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2004年12月26日苏门答腊特大地震是过去50年间在俯冲带发生的第三大地震。其破裂开始于锡默卢岛西北部30～40km深处(Lay et al,2005),传播1300km至安达曼群岛北部(Ammon et al,2005)。这次大地震是由俯冲的印度-澳大利亚板块与上部的巽他板块之间界面的突然滑动引起的(Rhie et al,2007;Vigny et al,2005)。尽管俯冲界面结构的详细认识对于确定大型逆冲地震潜在源非常重要,但是,目前为止可用的数据(Henstock et al,2006;Sibuet et al,2007;Dewey et al,2007;Engdahlet al,2007)还无法提供这样的信息。本文展示了震源区一条高质量的地震剖面,其展布从深海平原向下延伸到弧前下面40km。地震数据显示,俯冲地壳和大洋莫霍面(地壳-地幔边界)被陆向倾斜的逆冲断层损坏并移位,意味着此大型逆冲断层目前位于大洋地幔内。我们对增生楔前缘的活动逆冲断层成像,其特点与陡峭倾斜面上的逆冲型余震一致。我们的观测结果表明,是壳幔间的强耦合导致地幔岩石脆性破裂,从而引发此次异常大的地震。
The Sumatran earthquake on December 26, 2004 is the third major earthquake in the subduction zone in the past 50 years. The rupture began 30 to 40 km deep in the northwestern Semeru Island (Lay et al., 2005) and spread 1,300 km to the northern part of the Andaman Islands (Ammon et al., 2005). The massive earthquake was caused by a sudden slippage of the interface between the subducted Indo-Australian plate and the upper plate (Rhie et al, 2007; Vigny et al., 2005). Although detailed understanding of the subduction interface structure is important for identifying potential sources of large thrusts, the data so far available (Henstock et al, 2006; Sibuet et al, 2007; Dewey et al, 2007; Engdahlet al, 2007) Can not provide such information. This article shows a high-quality seismic section in the source area that extends from deep-sea plains down to 40 km below the arc. Seismic data show that the subducted crust and the oceanic Moho (crust-mantle boundary) are damaged and displaced by tending to tilt thrusts, meaning that this large thrust is currently within the oceanic mantle. We image the active thrust fault at the front of the accretionary wedge, which is consistent with the thrust-type aftershocks on the steeply sloped surface. Our observations show that the strong mantle interaction between the mantle and the mantle caused the brittle fracture of the mantle rock, triggering this unusually large earthquake.