Cornelis Wilhelmus Kreemer

Solid Earth Deformations Induced by the Sumatra Earthquakes of 2004–2005: GPS Detection of Co-Seismic Displacements and Tsunami-Induced Loading

The two great Sumatra earthquakes of December 26, 2004, and March 28, 2005, are associated with a number of geodynamic processes affecting Earth’s shape, gravity field and rotation on a wide range of spatial and temporal scales, including co-seismic strong motion, static co-seismic displacements, surface loading due to the tsunami, normal modes, and transient post-seismic deformations. The December 26, 2004, earthquake is the first one with Mw >0 observed with space-geodetic techniques. Thus, new insight into the earthquake processes and associated phenomena can be expected from studies of space-geodetic, and particularly GPS, observations. Here we focus on the static co-seismic offsets and the tsunami loading signal. The global patterns of the static co-seismic offsets induced by the earthquakes are determined from time series of daily displacements resulting from an analysis of the GPS data from selected stations of the global IGS network. Our estimates are compared to similar estimates computed in other studies. The differences between the independent estimates are mostly within the uncertainties of the offsets (2 to 4 mm). The global pattern of the computed offsets is in agreement with the spatial fingerprint predicted by a reasonable rupture model. Initial model predictions of the tsunami-induced loading signal show that the peak amplitudes are of the order of 10 to 20 mm. If detectable in GPS time series with low latency, the loading signal could be utilized in a tsunami early warning system.