Estimation of Regional Seismic Hazard in the Korean Peninsula Using Historical Earthquake Data between A.D 2 and 1995

Abstract

Located between the very active Japan and Ryukyu subduction zones and the northern China plate, the Korea Peninsula has been considered a part of the stable Eurasia continent and is very quiet in seismic and tectonic activity. Although there were many significant damaging earthquakes reported in historical times, seismic hazard in Korea has long been overlooked. Modern earthquake activity in the Korean Peninsula is very low and is not well recorded, at least until 1998 when the modernization of the Korean National Seismic Network was implemented. Thus, modern earthquake data are not adequate for evaluating seismic hazard in the Korean Peninsula. On the other hand, the historical earthquake catalog, which includes documented earthquake information from around the Korean Peninsula and can be dated back to as early as A.D. 2, provides the only available long-term database for the investigation of temporal and spatial patterns of earthquake activity. The importance of seismic hazard assessment has significantly increased in modern times because of the recent construction of many critical facilities, such as nuclear power plants, super-computer centers, large hospitals, and high-technology centers, throughout the entire Korean Peninsula. Although uncertainties on the historical earthquake locations and their magnitudes are expected to be large, information obtained from this historical earthquake catalog can at least provide a long-term scientific basis for an estimation of seismic hazard in Korea. For the entire Korean Peninsula, seismic hazard is evaluated in terms of the spatial distribution of seismicity and relative seismic energy release over the 2000 years of the historical record. Results from our preliminary analysis clearly demonstrate that seismic activity in the Korean Peninsula can be categorized into four prominent seismic zones, inside which seismic hazard is much higher than that in the surrounding regions. These four seismic zones include: (1) the western Korean seismic zone extending from Seoul to Pyongyang, which is characterized by a few concentrated regions of high seismicity and a high relative seismic energy release; (2) the eastern Korean seismic zone, which is characterized by a low seismic rate but a high relative seismic energy release from a few large historical events; (3) the northeastern Korean seismic zone, which is probably related to the deep Japan subduction-zone earthquakes underneath northeast China and has a very low seismicity but a very high relative energy release; and (4) the southern Korean seismic zone, which is characterized by many scattered patches of high seismicity and a few zones of high seismicity and high relative seismic energy release from a few large historical events. Among the three most seismically active regions near Pyongyang, Seoul, and Pusan, the probability of occurrence for an earthquake of magnitude greater than 5.0 is estimated to be about 1%, 2%, and 3% per year, respectively. Since significant damaging earthquakes (M ≥7.0) have occurred in these three regions in historical times, an effective assessment of seismic hazard potential in the Pyongyang, Seoul, and Pusan regions cannot be overlooked.