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，每年的地震次数随着深度的增加而迅速减少，下降到约300公里，然后在550-600公里左右达到峰值，然后在700公里附近突然终止。深源地震(DFEQ)，即发生在300公里以下深度的地震，尤其神秘，因为我们知道，在压力和温度都非常高的深度，岩石通常通过蠕变和流动变形，而不是通过脆性破裂。了解DFEQ的机制很重要，因为这些地震发生在俯冲带，在全球许多地区都构成了重大的地震危险。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发挥作用。该项目开发的实验能力将在远远超出地球科学的学科中得到广泛应用，包括材料科学、物理和工程。在这个项目中，研究人员将结合先进的实验技术和最先进的地震分析工具，获得关于高压高温下压裂物理机制的信息。所研究的物质为(Mg，Fe)2SiO4橄榄石(大洋岩石圈和上地幔的主要矿物)和方辉橄榄岩(大洋岩石圈的主要岩石组合)。样品将在一种新型的变形装置中进行变形，该装置配备了现场声发射(AE)监测以及X射线衍射和成像，在各种压力、温度、差应力、应变和应变率条件下进行变形。这些材料将在高达14 Gpa的压力下进行受控变形。一套最先进的地震学方法，包括事件探测、定位和震源特征，将应用于声发射事件的纳米地震图，以确定破裂机制。我们的目标是了解在实验室规模上将地震力学和矿物/岩石联系起来的物理，提供关于剪切局部化如何以及在什么条件下发生、影响和影响矿物反应平衡和动力学以及触发动态机械不稳定的基本见解。在实验过程中，应注意控制氧逸度和最大限度地减少水分。必须牢记实验室和俯冲带过程在规模上的巨大差异。该小组将进行对比研究，以检查声发射源特征与DFEQ的特征。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估热-化学-机械模型。结合这些方法，研究人员期望通过建立DFEQ的物理模型来显著增强我们对DFEQ机制的理解，其可测试性和可扩展性可以通过计算模拟来进一步检验。

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.