Upper-plate structure in Ecuador coincident with the subduction of the Carnegie Ridge and the southern extent of large mega-thrust earthquakes
Upper-plate structure in Ecuador coincident with the subduction of the Carnegie Ridge and the southern extent of large mega-thrust earthquakes
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DOI：
10.1093/gji/ggz558
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发表时间：
2020-03
影响因子：
2.8
通讯作者：
C. Lynner;C. Koch;S. Beck;A. Meltzer;L. Soto‐Cordero;M. Hoskins;J. Stachnik;M. Ruiz;A. Alvarado;P. Charvis;Y. Font;M. Régnier;H. Agurto‐Detzel;A. Rietbrock;R. Porritt
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文献类型：
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作者：
C. Lynner;C. Koch;S. Beck;A. Meltzer;L. Soto‐Cordero;M. Hoskins;J. Stachnik;M. Ruiz;A. Alvarado;P. Charvis;Y. Font;M. Régnier;H. Agurto‐Detzel;A. Rietbrock;R. Porritt
厄瓜多尔会聚边缘在过去的一个世纪中经历了许多大型逆冲地震，从 1906 年的一次地震开始，地震沿着板块界面传播了 500 公里。 1906 年破裂区的许多分段随后产生了 Mw ≥ 7.7 的事件，最终在 2016 年 4 月 16 日发生了 Mw 7.8 的佩德纳莱斯地震。有趣的是，似乎没有 Mw ≥ 7.7 的大型历史事件向南约 1° 传播，这与卡内基岭的俯冲相一致。我们将佩德纳莱斯地震后部署的临时地震台的数据与厄瓜多尔国家地震台网永久台记录的数据相结合，利用环境噪声断层扫描来辨别厄瓜多尔弧前和科迪勒拉的速度结构。环境噪声层析成像从环境噪声波场中提取 Vsv 信息，并提供对地壳和上地幔速度结构的详细约束。在厄瓜多尔弧前 10 公里处，我们看到了该地区沉积盆地最深处的证据，即普罗格雷索盆地和马纳比盆地。在 30 公里以下的深度，我们观察到增生的快速弧前地体与厄瓜多尔安第斯山脉厚地壳之间存在清晰的界限。在深度约 20 公里处，我们看到强烈的快速度异常，与俯冲的卡内基海岭以及大型逆冲地震的南部边界一致。我们的观察提出了一种可能性，即除了俯冲的卡内基海岭之外，上板块结构在沿厄瓜多尔边缘看到的大事件分割中也发挥了作用。
The Ecuadorian convergent margin has experienced many large mega-thrust earthquakes in the past century, beginning with a 1906 event that propagated along as much as 500 km of the plate interface. Many subsections of the 1906 rupture area have subsequently produced Mw ≥ 7.7 events, culminating in the 16 April 2016, Mw 7.8 Pedernales earthquake. Interestingly, no large historic events Mw ≥ 7.7 appear to have propagated southward of ∼1°S, which coincides with the subduction of the Carnegie Ridge. We combine data from temporary seismic stations deployed following the Pedernales earthquake with data recorded by the permanent stations of the Ecuadorian national seismic network to discern the velocity structure of the Ecuadorian forearc and Cordillera using ambient noise tomography. Ambient noise tomography extracts Vsv information from the ambient noise wavefield and provides detailed constraints on velocity structures in the crust and upper mantle. In the upper 10 km of the Ecuadorian forearc, we see evidence of the deepest portions of the sedimentary basins in the region, the Progreso and Manabí basins. At depths below 30 km, we observe a sharp delineation between accreted fast forearc terranes and the thick crust of the Ecuadorian Andes. At depths ∼20 km, we see a strong fast velocity anomaly that coincides with the subducting Carnegie Ridge as well as the southern boundary of large mega-thrust earthquakes. Our observations raise the possibility that upper-plate structure, in addition to the subducting Carnegie Ridge, plays a role in the large event segmentation seen along the Ecuadorian margin.