Roles of Fluid Injection, Stress State, Geological Structure, and Earthquake Interaction on Oklahoma Earthquakes

Abstract

In this dissertation, first I map seismogenic fault geometry using seismicity in Oklahoma. The basement fault structures from seismicity are compared to the previously mapped sedimentary structures, and the comparison reflects common tectonic control of the two types of fault structures. Then I analyze the stress state of faults using 3D Mohr's circle at both state scale and local cluster scale. The stress state can affect the fault rupture behavior under pressurization and the resulting maximum magnitude. The optimally oriented faults are at high-risk with potential runaway ruptures and large earthquakes. I also examine different driving mechanisms for the earthquakes in Oklahoma. Through the study in Woodward cluster, earthquake interaction proves to be substantial and can drive the sequence evolution. Finally, I study the relationship between wastewater injection and seismicity rate using machine learning methods. The results show that pore pressure increase and poroelastic stress change from injection are the primary and secondary mechanisms for seismicity. This study provides a better understanding of fault geometry, stress field, and the relationships among fault structure, stress state, injection, and potential seismic hazards in Oklahoma.