Complex Source Behaviors and Spatiotemporal Evolution of Seismicity During the 2015–2016 Earthquake Sequence in Cushing, Oklahoma. Issue 6 (9th June 2021)

• Record Type: Journal Article
• Authors: Meng, Qingjun; Ni, Sidao; Peng, Zhigang
• Is Part Of: Journal of geophysical research. Volume 126:Issue 6(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-06-09
• Subjects: finite fault model -- stress triggering -- induced earthquakes -- injection -- seismicity -- Oklahoma; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2021JB022168
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: In September and October 2015, three M 4+ earthquakes occurred as a sequence along a fault northwest of the Cushing city, Oklahoma, followed by another M 5 earthquake in November 2016. While previous studies have shown that moderate‐size earthquakes in Oklahoma are likely induced by wastewater injections, it is still not clear what controls the rupture process and spatiotemporal evolutions of seismicity during individual sequences. In this study, we investigated the rupture process of these four M 4‐5 events in 2015–2016 with finite fault model (FFM) inversions, and computed the static stress changes during this sequence. We found that the rupture processes of four M 4‐5 earthquakes were very complex, and each of them had several subevents with different rupture directivities. The 2016 M 5 earthquake started near the region where three M 4+ events initiated, but the majority of the slip occurred a few kilometers away in the northeast direction. In comparison, the 2015 M 4.3 event mainly ruptured toward the southwest direction. Due to data limitation and inversion uncertainties, we were unable to constrain the rupture directivities for the other two M 4+ events. The foreshocks 3 days before the first M 4+ earthquake in 2015 occurred in a region of positive shear stress changes caused by previous earthquakes in 2014–2015 on unmapped faults several kilometers to the south. Our results suggest small‐scale heterogeneity in controlling complex seismicity and rupture patterns in the 2015–2016 Cushing sequence, and possible triggering of this sequence by a small stress perturbation on order of a few kilopascals. Plain Language Summary: Cushing city, Oklahoma, the largest crude oil storage site in the US it is surrounded by wastewater disposal wells due to ongoing shale gas development. In September and October 2015, three earthquakes with magnitudes larger than 4 occurred along an unknown fault northwest of the Cushing city. In November 2016, another magnitude 5 earthquake occurred nearby. In this study, we found that these four earthquakes are very complex and each of them broke several fault patches. For the 2016 magnitude 5 event, the first fault patch started around the same place where the other three magnitude 4 events began, but the second fault patch broke a few kilometers to the northeast along the fault plane. In comparison, for the 2015 magnitude 4.3 event, the second fault patch broke to the southwest of the first fault patch. We were unable to constrain the rupture processes for the rest two events well due to smaller magnitudes. Before these four earthquakes, additional earthquake activities occurred in 2014–2015 to the south of the Cushing city. They likely brought the fault northwest of the Cushing city closer to failure and promoted the occurrence of the four earthquakes in this study. Key Points: Slip distributions of four M 4‐5 Cushing earthquakes are complex and include multiple subevents The 2016 M 5 earthquake started near the region where other M 4+ events initiated, but its major slip occurred a few kms to the NE direction The 2015–2016 Cushing sequence initiated in the region with positive shear stress changes from previous seismicity further south