Unconventional oil and gas production provides a rapidly growing energy source; however, high-production states in the United States, such as Oklahoma, face sharply rising numbers of earthquakes. Subsurface pressure data required to unequivocally link earthquakes to wastewater injection are rarely accessible. Here we use seismicity and hydrogeological models to show that fluid migration from high-rate disposal wells in Oklahoma is potentially responsible for the largest swarm. Earthquake hypocenters occur within disposal formations and upper basement, between 2- and 5-kilometer depth. The modeled fluid pressure perturbation propagates throughout the same depth range and tracks earthquakes to distances of 35 kilometers, with a triggering threshold of ~0.07 megapascals. Although thousands of disposal wells operate aseismically, four of the highest-rate wells are capable of inducing 20% of 2008 to 2013 central U.S. seismicity.

An unprecedented increase in earthquakes in the U.S. mid-continent began in 2009. Many of these earthquakes have been documented as induced by wastewater injection. We examine the relationship between wastewater injection and U.S. mid-continent seismicity using a newly assembled injection well database for the central and eastern United States. We find that the entire increase in earthquake rate is associated with fluid injection wells. High-rate injection wells (>300,000 barrels per month) are much more likely to be associated with earthquakes than lower-rate wells. At the scale of our study, a well's cumulative injected volume, monthly wellhead pressure, depth, and proximity to crystalline basement do not strongly correlate with earthquake association. Managing injection rates may be a useful tool to minimize the likelihood of induced earthquakes.

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Reinjection of saltwater, co-produced with oil, triggered thousands of widely felt and several damaging earthquakes in Oklahoma and Kansas. The future seismic hazard remains uncertain. Here, we present a new methodology to forecast the probability of damaging induced earthquakes in space and time. In our hybrid physical–statistical model, seismicity is driven by the rate of injection-induced pressure increases at any given location and spatial variations in the number and stress state of preexisting basement faults affected by the pressure increase. If current injection practices continue, earthquake hazards are expected to decrease slowly. Approximately 190, 130 and 100 widely felt M ≥ 3 earthquakes are anticipated in 2018, 2019 and 2020, respectively, with corresponding probabilities of potentially damaging M ≥ 5 earthquakes of 32, 24 and 19%. We identify areas where produced-water injection is more likely to cause seismicity. Our methodology can be used to evaluate future injection scenarios intended to mitigate seismic hazards.

The Mw 5.1 Fairview, Oklahoma, earthquake on 13 February 2016 and its associated seismicity produced the largest moment release in the central and eastern United States since the 2011 Mw 5.7 Prague, Oklahoma, earthquake sequence and is one of the largest earthquakes potentially linked to wastewater injection. This energetic sequence has produced five earthquakes with Mw 4.4 or larger. Almost all of these earthquakes occur in Precambrian basement on a partially unmapped 14 km long fault. Regional injection into the Arbuckle Group increased approximately sevenfold in the 36 months prior to the start of the sequence (January 2015). We suggest far‐field pressurization from clustered, high‐rate wells greater than 12 km from this sequence induced these earthquakes. As compared to the Fairview sequence, seismicity is diffuse near high‐rate wells, where pressure changes are expected to be largest. This points to the critical role that preexisting faults play in the occurrence of large induced earthquakes.

The ability of fluid-generated subsurface stress changes to trigger earthquakes has long been recognized. However, the dramatic rise in the rate of human-induced earthquakes in the past decade has created abundant opportunities to study induced earthquakes and triggering processes. This review briefly summarizes early studies but focuses on results from induced earthquakes during the past 10 years related to fluid injection in petroleum fields. Study of these earthquakes has resulted in insights into physical processes and has identified knowledge gaps and future research directions. Induced earthquakes are challenging to identify using seismological methods, and faults and reefs strongly modulate spatial and temporal patterns of induced seismicity. However, the similarity of induced and natural seismicity provides an effective tool for studying earthquake processes. With continuing development of energy resources, increased interest in carbon sequestration, and construction of large dams, induced seismicity will continue to pose a hazard in coming years.

The Raton Basin had the highest number of earthquakes in Colorado and New Mexico from 2008 to 2010. The rate of both wastewater injection and earthquakes in the basin increased dramatically starting in 1999 and 2001, respectively. We compare seismicity (ML 0.0–4.3) in the Raton Basin from 2008 to 2010 with the location of modeled pore pressure increases, estimated from cumulative wastewater injection volume beginning at the onset of well injection to present for all 28 injection wells in the basin. We find that modeled pore pressures in the New Mexico portion of the basin (above 0.08 MPa) reached that necessary to induce seismicity (0.01–0.1 MPa). We simulate a fault plane, 20 km long, inferred from seismicity in Vermejo Park (1355 of 1881 total earthquakes), in our model. We find that the relatively permeable fault allows pressures to migrate deeper into the basin at the onset of our study in 2008, providing an explanation for the observed seismicity in the basement. The Tercio lineament of earthquakes is similar to Vermejo Park fault in strike, but has fewer earthquakes (129) and is shorter in length (9 km). Seismicity in Vermejo Park occurs continuously, but earthquakes occur episodically in the remainder of the basin. The number of earthquakes we observe in seven seismic clusters increases as the cumulative injected volume from wells within 5 km increases. The modeled pore pressures, earthquake locations, and relationship between cumulative volume and number of earthquakes indicate that seismicity in the Raton Basin is likely induced.

Large-scale wastewater disposal has led to a fast-paced reawakening of faults in the Oklahoma/Kansas region. High-resolution earthquake relocations show that the inventory of ancient basement faults in the study region differs from results of seismic surveys and geologic mapping focused on the sedimentary cover. We analyze the evolution of seismic activity in the Guthrie-Langston sequence in central Oklahoma in greater detail. Here, seismic activity has reactivated a network of at least 12 subvertical faults in an area less than 10 km across. Recorded activity began in late 2013, peaked about six months later, and includes two M 4 earthquakes. These earthquakes characteristically occur at about 4 km depth below the top of the basement and do not reach the sedimentary cover. The sequence shows a radial growth pattern despite being no closer than 10 km to significant wastewater disposal activity. Hydrologic modeling suggests that activity initiated with a time lag of several years relative to early injection activity. Once initiated, earthquake interactions contribute to the propagation of seismicity along the reactivated faults. As a result, the spatiotemporal evolution of the seismicity mimics a diffusive pattern that is typically thought to be associated with injection activity. Analysis of the fault slip potential shows that most faults are critically stressed in the contemporary stress field. Activity on some faults, for which we find low slip probability, suggests a significant contribution of geomechanical heterogeneities to the reawakening of these ancient basement faults.