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Mw 5.4 Earthquake Strikes the Southeastern Korean Peninsula
In the early evening of 12 September 2016, a moderate earthquake (Mw 5.4) struck the southeastern coast of South Korea, about 50 minutes after a Mw 4.9 foreshock. The tremor was strong enough to be felt across South Korea and the northern coast of Kyushu, Japan. Photographs shared on social media showed minor damage to nearby cities; most being fallen plasters and ceilings, and minor ground cracks.
The tremor had also resulted in panic in the Gyeongju area, a popular tourist destination in South Korea located close to the earthquake’s epicentre. Usually, a magnitude-5.0 earthquake would not cause significant damage. However, in a region where seismic hazards have not been properly considered due to a low occurrence frequency, a magnitude-5.0 event could produce considerable damage to the community.
According to the United States Geological Survey, the earthquake’s epicentre is estimated to be located 8 kilometres (km) south of Gyeongju, also known as Kyongju (35.769°N, 129.227°E). The magnitude of this earthquake (Mw 5.4) is about 1.4 times greater than the recent man-made explosion in North Korea, which was felt in the northern part of the Korean Peninsula and along the North Korea-China border. Although the timing of both events are close, the distance between them and their magnitudes suggest that they are unrelated.
The seismic analysis of the Mw 5.4 earthquake, conducted by Japan’s National Research Institute for Earth Science and Disaster Resilience, suggests that this quake was caused by a strike-slip fault within the shallower layers of the Earth’s crust, where the ground on both sides of the fault move horizontally in opposite directions. Given the location of the epicentre and its strike-slip focal solution, it is believed that this earthquake is likely to have been generated by one of the NNE-SSW right-lateral active faults in the southeastern coast of South Korea. Some of these active faults have a very long and complicated slip history on the geological time scale.
Although the slip rates of active faults in South Korea are generally very low (i.e.
The slow activity of the fault in this area, together with historical records of the region's earthquake occurrence, suggest that the Korean Peninsula is not completely seismically quiet. Even though it is more than 500 km away from major plate boundary faults, the on-going tectonic motions between the Philippine Sea Plate and the Eurasian plate, as well as the tectonic deformation within northern China, are producing notable deformations in the peninsula, and reactivating the ancient fault in South Korea’s intraplate environment.