A statistical analysis on seismic belts in Chinese mainland

327Mge;5.0 earthquakes with relatively integrated data are investigated. The whole seismic area in Chinese mainland is divided into 5 study regions. We spatially scanned the data in each region for seismic belt pattern with a uniform criterion. It is found that the belt pattern exists before 96 moderate-strong earthquakes, being 29% of the total earthquakes. The ratio of earthquakes with pre-earthquake belts over total is 30% for North China region, 29% for southeastern China, 41% for Sichuan-Yunnan region, 24% for northwest marginal region of Qingzang plateau, and 16% in Xinjiang region. The ratio for Xinjiang region is the lowest and that for Sichuan-Yunnan region is the highest.Then we statistically analyzed the relationship between the magnitude M　of the mainshock, occurred after belt formation, and the belt parameters, such as belt duration time t, belt length L, and the magnitude M　of belt earthquakes. The results are lg t(month)=0.30M－1.03plusmn;0.38 (Mge;6.5) and lg L(km)=0.11M+1.73plusmn;1.75 (Mge;5.5) for China mainland earthquakes, and lg t(month)=0.20M-0.25plusmn;0.24 and lg L(km)=0.12M+1.75plusmn;0.16 (Mge;5.5) for Sichuan-Yunnan region. Due to less sample earthquakes and large data scattering, the relationships for other regions are not presented. Our study result indicates that no significant correlation exists between the mainshock magnitude M and the belt duration time t, and the belt length L, when the belt earthquake magnitude M5.5. When Mge;5.5,a linear relation would exist, but with poor data correlation. The lowest magnitudes of belt earthquakes are about ML2.5,ML3.0 and ML4.0 for the M5.0mdash;5.9, M6.0mdash;6.9 and Mge;7.0 mainshock, respectively. The mainshocks occurred at the belt terminals are more than those occurred inside the belts. Only 10% mainshocks are associated with crossing belts, and they are mainly Mge;7.0 earthquakes. The ratios of belts appeared before M5.0mdash;5.9, M6.0mdash;6.9 and Mge;7.0 mainshocks are 25%, 38% and 71%, respectively, showing that the seismic belt pattern may be an important abnormal precursory for Mge;7 .0 mainshocks.