The Sumatra subduction zone: A case for a locked fault zone extending into the mantle
The Sumatra subduction zone: A case for a locked fault zone extending into the mantle
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苏门答腊俯冲带：锁定断层带延伸至地幔的案例
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发表时间：
2004
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通讯作者：
P. Henry
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作者：
M. Simoes;J. Avouac;R. Cattin;P. Henry
[1]目前的观点是，在大的板间地震之间的时间间隔内保持锁定的俯冲界面部分，以下称为锁定断裂带(LFZ)，不会延伸到地幔，因为地幔楔体的蛇纹化将有利于稳定的无震滑动。在这里，我们在苏门答腊岛俯冲带的情况下测试了这一观点，在那里，LFZ的下倾端可以很好地受到珊瑚生长和GPS水平形变测量得出的隆起模式和速度的约束。这些大地测量数据由嵌入在弹性半空间中的蠕动位错模拟而成，表明LFZ从海沟延伸132±10/7公里，深度在35-57公里之间。将这一信息与二维重力模拟和地震活动所约束的板块界面的几何形状相结合，我们发现LFZ延伸到弧前莫霍面以下，距离海沟的水平距离为110公里，�深度估计为30公里。因此，在这个特殊的岛弧背景下，LFZ很可能延伸到地幔，这意味着地幔不是蛇纹状的，或者蛇纹岩的存在并不一定意味着稳定的滑动。根据热模拟，LFZ下倾端的温度估计为2 6 0±10 0�C，这一温度对于热激活的韧性流来说似乎太低，因此无地震滑动很可能是由于压力和/或温度诱导的稳态脆性滑动，可能是由俯冲板块释放的流体有利的。指标术语：7223地震学：地震危险性评估和预测；1206大地测量和重力：地壳运动-板间(8155)；1219大地测量和重力：局部重力异常和地壳结构；3902矿物物理：蠕变和变形；关键词：闭合断裂带，震间变形，苏门答腊岛
[1] A current view is that the portion of the subduction interface that remains locked in the time interval between large interplate earthquakes, hereinafter referred to as the locked fault zone (LFZ), does not extend into the mantle because serpentinization of the mantle wedge would favor stable aseismic sliding. Here, we test this view in the case of the Sumatra subduction zone where the downdip end of the LFZ can be well constrained from the pattern and rate of uplift deduced from coral growth and from GPS measurements of horizontal deformation. These geodetic data are modeled from a creeping dislocation embedded in an elastic half-space and indicate that the LFZ extends 132 ± 10/7 km from the trench, to a depth between 35 and 57 km. By combining this information with the geometry of the plate interface as constrained from two-dimensional gravimetric modeling and seismicity, we show that the LFZ extends below the forearc Moho, which is estimated to lie at a depth of � 30 km, at a horizontal distance of 110 km from the trench. So, in this particular island arc setting, the LFZ most probably extends into the mantle, implying that either the mantle is not serpentinized, or that the presence of serpentine does not necessarily imply stable sliding. From thermal modeling, the temperature at the downdip end of the LFZ is estimated to be 260 ± 100� C. This temperature seems too low for thermally activated ductile flow, so that aseismic slip is most probably due to pressure and/ or temperature induced steady state brittle sliding, possibly favored by fluids released from the subducting slab. INDEX TERMS: 7223 Seismology: Seismic hazard assessment and prediction; 1206 Geodesy and Gravity: Crustal movements—interplate (8155); 1219 Geodesy and Gravity: Local gravity anomalies and crustal structure; 3902 Mineral Physics: Creep and deformation; KEYWORDS: locked fault zone, interseismic deformation, Sumatra