From 1905 to 1945, earthquakes occurring in and in the vicinity of the Korean peninsula were monitored by the Meteorological Observatory of the Government General of Tyosen with one to six seismological stations. Seismological data of 323 earthquakes of the Meteorological Observatory during the period are analyzed in this study. Epicenters of earthquakes are estimated by reports in bulletins of the Meterological Observatory. Epicenters and magnitudes of events that occurred from 1926 to 1943 were determined previously based on the crustal structures of the peninsula and Japanese islands and Tsuboi's formula, respectively (Lee and Jung, 1980; Kim, 1980). The m>bm>-value determined from these events turned out to be about 0.8, which is between those values for earthquakes of the Japanese islands and China. The epicenter distribution of earthquakes during the period indicates rather diffuse seismicity over the peninsula not well related to major faults and much lower seismicity in the northeastern part of the peninsula compared with other regions. Previous studies of historical seismicity of the Korean peninsula showed that epicenters of destructive large earthquakes are well associated with major faults in the peninsula formed during Mesozoic tectonic activities (Lee, 1987) and lower seismicity in the northeastern part of the peninsula. The seismic-wave energy release during the period was rather steady, except for the period 1936–1938, during which the 1936 m>Mm> 5.1 Ssanggyesa earthquake, the largest event during the period, occurred in the southern part of the peninsula. The source mechanism of the Ssanggyesa earthquake indicates a thrust fault with a considerable strike-slip component (Shimazaki, 1984); one of the nodal planes trending north-northeast coincides with the strikes of adjacent faults. Reliable source mechanisms of earthquakes in the vicinity of the Korean peninsula indicate that the Korean peninsula is subject to compressive stresses parallel to the great circles from the Himalayas to the Japan trench. It appears that the earthquakes in the Korean peninsula occur along the faults formed during the Mesozoic by stresses transmitting from plate boundaries between the Eurasian plate and the Indian plate along the Himalayas in the southeast and the Pacific and Philippine plates along the Japan and Ryuku trenches in the east, respectively. The source mechanisms of large earthquakes in the peninsula are likely to be thrust faults with considerable strike-slip components in the trends of faults.
