Core-mantle boundary deformations and J2 variations resulting from the 2004 Sumatra earthquake

TL;DR

This study models the deformation at the Earth's core-mantle boundary caused by the 2004 Sumatra earthquake, analyzing coseismic and postseismic effects on gravity field variations, especially J2, for different viscosity models.

Contribution

It introduces a semi-analytic model to predict core-mantle boundary deformations and postseismic gravity field changes following a major earthquake.

Findings

Coseismic boundary deformation is on the order of millimeters.

Postseismic J2 variations depend on asthenosphere viscosity.

Detectable J2 signals are expected for viscosities below 10^18 Pa s.

Abstract

The deformation at the core-mantle boundary produced by the 2004 Sumatra earthquake is investigated by means of a semi-analytic theoretical model of global coseismic and postseismic deformation, predicting a millimetric coseismic perturbation over a large portion of the core-mantle boundary. Spectral features of such deformations are analysed and discussed. The time-dependent postseismic evolution of the elliptical part of the gravity field (J2) is also computed for different asthenosphere viscosity models. Our results show that, for asthenospheric viscosities smaller than 10^18 Pa s, the postseismic J2 variation in the next years is expected to leave a detectable signal in geodetic observations.