地球与行星物理学术报告通知 （202612期）- Yusuke Mukuhira

报告人简介：

Yusuke Mukuhira graduated from the Department of Environmental Science, Graduate School of Environmental Science, Tohoku University, Japan and obtained PhD in March 2013. After Ph.D., he was working as a JSPS Research Fellow PD at the Institute of Fluid Science, Tohoku University, and a JSPS Overseas PD at MIT, USA. Then, he became an assistant professor at the Institute of Fluid Science, Tohoku University in 2017. He was promoted to associate professor in 2025.

报告内容摘要：

Injection-induced seismicity is primarily controlled by geomechanical parameters such as stress state on existing fractures and pore pressure migration. While microseismic monitoring identifies shear failure locations, it cannot quantify pore pressure or fully explain the complex physics involved. To address this, we developed an integrated approach combining microseismic data with in-situ stress information, using datasets from the Enhanced Geothermal System (EGS) project in Basel, Switzerland.Applying the Coulomb failure criterion with in-situ stress models, we estimated the shear stress, normal stress, and pore pressure required to trigger slip on identified fault planes. This integration revealed three key findings. First, large-magnitude post-injection earthquakes occur because pore pressure continues migrating outward after shut-in, redistributing uniformly at the periphery of the seismic cloud and destabilizing large fault sections simultaneously. Second, pore pressure migration speed depends on pressure magnitude — lower pressures migrate faster, controlled by fracture permeability and stress criticality — suggesting that optimizing wellhead pressure can minimize seismic hazard while maximizing reservoir performance. Third, we discovered that b-value in induced seismicity negatively correlates with relative shear stress on individual fractures, rather than with differential stress as in natural seismicity. High-shear-stress fractures produce significantly lower b-values, indicating higher proportions of larger events. These results demonstrate that integrating crustal stress information into seismological analysis substantially deepens our understanding of induced seismicity.