Seminário: Megathrust slip behavior for great earthquakes along different subduction settings from GOCE Gravity Field Derivatives

01/07/2021 - 16:30
Transmissão online

O seminário do Departamento de Geofísica será ministrado por Orlando Alvarez (Universidad Nacional de San Juan - UNSJ/CONICET).

Resumo: The characterization of a seismogenic zone associated with the rupture process that occurs during great megathrust earthquakes has been approached from different perspectives. During the last two decades, space geodesy allowed mapping accurately rupture areas, slip distribution and seismic coupling by obtaining refined inversion models and greatly improving the study of great megathrust earthquakes. A better understanding of these phenomena involving large areas of hundreds of square kilometres over the interplate region came from the last gravity satellite mission that allowed detecting mass transfer through the Earth interior. After studding different megathrust earthquakes, mainly along the Chilean margin, we found that by performing a direct modelling of satellite GOCE (Gravity field and steady-state Ocean Circulation Explorer) derived gravity gradients, up to degree/order N=200 of the harmonic expansion, allows inferring mass heterogeneities located at an approximate depth of 31 km, just along the plate interface where most (but not all) significant slip occurs. From this we found that the maximum vertical displacements were located close to gravity gradient minima lobes in the forearc zone. We also observed that along strike seismic segmentation is correlated to gravity derivatives (along strike and along dip), being slip increased at gravity lows and arrested at gravity highs.
In this seminar I will present our results from comparing the vertical gravity gradient to well-constrained coseismic slip models for most of the last major earthquakes along the Southamerican, Sunda, and Japan margins. From a cross-spectral analysis we corroborated quantitatively that the vertical gravity gradient correlates to co-seismic slip distribution, with correlation coefficients ranging from 0.6 to 0.9 for different events at λ=200km. The degree of interseismic coupling also presents a good correspondence to the vertical gravity gradient, showing an inverse relationship, with low degrees of coupling over regions of relatively higher density. By combining this data with geodetical and seismological data it could be possible to delimit and monitor areas with a higher potential seismic hazard around the world.