报告地点：Zoom(ID:724-620-904)

报告时间：2020-05-22 从 15:00 到 16:30

报告人：马晓冬

报告人简介：

Dr. Xiaodong Ma is an Oberassistent (senior scientist) and lecturer at ETH Zürich. He is affiliated with the Swiss Competence Center for Energy Research and the Department of Earth Sciences. His research interest lies in crustal stress, reservoir geomechanics, geothermal energy, and experimental rock mechanics. He is currently leading the geomechanics efforts of the Bedretto Underground Laboratory (BUL) for field experiments related to enhanced geothermal systems and induced seismicity.

Dr. Ma obtained his PhD degree in geological engineering (2014) from University of Wisconsin-Madison, and subsequently conducted post-Doctoral research at the Stress and Crustal Mechanics Group, Stanford University before joining ETH Zürich. He had previously tackled on a variety of geomechanical challenges, including the experimental characterization of true triaxial mechanical response of porous sandstones, poroelastic behavior of unconventional reservoir rocks, and stress variation in shales and its effect on the effectiveness of hydraulic fracturing.

报告题目：Time-dependent relaxation of crustal stresses: through viscous flow or frictional slips?

报告内容简介

The assumption that the Earth’s upper crust is critically stressed at its frictional limit (i.e., the frictional equilibrium) is evident in that earthquakes triggered by extremely small perturbations of elevated pore pressure (fluid injection, reservoir impoundment) occurs ubiquitously worldwide. There are, however, many cases of substantially lower stress difference (i.e., not critically stressed) that are not explained by the frictional equilibrium. Examples are shown in the clay-rich shales in the US (previously presented at USTC in May 2017) and China. Varying degrees of viscous flow were attributed to explain the stress relaxation below the frictional limit, but questions remain on how laboratory-derived viscous flow constitutive law be upscaled to and representative of crustal rock masses. To bridge the scaling gap, a stochastic model has been proposed to incorporate another important mechanism of stress relaxation, frictional slip of the fractures and faults in the rock masses, which occur at various scales. The model offers an alternative perspective on crustal frictional equilibrium and can be adapted to simulate the stress evolution of various scenarios.