The Indonesian region is one of the most seismically active zones on the earth. On December 26, 2004, an M_S 8.7 earthquake (as measured by the China Seismograph Network, or M_w = 9.3 as measured by USGS) struck the west coast of northern Sumatra, Indonesia. By its magnitude it is classified as the world’s fourth largest earthquake since 1900 and the largest one since the 1964 Alaska earthquake. The spatial distribution of the relocation of larger aftershocks (M>4.5) following the main shock suggests a length and width of the rupture of about 1200km and 200km, respectively. The shock triggered massive tsunamis that affected several countries throughout South and Southeast Asia. It is a shallow interplate event of thrust type in the trench. Its epicenter is located at the northwestern end of the Indonesia-Melanesia plate boundary tectonic zone. In 2004, eight shocks of M≥7.0 occurred in this area, showing a migration from east to west. It implies that these shocks represent a correlated and consistent dynamic process along this subduction zone. These interplate events are associated with convergence of several plates and their fast motion in this region, which result in strong and complex structures and deformation. The India-Australia plate is underthrusting toward the Sunda continental block or Burma plate at a low angle, producing a great locked area on the shallow portion of the subduction zone where enormous strain is accumulated. Interseismic uplift recorded by coral growth and horizontal velocities measured by GPS show the geometry of the locked portion of the Sumatra subduction zone. The vertical and horizontal data reasonably match with a model in which the plate interface is fully locked over a significant width. This locked fault zone extends to a horizontal distance of 132km from the trench, which corresponds to a depth of 50km. The sudden ruptures and large-scale slip of this locked area as a release of stress occurred, are the direct cause of the M8.7 earthquake near Indonesia in 2004. On December 26, 2004, an M-S 8.7 earthquake (as measured by the China Seismograph Network, or M_w = 9.3 as measured by the USGS) struck the west coast of northern Sumatra , Indonesia. By its magnitude it is classified as the world’s fourth largest earthquake since 1900 and the largest one since the 1964 Alaska earthquake. The spatial distribution of the relocation of larger aftershocks (M> 4.5) following the main shock suggests a length and width of the rupture of about 1200km and 200km, respectively. The shock triggered massive tsunamis that affected several states throughout South and Southeast Asia. Its epicenter is located at the northwestern end of the Indonesia -Melanesia plate boundary tectonic zone. In 2004, eight shocks of M ≥ 7.0 occurred in this area, showing a migration from east to west. It implies that these shocks represent a correlat ed and consistent dynamic process along this subduction zone. These interplate events are associated with convergence of several plates and their fast motion in this region, which results in strong and complex structures and deformation. The India-Australia plate is underthrusting toward the Sunda continental block or Burma plate at a low angle, producing a great locked area on the shallow portion of the subduction zone where enormous strain is accumulated. Interseismic uplift recorded by coral growth and horizontal velocities measured by GPS show the geometry of the locked portion of the Sumatra subduction The vertical and horizontal data reasonably match with a model in which the plate interface is fully locked over a significant width. This locked fault zone extends to a horizontal distance of 132km from the trench, which corresponds to a depth of 50km. ruptures and large-scale slip of this locked area as a release of stress occurred, are the direct cause of the M8.7 eearthquake in Indonesia in 2004.