Abstract
Underground gas storages (UGSs) are important large-scale industrial facilities used to bridge the gap between natural gas consumption and supply. The cyclic operation of the UGS may alter the subsurface stresses and local seismicity. We examined seismicity around the Hutubi UGS from 2011 to 2019 using the matched filter technique (MFT) and double-difference location methods. More than 1300 earthquakes were detected with seismicity around the UGS showing a remarkable increase since the start of its operation and showing a clear correlation to seasonal gas production. About 684 detected earthquakes were located, most of them occurred within 6 km of the reservoir. The events can be grouped into two clusters. Both clusters initiated around the gas pressure boundary. The first cluster extinct after the first injection period. While the second cluster diffused upward along a pre-existing fault. We speculate that strain localization caused by non-uniform gas injection contributes to the initiation of seismicity clusters around the UGS, and the trapped crude oil/gas played an important role in the migration of the second surge. The revealed seismicity pattern contributes to a better understanding of the mechanism of induced seismic events and emphasizes the importance of seismic monitoring in the UGS region.