Collaborative Research: Investigating fault geometries and rupture processes in the Nepal Himalaya following the April 25, 2015 Gorkha earthquake

合作研究：调查 2015 年 4 月 25 日廓尔喀地震后尼泊尔喜马拉雅山的断层几何形状和破裂过程

• 批准号: 1620646
• 负责人: Marianne Karplus
• 金额: $ 21.32万
• 依托单位: University of Texas at El Paso
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-01 至 2021-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1620646&HistoricalAwards=false
• 关键词: Collaborative; Research; Investigating; fault; geometries

Following the April 25, 2015 Gorkha magnitude 7.8 and the May 12, 2015 magnitude 7.3 earthquakes, the largest earthquakes to occur in the central segment of the Himalaya in 80 years, a collaborative team from Oregon State University, U.C. Riverside, Stanford University, and the University of Texas at El Paso deployed an NSF RAPID-funded aftershock array of 45 seismic stations (41 broadband and short-period seismometers, 14 strong motion sensors) across the Main Himalayan Thrust (MHT) fault where the large earthquakes occurred. The array, known as the Nepal Array Measuring Aftershock Seismicity Trailing Earthquake (NAMASTE) remained in place for 11 months, allowing for a unique data set right over the active Himalayan thrust system. In this proposal, this same collaborative team will analyze the newly collected data set specifically to study the geometry of faults, including the MHT fault, the composition of the crust and upper mantle in the region, the rupture process of this earthquake sequence, and the broader geotectonic setting in the Himalaya and southern Tibet. Collaboration and cooperation between U.S. and Nepalese seismologists is essential to this project, thereby contributing to improvements of Nepalese scientific infrastructure.The newly collected, high quality NAMASTE array data will allow for a better understanding of the tectonic setting and rupture process of these large earthquakes and will both illuminate the processes causing large Himalayan earthquakes as well as large subduction zone earthquakes. Specifically, we will analyze the NAMASTE array data to address: 1) The geometry of the MHT fault zone, 2) the crustal composition in the MHT region, 3) the fault dynamics from aftershock characterization, and 4) the broader geotectonic setting. To address the geometry of the MHT, we will perform precise aftershock locations, develop a robust seismicity catalog from the NAMASTE and other regional arrays, and perform source characterization of aftershocks that will provide meaningful insights into the fault geometry, slip dynamics, source properties, and evolving state of stress during the aftershock sequence. To determine crustal composition, we will use local earthquake tomography and ambient noise tomography to derive crustal velocities and use known relationships between velocity and crustal composition and assess the presence and role of fluids in the crust, especially in the regions of active faulting. For fault dynamics, we will examine the spatiotemporal distribution of aftershocks and relation with rupture patches obtained by backprojection to allow for a better understanding of the rupture process and stress changes that occurred during the main shock and aftershocks. Finally, we will explore the broader geotectonic setting of the region by combining NAMASTE array data with other regional stations to derive tomographic velocity models, crustal and upper mantle anisotropy, and Moho and possibly lithospheric depths from receiver functions. We will further compare our seismology datasets with other geophysical and geological datasets (e.g., magnetotellurics, gravity, surface mapping, deformation) to derive the best possible understanding to date of the tectonics of the Himalaya and southern Tibet in Nepal and the surrounding countries.

在2015年4月25日Gorkha级7.8和2015年5月12日的7.3级地震之后，这是80年来喜马拉雅山中部地区发生的最大地震，是U.C.俄勒冈州立大学的一支合作团队。河滨，斯坦福大学和德克萨斯大学埃尔帕索分校部署了NSF快速资助的余震阵列，该阵列由45个地震电台（41个宽带和短期地震仪，14个强运动传感器，14个强运动传感器）部署在主要的喜马拉雅山脉（MHT）中，其中发生了大型地球。该阵列被称为尼泊尔阵列，测量了落后地震（Namaste）的余震地震性（NAMASTE）持续了11个月，从而可以在主动的喜马拉雅推力系统上建立独特的数据集。在该提案中，同样的合作团队将分析新收集的数据集，专门研究故障的几何形状，包括MHT故障，该地区的地壳和上层地幔的组成，地震序列的破裂过程，以及喜马拉雅山脉和西部西部的更广泛的地震环境。 Collaboration and cooperation between U.S. and Nepalese seismologists is essential to this project, thereby contributing to improvements of Nepalese scientific infrastructure.The newly collected, high quality NAMASTE array data will allow for a better understanding of the tectonic setting and rupture process of these large earthquakes and will both illuminate the processes causing large Himalayan earthquakes as well as large subduction zone earthquakes.具体而言，我们将分析NAMASTE阵列数据以解决：1）MHT断层区的几何形状，2）MHT区域中的地壳组成，3）3）来自余震表征的故障动力学，以及4）较宽的地理位置设置。为了解决MHT的几何形状，我们将执行精确的余震位置，从NAMASTE和其他区域阵列中发展出强大的地震性移动，并对余震的源表征进行源头表征，以提供有意义的见解，以提供有意义的几何学，滑动动力学，源动力学，源特性，以及在后圈后序列期间的应力状态。 为了确定地壳组成，我们将使用局部地震层析成像和环境噪声断层扫描来得出地壳速度，并使用速度和地壳组成之间的已知关系，并评估流体在地壳中的存在和作用，尤其是在主动断层区域。对于故障动力学，我们将检查余震的时空分布以及通过反向注射获得的破裂斑块的关系，以更好地了解破裂过程和主要冲击和余震过程中发生的应力变化。最后，我们将通过将NAMASTE阵列数据与其他区域站相结合，以推导层析成像速度模型，地壳和上地幔各向异性以及Moho以及Moho以及可能从接收器功能中的岩石圈dercths来探讨该区域的更广泛的地理环境。我们将进一步比较我们的地震学数据集与其他地质和地质数据集（例如，磁性纤维化，重力，表面映射，变形），以得出最佳的理解，即喜马拉雅山和南部西藏南部及其周围国家的构造阶层的最佳理解。