Earthquake Geology Along the Himalayan Frontal Thrust of India: Insight to Mechanics Earthquakes Along a Continental Convergent Plate Boundary

印度-欧亚板块边界是世界大陆辐合的典型例子。印度和欧亚大陆之间的持续融合导致了地球上最高的山脉和有记录以来最大的大陆内地震。这些事件中最大的一次发生在喜马拉雅锋面逆冲带上。喜马拉雅锋面冲力沿着喜马拉雅弧2500公里的长度连续延伸。喜马拉雅锋面逆冲沿走向表现为相对较短且不连续的山脉前崖，切割晚更新世和全新世的河流阶地和冲积扇。该项目由美国国家科学基金会地球科学部和国际科学与工程办公室支持，与印度瓦迪亚研究所的科学家合作开展，沿着喜马拉雅弧形进行实地研究，以确定印度喜马拉雅前缘逆冲断层地震破裂的时间、大小和横向程度。对喜马拉雅锋面逆冲断层沿弧长9处断裂带沟槽开挖引起的暴露进行了构造、地层学、成土学和放射性碳研究，以期为地震过程的力学模型和喜马拉雅锋面大地震造成的地震危险水平提供观测约束。由于整个印度-欧亚板块边界都在海平面以上，因此有可能在这里定义沿整个主要汇聚板块边界在地震中释放的累积地壳应变的空间、时间和表面特征，这种方式和细节在世界海洋汇聚板块边界上是不可能的，那里的冲断边界在水下。本研究拟应用地质技术提取印度喜马拉雅逆冲断层大地震的大小和发生频率信息。喜马拉雅锋面逆冲断层是喜马拉雅南缘的边界。正是这个断层上的位移产生了历史上有记录的许多最大的大陆地震，并且随着时间的推移反复发生，造成了喜马拉雅山脉的隆起。印度人口最密集的地区现在沿着喜马拉雅锋面冲断的南部边缘延伸。了解沿断层大地震的大小和发生率是教育公众和向政府机构提供审慎规划决策所需的信息所必需的，以减轻发生此类地震时沿断层前沿潜在的经济和生命损失风险。这项研究获得的信息还将为沿逆冲断层的地震过程的力学设置观测界限，这些知识可能随后被应用于北美西部和全球其他地方的地震危险性分析。

The Indian-Eurasian plate boundary is the world's type example of continental convergence. The ongoing convergence between India and Eurasia has resulted in the globes's highest mountain range and the largest recorded intracontinental earthquakes on record. The largest of these events have occurred along the Himalayan frontal thrust. The Himalayan frontal thrust extends continuously along the 2500 km length of the Himalayan arc. The Himalayan frontal thrust manifests itself along strike as relatively short and discontinuous range front scarps that cut late Pleistocene and Holocene fluvial terraces and alluvial fans. This project, carried out in collaboration with scientists from the Wadia Institute in India and supported by NSF's Division of Earth Sciences and Office of International Science and Engineering, is conducting field studies along the Himalayan arc to define the timing, size, and lateral extent of earthquake ruptures along the Himalayan frontal thrust fault in India. Structural, stratigraphic, pedogenic, and radiocarbon studies of exposures resulting from the excavation of trenches across fault scarps of the Himalayan frontal thrust fault at 9 sites along the length of the arc in order to provide observational constraints on mechanical models of the earthquake process and the level of seismic hazard imposed by large earthquakes along the Himalayan front. Because the entirety of the India-Eurasia plate boundary is above sea level, the potential exists here to define the spatial, temporal, and surficial, characteristics of accumulated crustal strain that is released in earthquakes along the entirety of a major convergent plate boundary, in a manner and detail not possible along the world's oceanic convergent plate boundaries where the thrust boundary is beneath water.The proposed research is to apply geological techniques to extract information of the size and frequency of occurrence of great earthquakes along the Himalayan frontal thrust fault of India. The Himalayan frontal thrust fault bounds the southern front of the Himalaya. It is the displacements on this fault that have produced a number of the largest continental earthquakes recorded historically and through repeated occurrence through time responsible for the uplift of the Himalaya. The most densely populated regions of India now stretch along the southern edge of the Himalayan frontal thrust. Knowledge of the size and occurrence rate of great earthquakes along the thrust is required for educating the public and providing government agencies the information needed to make prudent planning decisions to mitigate the potential financial and loss-of-life risks along the front in the event of such an earthquake. The information gained by this research will also place observational bounds on the mechanics of the earthquake process along thrust faults, knowledge that may then be applied to seismic hazard analysis in western North America and elsewhere around the globe.