Potentially induced earthquakes in Oklahoma, USA: Links between wastewater injection and the 2011 Mw 5.7 earthquake sequence

Abstract

Signifi cant earthquakes are increasingly occurring within the continental interior of the United States, including fi ve of moment magnitude (M w) ≥ 5.0 in 2011 alone. Concurrently, the volume of fl uid injected into the subsurface related to the production of unconventional resources continues to rise. Here we identify the largest earthquake potentially related to injection, an M w 5.7 earthquake in November 2011 in Oklahoma. The earthquake was felt in at least 17 states and caused damage in the epicentral region. It occurred in a sequence, with 2 earthquakes of M w 5.0 and a prolifi c sequence of aftershocks. We use the aftershocks to illuminate the faults that ruptured in the sequence, and show that the tip of the initial rupture plane is within ~200 m of active injection wells and within ~1 km of the surface; 30% of early aftershocks occur within the sedimentary section. Subsurface data indicate that fl uid was injected into effectively sealed compartments, and we interpret that a net fl uid volume increase after 18 yr of injection lowered effective stress on reservoir-bounding faults. Signifi cantly, this case indicates that decades-long lags between the commencement of fl uid injection and the onset of induced earthquakes are possible, and modifi es our common criteria for fl uid-induced events. The progressive rupture of three fault planes in this sequence suggests that stress changes from the initial rupture triggered the successive earthquakes, including one larger than the fi rst.

Geologic carbon storage is unlikely to trigger large earthquakes and reactivate faults through which CO2could leak

“…However, the earthquakes were induced in the critically stressed crystalline basement and not in the sedimentary formations where wastewater was injected. Wastewater was injected into the basal aquifer, which led to the pressurization of faults in the crystalline basement (27)(28)(29). In the case of the earthquakes of Guy and Greenbrier, Arkansas, wastewater was injected into the Ozark aquifer (3 km deep), which is placed right above the crystalline basement.…”

Race to unravel Oklahoma’s artificial quakes

“…The biggest earthquake ever recorded in Oklahoma was a magnitude-5.6 event near the town of Prague in November 2011, and many seismologists think that it was induced by nearby disposal wells 3 . Theoretical work 4 suggests that the potential size of a quake grows with the volume of fluid injected into the ground.…”

Gas injection may have triggered earthquakes in the Cogdell oil field, Texas

“…6). Thus, if one attributes the seismicity either to overpressuring reducing friction on faults, or to exceeding the capacity of "effectively sealed compartments," as Keranen et al (10) recently suggested might contribute to causing a 2011 M5.7 earthquake in Oklahoma, it is plausible that injected gas played a dominant role. This is an unusual and noteworthy instance where gas injection may have contributed to triggering earthquakes having magnitudes of 3 or larger, as the 2006-2012 sequence included 18 earthquakes with magnitudes exceeding 3, and an M W 4.4 earthquake that occurred September 11, 2011.…”

“…triggered seismicity | fluid injection | carbon sequestration I nduced seismicity related to underground injection of liquids has been widely reported (1)(2)(3)(4)(5)(6)(7)(8)(9)(10) but there are very few reports of gas injection triggering earthquakes large enough to be felt or cause damage at the surface. Thus, the injection-induced earthquakes of concern are not the tiny events accompanying hydrofracturing that have magnitudes of 1.5 or smaller; rather, they are the larger-magnitude earthquakes sometimes caused by injection for water flooding, enhanced production, or waste disposal.…”