A decade of Oklahoma earthquakes: past, present and future

Abstract

<p>In the last decade, Oklahoma has experienced significant changes in earthquake activities: earthquake rate dramatically increased since 2009, with a peak rate exceeding California, which has gradually decreased in recent years. This “accidental” large scale earthquake experiment provides us with rich datasets to further understand earthquake physics. Here, focusing on analyses of seismicity and accounting for the physics of earthquake nucleation, we link several studies to give a brief overview of Oklahoma earthquakes, and their implications for future studies in induced seismicity.  First, the analysis of spatiotemporal patterns of seismicity rate can help us infer the subsurface hydraulic parameters at both regional and local scales. At the regional level, the hydraulic diffusivities differ between Eastern and Western Oklahoma, separated by the Nemaha Fault, reflecting hydraulic properties of the Arbuckle Group (injection layer). At local scales within individual faults, the analysis suggested similar hydraulic diffusivities to crustal earthquake bursts from other tectonic regions, implying common properties of the crystalline basement.  Second, coupled poroelastic responses to injection on individual faults are essential, and produce seismicity rate forecast that more closely resemble observations. However, local stress tensor variations can significantly influence fault “criticality” and should be taken into account for modeling stress interactions. Third, in addition to injection-related stress changes, earthquake interactions and aseismic slip need to be considered in induced earthquake sequences, and detailed source modeling and statistical analysis are required to understand their roles in the evolutions of individual sequences further. Finally, Oklahoma seismicity offers opportunities to test short- to intermediate-term forecasting based on different physical models, and new windows into earthquake rupture initiations.</p>

Imaging the Deep Crustal Structure of Central Oklahoma Using Stacking and Inversion of Local Earthquake Waveforms

“…These high velocity anomalies correlate with gravity anomalies. Chen (2016) interpreted this anomaly as evidence for the extension of the MCR into northern Oklahoma. Our model extends deeper in this region and we observe that the velocity anomaly is only present in the upper‐middle crust extending down to about 20 km in depth (Figures 9 and 12c).…”

“…There have been two major studies that have developed regional P‐wave velocity models for the crust in Oklahoma. Chen (2016) developed a 3‐D velocity model for the upper crust (up to ∼15 km depth) using traditional travel time tomography applied to local earthquake waveforms. We correlate the velocity Regions A, B, and C with similar velocity anomalies observed in the cross sections A4 and A5 (Figure S9) from Chen (2016)’s model.…”

“…Estimating robust travel times at large offsets is challenging, particularly for small magnitude events. Consequently, traditional LET methods in Oklahoma where the earthquake depths are shallow (∼2–7 km depth) (Figure S1) can only represent velocity variations in the upper crust (Chen, 2016; Toth, 2014). Correlation and correct interpretation of individual travel times requires high‐quality data, and in the case of many observations (semi‐)automated phase correlation and picking routines (Chen, 2016; Thybo et al., 2006).…”

“…McGlannan and Gilbert (2016) reported a crustal depth variation from 30 to 55 km across Oklahoma based on the Earthscope Automated Receiver Survey using the US Transportable Array. In general, these passive seismic studies either do not have the necessary depth of investigation to image the deeper crustal structures (Chen, 2016; Toth, 2014), lack the resolution required to be able to comment on the regional crustal structure (Evanzia et al., 2014; McGlannan & Gilbert, 2016), or provide shear wave velocities only based on ambient noise tomography (Shen & Ritzwoller, 2016; H. Zhu, 2018). Likewise, gravity and magnetic data can provide some information on the crust (Bickford, Van, & Zietz, 1986; Sims et al., 2005; Van Schmus et al., 1996), but non‐uniqueness of these methods require constraints such as seismic data to infer robust interpretations.…”

“…There have been a few passive seismic studies targeting large‐scale crustal structure in Oklahoma. Local earthquake tomography (LET) by Chen (2016) and Toth (2014) obtained upper crustal (up to 15–20 km) seismic P‐ and S‐wave velocity distribution. Velocity anomalies observed in these models show close correlation to the major tectonic features like the Nemaha Fault Zone and the Wilzetta Fault Zone in Oklahoma.…”