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Site-specific Seismic Hazard Analyses in Oklahoma Addressing Both Tectonic and Induced Seismicity

Description: 

We have performed site-specific probabilistic seismic hazard analyses of the U.S. Bureau of Reclamation’s Altus and Fort Cobb Dams and East and Lugert Dikes located in southwestern Oklahoma (OK). The structures will be subject to ground motions from both tectonic and induced earthquakes, the latter which has dominated the seismicity in the state since 2009 due to wastewater injection. The Meers fault, which is within 55 km of all four sites, dominates the tectonic hazard in much of Oklahoma. Traditionally, induced seismicity is not included in seismic hazard analyses but the associated ground motions need to be accounted for in the seismic safety of the structures. Inputs into the PSHA include the 2012 EPRI/DOE/NRC CEUS seismic source model updated for the Meers fault and the NGA-East ground motion models (GMMs) adjusted for the bias observed by Ramos-Sepulveda et al. (2024). To account for hazard from induced earthquakes in the PSHA, we included a zone of gridded induced seismicity and induced seismicity GMMs. Altus Dam and the two dikes are located 73 km west of the zone. Fort Cobb Dam is located at the western boundary of the zone. We calculated recurrence for 12 induced seismicity catalogs covering time periods that had a common end date of July 2023 but starting dates that differed by a year (2011, 2012, etc. through 2022). This was done to examine temporal trends in rate due to declining induced seismicity since 2015. In the PSHA, we adopted the recurrence for the period starting in 2019. Altus Dam is located on rock whereas the other three sites are located on alluvium and required site response analyses. The 10,000-year return period hard rock PGA for Altus Dam was 0.42 g and about 0.6 g for the other sites on alluvium. The major contributor to hazard at all four sites was the Meers fault with very little contribution from induced earthquakes including Fort Cobb Dam which is outside the areas of highest seismicity in the zone. For a site in the highly active part of the induced zone and more distant from the Meers fault, the induced seismicity contributes to the PGA hazard up to about 30%.

Session: From Physics to Forecasts: Advancements and Future Directions of Induced Seismicity Research - II

Type: Oral

Date: 4/15/2025

Presentation Time: 11:30 AM (local time)

Presenting Author: Ivan

Student Presenter: No

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