Collaborative Research: Filling in the Central Himalayan Seismic Gap: A Structural, Neotectonic, and Paleoseismic Investigation of the Western Nepal Fault System

合作研究：填补喜马拉雅中部地震间隙：尼泊尔西部断层系的构造、新构造和古地震研究

• 批准号: 1827866
• 负责人: Michael Taylor
• 金额: $ 33.57万
• 依托单位: University of Kansas Center for Research Inc
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-08-15 至 2023-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1827866&HistoricalAwards=false
• 关键词: Collaborative; Research; Filling; Central; Himalayan

The 2015 Gorkha Mw 7.8 earthquake, which caused 9,000 fatalities, resulted from rupture along a megathrust - the Main Himalayan thrust - where the Indian sub-continent subducts beneath deformed Himalayan belt and the Asian continent. Most megathrust fault systems, where one tectonic plate is being forced underneath another tectonic plate, occur deep beneath the world's oceans where observations are limited due to difficult submarine access. These systems produce the largest recorded earthquakes in the world and typically consist of a primary fault and additional splay faults that work together to accommodate collision between the tectonic plates. A recently discovered complex fault system west of the Gorkha epicentral region, the Western Nepal Fault System (WNFS), appears to play a major role in accommodating the Himalayan collision and poses a major seismic hazard for a large region of Nepal. This project will document the long-term rate of motion, determine the timing and location of prehistoric earthquakes, and map out the full extent of the WNFS. The data will be used to develop constraints on the seismic hazard exposure of regional populations and provide recommendations for low-cost, sustainable, and culturally sensitive earthquake risk mitigation strategies. The project would advance other desired societal outcomes such as full participation of women in STEM, increased public scientific literacy and public engagement with STEM through participation in local public outreach activities, development of a diverse, globally competitive STEM workforce through undergraduate and graduate student training, and fostering international collaboration.Geologic and geophysical observations have long shown that areas of oblique plate convergence tend to form slip partitioned systems, where the basal megathrust accommodates margin-perpendicular convergence, and a strike-slip splay or backarc fault accommodates margin-parallel motion. Given the curvature of most convergent margins, convergence obliquity often varies along strike, becoming zero at some point. However, because these zones are usually inaccessible in offshore subduction zones, the kinematics and earthquake cycle behavior of these splay faults are poorly known. This project targets the newly discovered Western Nepal Fault System as a major, subaerial, well-exposed splay fault system within the Himalayan thrust wedge that appears to transfer dextral strain from the Karakoram Fault in the obliquely convergent northwest Himalayan backarc to the central Himalayan forearc where convergence is primarily margin-normal. The objective of this project is to test multiple working hypotheses that use the deformation patterns of the WNFS to constrain models of fault segmentation and linkage for regional slip-partitioning and splay faulting models: (1) strong strain partitioning hypothesis in which the WNFS is a well-connected system of active faults that transfer slip from the Karakoram- Gurla Mandhata/Humla fault system in the northwest, across the thrust wedge, and branches with the Main Frontal Thrust at the front of the wedge; (2) weak strain partitioning hypothesis in which the WNFS is a collection of disconnected faults that broadly accommodate arc-parallel strike-slip faulting and northwest translation of the Himalayan arc sliver; and (3) thrust faulting and oblique ramp hypothesis in which the WNFS is a collection of faults that accommodate shortening within the thrust wedge. To address these hypotheses and leverage new constraints on regional seismic hazard, the research team will carry out a three year multidisciplinary investigation consisting of three primary components: (1) structural geology, neotectonics, geomechanics, and geochronology with paleoseismology to constrain (a) the geometries and kinematics of active fault systems, (b) displacement magnitude, (c) fault slip rates, and (d) historical patterns of strain release using paleoseismology; (2) an updated probabilistic seismic hazard and risk analysis integrating the results of the geologic studies; and (3) a benefit-cost analysis of structural and non-structural vulnerability-reducing strategies at household to community scales to provide recommendations for reducing risk and promoting resilience through mitigation and recovery. The active fault mapping, slip rate, and paleoearthquake data are also fundamental components of seismic hazard analyses. Working with Nepali collaborators, the results will be used to provide updated probabilistic seismic hazard analysis and develop practical mitigation strategies for a region widely thought to be at heightened seismic risk.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

2015 年廓尔喀 7.8 级地震造成 9,000 人死亡，起因是沿喜马拉雅主逆冲断层的巨型逆冲断层发生破裂，印度次大陆在此处俯冲到变形的喜马拉雅带和亚洲大陆之下。大多数巨型逆冲断层系统（其中一个构造板块被迫压入另一个构造板块下方）发生在世界海洋深处，由于潜艇难以进入，观测受到限制。这些系统产生了世界上有记录的最大地震，通常由主断层和附加的张开断层组成，它们共同作用以适应构造板块之间的碰撞。最近在廓尔喀震中地区以西发现的一个复杂的断层系统，即尼泊尔西部断层系统（WNFS），似乎在容纳喜马拉雅碰撞中发挥了重要作用，并对尼泊尔大片地区构成了重大地震危险。该项目将记录长期运动速率，确定史前地震的时间和地点，并绘制 WNFS 的完整范围。这些数据将用于制定对区域人口地震灾害暴露的限制，并为低成本、可持续和文化敏感的地震风险缓解策略提供建议。该项目将促进其他期望的社会成果，例如女性充分参与 STEM、通过参与当地公共宣传活动提高公众科学素养和公众对 STEM 的参与、通过本科生和研究生培训培养多元化、具有全球竞争力的 STEM 劳动力队伍，地质和地球物理观测早已表明，倾斜板块汇聚区域往往形成滑动分区系统，其中基底巨型逆冲断层容纳边缘垂直汇聚和走滑张开或弧后断层适应边缘平行运动。考虑到大多数会聚边缘的曲率，会聚倾角通常沿走向变化，在某个点变为零。然而，由于这些区域通常无法进入近海俯冲带，因此人们对这些张开断层的运动学和地震循环行为知之甚少。该项目的目标是新发现的尼泊尔西部断层系统，作为喜马拉雅逆冲楔内的一个主要的、地面的、充分暴露的张开断层系统，该断层系统似乎将右旋应变从倾斜会聚的喜马拉雅西北弧后的喀喇昆仑断层转移到喜马拉雅前弧中部，其中收敛主要是边缘正态的。该项目的目标是测试多种工作假设，这些假设使用 WNFS 的变形模式来约束区域滑动分区和张开断层模型的断层分割和链接模型：（1）强应变分区假设，其中 WNFS 是连接良好的活动断层系统，从西北部的喀喇昆仑-古尔拉曼达塔/胡姆拉断层系统转移滑移，穿过逆冲楔，并与主锋面逆冲断层分支楔子的前面； （2）弱应变划分假说，其中WNFS是不连续断层的集合，广泛适应弧平行走滑断层作用和喜马拉雅弧条的西北平移； (3) 逆冲断层和斜坡假说，其中 WNFS 是适应逆冲楔内缩短的断层集合。为了解决这些假设并利用对区域地震灾害的新限制，研究小组将进行为期三年的多学科调查，包括三个主要组成部分：（1）构造地质学、新构造学、地质力学和地质年代学与古地震学，以限制（a）活动断层系统的几何形状和运动学，(b) 位移幅度，(c) 断层滑移率，以及(d) 使用古地震学的应变释放的历史模式； (2) 整合地质研究结果的最新概率地震灾害和风险分析； (3) 对家庭和社区层面的结构性和非结构性脆弱性减少战略进行效益成本分析，为通过缓解和恢复来降低风险和提高抵御能力提供建议。活动断层测绘、滑移率和古地震数据也是地震危险性分析的基本组成部分。与尼泊尔合作者合作，研究结果将用于提供更新的概率地震灾害分析，并为广泛认为地震风险较高的地区制定实用的缓解策略。该奖项反映了 NSF 的法定使命，并通过使用评估结果被认为值得支持。基金会的智力价值和更广泛的影响审查标准。