The Fine Structure of a Seismogenic Zone Revealed by Aftershocks of the 2014 Iquique Mw 8.1 Earthquake

全球大多数地震发生在俯冲带。在沿着这些汇聚的板块边界的大地震期间（m>8），板块之间的界面在深度约40公里处破裂。海沟标志着俯冲的开始，而发生大断裂的发震带几乎完全位于海洋前弧下方。该项目的目标是利用余震序列的高分辨率定位技术，培养我们对海洋前弧地震后松弛过程的结构影响的理解。在这里，我们想把重点放在智利北部的侵蚀边缘，那里2014年4月1日发生的8.1级伊基克地震使海洋前弧破裂。我们建议将2014年12月至2016年11月期间安装的14个海底站（OBS）的24个月连续数据与永久IPOC网络和临时陆地站的数据结合起来。海上OBS数据与陆上地震学数据的整合提供了一个海岸线交叉数据集，具有独特的能力，可以全面成像智利北部前弧的整体。以前的数据集只能捕捉到大陆架的近海区域，或者从弧形到海岸线的陆上部分。在这里，我们有一个独特的机会来弥合这一差距。特别是，我们想要调查2014年破裂区的地震活动性，以及向伊基克地震以南剩余地震间隙的过渡，伊基克地震上一次破裂是在1877年。在项目的第一阶段，我们计划探测和定位地震活动，以获得高分辨率的地震目录。这将有助于解决震后活动与构造特征之间的空间关系，如板块界面地形变化、展向断层、发震区内部结构或瞬态流体向上覆板块的迁移，从而建立脱水过程与上板块地震活动分布之间的可能相关性。然后，应用局部地震层析成像确定二维和三维vp和vp/vs速度结构，有助于更好地理解弧前的横向和下倾结构变化。这些发现将与最近的高分辨率反射地震网格和2016年由RV Langseth获得的3D折射实验数据集的结果共同解释。因此，这里提出的项目目标是将海岸线穿越地震学数据与二维和三维活动地震实验信息以及构造分割数据的结构约束相结合，采用独特的整体方法。

The majority of global earthquakes occur along subduction zones. During great earthquakes (M>8) along these convergent plate boundaries the interface between the plates ruptures down to depths of ~40 km. The trench marks the onset of subduction and the seismogenic zone where large ruptures occur is almost exclusively located beneath the marine forearc. The objective of the proposed project is to nurture our understanding of the structural influence on postseismic relaxation processes of a marine forearc using high-resolution location techniques of an aftershock sequence. Here, we want to focus on the erosive margin in North Chile where the Mw 8.1 Iquique earthquake on 1 April 2014 ruptured the marine forearc. We propose to combine 24 months of continuous data from 14 ocean bottom stations (OBS) installed between December 2014 and November 2016 with the data from the permanent IPOC network and temporary landstations. The integration of the offshore OBS data with the onshore seismology data provides a shore-line crossing data set with the exceptional capability to fully image the Northern Chilean forearc in its entity. Previous data sets were only capable to capture the offshore domain up to the continental shelf or the onshore portion from the arc to the coastline. Here, we have the unique opportunity to bridge this gap. In particular, we want to investigate seismicity in the 2014 rupture area and the transition to the remaining seismic gap to the south of the Iquique earthquake, which last ruptured in 1877. In the first phase of the project we plan to detect and locate the seismicity in order to obtain a high-resolution earthquake catalogue. This will allow resolving the spatial relation between postseismic activity and structural features such as variations in the topography of the plate interface, splay faults, internal structure of the seismogenic zone or transient fluid migration into the overriding plate, to establish a possible correlation between dehydration processes and the seismicity distribution in the upper plate. Then, local earthquake tomography will be applied to determine the 2D and 3D vp and vp/vs velocity structure and will contribute to a better understanding of lateral and downdip structural changes of the forearc. The findings will be jointly interpreted with the results of a recent high-resolution reflection seismic grid and a 3D refraction experiment dataset acquired during 2016 with RV Langseth. The project proposed here hence targets a unique holistic approach by combining shore-line crossing seismology data with information from 2D and 3D active seismic experiments and structural constraints on tectonic segmentation data.