Seismological Investigations of Induced Earthquakes Near the Hutubi Underground Gas Storage Facility

Abstract

The Hutubi underground gas storage facility in Xinjiang, China, with a maximum gas storage capacity of 10.7 billion m3, provides a good opportunity to study seismicity potentially induced by the annually cyclic injection and extraction of natural gas. To statistically distinguish induced seismicity from the tectonic background, we investigate the background seismicity probability of each event using the space‐time epidemic‐type aftershock sequence model and a stochastic declustering method. Our statistical results suggest a potential link between gas injection and two groups of seismicity, with very low background seismicity probabilities during the first and second injection periods in August 2013 and May 2014, respectively. To better understand the earthquake physics, we relocate earthquakes by incorporating a dedicated mobile seismic network after refining the regional 1D velocity model by utilizing an artificial source. After double‐difference relocations, those two groups of earthquakes move much closer to the faults bounding the rock storage units and are situated at a depth around 4 km, slightly deeper than the reservoir formation. Focal mechanism solutions of the two largest earthquakes (Mw 2.8 and 3.0) in August 2013 show a possibly unmapped reverse fault gently dipping to the south. Based on our high‐resolution earthquake locations, we propose that these on‐fault earthquakes are not hydrologically connected with the reservoir formation but are likely induced by poroelastic stress perturbations due to gas injection. Poroelastic stressing can have a larger impact on seismicity rate than pore pressure diffusion at large distances; hence, the distributions and sizes of preexisting faults might play a key role in seismic hazard assessments in our study region.

Physics‐Based Evaluation of the Maximum Magnitude of Potential Earthquakes Induced by the Hutubi (China) Underground Gas Storage

“…(2018), Zhou et al. (2019) and CEDC. Both Tang et al.…”

“…For strike‐slip faulting a 3D model may be necessary, but Zhou et al. (2019) have concluded that the induced earthquakes at the HUGS site developed by reverse faulting. In addition, Figure 1c shows the extension of injection wells parallel to the Hutubi fault, which indicates that a 2D model perpendicular to the fault is a reasonable approximation.…”

“…Consequently, Zhou et al. (2019) were able to better resolve the location and spatial clustering of the events associated with the first and second injection phases and to determine the focal mechanism solutions of the two largest events in August 2013 (Figure 1c). The catalog retrieved from CEDC comprises M L ≥ 0.1 earthquakes up to December 31, 2018 with a horizontal location precision of ∼15 km (Figures 1c and 4).…”

“…To examine the temporal and spatial variations of induced seismicity, we gather three catalogs, from Tang et al (2018), Zhou et al (2019) and CEDC. Both Tang et al (2018) and Zhou et al (2019) relocated earthquakes with magnitudes of M L ≥ 1.0 in the first two injection-extraction cycles as well as the third injection phase (Figure S2). Whereas Tang et al ( 2018) only analyzed regional seismological data from permanent stations in the Xinjiang province, Zhou et al (2019) included more data from a temporary network comprising 38 mobile stations.…”

“…Whereas Tang et al ( 2018) only analyzed regional seismological data from permanent stations in the Xinjiang province, Zhou et al (2019) included more data from a temporary network comprising 38 mobile stations. Consequently, Zhou et al (2019) were able to better resolve the location and spatial clustering of the events associated with the first and second injection phases and to determine the focal mechanism solutions of the two largest events in August 2013 (Figure 1c). The catalog retrieved from CEDC comprises M L ≥ 0.1 earthquakes up to December 31, 2018 with a horizontal location precision of ∼15 km (Figures 1c and 4).…”