Seven Thousand Felt Earthquakes in Oklahoma and Kansas Can Be Confidently Traced Back to Oil and Gas Activities

The seismicity levels in Oklahoma and southern Kansas have increased dramatically over the last 15 years. Past studies have identified the massive disposal of wastewater co-produced during oil and gas extraction as the driving force behind some earthquake clusters, with a small number of events directly linked to hydraulic fracturing (HF) stimulations. The present investigation is the first one to examine the role both of these activities played throughout the two states, under the same framework. Our findings confirm that wastewater disposal is the main causal factor, while also identifying several previously undocumented clusters of seismicity that were triggered by HF. We were able to identify areas where both causal factors spatially overlap, despite likely acting at different depth intervals. Overall, oil and gas operations are probabilistically linked at high confidence levels with more than 7000 felt earthquakes (M≥2.5), including 46 events with M≥4.0 and 4 events with M≥5. Our analysis employed newly compiled regional earthquake catalogs and established physics-based principles. It first hindcasts the seismicity rates after 2017 on a spatial grid using either actual or randomized HF and wastewater data as input, and then compares them against the null hypothesis of solely tectonic loading. In the end, each block is assigned a p-value, indicating the statistical confidence of its causal link with either HF stimulations or wastewater disposal.