Subsurface Fluid Pressure and Rock Deformation Monitoring Using Seismic Velocity Observations

Abstract

Abstract Fluid pressure within the Earth's crust is a key driver for triggering natural and human‐induced seismicity. Measuring fluid pressure evolution would be highly beneficial for understanding the underlying driving mechanisms and supporting seismic hazard assessment. Here we show that seismic velocities monitored on the 20‐m scale respond directly to changes in fluid pressure. Our data show that volumetric strain resulting from effective stress changes is sensed by seismic velocity, while shear dislocation is not. We are able to calibrate seismic velocity evolution against fluid pressure and strain with in situ measurements during a decameter‐scale fluid injection experiment in crystalline rock. Thus, our 4‐D seismic tomograms enable tracking of fluid pressure and strain evolution. Our findings demonstrate a strong potential toward monitoring transient fluid pressure variations and stress changes for well‐instrumented field sites and could be extended to monitoring hydraulic stimulations in deep reservoirs.