基于开源软件GMTSAR与iGPS的时序形变自动化处理工具研发及应用

Abstract

地表形变是地球内部多种物理过程的表现，是探索深部地球物理环境的重要工具. 近年来随着数据和软件的丰富，合成孔径雷达干涉（Interferometric Synthetic Aperture Radar, InSAR）技术常被作为探测地壳形变的首选手段，因而快速掌握处理技术成为构造地质和地震过程等研究领域从业者的迫切需求. 本文扩展了形变时序分析软件包iGPS的功能，开发了一套基于InSAR开源软件GMTSAR的辅助处理程序，实现了时序InSAR分析流程的自动化，具备数据自动获取、干涉自主组织、时序分析调用、形变结果分析与展示等功能，显著简化了处理过程；以青藏高原西部现今地壳形变探测为例，详述了自动化处理流程，并与GNSS速度场进行对比检验了形变结果的可靠性. 本文处理了2015年6月至2022年9月期间Sentinel-1卫星T12轨道的61期成像数据，获取了南北跨度上千千米的InSAR形变场，显示伴随青藏高原地壳东向挤出而产生的左旋剪切主要发生在高原北部，尤其是阿尔金断裂带、玛尔盖茶卡—昆仑断裂带之间的地带，吸收了大部分塔里木盆地与青藏高原之间的相对运动；带内活动断裂分布较近，构造形变混叠在一起难以有效分离，使得准确地估计阿尔金断裂带的现今滑动速率面临挑战. 本文系统地梳理了如何借助开源InSAR软件来实现形变时序的自动化处理，有助于地球物理等领域的研究者快速熟悉与掌握相关知识与技术.

Alternate abstract:

Surface crustal deformation is often used to explore physical processes within the interior of the Earth. The observable surface changes can reflect variable subsurface physical processes that are usually inaccessible to modern instruments. For example, surface displacement observations have been widely used to study the geometric parameters of faults and slip distributions of earthquakes, to estimate interseismic slip rates and locking depths of active faults, and to constrain the physical properties of rock at depth. Therefore, a comprehensive knowledge of crustal deformation plays a key role in evaluating the seismic hazard probability in areas with active faults, particularly for heavily populated areas such as the North-South (Nanbei) Seismic Belt in western China.The two most widely used techniques for monitoring crustal movement are the Global Navigation Satellite System (GNSS) and interferometric synthetic aperture radar (InSAR). The former involves extensive fieldwork and is only applicable at locations with convenient transportation facilities. The latter can cover a relatively large region at significantly lower cost. With the increase of SAR data since the launch of Sentinel-1A satellite in 2014, InSAR has been the preferred tool for monitoring crustal deformation. Thus, there is an urgent need for a proficient application of this technique. Based on the iGPS time series analysis package, we developed a suite of programs that incorporate the open source InSAR software-GMTSAR to automate and facilitate the processing procedure of time series InSAR analysis. It can automatically download data, organize the interferometric processing tasks, perform time series, conduct data analysis, and visualize results. We first introduce the interferometric functionalities of GMTSAR and iGPS software. The processing flowchart is described in detail by deriving the present-day slow crustal deformation of the western Tibetan Plateau as an example. Owing to high coherence inherently for the Tibetan Plateau, using Sentinel-1 ascending track T12 data collected during June 2015 to September 2022, we demonstrated that a dense InSAR average velocity map of high accuracy could be obtained for a vast area spanning over 1000 km. The InSAR results showed that the eastward extrusion of the Tibetan Plateau resulted in rapid shear slip within a narrow belt between the Altyn Tagh and Margai Caka-Kunlun fault zones, absorbing over half of the relative motion between the Tarim Basin and Tibetan Plateau.This study systematically introduced how to perform automated small baseline subset (SBAS) InSAR processing using open-access SAR data and InSAR software to detect subtle crustal deformation. In the future, InSAR operators can apply this method to conduct their own processing chains for crustal deformation studies with limited inputs.