Collaborative Research: The Peru Subduction Experiment (PeruSE), a Seismic Investigation of the Role of Water in the Lithospheric Dynamics of Subduction Zones

印尼、中国、海地和智利最近的地震历史表明，俯冲带会产生最大的地震。地震发生在岩石易碎且应力高到足以克服摩擦的地方。摩擦力取决于岩石的性质和水的含量，以及水是自由施加孔隙压力，还是在变质岩中被晶体束缚。释放的水引起爆炸性火山活动。了解力和地震机制对于估计灾害是很重要的。特别是，我们试图利用地震和跨学科的数据来了解秘鲁俯冲带的脱水是如何发生的，它对摩擦、流变学和火山作用的影响。这项工作对于估计该地区主要城市的地震和火山危险，以及了解过去的构造，以及导致构造结构和大陆矿化的过程都很重要。秘鲁是研究水流路径、地震、地震耦合和火山活动之间关系的绝佳地点。特别是，在秘鲁南部，板块有一个陡峭的倾斜，火山发生在板块的上方，板块的深度约为100公里。相比之下，更北的板块倾角较浅，没有火山，但深地震发生在约600公里的深度，是世界上最深的地震之一。地震阵列深探是推断地球深处性质的首要方法。目的是研究地壳和地幔性质的对比，以及从非火山平板到火山陡板俯冲过渡期间地震活动的对比，并推断水的路径。水对摩擦、地震速度、Q、变质变化、融化和地震的产生有主要影响。地震层析成像和地震活动性将用于绘制这些效应的三维地图。我们的地震阵列实验涉及秘鲁的一个由4个线性网络组成的宽带网络。1号线由50个车站组成，从阿雷基帕附近的海岸到的的喀喀湖，横跨陡峭的平板。3号线是平行的，但向北穿过库斯科的平板地区。2号线和4号线分别是安第斯山脉和海岸沿线的连接线。这四条线路形成了一个由125个车站组成的盒子状网络。每条线路由25到50个宽带地震站组成，间隔6-12公里，将记录一到两年，以提供该地区前所未有的结构和地震活动覆盖。我们想回答关于俯冲的力学和矿化的基本问题。我们的实验涉及许多秘鲁人，既有大学和研究所的专业人员，也有主持我们电台的普通民众。秘鲁受到大地震的威胁，例如2007年皮斯科发生的毁灭性地震和2001年发生的地震。海啸也是一个威胁。当地居民受教育程度越高，准备就越充分。我们会透过“综合注册资讯系统”把资料提供给社会各界。本项目由地球物理计划和国际科学与工程办公室美洲计划资助。

As the recent history of earthquakes in Indonesia, China, Haiti and Chile has demonstrated, subduction zones generate the largest earthquakes. Earthquakes occur where the rock is brittle and stresses are high enough to overcome friction. The friction depends on the properties of the rock and water content, and whether the water is free to exert pore pressure, or is crystallographically bound in metamorphic rocks. Released water causes explosive volcanism. Understanding the forces and earthquake mechanisms is important for estimating hazard. In particular, we seek to use seismic and interdisciplinary data to understand how dehydration takes place in the Peru subduction zone, its effect on friction, rheology and volcanism. The work is important both to estimate the earthquake and volcanic hazard of major cities in the region as well as understanding past tectonics, and the processes that led to the tectonic structure and the mineralization of continents.Peru is an excellent place to study the relationship between the pathways of water, earthquakes, seismic coupling and volcanism. In particular, in southern Peru the slab has a steep dip and volcanoes occur above it where the slab reaches depths of about 100 km. In contrast, further north the slab dip is shallow and there are no volcanoes, but deep earthquakes occur at depths of ~600 km, some of the deepest in the world. Seismic array deep-sounding is the premier method to infer properties deep in the Earth. The goals are to investigate the contrasts in the properties of the crust and mantle, and contrasts in earthquake activity across the transition from non-volcanic flat-slab to volcanic steep-slab subduction and to infer the water pathways. Water has a major effect on friction, seismic velocities, Q, metamorphic changes, melting, and the generation of earthquakes. Seismic tomography and seismicity will be used to map these effects in 3D. Our seismic array experiment involves a broadband network in Peru comprised of 4 linear networks. Line 1 consists if 50 stations that run from the coast near Arequipa to Lake Titicaca across the steep slab. Line 3 is parallel but runs further north through Cusco above the flat-slab region. Lines 2 and 4 are connecting lines along the Andes and the coast respectively. The four lines form a box-shaped network of 125 stations spanning the transition. Each line is comprised of twenty five to fifty broadband seismic stations at 6-12 km spacing and will record for one to two years to give an unprecedented coverage of the structures and seismicity of the region. We would like to answer fundamental questions on the mechanics and mineralization of subduction.Our experiment involves many Peruvians both professionally in universities and institutes and the general population who host our stations. Peru is threatened by large earthquakes, such as the recent Pisco 2007 devastating earthquake and the 2001 event demonstrated. Tsunamis are also a threat. The more educated are the local population the better prepared. We will make the data available to the community through IRIS.This project is funded by the Geophysics Program and the Americas Program of the Office of International Science and Engineering.