Today's 2.6 Magnitude Earthquake Off Yeongdeok, Gyeongbuk... Why the 'East Sea Again?' Unease
This afternoon (the 14th), the sea off Yeongdeok in Gyeongbuk province gave a slight jolt. A 2.6 magnitude earthquake struck 31km east of Yeongdeok-gun, Gyeongbuk. With its shallow epicentre, residents in Yeongdeok, as well as parts of Ulsan and Pohang, likely felt a distinct 'thud'. For those living along the east coast, these tremors are no longer something to just brush off. The memory of tsunami waves crashing ashore following major earthquakes off Japan is still painfully fresh.
Today's Tremors, as Captured by Seismographs
This earthquake's epicentre was under the East Sea, quite close to the mainland. Seismographs would have clearly recorded the seismic wave patterns typical of a shallow earthquake. The time difference between the arrival of P-waves (primary waves) and S-waves (secondary waves) would have been minimal, meaning anyone near the epicentre might have felt a sudden, brief swaying of buildings accompanied by a 'thumping' sound. Fortunately, no damage has been reported so far.
Why Does It Keep Happening in the East Sea? The Seismic Profile of This Region
The East Sea has long been considered the most 'tectonically active area' on the Korean Peninsula. In terms of plate tectonics, it acts as a conduit directly influenced by the Pacific Plate subducting towards the Japanese archipelago. In fact, earthquakes around magnitude 3.0 occur fairly frequently along the east coast. The seas off Ulsan and the Yeongdeok area are known to have particularly complex, intertwined fault systems. It's accurate to view today's earthquake as a natural event stemming from this geological backdrop.
How Did the Shaking Feel Locally? A Look at Intensity Levels
Compiling the on-the-ground reports, this earthquake was felt across a wider area than initially expected.
- Yeongdeok-gun, Uljin-gun (Gyeongbuk): Intensity III (Felt noticeably indoors, especially on upper floors of buildings).
- Ulsan Metropolitan City, Gyeongju-si: Intensity II (Felt by a few people at rest, or on upper floors of buildings).
- Parts of Pohang-si, Daegu Metropolitan City: Intensity I (Not felt noticeably, 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? No Need for Alarm, For Now
Given its magnitude, there is naturally no concern about a tsunami. However, the topography off Korea's east coast features areas where the seabed drops away sharply. This means that if a major earthquake were to occur near Japan, a tsunami could potentially reach our shores within one to two hours. Even when things are calm, every time the ground shakes here, thinking about the 'what if' scenario has become a survival instinct for people living along the east coast.
The Yeongdeok offshore area previously experienced a 3.1 magnitude earthquake in 2023. Back then, the reaction was similar, 'Yeongdeok again'. Today's event released slightly less energy than that one. However, experienced observers see it as a sign that tectonic movements in the area haven't ceased. Considering the earthquake mechanism, the propagation speed of seismic waves, and the analysis of the epicentre, it's highly likely that similar tremors will continue along the east coast in the future.
Late in the afternoon, anyone who felt that sudden, solitary 'jolt' in their office likely reached for their smartphone to confirm it. Earthquakes are no longer an unfamiliar disaster for us. We don't need to wait for research findings to confirm that the Korean Peninsula is no longer a safe zone from earthquakes – we feel it in our bones. Even with a small tremor like today's, we must keep practising how to read the movements of the peninsula's crust within these shakes.