Core-mantle boundary deformations triggered by the Sumatra earthquake

Abstract

The devastating megathrust earthquake of December 26 2004 off the west coast of northern Sumatra has been probably the largest since the 1960 Chile event. The occurrence of this event revived the debate, among the scientific community, upon several open geophysical problems possibly connected with the energy release of giant earthquakes. One of these problems concerns the origin of geomagnetic jerks and its eventual relationship with large seismic activity. Though a final answer to this question seems not to be at hand presently, this answer (whatever positive or negative) appears to be connected with the possibility that giant seismic events could cause significant changes in the CMB topography. Until now, no attempts have been made to compute the impact of a seismic event on the CMB: the great Sumatra earthquake, for the first time, gave unambiguous instrumental evidence that the deformation field associated with a giant event is detectable at distances up to several thousands of km with a magnitude of the displacements of the order of 1 mm. Since perturbations to the CMB even smaller than this value are likely to be able to produce a geomagnetic jerk, a precise evaluation of the CMB topography perturbation associated with a giant earthquake like Sumatra has become an important scientific question.