Collaborative Research: A joint seismic and geodetic investigation into the structure and behavior of an intracontinental subduction zone, Nepal

合作研究：对尼泊尔大陆内俯冲带的结构和行为进行联合地震和大地测量调查

• 批准号: 1645014
• 负责人: William Barnhart
• 金额: $ 14.26万
• 依托单位: University of Iowa
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-04-01 至 2021-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1645014&HistoricalAwards=false
• 关键词: Collaborative; Research; joint; seismic; geodetic

Subduction zones, where one tectonic plate slides beneath another, produce the world's largest and often most destructive earthquakes. The earthquake-generating portions of typical subduction zones, where the downgoing plate is oceanic, are located offshore and under water, beneath several kilometers of ocean. The most severe hazard in many of these regions is posed by tsunami rather than by the shaking during the earthquake itself. Because of the submarine location, it is difficult to address the detailed characteristics of most subduction zone megathrust faults: what is the shape of the megathrust; is it a sharp, discrete interface or a thicker, distributed shear layer; how do these characteristics behave during the build-up time, generation, and propagation of great earthquakes? Under the Himalaya, however, the continental Indian plate subducts beneath Tibet, creating a unique situation where the entire subduction zone is on land and is instrumented by seismic stations, imaged from space, and monitored by continuous geodetic markers. Because large population centers sit immediately atop the shallow portions of the megathrust, the risk from shaking is much higher than in typical oceanic subduction zones. The large 2015 Gorkha, Nepal earthquakes (magnitude Mw7.8 and 7.3) that devastated Kathmandu, Everest basecamp, and surrounding regions provide a rare opportunity to investigate the general properties of megathrust faults more directly by studying data from this continental subduction zone. The Gorkha earthquakes ruptured the Main Himalayan Thrust - the megathrust plate boundary fault between India and Eurasia. The earthquakes and their aftershocks were recorded by seismic sensors (which record shaking during earthquakes) and geodetic satellites (which record surface deformation caused by the earthquakes) in a way that is unprecedented for subduction zone settings. This project aims to exploit these unique data sets to image the buried structure of the Main Himalayan Thrust with the goal to better understand the detailed structure and mechanics of a subduction megathrust, improve our knowledge of the seismogenic zone and resulting earthquake hazard along the Himalayan front, and explore new methods for the joint analysis of seismic and geodetic observations in imaging Earth structure.This investigation entails the use of detailed aftershock relocations, anisotropic receiver function analysis, and finite fault slip inversions to address the following questions: 1. Does a subduction channel shear zone characterize the Main Himalayan Thrust at seismogenic depths?; 2. Did the Gorkha earthquakes rupture the top, bottom, or interior of this subduction channel?; 3. Is a shear fabric present within the channel, and if so, has it formed along the hanging or footwall of the Main Himalayan Thrust?; 4. If the subduction channel model is relevant, are there along-strike structural variations in the Main Himalayan Thrust that influence rupture area? Using existing data from pre- and post-event regional broadband seismometer installations, the investigators will conduct joint analysis of radial and transverse component receiver functions to map the width, depth, velocity and shear fabric structure, and along-strike geometry of the Main Himalayan Thrust. Additionally, the will use detailed earthquake relocations to elucidate permissible depth ranges and thicknesses of the proposed subduction channel that are illuminated by the Gorkha aftershock sequence. Interferometric synthetic aperture radar (InSAR), Landsat-8 imagery, and GPS offsets will be used to map the co-seismic source of the Mw7.8 and 7.3 events with an emphasis on defining a population of fault geometries (dip and depth range) that are consistent with the available seismic and geodetic observations. Lastly, the team will iterate between the seismic and geodetic results to define internally consistent descriptions of the nature and structure of the Main Himalayan Thrust.

俯冲带在另一个构造板滑落下面的俯冲区，产生了世界上最大，通常是最具破坏性的地震。典型的俯冲带的地震生成部分（下板是海洋的）位于近海和水下，在几公里的海洋之下。这些地区中许多最严重的危害是海啸构成的，而不是地震本身的震动。由于潜艇位置，很难解决大多数俯冲带的详细特征。它是尖锐，离散的界面还是较厚的分布剪切层；这些特征在大地震的积累时间，产生和传播中如何表现？然而，在喜马拉雅山下，西藏下面的印度大陆板托架构成了独特的情况，在该情况下，整个俯冲带都在陆地上，并由地震站进行了仪器，从太空成像，并由连续的大地测量标记进行监控。由于大型人口中心立即坐在大型巨星的浅水区域上，因此摇动的风险远高于典型的海洋俯冲带。大型2015年戈尔卡（Gorkha），尼泊尔地震（MW7.8和7.3级），摧毁了加德满都，珠穆朗玛峰基本及周边地区，这为罕见的机会提供了一个难得的机会，可以通过从这个大陆俯冲区域中研究数据，从而更直接地研究大型断层的一般特性。戈尔哈地震破裂了主要的喜马拉雅推力 - 印度和欧亚大陆之间的大型板块边界断层。地震及其余震是通过地震传感器（在地震期间记录的）和大地卫星（记录了地震引起的表面变形）的记录，这种方式以前所未有的俯冲区设置为前所未有的方式。该项目旨在利用这些独特的数据集，以形象地图，主要是喜马拉雅主要施加的埋藏结构，以更好地了解俯冲象征的详细结构和机制，改善我们对地震生成区域的了解，并导致地震危险沿喜马拉雅人阵线，并探索对地震观察的新方法，并探索地球上的新方法，这些方法是在地球上进行的，地球上的地球构成了地球上的地球上的结构。余震重新搬迁，各向异性接收器函数分析和有限的断层滑移反转以解决以下问题：1。俯冲通道剪切区是否表征了喜马拉雅的主要推力在地震深度上？ 2。戈尔哈地震是否破裂了该俯冲通道的顶部，底部或内部？ 3。是否存在通道内的剪切织物，如果是的话，它是否沿主要喜马拉雅主要推力的悬挂或脚壁形成？ 4。如果俯冲通道模型相关，那么在影响破裂区域的主要喜马拉雅推力中是否存在沿形成型结构变化？ 使用事前和事后区域宽带地震仪安装的现有数据，研究人员将对径向和横向成分接收器功能进行联合分析，以绘制主要喜马拉雅式推力的宽度，深度，速度和剪切织物结构，并沿着沿着主动性的几何形状进行绘制。此外，将使用详细的地震搬迁来阐明允许的深度范围和拟议的俯冲通道的厚度，这些俯冲通道被Gorkha余震序列照亮。干涉合成孔径雷达（INSAR），Landsat-8图像和GPS偏移将用于绘制MW7.8和7.3事件的共同声明来源，重点是定义故障几何（DIP和深度范围），这些事件与可用的地震和地理质量观察一致。最后，团队将迭代地震和大地测量结果之间，以定义对主要喜马拉雅主要推力的性质和结构的内部一致描述。

项目成果

Impacts of Topographic Relief and Crustal Heterogeneity on Coseismic Deformation and Inversions for Fault Geometry and Slip: A Case Study of the 2015 Gorkha Earthquake in the Central Himalayan Arc

地形起伏和地壳非均质性对断层几何和滑移的同震变形和反演的影响：以2015年喜马拉雅中部弧廓廓尔喀地震为例

• DOI: 10.1029/2020gc009413
• 发表时间: 2020
• 期刊: Geosystems
• 作者: Li, Shaoyang;Barnhart, William D.
• 通讯作者: Barnhart, William D.