The Korean peninsula lies in the Eurasian Plate. Its seismicity shows an irregular strain release typical of intraplate seismicity. Historical earthquake records of Korea from the first to the 19th centuries greatly outnumber instrumental ones during the 20th century. Analyses of these historical data are of paramount importance for seismicity and seismic hazard studies of the peninsula. In order to quantify sizes of historical Korean earthquakes better, a linear regression relationship between Richter magnitude, ML, and epicentral Modified Mercalli intensity, I0, of the earthquakes in the Sino-Korean craton was obtained in this study. The northeastern part of China is connected with the Korean peninsula geologically, and the patterns of strain release in these two regions are similar. Sixty-four earthquakes with surface-wave magnitude Ms ≥ 4.7 in the Sino-Korean craton were used in this study. The data were drawn from the Chinese and Korean earthquake catalogs. Since ML is generally used in magnitude-intensity relationships at regional distances, Ms of the earthquakes in this study were converted into ML. Least-square fitting of magnitude and intensity data of earthquakes in the Sino-Korean craton gives ML = 1.75 + 0.58I0.
A comparison of this relationship with those for highly seismic southern California and rather stable Australia was made. The magnitude-intensity relationship in the Sino-Korean craton will lead to more reliable seismicity and seismic hazard studies of Korea.