Assessing Potential Seismic Hazard in Enhanced Geothermal Systems: Insights from Comparing Gonghe and Pohang Reservoirs

Abstract Evaluating and predicting the seismic hazard induced by fluid injection in enhanced geothermal systems (EGSs) is critical for safe and effective operations. This study compares the Gonghe project, a pioneering EGS initiative in China, with the well-studied Pohang EGS in South Korea, within a broader context of global fluid injection practices. We assessed the potential seismic hazard at these two sites based on their seismogenic indices (Σ). We find that Σ of the Gonghe EGS generally decreases from 0.4 to −0.7, consistent with the typical ranges of Σ in EGS sites, including Pohang. Our results indicate that real-time Σ is a more reliable measure for assessing seismic hazard in Gonghe because it offers insights into the maximum magnitude, exceedance probabilities, and expected numbers of earthquakes. Conversely, in Pohang, maximum Σ proves more effective for seismic hazard assessment. However, predicting the seismic hazard after the Mw 3.2 earthquake in Pohang remains challenging, particularly for the runaway rupture associated with the subsequent Mw 5.5 earthquake, highlighting the complexities involved. This study suggests that the use of real-time Σ is viable for assessing seismic hazard in EGS reservoirs characterized by descending Σ and seismic injection efficiency. Conversely, for reservoirs with ascending Σ and seismic injection efficiency, such as Pohang, maximum Σ could offer better insights into seismic hazard assessment, although precise earthquake magnitude constraints may be elusive due to dominant tectonic influences.