Seismologists say that the Yangsan Fault that caused the recent earthquakes in Gyeongju is an active fault. The Korea Meteorological Administration projects that there will be more aftershocks in the 3 and 4 magnitude range for some time.
Following the main 5.8-magnitude shock, more than 420 aftershocks occurred over the next ten days. Epicenters marked on a map showed that most of them were clustered within the 5-kilometer-radius area near Naenam-myeon in Gyeongju. The foreshock, main shock, and two aftershocks larger than magnitude 4 occurred in the south-southwest direction. The average depth of epicenter was 15.2 kilometers, about 5 kilometers deeper than other focus depths recorded on the Korean Peninsula. The Korea Meteorological Administration announced that aftershocks could continue for many more months at the longest.
[Soundbite] Yoo Yong-gyu(Earthquake and Volcano Monitoring Division, KMS) : "The probability for an aftershock stronger than the main shock occurring is low, but aftershocks between magnitudes 3 and 4 are quite possible."
Seismologists who have taken part in the detailed analysis said the possibility of stronger quakes occurring due to chain reaction wasn't very high.
[Soundbite] Prof. Lee Jun-kee(Seoul Nat'l Univ.) : "We can say that the probability of a stronger earthquake occurring is very low."
They also agreed that the recent Gyeongju earthquake proved that the Yangsan Fault is an active fault line.
The experts assessed the areas around the Yangsan Fault as a seismic hazard zone, which could repeatedly see strong tremors around magnitude 6 not immediately, but within several decades.