Earthquake of Magnitude 2.6 Strikes Off Yeongdeok Coast... Why the East Sea Has Residents on Edge

The sea off Yeongdeok gave a little shudder this afternoon. A 2.6 magnitude earthquake struck 31 kilometres east of Yeongdeok-gun, North Gyeongsang Province. With its shallow epicentre, residents in Yeongdeok, and even some in Ulsan and Pohang, would have felt a distinct jolt. For those living along the east coast, these tremors are no longer just passing events. The memory of the tsunami that followed that massive earthquake in Japan is still all too vivid.

Today's Tremors, as Recorded by Seismographs

This quake's epicentre was on the East Sea bed, fairly close to the land. The seismographs would have clearly picked up the typical seismic wave pattern of a shallow earthquake. The time difference between the arrival of the P-waves (primary) and S-waves (secondary) would have been minimal, so if you were in the area at the time, you might have felt a sudden thud followed by a brief tremor shaking buildings. Fortunately, no damage has been reported so far.

Why the East Sea? The Region's Seismic Character

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 for the forces generated by the Pacific Plate as it subducts towards the Japanese archipelago. Indeed, earthquakes around magnitude 3.0 are a fairly common occurrence along the east coast. The waters off Ulsan and the Yeongdeok area are known to have particularly complex and interwoven fault systems. It's highly likely that this earthquake was a natural event stemming from that geological context.

Regional Shaking: How Strong Was It Felt?

Gathering reports from the scene, the tremor was felt across a wider area than initially expected.

• Yeongdeok-gun and Uljin-gun, North Gyeongsang Province: Intensity III (Felt noticeably indoors, especially on upper floors of buildings).
• Ulsan Metropolitan City and Gyeongju-si: Intensity II (Felt by a few people at rest, particularly on upper floors).
• Parts of Pohang-si and Daegu Metropolitan City: Intensity I (Not felt by people, but recorded by instruments).

Residents in high-rise apartments would have been particularly sensitive to this swaying. This is because seismic waves with longer periods can resonate with tall buildings, amplifying the motion.

Tsunami Fears? No Need to Worry, For Now

At this magnitude, there is, of course, no risk of a tsunami. However, the topography of the East Sea bed, with its steep drop-offs near the coast, means that a major earthquake near Japan could send a tsunami reaching our shores within one to two hours. Even when things are calm, every tremor on home soil triggers a 'what if' thought – it's a survival instinct for east coast residents.

The Yeongdeok waters experienced a 3.1 magnitude earthquake back in 2023. The thought then was, "Yeongdeok again," and today's quake released slightly less energy than that one. But for seasoned observers, it's a sign that fault movements haven't ceased. Considering the earthquake mechanism, the speed of seismic wave propagation, and the epicentre analysis, similar tremors are likely to continue along the east coast.

Late in the afternoon, anyone who felt a sudden lurch while alone in their office probably reached for their smartphone to check. Earthquakes are no longer a strange disaster for us. We don't need research reports to tell us the Korean Peninsula is no longer a safe zone from earthquakes; we feel it in our bodies. Even with a minor tremor like today's, we must keep practising how to read the movements of the peninsula's crust.