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

2011年3月11日，日本东北部发生了毁灭性的东北大地震及其海啸，造成15，000多人死亡和严重破坏。日本的丹麦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事件。海底大地测量站记录到地震期间超过10米的水平位移。高分辨率地震测深数据表明，断裂到达了海沟。模型反演研究表明，在一个显著的紧凑的区域，沿沿着走向400 km，宽200 km，滑动分布高达~50 m。以前所未有的高空间和时间分辨率和精度记录的同震和震后地壳变形使研究人员能够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，以限制上地幔和下地壳的三维（3D）流变学和瞬态滑动的巨型逆冲断层的演变。本项目的研究范围非常广泛，其结果也适用于其他俯冲边缘地区（苏门答腊、智利、阿拉斯加、卡斯卡迪亚），这些地区目前正处于俯冲地震周期的不同阶段。本项目将对2011年东北冲地震的震后变形进行研究。在以前的研究中，将余震对特大逆冲断层的贡献与上地幔地震引起的应力的粘弹松弛区分开来一直是一个挑战。会聚边缘复杂的三维流变学对俯冲带地震变形的影响还有待于更好地理解。在拟议的研究中，我们试图了解：（一）什么是大地震后的大逆冲断层上的后滑的分布和演化？(b)地球三维流变学如何控制震后地壳形变？(c)大洋和大陆上地幔的流变学性质是什么？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台站记录的全球定位系统（GPS）数据。他们还将利用重复地震来限制后滑。三维有限元代码将结合复杂的俯冲板几何形状和先进的地幔流变学在地球上。

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.