Collaborative Research: Earthquake Geology of the Pakistani Himalaya: Characterizing Slip Rates and Recurrence of Potentially Devastating Earthquake Sources

2005年10月8日发生的克什米尔7.6级地震造成7.3万多人死亡，是印度次大陆发生的地震中伤亡人数最多的一次。这也是巴基斯坦最严重的自然灾害，引起了巴基斯坦和印度政府的警惕，因为两国都位于地震活跃且城市人口不断增加的喜马拉雅地区。人们认为，喜马拉雅地区毁灭性的大地震与喜马拉雅基底沉降有关，即印度-亚洲板块边界。过去两个世纪的历史地震使这个断层破裂，但没有到达喜马拉雅逆冲前缘的地表。相比之下，大约900年前和600年前，尼泊尔和印度西北部的冲断前缘确实发生了地表破裂。在巴基斯坦喜马拉雅西北地区，板块边界地震时逆冲前缘是否发生断裂尚不清楚。2005年克什米尔地震发生在造山带内的断层上，而不是在逆冲前缘，这表明巴基斯坦的一些印亚辐合被内部断层吸收。第二个主要的未知问题是内部断层和前缘逆冲断层系统之间的应变和收敛是如何划分的。俄勒冈州立大学和加州州立大学北岭分校的研究小组正在进行一项为期三年的研究项目，目的是限制巴基斯坦的印度-亚洲板块边界地震周期，以便提供地震复发和活动结构滑动率的第一个限制条件。这些数据代表了对威胁主要人口中心（伊斯兰堡、拉瓦尔品第和白沙瓦总共约有600万人口）的断层进行地震危险表征的急需的第一步。喜马拉雅板块边界地震威胁着该地区不断增长的人口，而该地区很可能受到下一次喜马拉雅大地震的广泛影响。超过4000万人居住在喜马拉雅以南的恒河平原上，喜马拉雅山麓点缀着许多城市，规模从50万到200多万不等。2005年克什米尔地震在巴基斯坦造成近8万人死亡，这凸显了喜马拉雅地震带来的巨大危害。尽管巴基斯坦历史上曾发生过毁灭性的地震（1935年奎达地震造成3.5万人死亡），但整个国家在很大程度上对未来的地震没有准备，也没有一支受过地震地质学训练的科学家队伍。在这个项目中，科学小组将确定巴基斯坦主要活动断层的地震历史，同时培训巴基斯坦科学家掌握世界各地广泛使用的技术，以限制该领域的地震危险。这个项目的科学贡献将是对喜马拉雅山西北部地震如何表现出印度-亚洲碰撞的新认识。该项目的社会遗产将是关于威胁一些主要人口中心的大地震概率预测的新信息，从而改进建筑规范和灾害预防，并培养新一代接受现代地震科学技术培训的科学家。这些巴基斯坦地球科学家将有能力在未来系统地描述巴基斯坦的地震危险和活动断层的地震历史。该奖项由美国国家科学基金会国际科学与工程办公室共同资助。

The magnitude 7.6 Kashmir earthquake of October 8, 2005 caused the deaths of more than 73,000 people, the greatest loss of life of any earthquake in the Indian subcontinent. It also was Pakistan's worst natural disaster of any kind, a source of alarm to the governments of Pakistan and India because both countries share the seismically-active and increasingly urban-populated Himalaya. Large, devastating earthquakes in the Himalaya are thought to be associated with the Himalayan basal decollement, the India-Asia plate boundary. Historic earthquakes in the past two centuries have ruptured this fault but have not reached the surface at the Himalayan thrust front. In contrast, surface rupture at the thrust front did occur in Nepal and northwest India approximately 900 and 600 years ago, respectively. In the northwestern Himalaya of Pakistan, it is unknown whether ruptures occur at the thrust front during plate-boundary earthquakes. The 2005 Kashmir earthquake occurred on a fault within the orogenic belt and not at the thrust front, which indicates that some of the India-Asia convergence in Pakistan is absorbed by internal faults. A second major unknown is how strain and convergence are partitioned between the internal faults and the frontal thrust fault systems. The Oregon State University and California State University, Northridge, research team are conducting a three-year research project with the goal of constraining the India-Asia plate boundary earthquake cycle in Pakistan in order to provide the first constraints on the earthquake recurrence and slip rate of active structures. These data represent a much-needed first step in seismic hazard characterization of faults threatening major population centers (Islamabad, Rawalpindi, and Peshawar have a combined population of approximately 6,000,000).Plate boundary earthquakes in the Himalaya threaten an ever-increasing population across a region in harm's way that is likely to be widely affected by the next great Himalayan earthquake. Over forty million people live in the Ganges plain south of the Himalaya, and the Himalayan foothills are dotted by numerous cities ranging in size from about 500,000 to more than 2 million people. The nearly 80,000 deaths in Pakistan during the 2005 Kashmir earthquake emphasize the magnitude of the hazard associated with Himalayan earthquakes. Although Pakistan has had historic devastating earthquakes (1935 Quetta, 35,000 killed), the country as a whole is largely unprepared for future events and does not have a cadre of scientists trained in earthquake geology. In this project, the scientific team will determine the earthquake history of key active faults in Pakistan and simultaneously train Pakistani scientists in the techniques used widely around the world to constrain earthquake hazard in the field. The scientific contribution of this project will be a new understanding of how the India-Asia collision is manifested by earthquakes in the northwest Himalaya. The societal legacy of this project will be new information on probabilistic forecasting of large earthquakes threatening some of the major population centers, leading to improved building codes and disaster prevention, and a new generation of scientists trained in the modern techniques of earthquake science. These Pakistani earth scientists will be equipped to carry forward into the future a systematic characterization of seismic hazards and earthquake history of active faults in Pakistan.This award was co-funded by NSF's Office of International Science and Engineering.