Collaborative Research: Experimental Study of the Origin and Nature of High Pressure Faulting Relevant to Earthquakes in Subducting Lithosphere

合作研究：俯冲岩石圈与地震相关的高压断层的起源和性质的实验研究

• 批准号: 0125938
• 负责人: Harry Green
• 金额: $ 36万
• 依托单位: University of California-Riverside
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-12-15 至 2005-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0125938&HistoricalAwards=false
• 关键词: Collaborative; Research; Experimental; Study; Origin

Green EAR-0125938 Conventional brittle failure is impossible at significant depth within Earth because the combination of pressure and temperature ensures that the flow strength of rocks is exceeded before the fracture strength. Nevertheless, earthquakes occur abundantly within descending slabs of oceanic lithosphere in subduction zones, in several cases to depths as great as 680 km, where they stop abruptly. Although the mechanism by which these earthquakes occur is unknown, their seismic signals ensure that they represent sudden failure of rock along a fault. There are two mechanisms presently known that can enable faulting to occur at high pressure. The first, dehydration embrittlement, involves generation of a free fluid phase by breakdown of hydrous minerals; the free fluid assists in opening of microcracks which is a crucial step leading to shear failure. So far as is known, this mechanism could potentially explain all earthquakes if appropriate hydrous phases are present in the mantle and if their stability fields are such that they dehydrate under appropriate conditions to yield the observed depth distribution. The second, phase-transformation-induced faulting can be triggered during the phase transformations of olivine to its denser polymorphs, which occur with increasing depth. This mechanism can potentially explain the bimodal depth distribution of earthquakes and their abrupt termination at the base of the upper mantle if metastable olivine is preserved in the cold cores of subduction zones at transition-zone depths. However, given current understanding of the phase distribution within subducting lithosphere, neither mechanism can comfortably explain the occurrence of very large earthquakes at depths exceeding 500 km. The investigators will apply their collective expertise in high-pressure technology, experimental deformation, and seismology to achieve the following: (1) test the hypothesis of reactivation of hydrated faults; (2) monitor experiments on dehydration embrittlement and transformation-induced faulting by detection and location of acoustic emissions; (3) develop improved high-pressure experimental assembly designs for in situ synchrotron experiments on shear failure; (4) use faulting experiments on both dehydration embrittlement and phase-transformation-induced faulting to place new constraints on these two faulting mechanisms.

绿色EAR-0125938传统的脆性故障在地球内的显着深度不可能，因为压力和温度的组合可确保在断裂强度之前超过岩石的流动强度。 然而，地震发生在俯冲带中的海洋岩石圈的下降平板内，在几种情况下，深度高达680 km，它们突然停止。 尽管这些地震发生的机制尚不清楚，但它们的地震信号确保它们代表了沿断层的岩石突然失败。 目前已知有两种机制可以使断层在高压下发生。 第一个是脱水的封闭，涉及通​​过含水矿物的分解来产生自由液相。自由流体有助于开放微裂纹，这是导致剪切故障的关键步骤。 据已知，如果地幔中存在适当的含水相，并且它们的稳定性场是在适当的条件下脱水以产生观察到的深度分布，则该机制可能会解释所有地震。在橄榄石的相变向其密集的多晶型物的相变，可以触发第二个相变诱导的断层，这些断层随着深度的增加而发生。 如果在过渡区深度的俯冲带中保存亚稳定的橄榄石，则这种机制可以解释地震的双峰深度分布及其在上地幔底部的突然终止。 但是，鉴于当前对岩石圈俯冲内的相分布的理解，这两个机制都无法舒适地解释在超过500 km的深度时发生非常大的地震的发生。研究人员将在高压技术，实验变形和地震学上运用其集体专业知识来实现​​以下方面：（1）测试水合断层重新激活的假设； （2）通过检测和位置进行声学排放的检测和位置，监测有关脱水封闭和转化引起的断层的实验； （3）开发了改进的高压实验组装设计，用于对剪切失效的原位同步体实验； （4）在脱水封闭和相变诱导的断层上使用断层实验对这两种断层机制施加了新的约束。