Constructing a 3‐D Radially Anisotropic Crustal Velocity Model for Oklahoma Using Full Waveform Inversion.

Over the past decade, the seismicity rate in the state of Oklahoma has increased significantly, which has been linked to industrial operations, such as saltwater injection and hydraulic fracturing. Taking advantage of induced earthquakes and recently deployed seismometers, we construct a 3‐D radially anisotropic seismic velocity model for the crust of Oklahoma by using full waveform inversion. To mitigate the well‐known cycle‐skipping problem, we use misfit functions based on phase and waveform differences in several frequency bands. Relative velocity perturbations in the inverted model allow us to delineate major geological provinces in Oklahoma, such as the Anadarko Basin and the Cherokee Platform/Shelf. In addition, radial anisotropy in the inverted model reflects deformation within the crust of Oklahoma, which might correlate with sedimentary layering, microcracks/fractures, as well as dominant orientation of anisotropic minerals. The crystalline basement beneath Oklahoma can be inferred from the new velocity model, which enables us to better classify induced seismicity in current earthquake catalogs. Furthermore, synthetic experiments suggest that the new velocity model enables us to better constrain earthquake locations in Oklahoma, especially for determining their depths, which are important for investigating induced seismicity. Plain Language Summary: Taking advantage of induced earthquakes and seismometers deployed in Oklahoma in the last decade, we construct a radially anisotropic seismic velocity model for the crust beneath Oklahoma by using full waveform inversion. The data misfit is iteratively reduced by about 40%, and predicted seismograms based on the new velocity model can fit observations very well. We can identify geological structures from the velocity model, such as low velocity anomalies associated with the Anadarko Basin, and fast anomalies related to the Cherokee Platform. Positive radial anisotropy (RA) in the shallow crust might reflect layered sedimentary structure, while negative RA within the middle crust may relate to preferred orientation of anisotropic minerals, such as plagioclase, mica, and amphibole. Furthermore, synthetic tests are used to illustrate the impact of lateral variations of seismic velocity on earthquake locations, especially for focal depths. Therefore, this new 3‐D model provides us an opportunity to improve current earthquake catalogs in Oklahoma, as well as improving our understanding of the triggering mechanisms of induced earthquakes. Key Points: We use full waveform inversion to construct a 3‐D radially anisotropic seismic velocity model for the crust of OklahomaSpatial distributions of inverted velocity and radial anisotropy agree with geological provinces and tectonic deformation in OklahomaLateral velocity heterogeneities have strong impact on earthquake locations, especially for focal depths [ABSTRACT FROM AUTHOR]