The nature of the subduction wedge in an erosive margin: Insights from the analysis of aftershocks of the 2015 Mw 8.3 Illapel earthquake beneath the Chilean Coastal Range
The nature of the subduction wedge in an erosive margin: Insights from the analysis of aftershocks of the 2015 Mw 8.3 Illapel earthquake beneath the Chilean Coastal Range
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DOI：
10.1016/j.epsl.2019.05.033
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发表时间：
2019-08-15
影响因子：
5.3
通讯作者：
Russo, Raymond
中科院分区：
文献类型：
--
作者：
Comte, Diana;Farias, Marcelo;Russo, Raymond
智利-伊拉佩尔余震实验 (CHILLAX) 地震台网对 2015 年 9 月 16 日智利中部 M8.3 伊拉佩尔地震的余震进行了为期一年的记录。一种新颖的自动拾取算法生成了约 100,000 个事件的初始目录，该算法将自回归检测/起始估计方法与一些最近开发的窗口技术相结合。我们将约 9,000 个最佳记录事件的 P 波和 S 波到达时间与远震 P 波的相对到达时间以及从环境噪声中恢复的瑞利波的相位延迟相结合，生成位于网络下方的安第斯边缘部分的 P 波和 S 波速度的三维图像。最终模型中的余震震源似乎分为四个不同的区域：两个较低的平行区域，向东倾斜约 20 度，一个上部高度活跃的区域，向东倾斜约 30 度，以及一个位于该上部区域和地表之间的较小事件的扩散区域。几乎所有 M > 4 的事件都位于高度活跃区的底部边缘，并定义了一个向东倾斜约 26 度的平面。大多数这些事件具有几乎相同的推力机制，并且通过波速增加的陡峭梯度与较低区域分开。上部区域的下端，深度约 55 公里，以另一个向西倾斜的速度梯度为标志，该速度梯度限制了扩散的浅层活动，并投射到高安第斯山脉以西的地表。我们假设这两个高波速梯度界定的三角形区域是俯冲楔，它是通过俯冲侵蚀从上板块前缘去除材料而产生的，随后在深度处欠镀回到上方板块。该模型解释了我们在地震活动和波速中观察到的许多特征，并且与智利海岸边缘这部分地区的隆起和伸展的地质观察结果一致。该楔子的特征，例如其形状以及与同期弧后构造环境缺乏相关性，表明高安第斯山脉与俯冲界面的行为没有直接关系。 (C) 2019 Elsevier B.V. 保留所有权利。
Aftershocks of the 16 September 2015 M8.3 Illapel earthquake in central Chile were recorded for a period of one year by the Chile-Illapel Aftershock Experiment (CHILLAX) seismic network. An initial catalog of about 100,000 events was generated by a novel automated picking algorithm that combines an auto-regressive detection/onset estimation method with some recently developed windowing techniques. We combine arrival times of P and S waves from about 9,000 of the best recorded of these events with relative arrival times of teleseismic P waves and phase delays of Rayleigh waves recovered from ambient noise to generate a three-dimensional image of P and S wavespeeds in that part of the Andean margin located beneath the network. Hypocenters of aftershocks located in the final model appear to be grouped into four distinct zones: two lower parallel zones that dip about 20 degrees to the east, an upper, highly active zone that dips about 30 degrees to the east, and a diffuse zone of smaller events located between this upper zone and the surface. Nearly all of the events with M > 4 are located at the bottom edge of the highly active zone and define a plane dipping about 26 degrees to the east. Most of these events have almost identical thrust mechanisms and are separated from the lower zones by a steep gradient in increasing wavespeeds. The lower end of the upper zone, at about 55 km depth, is marked by another velocity gradient dipping to the west that bounds the diffuse shallow activity and projects to the surface west of the high Andes. We postulate that the triangular region delimited by these two high wavespeed gradients is a subduction wedge, generated by the removal of material from the leading edge of the upper plate by subduction erosion, and subsequently underplated back on to the overriding plate at depth. This model explains many of the features we observe in the seismicity and wavespeeds and is consistent with geologic observations of uplift and extension in this part of the Chilean coastal margin. Characteristics of this wedge, such as its shape and the lack of correlation with the coeval back-arc tectonic setting, suggest that high Andes are not directly coupled with the behavior of the subduction interface. (C) 2019 Elsevier B.V. All rights reserved.