Historical seismicity of Korea

The Korean peninsula lies in the Eurasian plate, neighboring seismically active China and the Japanese Islands. Instrumental observation of earthquakes began in Korea in 1905, and about one thousand events of mostly small magnitude, less than 4.0, have been detected to date in and near the peninsula. Strain release due to these earthquakes is almost negligible compared to that due to about 2186 historical earthquakes that occurred from 2 to 1904 A.D. in the peninsula. In this study, these historical earthquakes are cataloged from Korean historical documents, and their epicenters and intensities are estimated as best as possible. Temporal variations of the historical seismicity of Korea clearly reveal a very irregular strain release pattern over the nineteen centuries, with low to moderate seismicity most of the time except for the unusually high seismicity from the fifteenth to the eighteenth centuries. This highly irregular strain release pattern clearly indicates the characteristics of intraplate seismicity of the peninsula. Epicenters of large earthquakes appear to be well associated with the major faults and the boundaries of major geological units in the peninsula. It is to be noted that the major faults associated with large historical earthquakes were created by the Mesozoic tectonic activities that severely disrupted crustal layers of the peninsula. Historical earthquakes occurred all over the peninsula; however, the northeastern part appears relatively less seismic, probably due to the area being less disrupted during the Mesozoic. The b value in the magnitude-frequency relation determined from historical Korean earthquakes is 0.71, which is between those of the Japanese Islands and Eastern China and is lower than in many stable intraplate regions.