Co-seismic fault geometry and slip distribution of the 26 December 2004, giant Sumatra–Andaman earthquake constrained by GPS, coral reef, and remote sensing data

Abstract

We analyze co-seismic displacement field of the 26 December 2004, giant Sumatra–Andaman earthquake derived from Global Position System observations, geological vertical measurement of coral head, and pivot line observed through remote sensing. Using the co-seismic displacement field and AK135 spherical layered Earth model, we invert co-seismic slip distribution along the seismic fault. We also search the best fault geometry model to fit the observed data. Assuming that the dip angle linearly increases in downward direction, the postfit residual variation of the inversed geometry model with dip angles linearly changing along fault strike are plotted. The geometry model with local minimum misfits is the one with dip angle linearly increasing along strike from 4.3o in top southernmost patch to 4.5o in top northernmost path and dip angle linearly increased. By using the fault shape and geodetic co-seismic data, we estimate the slip distribution on the curved fault. Our result shows that the earthquake ruptured ~200-km width down to a depth of about 60 km. 0.5–12.5 m of thrust slip is resolved with the largest slip centered around the central section of the rupture zone 7ºN–10ºN in latitude. The estimated seismic moment is 8.2 × 1022 N m, which is larger than estimation from the centroid moment magnitude (4.0 × 1022 N m), and smaller than estimation from normal-mode oscillation data modeling (1.0 × 1023 N m).