Narrow Spatial Aftershock Zones for Induced Earthquake Sequences in Oklahoma

Abstract

The current paradigm for estimating regional long-term seismic hazard involves declustering whereby aftershocks are removed from an earthquake catalog to identify the underlying background seismicity rate. Inaccurate declustering can ultimately underestimate or overestimate the regional seismic hazard. In Oklahoma, estimating a background seismicity rate is complicated by the highly variable seismicity rate over the last decade. To improve conventional declustering methods used in hazard modeling in Oklahoma, we scrutinize the aftershock windows used for declustering and investigate how aftershocks decay in space and time to establish data-driven parameters for aftershock windowing. We observe that the spatial decay of aftershocks is more rapid in Oklahoma than in Southern California, motivating the need for smaller spatial declustering windows in Oklahoma. Temporal aftershock decay is statistically indistinguishable between Oklahoma and Southern California, suggesting that temporal declustering windows derived for Southern California are likely sufficient for Oklahoma.