From Seismic Quiescence to Surged Activity After Decades of Wastewater Disposal: A Case Study in Central‐West Alberta, Canada

Abstract

Abstract Injection‐induced earthquakes associated with wastewater disposal (WD) in the Western Canadian Sedimentary Basin are much fewer than those linked to hydraulic fracturing. Recently, 43 WD‐related earthquakes (M1.3–3.9) occurred in a historically seismically quiet area where long‐term injections became intensive since 2018, foreshadowing a critical stress state accumulated from long‐term injections. Our improved earthquake locations show that the injection well targeting the deeper middle‐upper Devonian aquifer system causes more vigorous seismicity with a wide range of stress drop values (0.8–230 MPa) compared to other shallower wells. Three physical mechanisms may collectively lead to the observed seismic pattern: (a) the underlying Devonian reef system makes it easier for injected fluids to migrate horizontally, (b) fluids can be channeled into the widespread critical faults and migrate vertically to cause earthquakes along it, and (c) aseismic slip probably triggered within the Duvernay formation by fluid migrating can further facilitate seismicity at shallower depths.