Riazi, NaimehEaton, David W.2020-10-212020-10-212020-10-18http://hdl.handle.net/1880/112702https://doi.org/10.11575/PRISM/46082Tectonically active fault networks are often inter-connected, but in the case of injection-induced seismicity, prior knowledge of fault architecture tends to be severely limited. In most cases, reactivated faults due to fluid injection are inferred, after-the-fact, by the spatial distribution of induced-seismicity hypocenters; such reliance on post-injection seismicity impedes any pre-operational risk analysis, as well as development of a more holistic understanding of fault-system models. By combining high-resolution, depth-migrated 3-D seismic data with a new focal-depth estimation method that reduces spatial uncertainty of hypocenters, this study pinpoints microearthquake fault activation within a buried thrust belt in the Montney Formation in western Canada (British Columbia). During hydraulic-fracturing operations, rupture nucleation occurred on seismically imaged thrust ramps that cut through the Debolt Formation, a massive carbonate layer that underlies the stimulated zone. High-resolution seismic images reveal transverse structures, interpreted as basement-controlled fold hinges or tear faults that transferred displacement between thrust faults during Late Cretaceous - Paleogene compressional shortening. The spatio-temporal pattern of induced seismicity suggests that these transverse structures provide permeable pathways for aseismic pore-pressure diffusion, thus connecting distinct thrust faults and enabling earthquake triggering on a timescale of days and at distances of up to 2 km from the injection wells. Inferred relationships highlight how the fault system is connected, including apparent stress concentrations at the intersections of transverse structures and orogen-parallel thrust ramps.engUnless otherwise indicated, this material is protected by copyright and has been made available with authorization from the copyright owner. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.Focal Induced seismicityFault imagingEarthquake depthjournal articlehttp://dx.doi.org/10.1016/j.tecto.2020.228640