Experimental constraints on the rheology of the mantle lithosphere at the base of the seismogenic zone

最大和最具破坏性的地震发生在岩石圈俯冲到大陆下面的板块边界。地球科学家已经发现，在这些地区发生了广泛的断层滑动过程，并且通过将地球物理观测与实验室实验的模型和约束条件相结合，在理解这些事件方面取得了重大进展。然而，我们对相关条件下的力学性能的理解仍然存在空白。以前在这些条件下的工作受到实验期间施加在样品上的应力的相对较差的分辨率的阻碍。研究人员对他们的高压设备进行了新的改进，这将大大提高测量应力的能力，并描述发生在俯冲带环境中的断层滑动行为。研究结果将提供必要的新约束，以理解地震滑动是如何开始的，并解释为什么地震发生的深度范围有限。该项目将资助两名博士生（一名在项目期间完成论文，另一名在项目期间开始论文）。外展将与该部门的deepstep（普罗维登斯公立学校的STEM）计划协调。岩石力学与工程有着紧密的联系，有可能弥合与URM STEM学生之间的差距，这些学生在地球科学领域的代表性仍然严重不足。该项目涉及的实验包括：(a)在干燥和潮湿条件下的高温下量化摩擦行为；(b)研究了橄榄石聚集体在脆性-塑性转变附近的高压条件下的低温塑性，这也与将速率-状态摩擦定律外推到地幔条件有关；(c)限制脱水反应对岩石圈摩擦稳定性的作用；(d)确定高压蚀变阶段的摩擦行为和流动规律参数，以约束蚀变岩石圈的强度（以及脱水前的应力状态）。研究者设备的改进增强了以下能力：(a)进行蠕变试验，这将允许获得更好的数据来约束流动规律参数；(b)解析瞬态变形，这大大提高了在地震活动发生的高压条件下量化速率和状态摩擦参数的能力。这些结果将为许多对变质作用、地球动力学、地震学、地震物理学和流体输运等不同领域感兴趣的科学家提供约束。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The largest and most damaging earthquakes occur along plate boundaries where lithosphere is subducted beneath the continents. Geoscientists have discovered that a wide range of fault slip processes occur in these regions, and significant progress has been made understanding these events by integrating geophysical observations with models and constraints from lab experiments. However, there are still gaps in our understanding of mechanical properties at the relevant conditions. Previous work at these conditions has been hindered by relatively poor resolution of the stresses being imposed on the sample during an experiment. The investigators have made new modifications to their high-pressure equipment that will lead to significant improvement in the ability to measure stress and characterize the fault slip behavior that occurs within the subduction zone environment. The results will provide new constraints necessary to understand how earthquake slip initiates and to explain why there is a limited depth range over which the earthquakes occur. The project will fund two Ph.D. students (one completing a thesis and another starting a thesis during the duration of the project). Outreach will be coordinated with the Department’s DEEPS STEP (STEM in Providence Public Schools) program. Engagement in rock mechanics, with its strong links to engineering, has the potential to bridge a gap to URM STEM students, who remain dramatically underrepresented in Earth Sciences.This project involves experiments to: (a) quantify frictional behavior at high-temperature under both dry and wet conditions; (b) investigate low temperature plasticity of olivine aggregates at high pressure conditions near the brittle-plastic transition, which is also relevant for constraining the extrapolation of rate-and-state friction laws to mantle conditions; (c) constrain the role of dehydration reactions on the frictional stability of the lithosphere; and (d) determine frictional behavior and flow law parameters for alteration phases at high pressure to constrain the strength of altered lithosphere (and stress state prior to dehydration). The improvements to the investigator's apparatus enhances the ability to: (a) conduct creep tests, which will allow acquisition of better data to constrain flow law parameters; and (b) resolve transient deformation, which significantly improves the ability to quantify rate-and-state friction parameters at the high pressure conditions where seismicity occurs. The results will provide constraints for a wide range of scientists interested in the diverse fields of metamorphism, geodynamics, seismology, the physics of earthquakes, and fluid transport.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.