Subsurface stress conditions evolve in response to earthquakes or fluid injection. Using observations of an induced seismicity sequence from a dense local array, anisotropy analysis is employed to characterize stress changes around a fault. The dataset comprises high signal‐to‐noise ratio S‐wave data from 300 events, ranging in magnitude from −0.45 to 4.1, recorded on 98 three‐component geophones cemented in shallow wells. It is found that the orientation of the fast S‐wave direction remains relatively constant for all stations over time, but the magnitude of the anisotropy, as measured by the delay time between the fast and slow S wave, exhibits significant local variations. Some stations experience a systematic increase or decrease in the delay time, with a spatial coherence about the injection well. The stress changes due to hydraulic fracturing, aseismic slip, and observed earthquakes are modeled to determine the best fit to the observed anisotropy changes. Our analysis indicates that the creation of a network of tensile hydraulic fractures during fluid injection is likely to be the cause of the observed anisotropy changes. This study confirms that the measurements of seismic anisotropy over time reflects the evolving stress state of a fault prior to and during rupture.

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