Multiscale Analysis of Spatiotemporal Relationship Between Injection and Seismicity in Oklahoma
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AbstractMany previous studies have suggested that wastewater disposal is the most probable factor affecting increased seismicity in Oklahoma since 2009. While this relationship is clear at the state scale, a systematic quantitative analysis of the spatiotemporal relationships between injection and seismicity is needed. We first apply multiscale analyses to assess the temporal correlation between injection rate and seismicity rate at a range of different grid sizes, which demonstrate clear temporal correlations within the two main seismic regions at variable time delays. The time delay variability decreases with larger grid sizes, whereby the average time delay ranges from 150 to 220days. The average time delay at large scales is consistent with inferred largescale diffusive migration away from areas of high injection rates with diffusivities of 0.5 to 2.0m2/s. The inferred largescale diffusivities are consistent with an expected range of diffusivity within the Arbuckle Group where wastewater disposals are occurring. However, individual earthquake clusters have diffusivities that are about one to two orders lower than the largescale models. We interpret this as a manifestation of a twolayered diffusion model with high diffusivity within the injection layer above basement, which facilitates stress transfer at a larger spatial footprint, triggering seismic slip at multiple seismogenic faults within the crystalline basement with low diffusivity, similar to fluiddriven clusters in other tectonic regions.
