Ground Motion Simulation of Recent Korean Earthquakes Using the Spectral Element Method

The Korean Peninsula, generally tectonically stable, has experienced occasional seismic activity, with 19 earthquakes of magnitude Mw ≥ 4.0 since 2013. The largest inland earthquake, a magnitude ML 5.8 event, struck Gyeongju in 2016, causing significant damage and casualties. It was preceded by a foreshock and followed by numerous aftershocks. In 2017, an ML 5.4 earthquake in Pohang, potentially related to enhanced geothermal system exploration, caused major damage. In 2024, a 4.8 ML earthquake occurred near Buan-gun, indicating continued seismic activity in the region. This study simulates the ground motions of the recent inland earthquakes, with a focus on the 2016 Gyeongju and 2017 Pohang earthquakes, along with their associated foreshocks and aftershocks, utilizing existing source and velocity model data and rise time scaling relationships. We investigated whether we can consistently simulate the recent Korean earthquakes with existing models and data, with an overarching goal of improving earthquake simulation accuracy for future applications in the Korean peninsula. The simulations were performed using the Spectral Element Method via SPECFEM3D, an open-source software for high-accuracy seismic modeling. We found that simulated ground motions were overall consistent with Gyeongju mainshock observations when an existing risetime scaling relationship was assumed. The results also showed some dependence on the assumed risetime scaling relationship for the Gyeongju and Pohang mainshocks, meaning that a region-specific scaling relationship might improve the overall accuracy of the simulation. We also found that the simulations were less dependent on the risetime scaling for earthquakes with magnitudes less than 5. Simulation of the 2017 Pohang mainshock was significantly underpredicting the recorded motions, when the simulation assumptions was consistent with the Gyeongju event. 2017 Pohang earthquake records were showing very pronounced surface waves that the simulation failed to reproduce using the current model. Simulations of smaller earthquakes showed varied levels of consistency. We are currently investigating the causes of the inconsistency in the simulation of recent earthquakes by comparing them with recorded motions, and we hope that we will eventually find a way to consistently reproduce earthquake ground motions for future applications.