Magnitude 4.0 Earthquake in Gyeongju, Gyeongbuk... Five Aftershocks Within an Hour (Comprehensive)

At around 4:55 a.m. on the 30th, an earthquake with a magnitude of 4.0 occurred 19 km southeast of Dongnam-dong, Gyeongju-si, Gyeongbuk. The epicenter was identified at 35.79°N latitude and 129.42°E longitude, with a depth of 12 km.

[Photo by Korea Meteorological Administration]

The Korea Meteorological Administration (KMA) initially estimated the magnitude at 4.3 based on the analysis of the faster P-waves and sent emergency disaster messages nationwide. After additional manual analysis, the magnitude was revised downward to 4.0. For inland earthquakes, if the magnitude is 4.0 or higher, emergency disaster messages are sent nationwide regardless of the location of occurrence. This emergency disaster message was sent within 8 seconds of the event.

The "instrumental intensity," which indicates the degree of shaking felt in each region, was 5 in Gyeongbuk, 4 in Ulsan, and 3 in Gyeongnam and Busan. At an instrumental intensity of 3, people indoors, especially those on upper floors of buildings, feel the shaking distinctly, and stationary cars shake slightly. At 4, many people indoors feel the earthquake, some wake up at night, and dishes and windows shake. At 5, almost everyone feels the vibration, dishes and windows may break, and unstable objects topple over.

Following the earthquake, there were five aftershocks over about an hour until 5:50 a.m. that day. The largest aftershock was a magnitude 1.5 earthquake that occurred around 5 a.m. The fire department received about 70 earthquake-related reports. However, no damage reports were filed.

According to the KMA, since 1978, a total of 418 earthquakes of magnitude 2.0 or higher have occurred within a 50 km radius of this earthquake’s epicenter. Among them, there were 3 earthquakes with magnitudes between 5.0 and less than 6.0, 5 between 4.0 and less than 5.0, and 45 between 3.0 and less than 4.0. The southeastern region including Gyeongju was confirmed to have 14 active faults during a fault structure survey of the Korean Peninsula conducted after the largest recorded instrumental earthquake of magnitude 5.8 occurred on September 12, 2016.

This earthquake is the second largest among the 99 earthquakes of magnitude 2.0 or higher that have occurred this year in the Korean Peninsula and surrounding waters. The largest was a magnitude 4.5 earthquake that occurred on May 15 in the sea 52 km northeast of Donghae-si, Gangwon-do.

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