On the 7th at 2:35 a.m., an earthquake occurred in Chungju, North Chungcheong Province. This earthquake had an actual magnitude of 3.1, but the Korea Meteorological Administration reported it as 4.2 immediately after it occurred and sent emergency disaster text messages not only to Chungju but also to several regions nationwide. Since emergency disaster text messages are accompanied by a mobile phone notification sound of at least 40dB, many citizens lost their sleep that night. After only 3 minutes, the magnitude was adjusted down to 3.1, and a safety notification message was sent out again.
In the case of domestic earthquakes, emergency disaster text messages that include mobile phone notification sounds are only sent if the magnitude is 3.5 or higher. If the Korea Meteorological Administration had accurately confirmed the earthquake's magnitude to begin with, there would have been no reason for citizens to lose sleep over this earthquake with an actual magnitude of 3.1.
The Korea Meteorological Administration has faced several issues related to emergency disaster text messages in the past. On Nov. 30, 2023, during the Gyeongju earthquake, which had a magnitude of 4.0, emergency disaster text messages were sent nationwide. Messages were sent to residents in the metropolitan area who did not feel the tremors, causing significant inconvenience. In contrast, in the case of the Chilgok earthquake on April 22, 2024, with a magnitude of 2.6, nearby residents felt the tremors, but no emergency disaster messages were sent due to the low magnitude.
As these issues continued, the Korea Meteorological Administration improved the criteria for sending disaster messages in October last year. They revised it so that earthquakes with a magnitude of 4.0 or higher would no longer prompt nationwide emergency disaster messages, raising the threshold to 5.0. Instead, if an earthquake of magnitude 3.5 or higher occurs, with a maximum expected intensity of 'V(5)' or above, emergency disaster messages are to be sent to regions where the expected intensity is 2 or higher. Intensity refers to the concept of the relative size of shaking, with emergency disaster messages being sent along with warning sounds.
In the case of the recent Chungju earthquake, emergency disaster messages were sent to several regions, including North Chungcheong Province, as the initial analysis value indicated 4.2, along with areas such as the metropolitan area, Gangwon, North Jeolla, North Gyeongsang, and South Gyeongsang, where an intensity of 2 or higher was expected. After the magnitude was adjusted to 3.1, a safety notification message was sent out.
Despite the implementation of a new system to eliminate inconvenience to citizens due to the sending of earthquake disaster messages, the failure to prevent this confusion is attributed to the limitations of the Korea Meteorological Administration's earthquake analysis system. The Korea Meteorological Administration's earthquake analysis system uses the speed difference between Primary wave (P wave) and Secondary wave (S wave) to issue prompt earthquake early warnings. Since P waves travel about 1.7 times faster than S waves, the P wave that arrives first is analyzed automatically to detect the occurrence of an earthquake and send out alerts. Subsequently, an analyst manually reviews the data to correct the earthquake's magnitude. There will inevitably be a difference between the initial analysis value and the later corrected value.
However, in this particular case of the Chungju earthquake, the difference was unusually large. Hong Taekyung, a professor at Yonsei University in the Department of Earth System Science, noted, "It is unusual for the difference between the initial and corrected values to be more than 1." Earthquake magnitudes are measured on a logarithmic scale, and the energy released increases by about 32 times for each unit increase in magnitude. In this instance, the energy released with the initial magnitude of 4.2 and the later corrected magnitude of 3.1 differs by about 44 times.
Professor Hong explained, "When earthquakes are automatically analyzed by machines, the magnitude is computed based on the strongest signals, and there is a possibility of errors due to abrupt amplification of seismic waves or mechanical noise," and added that "additional analysis is needed to identify the exact cause."
Park Sooncheun, the head of the Earthquake and Volcanic Research Division at the Korea Meteorological Administration, stated, "Automated analysis aims to quickly inform of an earthquake's occurrence, using only the measurements from at least four observation stations closest to where the earthquake happened," and noted, "Because of this, it is possible that the value may have been significantly influenced by a specific observation station, so we are conducting further analysis on this matter."
The initial analysis method used by the Korea Meteorological Administration prioritizes speed, which may lead to overestimation or underestimation of the earthquake's magnitude. There are calls for improving the current early warning system. It is necessary to consider implementing a system that differentiates between initial alerts and subsequent precise analyses to provide information gradually, as opposed to the current uniform method of sending disaster text messages.
Professor Hong added, "In the case of relatively smaller earthquakes, if alerts are sent incorrectly, there is a high possibility that disaster messages will be sent to extensive areas regardless of actual damage," and emphasized that "internal regulations should be established to manage the margin of error in earthquake magnitudes within a certain range, and the regions to which alerts are sent should be selected more precisely, taking into account the error rate of the early warning system to reduce unnecessary message dispatches."