip occurs. Then, we compared the verticalgravity gradient to well-constrained coseismic slip models for three of the last majorearthquakes along the Sunda interface. We analyzed seismic rupture behavior for recentand for historical earthquakes along this subduction margin and the relationship of the degreeof interseismic coupling using the gravity signal. From this, we found that strong slip patchesoccurred along minima gravity gradient lobes and that the maximum vertical displacementswere related quantitatively to the gravity-derived signal. The degree of interseismic couplingalso presents a good correspondence to the vertical gravity gradient, showing an inverserelationship, with low degrees of coupling over regions of relatively higher density. This alongstrikesegmentation of the gravity signal agrees with the along-strike seismic segmentationobserved from recent and historical earthquakes. The thermally controlled down-dip ending ofthe locked fault zone along central Sumatra also presented an inverse relationship with thedensity structure along the forearc inferred using our modeling. From this work, we inferreddifferentmass heterogeneities related to persistent tectonic features along themegathrust andalong the marine forearc, which may control strain accumulation and release along themegathrust. Combining these data with geodetical and seismological data could possiblydelimit and monitor areas with a higher potential seismic hazard around the world.