Megathrust Earthquakes

Study of Fault Slip and Stress Relaxation Using Satellite Gravity Observations

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Published Date

14-03-2014

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Faculty

Aerospace Engineering

Department

Astrodynamics and Satellite Missions

Abstract

During earthquakes large scale mass displacements take place when slip on a fault deforms the earth’s crust. Besides, in the days to decades after the main shock ongoing deformation is usually observed that is related to relaxation of stresses caused by the earthquake. In this thesis I relate gravity changes as observed by the GRACE satellite mission to solid earth deformation caused by earthquakes. Special attention is given to modeling the contribution of ocean mass redistribution to gravity changes, and its relation to changes in bathymetry. I show that common modeling practices are usually not properly taking into account the effect of ocean water redistribution when computing seismic gravity changes. Using a combination of GRACE data and GPS observations I interpret ongoing gravity changes and crustal motions after the 2004 Sumatra-Andaman earthquake as dominantly caused by viscoelastic mantle flow. Contrasts in relaxation styles from both observation types are related to lateral variations in mantle rheology below the subduction zone. The combined analysis of GPS and GRACE data strongly suggest that the mantle at the continental side of the subduction zone is weaker than the oceanic side.