The November 2017 M _w 5.5 Pohang earthquake: A possible case of induced seismicity in South Korea

Abstract

The moment magnitude () 5.5 earthquake that struck South Korea in November 2017 was one of the largest and most damaging events in that country over the past century. Its proximity to an enhanced geothermal system site, where high-pressure hydraulic injection had been performed during the previous 2 years, raises the possibility that this earthquake was anthropogenic. We have combined seismological and geodetic analyses to characterize the mainshock and its largest aftershocks, constrain the geometry of this seismic sequence, and shed light on its causal factors. According to our analysis, it seems plausible that the occurrence of this earthquake was influenced by the aforementioned industrial activities. Finally, we found that the earthquake transferred static stress to larger nearby faults, potentially increasing the seismic hazard in the area.

Hydraulic Fracturing Induced Seismicity in the Southern Sichuan Basin Due to Fluid Diffusion Inferred From Seismic and Injection Data Analysis

“…In recent years, small and moderate earthquakes induced by subsurface fluid injection have been reported worldwide (e.g., Bao & Eaton, 2016;Clarke et al, 2014;Ellsworth, 2013;Goebel & Brodsky, 2018;Grigoli et al, 2017;Grigoli et al, 2018;Kim et al, 2018;Lei et al, 2017;Weingarten et al, 2015). Two most conspicuous regions with a large number of induced earthquakes reported are midcontinental United States and western Canada, which have a long history of wastewater disposal, enhanced oil recovery, and shale gas hydraulic fracturing (e.g., Atkinson et al, 2016;Friberg et al, 2014;Frohlich, 2012;Frohlich et al, 2016;Holland, 2013;Horton, 2012;Keranen et al, 2014;Schultz et al, 2015;Schultz et al, 2017;Schultz et al, 2018;Skoumal et al, 2015;Yoon et al, 2017).…”

Spatiotemporal Variations in Crustal Seismic Anisotropy Surrounding Induced Earthquakes Near Fox Creek, Alberta

“…The Alberta basin has experienced increased levels of induced earthquakes associated with hydraulic fracturing (HF) stimulation in recent years (Atkinson et al, ; Schultz et al, ), most notably within the Duvernay Formation (the largest shale gas formation in central Alberta) near the town of Fox Creek, Alberta (Bao & Eaton, ; Schultz et al, ). One likely triggering mechanism is fluid migration along the fault damage zone (Galloway et al, ) via existing hydrological connections between the HF networks and macroscopic faults (Ellsworth, ; Grigoli et al, ; Langenbruch & Zoback, ). The strike‐slip focal mechanisms of the HF‐induced earthquakes (Figure ) in central‐southern Alberta have direct implications for the sizes and orientations of reactivated fault zones, and seismic moment tensors of regional earthquakes show approximately NE‐oriented P axes (Schultz et al, ; Wang et al, , ).…”

Addressing the risks of induced seismicity in subsurface energy operations

“…Nevertheless, in September 2016, the largest ever recorded earthquake of natural origin in the country occurred at a depth of 14 km at Gyeongju, measuring 5.8 M L . Subsequent to the third injection phase on April 15, 2017, a 3.1 M L earthquake struck near to the well bottom at the EGS site (Grigoli et al, ). On November 15, 2017, a 5.4 M w magnitude earthquake occurred at the Pohang EGS site, at a depth of around 4.5 km, and being associated with six foreshocks and 210 aftershocks.…”