关键词: 印尼8.7级大地震, 俯冲带, 地震迁移, 闭锁区

Abstract: The Indonesia region is one of the most seismically active zones of the earth. On December 26, 2004 an M_S 8.7 (given by China Seismograph Network, M_W=9.3 given by USGS) earthquake occurred off the west coast of northern Sumatra, Indonesia. Its magnitude classifies it as the fourth largest earthquake in the world since 1900 and the largest 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 events of M≥7 happened in this zone, 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 are reasonably well reconciled 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 the release of stress are the direct cause of the M 8.7 earthquake near Indonesia in 2004.

Key words: M 8.7 earthquake near Indonesia, subduction zone, earthquake migration, locked area