A PRELIMINARY STUDY ON SEISMOGEOLOGIC EVIDENCE FOR MODERATE EARTHQUAKES IN EAST CHINA

Few large earthquakes(MS≥7)have ever occurred in the historical records in eastern China,especially in southeast continental region of 105°～120°E,20°～35°N. However,many moderate-strong earthquakes with magnitude between 5 and 6 occurred there,such as the 1962 Heyuan MS 6.4 earthquake and 1969 Yangjiang MS 6.7 earthquake in Guangdong province,the 1974 Liyang MS 6.0 earthquake in Jiangsu province,1979 Guzhen MS 5.0 earthquake in Anhui province,and the 2005 Jiujiang MS 5.7 earthquake in Jiangxi province and so on. These earthquakes have no significant earthquake ruptures,and few late Pleistocene active faults were discovered. So,the seismogeological background of the above moderate-strong earthquakes is still unclear up to the present,that is to say, it is very necessary to study the seismogeologic evidence for moderate earthquakes. In the paper,by analysis of the seismogeologic evidence of the 1979 Liyang MS 6.0 earthquake in Jiangsu province,the 2005 Jiujiang-Ruichang MS 5.7 earthquake in Jiangxi province,the 1710 Xinhua MS 51/2 earthquake in Hunan province,the 1917 Huoshan MS 61/4 earthquake in Anhui province and the moderate-strong earthquakes around Dongting Lake,some conclusions are obtained as follows: 1)most moderate-strong earthquakes in east China occurred at regions near the early Quaternary active faults,and regions with early-middle Pleistocene active faults; 2)most moderate-strong earthquakes in East China are related to the development and distribution of the Quaternary down-faulted basins. 3)moderate-strong earthquakes in East China may occur at regions with evident active tectonic geomorphological characteristics in Quaternary,such as the areas with linear fault geomorphology or geomorphologic surface; 4)moderate-strong earthquakes may occur in the seismic gaps along the seismic zones where earthquakes with magnitudes 4～5 occurred in the history.