Microseismicity illuminates open fractures in the shallow crust

Successful delivery of geological carbon storage and/or radioactive waste disposal relies on the ability to predict the transport of waste stored/disposed of at depth, over 103 to 106 years. Field evidence shows that faults and fractures can act as focused pathways for contaminant migration. Hence, transport predictions require detailed characterization of fracture location, orientation and hydraulic properties. We show that microseismic monitoring can delineate the three‐dimensional structure and hydraulic characteristics of flowing fractures at 2 to 3 km depth. Individual fracture planes are validated by independently derived composite focal mechanisms. Local field observations confirm the presence of open fractures with lengths and orientations matching the seismically‐derived fracture planes. The temporal evolution of seismicity within individual fractures allows us to estimate depth‐averaged transmissivity and in‐plane fluid velocity distributions. Our results demonstrate the potential of microseismic monitoring to characterize flowing fractures, for non‐invasive site investigation at CO2 and radioactive waste storage/disposal sites.