Anatomy of a Subduction Zone from Ocean Mantle to Crust: Seismicity and Seismic Structure in Northern Chile

该项目的主要目的是研究与俯冲有关的地震结构，包括大型逆冲剪切带和海底海洋板块的精细结构，以及智利北部前弧的震源，采用一套创新的地震活动处理、成像和解释方法。我们将利用这种特殊情况，在那里，包括永久IPOC网络和几个临时网络在内的大量地震台站记录了近十年来异常高的地震活动性。智利北部，特别是最近在梅吉罗内斯半岛安装的MEJIPE网络，也提供了一个难得的机会来监测至少部分陆上地震带。因此，我们期望以尽可能高的分辨率对这个俯冲带的构造和地震结构进行成像。为了详细成像地震结构，我们将应用最近开发的基于微地震偏移的方法，辅以近源反射和转换的建模，以及从精确的差分到达时间估计泊松比的局部变化。我们还将使用时域矩张量反演和地震记录谱分析来描述震源本身，以得出应力降和辐射效率等其他震源参数。综合结果将有助于测试俯冲系统中的主要地震特征是否受流体控制。水合矿物的脱水、流体的圈闭和加压以及流体运移等过程应在地震活动性的弹性参数和时空特征上留下深刻的印记。我们的研究将检测到这种印记，例如，作为超低流速和/或异常高局部Vp/Vs比的区域。该项目的一个重要组成部分将是详细研究智利北部新确认的浅层三重地震带的最深、上层海洋地幔层的地震活动性和相关物理过程。最终，这将有助于总体上提高对中深度地震的理解。

The principal aim of this project is the investigation of subduction-related seismic structures, including the fine-scale structure of the megathrust shear zone and underlying oceanic plate, and of earthquake sources in the northern Chile forearc employing a suite of innovative methods of seismicity processing, imaging and interpretation. We will exploit the specific situation, where an extraordinarily high rate of seismicity has been recorded for almost ten years on a large number of seismic stations, including the permanent IPOC network and several temporary networks. Northern Chile, in particular the recently installed MEJIPE network on the Mejillones peninsula, also offers a rare chance to monitor at least a part of the seismogenic zone onshore. We therefore expect to image the structural and seismic architecture of this subduction zone at highest possible resolution.In order to image seismic structures in detail, we will apply a recently developed micro seismic migration-based approach, complemented by the modelling of near-source reflections and conversions and the estimation of local variations of the Poisson ratio from precise differential arrival times. We will also characterize the earthquake sources themselves using moment tensor inversion in the time domain and the analysis of seismogram spectra to derive other source parameters like stress drop and radiation efficiency.The synthesis of the results will allow to test, if the major seismic signatures in the subduction system are fluid controlled. Processes such as dewatering of hydrated minerals, trapping and pressurization of fluids and fluid migration should leave a strong imprint on the elastic parameters and the spatio-temporal characteristics of seismicity. This imprint will be detectable by our study, e.g. as zones of ultra low velocity and/or anomalous high local Vp/Vs ratios.An important component of the project will be the detailed study of seismicity and related physical processes in the deepest, upper ocean mantle layer of the newly confirmed shallow triple seismic zone in northern Chile. Eventually this will contribute to advance the understanding of intermediate depth earthquakes in general.