SEISMICITY INDUCED BY HYDRAULIC FRACTURING AND FLOWBACK IN MONROE COUNTY, OHIO

Over the last decade, there has been a marked increase in the seismicity rate of the Central and Eastern United States, most of which has been attributed to wastewater disposal (WD). Recent research in Ohio, where WD is spatially separated from hydraulic fracturing (HF), has identified that seismicity associated with HF is more prevalent than seismicity induced by WD. In this paper we examine 2 new cases of seismicity associated with HF, beginning in 2016, located further south than previous cases in Ohio. A case in Monroe County had two bursts of seismicity, enhanced using template matching and repeating signal detector approaches. The first burst intensified between stimulation of two separate well laterals, and the second burst intensified during flowback several months later, including the large event (ML 3.0) in the sequence. These observations are somewhat different than those of previous cases of HF-induced seismicity in Ohio which were often more temporally correlated with active stimulation. To understand why this case is different from previous cases, we attempt to investigate the influence of flowback on the observed seismicity. The second studied case, Noble County, is even more unusual, producing the largest (ML 3.7, Mw 3.4) HF-induced event in Ohio, and possibly in the USA. Using enhanced detection only revealed 15 additional events and a nonlinear FMD that would make it difficult to forecast the larger magnitude event. There are also very few aftershocks associated with this large event, suggesting it may have occurred in rocks unable to maintain the stresses needed to sustain aftershock activity.