Deformation, Fragmentation and Seismic Hazards on the Western Edge of India

2005年发生在克什米尔的里氏7.6级大地震（死亡人数85,000人）是地震学家预测到的几次地震之一，因为已知喜马拉雅地区有地震危险，在过去的1000年里，喜马拉雅地区发生过类似的破坏性地震。那里的地震是由印度以每年2英寸的速度向北移动到亚洲引起的。由于同样的原因，地震也发生在印度板块的西部和东部边缘。东部最大的地震是2004年苏门答腊/安达曼9.1级地震（造成30万人死亡）。最近在印度板块西缘的巴基斯坦没有发生大地震，但是有充分的理由认为应该发生大地震。巴基斯坦西南部的地震可能会使拥有1200万人口的巴基斯坦最大城市卡拉奇陷入瘫痪，就像1935年奎达被7.7级地震摧毁（死亡人数为3.5万人）一样。卡拉奇的毁灭对巴基斯坦的经济来说将是灾难性的。和洛杉矶一样，卡拉奇在250年前也是一个渔村，直到最近50年才成为特大城市。与洛杉矶不同，这里没有抗震设施，也没有破坏性地震的历史。该项目的目的之一是找出历史上没有地震是因为没有发生地震，还是像我们怀疑的那样，是因为地震间隔太长而无法被其200年的殖民历史记录下来。印度板块的边缘，从南部的卡拉奇以西的海岸，到北部的喀布尔以东的阿富汗和巴基斯坦之间的山脉，可能会被锁定，为未来的地震做准备，它可能会发生抗震滑动（就像加利福尼亚中部的部分地区一样），或者它可能是一个广泛的旋转地质块区域，就像滚珠轴承一样，允许板块相互滑动。我们计划一系列的全球定位系统（GPS）测量，将唯一区分这三种可能性。测量结果将告诉我们板块边缘的相对速度、变形带的宽度以及两个板块被锁定的深度——这些信息将用于量化该地区的地震生产力，并确定未来最有可能发生破坏性地震的位置。这些信息对该地区的地震工程师至关重要，并将决定未来30年的建筑政策。这些测量还将提供重要的物理约束和应力的性质，这些应力允许大陆转换板块边界，如圣安德烈亚斯断层，随着时间的推移滑动和演变。实地调查是在巴基斯坦三所大学和印度两所大学的科学家和工程师的密切合作下进行的，并因此建立了对美国在这些发展中国家的形象大有裨益的国际关系。由于该项目的国际性质，这项工作由地球物理计划和国际科学与工程办公室共同资助。

The 2005 catastrophic Mw7.6 earthquake in Kashmir (death toll 85,000) was one of several earthquakes that were anticipated by seismologists because of the known seismic hazard of the Himalaya where similar damaging earthquakes have occurred throughout the past 1000 years. The earthquakes there are caused by the northward movement of India towards Asia at a rate of 2 inches/year. For the same reasons earthquakes also occur along the western and eastern edges of the Indian plate. The largest in the east was the Mw9.1 Sumatra/Andaman earthquake of 2004 (death toll 300,000). No great earthquakes have occurred recently on the western edge of the Indian plate in Pakistan, yet there are good reasons to suppose that they should. An earthquake in SW Pakistan could cripple Karachi, Pakistan's largest city with 12 million people, just as Quetta was destroyed in 1935 by an Mw7.7 earthquake (death toll 35,000). The destruction of Karachi would be catastrophic to the economy of Pakistan. Like Los Angeles, Karachi is a city that was a fishing village 250 years ago and has only in the past 50 years achieved megacity status. Unlike Los Angeles no earthquake resistance is in place, and no history of damaging earthquakes has survived. One aim of the project is to find out whether the historical absence of earthquakes is because no earthquakes occur, or whether, as we suspect, it is because they recur at intervals too long to be recorded by its 200 year colonial history.The edge of the Indian plate, which passes from the coast west of Karachi in the south, to the mountains that separate Afghanistan from Pakistan east of Kabul in the north, could be locked, preparing for a future earthquake, it could be sliding aseismically (like parts of central California, or it could be a wide region of rotating geological blocks, that act like ball-bearings permitting the plates to slide past each other. We plan a series of Global Positioning System (GPS) measurements that will uniquely distinguish between these three possibilities. The measurements will tell us the relative velocities at the edge of the plate, and the width of the zone of deformation, and the depth at which the two plates are locked - information that will be used to quantify the seismic productivity of the region, and identify the most probable future location of future damaging earthquakes. This information is of fundamental importance to earthquake engineers in the region, and will dictate building policies for the next 30 years. The measurements will also provide important constraints on the physics and nature of the stresses that permit continental transform plate boundaries, like the San Andreas fault, to slip and evolve with time. The field investigations are being undertaken in close collaboration with scientists and engineers from three Pakistan, and two Indian Universities, and as such forge international ties that are of great benefit to the image of the United States in these developing nations. Because of the international nature of the project, this work is jointly funded by the Geophysics Program and the Office of International Science and Engineering.