Minor Earthquake of Magnitude 2.6 Strikes Waters Off Yeongdeok, Gyeongbuk... Why 'Another One in the East Sea?' Sparks Anxiety
This afternoon (the 14th), the sea off the coast of Yeongdeok, Gyeongbuk, gave a slight shudder. A magnitude 2.6 earthquake struck 31km east of Yeongdeok-gun, Gyeongsangbuk-do. With its epicentre shallow, residents in Yeongdeok, as well as some in Ulsan and Pohang, likely felt a sudden 'thud' or jolt. For those living along the east coast, these tremors are no longer just passing events. The memory of tsunami waves hitting following major earthquakes off Japan is still fresh in their minds.
Today's Tremor as Recorded by Seismographs
This earthquake's epicentre was under the East Sea, quite close to the land. It's almost certain that seismographs recorded the typical seismic wave pattern of a shallow earthquake. The time difference between the arrival of the P-waves (primary waves) and S-waves (secondary waves) would have been minimal, so anyone near the epicentre might have felt a sudden 'thump' accompanied by an immediate shaking of buildings. Fortunately, no reports of damage have been received so far.
Why Does It Keep Happening in the East Sea? The Seismic Characteristics of This Body of Water
The East Sea has long been considered the most 'tectonically active area' on the Korean Peninsula. From a plate tectonic perspective, it acts as a conduit directly transmitting the forces from the Pacific Plate subducting towards the Japanese archipelago. In fact, earthquakes around magnitude 3.0 occur fairly frequently along the east coast. The waters off Ulsan and the Yeongdeok area are known to have particularly complex fault systems. It is reasonable to view this latest earthquake as a natural event stemming from this geological backdrop.
What Were the Perceived Intensities Like in Different Regions?
Compiling the on-site reports of how the quake felt, it was perceptible across a wider area than initially expected.
- Yeongdeok-gun and Uljin-gun, Gyeongbuk: Intensity III (Felt noticeably indoors, especially on upper floors of buildings)
- Ulsan Metropolitan City and Gyeongju-si: Intensity II (Felt by only a few people at rest, particularly on upper floors of buildings)
- Parts of Pohang-si and Daegu Metropolitan City: Intensity I (Not felt except by a very few under especially favourable conditions, but recorded by instruments)
Residents in high-rise apartments likely felt this tremor more acutely. This is because seismic waves with longer periods can resonate with tall buildings, amplifying the motion.
Should We Worry About a Tsunami? Probably Not Yet
Given the magnitude, there is naturally no concern about a seismic sea wave (tsunami). However, the topography off Korea's east coast features areas where the seafloor drops off sharply, meaning a major earthquake near Japan could send a tsunami reaching our shores within one to two hours. Even when things are usually calm, every tremor on home soil triggers a 'what if' thought process – it's almost a survival instinct for people living along the east coast.
The Yeongdeok offshore area previously experienced a magnitude 3.1 earthquake in 2023. Back then, the reaction was also 'Yeongdeok again?', but today's quake released slightly less energy. Nevertheless, experienced observers interpret this as a sign that fault movements in the area haven't ceased. Combining the analysis of the earthquake mechanism, seismic wave propagation speeds, and the epicentre location suggests that similar tremors are likely to continue occurring along the east coast in the future.
Late in the afternoon, people who experienced that brief 'jolt' alone in their offices likely pulled out their smartphones to check for confirmation. Earthquakes are no longer unfamiliar disasters for us. We don't need to wait for research findings to know that the Korean Peninsula is no longer a safe zone from earthquakes – we feel it in our bones. Even with small tremors like today's, we must continue to practice reading the movements of the peninsula's crust within them.