Anatomy of a megathrust: The 2010 M8.8 Maule, Chile earthquake rupture zone imaged using seismic tomography
Anatomy of a megathrust: The 2010 M8.8 Maule, Chile earthquake rupture zone imaged using seismic tomography
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DOI：
10.1016/j.epsl.2014.08.028
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发表时间：
2014-11
影响因子：
5.3
通讯作者：
S. Hicks;A. Rietbrock;I. Ryder;Chao‐Shing Lee;Matthew Miller
中科院分区：
文献类型：
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作者：
S. Hicks;A. Rietbrock;I. Ryder;Chao‐Shing Lee;Matthew Miller
俯冲带孕震部分的地震速度知识可以揭示物质性质如何影响大破裂。2010年智利马乌莱Mw 8.8地震后的余震观测提供了一个特殊的数据集，以检查一个大推力断裂带的物理特性。我们手动分析了来自陆上地震台站和海底地震仪的余震，利用当地地震层析成像得出破裂带的3-D速度模型。从海沟到岩浆弧，我们的速度模型阐明了俯冲带内的主要特征。我们解释了一个东倾的高P波速度异常（> 6.9 km/s）作为俯冲洋壳和低P波速度（< 6.25 km/s）在海洋前弧作为增生杂岩。我们发现两个大的P波速度异常（17.8公里/秒）下的海岸线。这些速度表明，超镁铁质成分，可能与伸展和地幔上涌在三叠纪。我们评估的物理异质性在管理巨型逆冲行为所发挥的作用。在Maule地震期间，最大的滑动发生在中等P波速度（6.5-7.5 km/s）的地区，那里的界面在结构上更均匀。在浅层，高流体压力可能影响地震活动的上倾极限。高速体位于板块界面的上方，在那里同震滑动减少，震后活动最少。北方的速度异常可能作为一个结构不连续的弧前，影响明显的地壳地震活动在Pichilemu地区。我们的工作为前弧的古地质结构如何影响俯冲巨型逆冲断层的地震行为提供了证据。
Abstract Knowledge of seismic velocities in the seismogenic part of subduction zones can reveal how material properties may influence large ruptures. Observations of aftershocks that followed the 2010 M w 8.8 Maule, Chile earthquake provide an exceptional dataset to examine the physical properties of a megathrust rupture zone. We manually analysed aftershocks from onshore seismic stations and ocean bottom seismometers to derive a 3-D velocity model of the rupture zone using local earthquake tomography. From the trench to the magmatic arc, our velocity model illuminates the main features within the subduction zone. We interpret an east-dipping high P-wave velocity anomaly (> 6.9 km/s) as the subducting oceanic crust and a low P-wave velocity (< 6.25 km/s) in the marine forearc as the accretionary complex. We find two large P-wave velocity anomalies (∼ 7.8 km/s) beneath the coastline. These velocities indicate an ultramafic composition, possibly related to extension and a mantle upwelling during the Triassic. We assess the role played by physical heterogeneity in governing megathrust behaviour. Greatest slip during the Maule earthquake occurred in areas of moderate P-wave velocity (6.5–7.5 km/s), where the interface is structurally more uniform. At shallow depths, high fluid pressure likely influenced the up-dip limit of seismic activity. The high velocity bodies lie above portions of the plate interface where there was reduced coseismic slip and minimal postseismic activity. The northern velocity anomaly may have acted as a structural discontinuity within the forearc, influencing the pronounced crustal seismicity in the Pichilemu region. Our work provides evidence for how the ancient geological structure of the forearc may influence the seismic behaviour of subduction megathrusts.