Causal factors of elevated seismicity in Oklahoma: wastewater disposal or hydraulic fracturing?

Abstract:

Identifying the direct cause of elevated seismicity rates in areas of multiple oil and gas activities has always been a challenging issue that is lacking a homogeneous response. The criteria used to establish a probable link are usually based on qualitative considerations and often include arbitrary numerical thresholds, which are often revised on a case-by-case basis. To draw useful conclusions, we need to rigorously establish how well the seismicity is associated with each human activity, ruling out coincidental correlations. To do this, we combine the framework of McClure et al. (2017; 10.1002/2016JB013711) with the injection-driven earthquake recurrence model and data aggregation scheme in Grigoratos et al. (2020; 10.1785/0120200079). The results in our case study, Oklahoma, show that the vast majority of the seismically active 5-km blocks in the state are associated with wastewater disposal at the 95% confidence level. The model links most of the remaining seismicity with hydraulic fracturing at the same confidence level. These results are in agreement with past qualitative estimates. Very few of the seismically active blocks are linked to both activities, indicating that the methodology is capable of distinguishing their effects, even though the equations to test both hypotheses are identical.