The role of lithology in fault re-strengthening: A case study of the 2011 Prague, Oklahoma induced earthquake sequence

Kristina K. Okamoto, Heather M. Savage, Kathleen M. Keranen, & Brett M. Carpenter

Published August 13, 2019, SCEC Contribution #9488, 2019 SCEC Annual Meeting Poster #156 (PDF)

Faults dynamically weaken during earthquakes and strengthen between them. Thus, fault healing is an important part of the seismic cycle, which depends on in situ conditions as well as lithology. Understanding how faults re-strengthen after earthquakes can be studied at the large scale by repeating earthquakes and at the small scale through slide-hold-slide friction experiments. Repeating earthquakes are readily analyzed through seismic data, however it is usually difficult to pinpoint the lithology in which they occur. This limits our ability to connect laboratory and observational data. Here, we analyze events from the 2011 Prague, Oklahoma induced earthquake sequence. The catalog includes three Mw 5 + earthquakes and earthquake locations have high resolution in depth. The Prague earthquake sequence occurred in nearly flat lying sedimentary layers as well as the underlying basement. Because of the regularity of the geology and the resolution of our earthquake locations, we can identify repeating sequences occurring in both the Arbuckle group and the granitic basement. To compare our repeating earthquakes to laboratory derived healing rates, we sampled cores at the Oklahoma Petroleum Information Center (OPIC), as well as basement rocks from outcrop. We measured frictional strength and healing in a triaxial deformation apparatus at confining pressures of 25-100 MPa to mimic lithostatic stress of each lithological layer and fluid pressures ranging from 10 to near lithostatic. We compare the healing rates measured within the lab with those from repeating earthquakes and determine how healing rates might differ within a single fault due to lithologic differences, and whether such differences in healing rates are responsible for future strength heterogeneity at the end of the next seismic cycle.

Citation
Okamoto, K. K., Savage, H. M., Keranen, K. M., & Carpenter, B. M. (2019, 08). The role of lithology in fault re-strengthening: A case study of the 2011 Prague, Oklahoma induced earthquake sequence. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)