The Upper Transition From Seismic To Aseismic Faulting on Subduction Megathrusts

智力价值：这项研究调查了世界上最大的地震的原因，这些地震发生在俯冲板块边界。这些“大逆冲”地震破坏了板块边界的部分，但我们仍然不明白这些破裂斑块的界限是如何确定的。这项工作的目标是确定为什么俯冲板块边界的某些部分在大地震中灾难性地失败，而其他部分则因地震蠕变而失败。识别这些过程对于理解地震周期和预测与海啸产生和地震危险相关的俯冲带的行为在时间尺度上是至关重要的。该研究利用一套互补的实验室方法，对孕震带上倾极限的两个假设进行了验证，这些方法主要关注：(1)摩擦特性，包括岩化和固结状态、粘土矿物学、有效应力和排水条件对摩擦本构特性的影响；(2)岩化和固结状态之间的流体输运特性、组成、渗透率和流变性。来自海洋钻探岩心、挖掘出的断层和合成断层泥的样品将在精心控制的实验室实验中对自然和合成样品进行分析，包括P-T、流体、矿物学、胶结和压实条件，这些条件跨越稳定性转变。实验包括摩擦测量、固结测试、弹性性能和渗透率的测量以约束弹性刚度，以及有效应力的测量。将进行双轴和摩擦剪切试验，以及单轴变形和流动试验。更广泛的影响：这项研究具有潜在的重大社会影响，因为它提高了对断层力学和地震物理学的理解，包括海啸的产生和地震危害评估。这项工作还补充了NSF IODP和margin计划。该项目将培养两名研究生和四名本科生，这些学生也有机会在专业会议上展示他们的研究成果。

Intellectual Merit: This research investigates the cause of the world's largest earthquakes, which occur along subduction plate boundaries. These "megathrust" earthquakes rupture sections of the plate boundary, but we still do not understand how the limits of these rupture patches are determined. Goals of the work are to identify reasons why some sections of subduction plate boundaries fail catastrophically in large earthquakes whereas other sections fail by aseismic creep. Identifying these processes is essential to understanding the seismic cycle and predicting the behavior of subduction zones on time scales relevant to tsunami generation and seismic hazard. The research tests two hypotheses for the up dip limit of the seismogenic zone using a complementary set of laboratory-based approaches that focus on (1) frictional properties, including the effect of lithification and consolidation state, clay mineralogy, effective stress, and drainage conditions on frictional constitutive properties; and (2) fluid transport properties between lithification and consolidation state, composition, permeability, and rheology. Samples from ocean drilling cores, exhumed faults, and synthetic fault gouge will be analyzed in carefully controlled laboratory experiments on natural and synthetic samples over P-T, fluid, mineralogical, cementation, and compaction conditions that span the stability transition. Experiments include friction measurements, consolidation tests, measurement of elastic properties and permeability to constrain elastic stiffness, and measurements of effective stress. Biaxial and frictional shear experiments will be carried out as will uniaxial deformation and flow through tests. Broader Impacts: This research has the potential for significant societal impact from an improved understanding of fault mechanics and earthquake physics including tsunami generation and seismic hazard assessment. The effort also complements the NSF IODP and MARGINS programs. The project will train two graduate students and four undergraduate students with the students also getting opportunities to present the results of their research at professional meetings.