Probing the Deep Rheology of Tibet

该项目的研究人员利用干涉合成孔径雷达（InSAR）卫星技术，研究了最近在西藏北部发生的两次大地震后的地面变形，以限制青藏高原深处岩石的力学特性。这个地区是世界上构造最活跃的地区之一。它位于广阔的印度-欧亚碰撞带内，印度板块向欧亚板块的快速运动导致喜马拉雅锋面向北变形数千英里。许多活动断层解剖了高原，包括几个非常长的构造，如喀喇昆仑，阿尔金塔格和昆仑断层。目前，关于西藏的表现更像是一种弱粘性流体，还是主要断层之间的一系列刚性块体，存在着激烈的争论。通过研究与大地震有关的变形，可以潜在地了解这种流变学争论。从这个意义上说，大地震标志着岩石圈尺度岩石力学实验的开始。主震后发生的瞬态地震变形是对地震引起的深部应力变化的响应。观测到的震后信号的大小和空间分布，以及最初快速运动趋于平稳的时间尺度，都取决于岩石圈中岩石的流变结构和性质。反过来，流变学的特性控制了地震后下地壳和上地幔应力重新分布的速率。数据分析的一个特别重点是阐明西藏东北部昆仑断层发震部分下变形的局部化程度，并诊断下地壳和上地幔粘性强度的显著变化。伴随着InSAR数据集的还有来自昆仑断裂带44个站点的GPS数据。正在运行计算机模型来针对这个丰富的数据集测试各种候选流变学。为了帮助回答他们的问题，研究人员还计划利用来自西藏各种岩石圈研究的互补地球物理数据，以及来自更西的昆仑断层和阿尔金塔格断层研究的地质信息。这项工作的更广泛的影响之一是，它将有助于进一步了解地震周期，帮助告知地震危害研究人员。该提案还将有助于支持和培养博士后。

The researchers in this project are using the satellite technique of InSAR (Interferometric Synthetic Aperture Radar) to study ground deformation following two large earthquakes that occurred recently in northern Tibet, in order to constrain the mechanical properties of the rocks at depth beneath the Tibetan plateau. This region is one of the most tectonically active in the world. It lies within the broad India-Eurasia collision zone, in which the rapid motion of the Indian plate towards the Eurasian plate causes deformation from the Himalayan front northwards for thousands of miles. Numerous active faults dissect the plateau, including several very long structures such as the Karakorum, Altyn Tagh and Kunlun faults. There is currently vigorous debate as to whether Tibet behaves more as a weak viscous fluid or a series of rigid blocks between the major faults. This rheological debate can potentially be informed by studying the deformation associated with large earthquakes. In this sense, large earthquakes signal the beginning of a lithospheric-scale rock mechanics experiment. Transient aseismic deformation which occurs after the main shock is a response to the stress changes at depth brought about by the earthquake. The magnitude and spatial distribution of the observed postseismic signal, and the timescale over which the initially rapid motion levels off, all depend on the rheological structure and properties of the rocks in the lithosphere. In turn, the specifics of the rheology control the rate at which stress is redistributed in the lower crust and upper mantle following an earthquake. A particular focus of the data analysis is the elucidation of the degree to which deformation is localized beneath the seismogenic part of the Kunlun fault in northeastern Tibet, and to diagnose significant variations in viscous strength in the lower crust and upper mantle. The InSAR datasets are accompanied by GPS data from a network of 44 sites across the Kunlun fault. Computer models are being run to test various candidate rheologies against this rich dataset. To help answer their questions, the investigators also plan to use complementary geophysical data from various lithospheric studies in Tibet, as well as geological information from studies across the Kunlun fault and Altyn Tagh fault further west. Among the broader impacts of this work are that it will contribute to further understanding of the earthquake cycle, helping inform earthquake hazard researchers. The proposal will also contribute to the support and training of a postdoc.