SUMMARY

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 M_w ≥ 7.7 events, culminating in the 16 April 2016, M_w 7.8 Pedernales earthquake. Interestingly, no large historic events M_w ≥ 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.

中文翻译：

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厄瓜多尔的上板块构造与卡内基岭俯冲和南部大型特大推力地震同时发生

概要

厄瓜多尔的会聚边缘在上个世纪经历了许多大的特大推力地震，始于1906年的地震，沿板块界面延伸了500 km。1906年破裂区的许多小分段随后生产中号_W¯¯  ≥7.7的事件，在2016年4月16日，男最终_W¯¯ 7.8佩德纳莱斯地震。有趣的是，没有大的历史事件中号_{w ^} ≥7.7似乎已向南延伸约1°S，这与卡内基岭俯冲相吻合。我们将Pedernales地震后部署的临时地震台站的数据与厄瓜多尔国家地震台网的永久台站记录的数据结合起来，以使用环境噪声层析成像技术识别厄瓜多尔前臂和科迪勒拉的速度结构。环境噪声层析成像技术从环境噪声波场中提取Vsv信息，并提供了对地壳和上地幔速度结构的详细约束。在厄瓜多尔前臂的上10公里，我们看到该地区沉积盆地最深的部分，即Progreso和Manabí盆地的证据。在30公里以下的深度，我们观察到增生的快速前臂地形与厄瓜多尔安第斯山脉的厚皮之间有清晰的轮廓。在约20 km的深度处，我们看到了一个强烈的快速速度异常，该异常与俯冲卡内基山脊以及大型超推力地震的南部边界重合。我们的观察结果提出，除了俯冲的卡内基岭外，上板块结构在沿厄瓜多尔边缘看到的大事件分割中也起作用。