2004年12月26日苏门答腊—安达曼大地震构造特征及地震海啸灾害

The Dec. 26, 2004 Sumatra-Andaman earthquake: Tectonic setting and the tsunami disaster.

2004年12月26日在印度尼西亚苏门答腊岛西侧海域发生的地震是自1964 年阿拉斯加大地震以来最大的地震,震级达到9级或9级以上。它是由印度洋板块向缅甸微板块底下俯冲过程中的逆断层作用造成的。印度洋板块以每年6~7 cm的速率向北北东方向运动,与南亚板块发生斜向聚敛俯冲,此运动在该地区解耦为印度洋板块沿巽他海沟的正向俯冲及缅甸微板块东侧的右旋走向平移运动。主震破裂模型研究的结果表明,破裂是由南向北传播的,地震破裂带长达1 200余km,宽度约100 km,最大位移约为20 m,地震断层向上穿透海沟底面,估计约有10 m左右的错距。这次大地震的同震效应导致地球自转轴摆动、地球自转加速,日长缩短。据目前统计,地震引发的大海啸造成305 276人死亡,被此次海啸夺走生命的人数超过了有史以来历次大海啸灾难中死亡人数的总和。

A great earthquake occurred off the west coast of northern Sumatra, Indonesia, on Dec.26, 2004 with M_w 9.0 or above. This earthquake is the largest since the Alaska earthquake in 1964. This devastating earthquake occurred as the result of subduction of the India plate beneath the Burma microplate. The India plate moves toward the north-northeast with respect to the interior of the Eurasia plate with velocities of about 6～7 cm/a in the region of the earthquake. This results in oblique convergence along the Sunda trench. The oblique motion is partitioned into thrust-faulting, which occurs at the interface between the India plate and the Burma microplate.A slip component is directed at a large angle to the orientation of the trench.Strike-slip faulting, which occurs on the eastern boundary of the Burma microplate has a slip component directed approximately parallel to the trench. Currently available models of the December 26 main fault displacement indicates that the fault-rupture propagated to the north-northwest from the epicenter and extended for more than 1 200 kilometers. The finite fault model implies that the width of the earthquake rupture, measured perpendicular to the Sunda trench, was about 100 kilometers, and that the maximum displacement on the fault plane was about 20 meters. The sea floor overlying the thrust fault would have been uplifted by about 10 meters. The December 26 earthquake has left a co-seismic kink in the polar path and the reduction of the length-of-day. This mega-earthquake produced a destructive tsunami. The death toll caused by this tsunami is estimated at about 305 276 exceeding the total of previous mega-earthquakes.