How faults wake up: The Guthrie-Langston, Oklahoma earthquakes

Abstract

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.

Accelerated Fill‐Up of the Arbuckle Group Aquifer and Links to U.S. Midcontinent Seismicity

“…Though a small change in pore pressure (0.01–0.1) in the crystalline basement is enough to reactivate optimally oriented faults (Townend & Zoback, ), it appears that a pore pressure change of 0.6 MPa in the Arbuckle is enough to satisfy this condition and trigger M 3+ seismicity. The observed pore pressure change in the Arbuckle is similar to modeled pore pressure changes in the Arbuckle for Oklahoma's Guthrie‐Langston earthquake sequence (Schoenball et al, ). In addition, Norbeck & Rubinstein, use analytical solutions and show that pressurization at 3 to 4 km depth where seismicity occurs can reach 25% of the pressurization in the aquifer.…”

Aeromagnetic Data Reveal Potential Seismogenic Basement Faults in the Induced Seismicity Setting of Oklahoma

“…Key tectonic events affecting the sedimentary rocks and the basement include the late Paleozoic Ouachita and Alleghenian orogenies, which contributed variations in basement relief of over 10 km in southern Oklahoma (e.g., Crain & Chang, 2018;Johnson, 2008;Northcutt & Campbell, 1995). In contrast, north central Oklahoma, which would have experienced these events distally, if at all, shows faults trending mostly NNW and NNE ( Figure 1; Schoenball et al, 2018). In contrast, north central Oklahoma, which would have experienced these events distally, if at all, shows faults trending mostly NNW and NNE ( Figure 1; Schoenball et al, 2018).…”

“…Red lines mark contacts that are optimally oriented for vertical strike-slip fault movement in the current stress regime, based on a principal stress direction of N80°E-N90°E over most of Oklahoma (Alt & Zoback, 2017). (bottom) Rose histograms showing the cumulative distance of mapped faults (blue) and earthquake sequences (gray), after Schoenball et al (2018), and a count of linear magnetic contacts that may represent faults (orange). (bottom) Rose histograms showing the cumulative distance of mapped faults (blue) and earthquake sequences (gray), after Schoenball et al (2018), and a count of linear magnetic contacts that may represent faults (orange).…”

“…Wastewater fluid injection in Oklahoma has led to thousands of induced earthquakes since 2009, creating an unprecedented level of seismicity in an intraplate setting (Ellsworth, 2013;Keranen et al, 2013;Weingarten et al, 2015). Many of these earthquakes form linear sequences aligned in directions of optimal fault slip for the regional stress field (Alt & Zoback, 2017;McNamara et al, 2015;Schoenball & Ellsworth, 2017;Schoenball et al, 2018; Figure 1), suggesting that they represent the reactivation of preexisting faults. However, few of the sequences are aligned with or near faults in existing maps (Marsh & Holland, 2016).…”

Faults and Non‐Double‐Couple Components for Induced Earthquakes

“…In many cases, focal mechanism solutions are used to infer the orientation and stress condition surrounding (often unmapped) reactivated faults. The double‐couple (DC) component therein directly reflects the size and orientation of the reactivated fault and are generally well constrained in induced seismogenic zones (e.g., western Canada (Wang et al, ); Oklahoma, USA (Chen et al, ; Schoenball et al, )). The non‐DC components reflect fault or fracture growth due to possible volume changes associated with fluid injection/extraction.…”