Today's 2.6-Magnitude Quake Off Yeongdeok, Gyeongbuk... Why 'Another One in the East Sea?' Has Everyone on Edge

This afternoon (the 14th), the sea off Yeongdeok, Gyeongbuk, experienced a slight tremor. A 2.6-magnitude earthquake struck 31km east of Yeongdeok-gun, Gyeongbuk. With its shallow epicentre, folks in Yeongdeok, and even some in Ulsan and Pohang, probably felt a sudden jolt. For those living along the east coast, these tremors are hard to ignore now. The memory of the tsunami that hit following that massive earthquake near Japan is still fresh in everyone's mind.

Today's Tremors as Recorded by Seismographs

This earthquake's epicentre was under the East Sea, quite close to the mainland. It's almost certain that seismographs captured the typical seismic wave patterns 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 if you were in the area at the time, you might have felt a sudden, brief shake of buildings, accompanied by a sound like a dull thud. Fortunately, there have been no reports of damage 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 zone' on the Korean Peninsula. In terms of plate tectonics, it acts as a conduit where the full force of the Pacific Plate subducting towards the Japanese archipelago is transmitted. In fact, earthquakes around magnitude 3.0 occur quite frequently on the east coast. Among these areas, the waters off Ulsan and the Yeongdeok region are known to have particularly complex fault systems. It's safe to view this latest earthquake as a natural one originating from that geological backdrop.

How Strong Were the Tremors in Different Areas?

Putting together the on-the-ground reports, this earthquake was felt over 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 City: Intensity II (Felt only by a few people at rest, or on upper floors of buildings)
• Pohang City and parts of Daegu Metropolitan City: Intensity I (Barely felt, but recorded by instruments)

Folks living in high-rise apartments would have felt this sway more acutely. This is because seismic waves with longer periods can resonate with tall buildings, amplifying the motion.

Should We Worry About a Tsunami? Still Safe for Now.

Given the magnitude, there's naturally no concern about a tsunami. However, the east coast features seabed topography that plunges into deep water quite abruptly. This means if a major earthquake occurs near Japan, a tsunami could reach our shores within one to two hours. Even though things are usually calm, every time the ground shakes, thinking about the 'what if' scenario is second nature for people living on the east coast.

The Yeongdeok offshore area previously experienced a 3.1-magnitude earthquake in 2023. Back then, the reaction was similar, 'Yeongdeok again?'—but today's tremor released slightly less energy. However, among experienced observers, it's seen as a sign that fault movements haven't ceased. Considering the earthquake mechanism, the propagation speed of seismic waves, and the epicentre analysis, it's highly likely that similar tremors will continue along the east coast.

Late in the afternoon, anyone who felt that sudden 'jolt' alone in their office probably grabbed their phone to check. Earthquakes are no longer a foreign disaster to 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 can feel it ourselves. Even with a small tremor like today's, we must keep practising how to read the movements of the peninsula's crust from these events.