Space geodetic observations and modeling of co- and post-seismic deformation due to the 2015 M7.8 Gorkha (Nepal) earthquake

2015年尼泊尔廓尔喀7.8级地震是近80年来西藏南缘发生的最大地震。我们将使用精确的地表变形测量来研究地震破裂，以及地球的缓慢松弛。美国的地壳在地震后形成。这些测量结果将对长期以来关于西藏下地壳和上地幔组成的岩石的力学特性和强度的争论产生影响。我们将把观测到的2015年廓尔喀地震造成的变形与该地区其他大事件的观测结果进行比较和对比，特别是2005年克什米尔（巴基斯坦）地震。这将有助于更好地了解尼泊尔及周边地区的地震灾害。最近发射的干涉合成孔径雷达（InSAR）任务，如ALOS-2和Sentinel-1，对2015年廓尔喀地震进行了很好的成像。新运行卫星的短重访时间和大范围覆盖将使我们能够以前所未有的细节测量一次主要浅层逆冲地震造成的震后变形。我们将使用来自不同视距的同震雷达干涉图来推导2015年廓尔喀地震的良好约束有限滑动模型。由于地震震中区域的特征是高度可变的地形，我们将通过比较假设弹性半空间的反演结果和明确考虑地形的有限元模型来评估地形的影响。这些模型还将准确地解释地壳的三维弹性结构，根据地震断层扫描数据推断。我们将处理和分析地震区丰富的2年雷达采集目录，生成震后变形的时间序列，并结合现有的InSAR和GPS数据来研究震后松弛的机制。在这个项目主持下产生的数据和建模结果将提供给更广泛的研究界。

The 2015 magnitude 7.8 Gorkha (Nepal) earthquake was the largest earthquake at the southern edge of Tibet in the last 80 years. We will use precise measurements of surface deformation to study the earthquake rupture, as well slow relaxation of the Earth?s crust following the earthquake. These measurements will bear on a long-standing debate about mechanical properties and strength of rocks comprising the lower crust and upper mantle beneath Tibet. We will compare and contrast the observed deformation due to the 2015 Gorkha earthquake with observations from other large events in the region, in particular the 2005 Kashmir (Pakistan) earthquake. This will result in better understanding of seismic hazards in Nepal and surrounding areas. The 2015 Gorkha earthquake was well imaged by the recently launched Interferometric Synthetic Aperture Radar (InSAR) missions, such as ALOS-2 and Sentinel-1. Short revisit times and wide-swath coverage of new operating satellites will allow measurements of postseismic deformation due to a major shallow thrust earthquake in unprecedented details. We will use coseismic radar interferograms from different lines of sight to derive a well-constrained finite slip model of the 2015 Gorkha earthquake. Because the earthquake epicentral area is characterized by a highly variable relief, we will evaluate the effects of topography by comparing results of inversions assuming elastic half-space, and finite element models that explicitly account for topography. These models will also accurately account for the 3-D elastic structure of the crust, as inferred from seismic tomography data. We will process and analyze a rich 2-year-long catalog of radar acquisitions in the earthquake area, generate time series of postseismic deformation, and combine available InSAR and GPS data to investigate the mechanisms of postseismic relaxation. Data and modeling results generated under the auspices of this project will be made available to a wider research community.