Abstract At transition zone depths in subduction zones, deep-focus earthquakes (300–690 km depth) are thought to be associated with faulting that arises from phase transformations. In order to test the viability of this mechanism experimentally, an investigation was conducted on fayalite at high pressure, P, and high temperature, T, under deviatoric stress in order to initiate transformational faulting. Experiments were performed in a 3000-ton multi-anvil press using an 18/11 octahedral cell with 6 piezoelectric transducers mounted on the rear side of the anvils to monitor acoustic activity in situ. Acoustic emission (AE) signals were collected at a sampling rate of 40 MHz using a triggered system and a data buffer for capturing full waveforms of AE events. The use of multiple transducers distributed in a micro-seismic array allowed for events to be located within the sample based on the arrival time of signals and non-linear least squares inversion techniques. Uncertainty in location estimates were on the order of ~1 mm. The system was tested by comparing the contrasting mechanical properties of quartz beads and AgCl samples. The multi-anvil apparatus constitutes an inherently noisy environment both acoustically and electrically, therefore methods of noise reduction were developed. Results of AE experiments on Fe2SiO4 under high pressure (3.7–9.2 GPa) and high temperature (673–1273 K) conditions in the spinel stability field showed acoustic events that locate within or within 1σ of the sample in five experiments defined by the P,T envelope P = 3.9–8.4 GPa and T = 748–923 K. Optical and scanning electron microscopy of the recovered specimens displayed conjugated faulting associated with transition from fayalite (olivine structure) to ahrensite (spinel structure) and microstructural analysis revealed microstructural morphology identical to that found in similar faulting experiments on Mg2GeO4. This is the first time an olivine→spinel structured transition in a silicate mineral has demonstrated macroscopic faulting and associated microstructures, as well as acoustic activity, under conditions that nominally promote plastic deformation.

中文翻译：

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通过原位声发射检测 Fe2SiO4 中的高 P、T 转换断层：与深源地震的相关性

摘要 在俯冲带过渡带深度，深源地震（300-690 公里深度）被认为与相变引起的断层有关。为了通过实验测试这种机制的可行性，在偏应力下在高压 P 和高温 T 下对铁橄榄石进行了研究，以引发转变断层。实验在 3000 吨多砧压机中进行，使用 18/11 八面体单元，6 个压电换能器安装在砧座后侧，以原位监测声学活动。使用触发系统和数据缓冲器以 40 MHz 的采样率收集声发射 (AE) 信号，以捕获 AE 事件的完整波形。使用分布在微地震阵列中的多个换能器允许基于信号的到达时间和非线性最小二乘反演技术将事件定位在样本内。位置估计的不确定性约为 1 毫米。通过比较石英珠和 AgCl 样品的机械性能对比，对该系统进行了测试。多砧装置在声学和电学上都构成固有的嘈杂环境，因此开发了降噪方法。在尖晶石稳定场中的高压 (3.7–9.2 GPa) 和高温 (673–1273 K) 条件下对 Fe2SiO4 的 AE 实验结果表明，在由 P 定义的五个实验中，声学事件位于样品的 1σ 以内或以内。 T 包络 P = 3.9–8.4 GPa 和 T = 748–923 K。回收样品的光学和扫描电子显微镜显示共轭断层与从铁橄榄石（橄榄石结构）到阿伦石（尖晶石结构）的转变相关，微观结构分析显示其微观结构形态与在 Mg2GeO4 上的类似断层实验中发现的相同。这是硅酸盐矿物中橄榄石→尖晶石结构转变第一次在名义上促进塑性变形的条件下证明宏观断层和相关的微观结构以及声学活动。