Hunan In Central And Southern Seismic Zoning Study

Hunan province is located in the transition area from strong earthquake area of north China to moderate earthquake area of south China. There are no faults after late Pleistocene except Taiyangshan fault and Yueyang—Linxiang fault. It is a typical region of moderate seismicity, in the middle and south part of Hunan province. There is no record of strong earthquakes (M>6.0) except Changde earthquake (M=6.8) in 1631 in Hunan province. Earthquake disaster in this region is mainly caused by moderate earthquakes (M ≤ 6.0). Nearly 70 percent of Hunan province is classified as low intensity region ( I<6 or a<0.05g) both in the "Seismic intensity zoning Map in China (1990)" and in the "Seismic zoning Map of Ground Motion Parameters in China (GB 18306-2001) ",. According to the regulations of China, seismic design is not required in many cities in middle and south Hunan Province.In recent years, many moderate earthquakes in china caused serious damages. There are many moderate earthquakes occurred in Hunan Province or adjacent region which caused large amount of life and economic losses such as Jiujiang earthquake with magnitude 5.7. At the same time, the data also shows that it is possible that earthquake with magnitude 5 will occurred anywhere in the research region. History earthquake data also shows that the soil condition of middle and south Hunan amplified the earthquake effects. Strong motion records show that the moderate earthquake with magnitude smaller 5.0 can cause strong ground motion (PGA exceeds 0.05g). So we must pay much attention to the seismic zonation in the region like middle and south Hunan Province.Based on the basic data of seismic hazard assessment in Hunan, and the new research works on attenuation relationship of moderate earthquakes (M ≤ 6.0) as well as the results of the study of background seismicity, a new result of seismic zonation for middle and south Hunan province is provided. The area with PGA equal or greater than 0.05g in the new map obviously increased compared with the currently used map. The result is consistent with the characters of the disaster of moderate earthquakes. The results of this paper will be benefit to the new generation of seismic zonation of China and seismic hazard assessment in the moderate seismicity region.