This proposal requests support to immediately begin both continuous and campaign GPS measurements of ephemeral, post-seismic crustal deformation in the source region of the great Northern Sumatra earthquake of December 2004. This event was one the largest earthquakes in the last 100 years and is the largest to have occurred since the development of GPS, a technology that provides an extraordinary ability to precisely measure tectonic motions. The proposed GPS measurements will provide an unprecedented opportunity to observe the post-seismic time evolution of earth.s response to great earthquakes and their effects on ongoing tectonic activity in this geologically active and complicated area. A rapid response to this earthquake, through the installation and operation of both continuous and campaign GPS stations, is essential to capture the ephemeral, non-secular crustal deformation signals and to support a more widespread campaign GPS effort. An important broader impact of this work will be a contribution to updating seismic and tsunami hazard for the region. The changes in stress caused by this earthquake may trigger significant activity on the other faults in the region. Developments in real time GPS data processing will allow data from the continuous station to be incorporated into the tsunami warning system being developed for the Indian Ocean. Real time displacement data from GPS will compliment seismic data. This is especially important in the case of tsunami generation by slow earthquakes, which are invisible seismically.
