Assessment Of Seismic Intensity With Mean Damage Index In An Earthquake-resistant Region

China is one of the countries which suffer the most devastating earthquake disasters in the world. 60% of the cities, with population more than 500000, locate at the high -intensity zone in which the earthquake intensity is more than or equal to seven. This is the potential threat to the economic construction and people's lives. The term earthquake intensity is used as a simple measure of earthquake damage and as a simple macroseismic scale for the strength of earthquake motion for seismologists, also as a rough but convenient index to sum up experience on earthquake engineering construction and to depict zones of seismic hazard. The rapid intensity assessment after earthquake is the base of earthquake relief, resumption of production and home rebuilding.In this paper, the major intensity scales in the world are compared, and the indicators to earthquake intensity assessment are summed up. In China Intensity Scale, the damage state of buildings is the major index to assess seismic intensity in the zones whose earthquake intensity is six to ten. And the mean damage index is as a special index in China Intensity Scale. Before 2008, the buildings referred in China Intensity Scale are those without seismic design. But with the economy development of China, the amount of the buildings without earthquake-resistant design is decreasing, and the number of masonry structures and RC structures is increasing. The assessment of seismic intensity based on the damage state of buildings with the seismic design (such as masonry structures and RC structures) is urgently needed.In this paper, according to the seismic damage matrix of RC structures and masonry structures in 2000s, the relationship between seismic damage matrix and mean damage index is created, and the seismic intensity scale of the mean damage index for frame structure and masonry structure with different seismic design level is proposed. The negative slopes of the fitting straight lines are the decrement of the mean damage index when the earthquake intensity increases one under the same earthquake action. In this paper, the mean damage indices are collected which occurred in China mainland in about 2000, and on the basis of the range of the mean damage index induced in this paper, the comparisons between this method and site assessment are given. The intensity according to this method is consistent with the result based on site assessment in generally.The method in this paper can surmount the disadvantage of the inconsideration to the variation of the seismic capacity, and ensure the consistence and furtherance of the intensity assessment.