Collaborative research: Probing the effects of 3D rheology on postseismic deformation following the 2011 Tohoku-Oki earthquake

2011年3月11日，日本东北大地震及其引发的海啸在日本东北部造成1.5万多人死亡和严重破坏。日本最密集的大地测量和地震网络使这次地震成为有史以来记录最好的地震。海底大地测量站在地震期间记录了超过10米的水平位移。高分辨率地震测深数据表明，破裂到达了海沟。模式反演研究表明，在沿走向400公里、宽度200公里的显著致密区域内，滑动分布高达50米。以前所未有的高时空分辨率和精度记录的同震和震后地壳形变，使研究人员进一步了解地球的流变结构和俯冲带过程。特别是，高质量的大地测量数据提供了一个独特的机会来约束上地幔和下地壳的三维流变学和大逆冲断层上瞬变滑动的演化。该项目的范围将足够广泛，其结果将适用于其他俯冲边缘（苏门答腊、智利、阿拉斯加和卡斯卡迪亚），这些地方的变形目前处于俯冲地震周期的各个阶段。该项目将研究2011年东北大地震的震后变形。在以前的研究中，将大逆冲断层的余震作用与上地幔地震诱发应力的粘弹性松弛分离开来一直是一个挑战。汇聚边缘复杂的三维流变学对俯冲带地震变形的影响尚未得到更好的认识。在拟议的研究中，我们试图了解：(a)大地震后巨型逆冲断层的余震分布和演变是什么？(b)地球的三维流变如何控制震后地壳变形？(c)海洋和大陆上地幔的流变特性是什么？在这项工作中，研究人员将受益于日本国家网络以及东亚地区站点记录的丰富的全球定位系统（GPS）数据。它们还将利用重复的地震来抑制余震。三维有限元代码将结合地球上复杂的俯冲板块几何形状和先进的地幔流变学。

The devastating March 11, 2011 Tohoku-Oki earthquake and its tsunami caused more than 15,000 fatalities and severe damage in NE Japan. The densest geodetic and seismic networks in Japan made this earthquake the best-recorded event ever. Seafloor geodetic stations recorded over 10s of m horizontal displacements during the earthquake. High-resolution seismic bathymetry data indicate that the rupture reached the trench. Model inversion studies indicate a slip distribution of up to ~50 m over a remarkable compact area of 400 km along strike and 200 km wide. Coseismic and postseismic crustal deformation recorded at unprecedented high spatial and temporal resolution and precision allow the researchers to further their understanding of the rheological structure of the Earth and the subduction zone processes. In particular, the high quality geodetic data provide a unique opportunity to constrain the three-dimensional (3D) rheology of the upper mantle and lower crust and the evolution of transient slip on the megathrust. The scope of the project will be broad enough such that results will be applicable to other subduction margins (Sumatra, Chile, Alaska and Cascadia) where deformation is currently at various stages of the subduction earthquake cycle.This project will examine the postseismic deformation of the 2011 Tohoku-Oki earthquake. In previous investigations, it has been a challenge to separate the contributions of afterslip on the megathrust from viscoelastic relaxation of the earthquake-induced stresses in the upper mantle. Effects of the complex 3D rheology of convergent margins on subduction zone earthquake deformation have yet to be better understood. In the proposed research, we seek to understand: (a) What is the distribution and evolution of the afterslip on the megathrust following a giant earthquake? (b) How does the 3D rheology of the Earth control the postseismic crustal deformation? (c) What are the rheological properties of the oceanic and continental upper mantle? In this work the researchers will benefit from access to the wealth of Global Positioning System (GPS) data recorded by the Japan national network as well as regional stations across East Asia. They will also constrain afterslip using repeating earthquakes. A 3D finite element code will incorporate complex subduction slab geometry and advanced mantle rheology in the Earth.