Building a new catalog for induced earthquakes in Oklahoma based on a 3-D velocity model

Shuo Zhang, Bingxu Luo, & Hejun Zhu

Submitted August 12, 2020, SCEC Contribution #10443, 2020 SCEC Annual Meeting Poster #055

Over the past decade, seismologists observed a significant increase in the seismicity rate in Oklahoma, which reached to a maximum level in 2016, then gradually decreased to a normal level recently. Unlike inter-plate earthquakes, these intra-plate events have complex triggering processes. Previous studies use statistical methods and link these induced events with industrial operations, like wastewater injection and hydraulic fracturing. However, the latest earthquake catalog for Oklahoma is still based on 1-D crustal velocity models, which leads to large uncertainties to earthquake locations, especially for depths. In addition, the distribution of Oklahoma earthquakes in the recent catalog is deviated from fault traces observed at the Earth’s surface. In this study, based a 3-D crustal velocity model for central Oklahoma, we relocate 523 earthquakes in Oklahoma from 2010 to 2018. A machine learning algorithm allow use to automatically pick-up P-wave arrival times for each seismic recording. Next, we use the fast-marching method and Bayes’ theorem to iteratively search for the locations of earthquakes that minimize the arrival times differences between observed and synthetic recordings. Earthquakes in our new catalog is more focus around the mapped fault traces in Oklahoma. For the Prague sequence, events in the new catalog are distributed around one branch of the Wilzetta fault zone, and move to shallower depths, and become closer to the formation where wastewater injection occur. Moreover, the new catalog reveals some faults that have not been mapped in the current fault system map. The distribution of these earthquakes is consistent with the orientation of local tectonic stresses. With the new catalog, we will use full waveform method to estimate their moment tensor solutions, which enable us to better understand the triggering processes of earthquakes occurred in Oklahoma.

Zhang, S., Luo, B., & Zhu, H. (2020, 08). Building a new catalog for induced earthquakes in Oklahoma based on a 3-D velocity model. Poster Presentation at 2020 SCEC Annual Meeting.

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