Kinematics and source zone properties of the 2004 Sumatra‐Andaman earthquake and tsunami: Nonlinear joint inversion of tide gauge, satellite altimetry, and GPS data

Abstract

We (re)analyzed the source of the 26 December 2004 Sumatra‐Andaman earthquake and tsunami through a nonlinear joint inversion of an inhomogeneous data set made up of tide gauges, satellite altimetry, and far‐field GPS recordings. The purpose is twofold: (1) the retrieval of the main kinematics rupture parameters (slip, rake, and rupture velocity) and (2) the inference of the rigidity of the source zone. We independently estimate the slip from tsunami data and the seismic moment from geodetic data to derive the rigidity. Our results confirm that the source of the 2004 Sumatra‐Andaman earthquake has a complex geometry, constituted by three main slip patches, with slip peaking at ∼30 m in the southern part of the source. The rake direction rotates counterclockwise at the northern part of the source, according to the direction of convergence along the trench. The rupture velocity is higher in the deeper than in the shallower part of the source, consistent with the expected increase of rigidity with depth. It is also lower in the northern part, consistent with known variations of the incoming plate properties and shear velocity. Our model features a rigidity (20–30 GPa) that is lower than the preliminary reference Earth model (PREM) average for the seismogenic volume. The source rigidity is one of the factors controlling the tsunami genesis: for a given seismic moment, the lower the rigidity, the higher the induced seafloor displacement. The general consistence between our source model and previous studies supports the effectiveness of our approach to the joint inversion of geodetic and tsunami data for the rigidity estimation.