The Deep Inland Areas of the Korean Peninsula Are Not Safe Zones

Korea Institute of Geoscience and Mineral Resources Publishes Research Report on October Goesan Earthquake

[Asia Economy Reporter Kim Bong-su] Even the deep inland areas of the Korean Peninsula are no longer safe zones from earthquakes." This is the conclusion of a report analyzing the cause of the Goesan earthquake that surprised the entire nation on the morning of Saturday, October 29.

On the 20th, the Korea Institute of Geoscience and Mineral Resources (KIGAM) published the "Goesan Earthquake Report," containing key information about the magnitude 4.1 earthquake (Goesan earthquake) that occurred at 8:27 a.m. on October 29, about 11 km northeast of Goesan County, Chungcheongbuk-do.

The location where the Goesan earthquake occurred is an area where no earthquakes of magnitude 2.0 or higher have occurred within 10 km of the epicenter for the past 20 years. However, since the 1978 Songnisan earthquake (magnitude 5.2) occurred about 30 km away from the Goesan earthquake epicenter, it is difficult to guarantee the seismic stability of the region.

To understand the characteristics of the Goesan earthquake, the research team investigated the main shock (magnitude 4.1) on October 29 and the aftershocks that occurred intensively 144 times over about 12 days. In particular, on the day of the earthquake, the team was quickly dispatched to the site to install and operate four temporary seismic observation stations. To identify the characteristics of the event and the causative fault, they analyzed seismic observation data and topographic data around the epicenter and conducted surface geological surveys.

The research team analyzed the fault plane solutions of the main shock (magnitude 4.1) and the largest foreshock (magnitude 3.5), as well as waveform similarities of 144 detected earthquakes and 36 located earthquakes. The fault plane solution is a method of interpreting seismic wave data observed at stations to express the geometry, movement direction, and stress characteristics of the causative fault. As a result, the cause of the Goesan earthquake was identified as a left-lateral strike-slip fault movement in the west-northwest to east-southeast direction at a depth of about 12 to 14 km. This is a typical depth for inland earthquakes, similar to the 2016 Gyeongju earthquake, which occurred at a depth of 11 to 16 km.

Topographic analysis and surface geological surveys of the Jogok Fault, located about 500 m from the epicenter in the west-northwest to east-southeast direction, confirmed the outcrop of a fault zone composed of a fault core and damage zone, as well as surface ruptures associated with past earthquakes.

The research team concluded that the fault movement causing the Goesan earthquake was a left-lateral slip occurring on a part of the underground area of the Jogok Fault zone or a small-scale underground fault. In particular, the fault movement type of this Goesan earthquake was confirmed to be consistent with the tectonic stress field environment acting on the Korean Peninsula, similar to the Gyeongju earthquake. Furthermore, the high-magnitude earthquake surface rupture records identified through this surface geological survey suggest the possibility of moderate earthquakes occurring during the ongoing seismic structural environment. Notably, such high-magnitude earthquake surface rupture records have recently been reported near Goesan in Cheongju Oebuk and Eumseong Baekmaryeong through KIGAM’s research.

The research team has established plans for additional investigations, including high-resolution topographic surveys (drone LiDAR), shallow geophysical surveys (electrical resistivity survey, ground-penetrating radar survey), drilling, and excavation to detect precise high-magnitude earthquake records. They plan to continuously monitor earthquakes in the Goesan and Songnisan areas. In 2023, they will establish 10 high-density observation stations to continue research on ▲ monitoring microearthquakes, ▲ precise relocation, ▲ fault plane composition, and ▲ maximum magnitude estimation.

Song Seok-gu, head of the Geological Disaster Research Division at KIGAM, said, “The recent frequent occurrence of earthquakes across the entire Korean Peninsula, including the Goesan earthquake, shows that the Korean Peninsula is no longer a safe zone from earthquakes.”

This content was produced with the assistance of AI translation services.