Himalayan megathrust geometry and relation to topography revealed by the Gorkha earthquake
Himalayan megathrust geometry and relation to topography revealed by the Gorkha earthquake
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DOI：
10.1038/ngeo2623
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发表时间：
2016-02-01
影响因子：
18.3
通讯作者：
Stevens, V. L.
中科院分区：
文献类型：
--
作者：
Elliott, J. R.;Jolivet, R.;Stevens, V. L.
喜马拉雅山脉是一些最大的大陆地震的发生地，包括 2015 年发生的 7.8 级廓尔喀地震。相互竞争的假设表明，喜马拉雅山的地形是持续的，板块汇聚要么主要在主板边界断层上，要么更广泛地跨越多个较小的逆冲断层。在这里，我们使用地表位移的大地测量来表明廓尔喀地震使喜马拉雅主逆冲断层破裂。地震使加德满都盆地抬升约1m，但导致更北的喜马拉雅山高地下沉约0.6m。我们利用大地测量数据，结合地质、地貌和地球物理分析，来约束加德满都地区喜马拉雅主冲断层的几何形状。结构分析以及震间和同震位移最好的解释是陡峭的浅逆冲断层在 5 至 15 公里深度处变平，并连接到中地壳更陡的逆冲断层。我们认为，目前横跨喜马拉雅山的汇聚主要是由该断层调节的——较小的逆冲断层不需要发生明显的运动。此外，考虑到廓尔喀地震导致喜马拉雅高山下沉，并且我们的断层几何形状解释了测量到的震间位移，我们认为喜马拉雅地形的增长可能主要发生在持续的震后阶段。
The Himalayan mountain range has been the locus of some of the largest continental earthquakes, including the 2015 magnitude 7.8 Gorkha earthquake. Competing hypotheses suggest that Himalayan topography is sustained and plate convergence is accommodated either predominantly on the main plate boundary fault, or more broadly across multiple smaller thrust faults. Here we use geodetic measurements of surface displacement to show that the Gorkha earthquake ruptured the Main Himalayan Thrust fault. The earthquake generated about 1m of uplift in the Kathmandu Basin, yet caused the high Himalaya farther north to subside by about 0.6 m. We use the geodetic data, combined with geologic, geomorphological and geophysical analyses, to constrain the geometry of the Main Himalayan Thrust in the Kathmandu area. Structural analyses together with interseismic and coseismic displacements are best explained by a steep, shallow thrust fault flattening at depth between 5 and 15 km and connecting to a mid-crustal, steeper thrust. We suggest that present-day convergence across the Himalaya is mostly accommodated by this fault-no significant motion on smaller thrust faults is required. Furthermore, given that the Gorkha earthquake caused the high Himalayan mountains to subside and that our fault geometry explains measured interseismic displacements, we propose that growth of Himalayan topography may largely occur during the ongoing post-seismic phase.