Unified hydromechanical and nucleation models for induced seismicity in Western Oklahoma and South-Central Kansas

Guang Zhai, Manoochehr Shirzaei, & Michael Manga

Published August 15, 2019, SCEC Contribution #9733, 2019 SCEC Annual Meeting Poster #034

Induced seismicity has expanded into south-central Kansas, an area with low risk of damaging natural earthquakes (Peterie et al., 2018, GRL). Historically, the region has an average of one M3.0+ earthquake every one or two years. The rapid increase of seismicity since 2014 makes Kansas the state with the second-highest seismicity rate in the central US after Oklahoma. Independent from local injection operation, the abrupt increase of formation pressure evident from bottom-hole pressure data, together with the northward propagating seismicity suggests that fluid diffusion process due to high-volume injection at wells near the Oklahoma-Kansas border may play a role. To test this hypothesis, here we investigate the effects of large-scale injection in the combined area of western Oklahoma and south-central Kansas during 2010-2018 and its link to the observed seismicity. Using the physics-based induced seismicity forecasting approach of Zhai et al. (2019, PNAS), we construct a unified hydromechanical and seismicity rate model within the two states. Although we find a causal relationship between observed seismicity and injection operations, there are zones of large predicted seismicity rate increase with almost no observed seismicity, indicating spatial heterogeneity of the background seismic productivity (a-value). The mapped productivity distribution combined with the seismicity rate model can reproduce the observed earthquake magnitude-time distribution. Furthermore, using this unified model, we investigate the impact of Oklahoma injection on the spatiotemporal evolution of pore pressure, stress, and seismicity rate. Injection in Oklahoma can amplify the total coulomb stress change and seismicity rate in south-central Kansas by 1.5-fold and 3-fold, respectively. These long-distance interactions systematically increase the annual earthquake magnitude exceedance probability, with a maximum increase of ~36% in 2015. We conclude that fluid diffusion from far-field injection in Oklahoma plays an essential role in elevating seismic hazard in south-central Kansas.

Key Words
Induced Seismicity, Poroelasticity, Seismic Hazard, Injection

Citation
Zhai, G., Shirzaei, M., & Manga, M. (2019, 08). Unified hydromechanical and nucleation models for induced seismicity in Western Oklahoma and South-Central Kansas. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP)