CSEDI Collab. Research: A joint mineral physics and nano-seismological study on high-pressure faulting in metastable olivine and harzburgite with implications to deep earthquakes

在世界范围内，每年的地震数量随着深度下降到~300 km而迅速减少，然后在550 - 600 km左右达到峰值，然后在700 km附近突然终止。深源地震（DFEQs），即，那些发生在300公里以下深度的岩石特别神秘，因为我们知道，在这些压力和温度都很高的深度，岩石通常通过蠕变和流动而不是脆性断裂变形。了解DFEQs的机制很重要，因为这些地震发生在俯冲带，并在地球仪的许多地区造成重大的地震危险。它还有助于了解岩石的性质和行为以及板块构造如何在地球内部起作用。在该项目中，研究人员将联合收割机先进的实验技术和最先进的地震学分析工具，获得有关高压和高温下破裂的物理机制的信息。所研究的物质是（Mg，Fe）2SiO 4橄榄石（大洋岩石圈和上地幔中的主要矿物）和方斑玄武岩（大洋岩石圈中的主要岩石组合）。样品将在一种新型的变形装置中变形，该装置配备有现场声发射（AE）监测以及X射线衍射和成像，在压力、温度、差应力、应变和应变率的各种条件下。将在高达14 GPa的压力下对这些材料进行受控变形。一套最先进的地震学方法的事件检测，定位和源特性将被应用到AE事件的纳米地震图，以确定破裂机制。我们的目标是了解在实验室尺度上连接地震力学和矿物/岩石的物理学，提供关于剪切局部化如何以及在什么条件下发生的基本见解，影响矿物反应平衡和动力学，并触发动态力学不稳定性。实验过程中应注意控制氧逸度和尽量减少水含量。必须记住，实验室和俯冲带过程在尺度上存在巨大差异。该小组将进行比较研究，以检查AE源特性与DFEQs的特性。然后将根据实验数据和地震观测以及大规模俯冲带过程，开发和评价热化学力学模型。结合这些方法，研究人员预计通过建立DFEQs的物理模型，其可测试性和可扩展性可以通过计算模拟进一步研究，从而显着增强我们对DFEQs机制的理解。

Worldwide, the number of earthquakes per year decreases rapidly with depth down to ~300 km, then peaks around 550 - 600 km, before terminating abruptly near 700 km. Deep-focus earthquakes (DFEQs), i.e., those occurring at depths below 300 km, are particularly mysterious, as we know that rocks generally deform by creep and flow, rather than by brittle fracture, at these depths, where pressures and temperatures are both very high. Understanding the mechanisms of DFEQs is important because these quakes occur in subduction zones and pose significant seismic hazards in many regions around the globe. It also helps understand properties and behaviors of rocks and how plate tectonics works in the Earth's interior. The experimental capabilities developed in the project will find broad applications in disciplines far beyond earth science, including materials science, physics, and engineering.In this project, the investigators will combine advanced experimental techniques and state-of-the-art seismological analytical tools to obtain information on the physical mechanisms of fracturing under high pressure and high temperature. The materials to be studied are (Mg,Fe)2SiO4 olivine (the dominant mineral in the oceanic lithosphere and the upper mantle) and harzburgite (the dominant rock assemblage of the oceanic lithosphere). Samples will be deformed in a new class of deformation apparatus equipped with in-situ acoustic emission (AE) monitoring as well as x-ray diffraction and imaging, under a wide range of conditions of pressure, temperature, differential stress, strain, and strain rate. Controlled deformation will be conducted on these materials at pressures up to 14 GPa. A suite of state-of-the-art seismological methods of event detection, location, and source characterization will be applied to the nanoseismograms of AE events to determine rupture mechanisms. Our goal is to understand the physics that connects earthquake mechanics and minerals/rocks at laboratory scales, to provide fundamental insight as to how and under what conditions shear localization occurs, affecting, and affected by, mineral reaction equilibrium and kinetics, and triggers dynamic mechanical instability. Attention will be paid to controlling oxygen fugacity and minimizing water content during the experiments. It must be kept in mind the vast difference in scales between laboratory and subduction zone processes. The team will conduct comparison studies to examine AE source characteristics against those of DFEQs. Thermo-chemo-mechanical models will then be developed and evaluated based on experimental data and seismic observations, and large-scale subduction zone processes. Combining these approaches, the investigators anticipate a significant enhancement of our understanding of the mechanisms for DFEQs by establishing physical models for DFEQs whose testability and scalability can be further examined by computational simulations.