关键词: 地震, 概率分布, 京西北模型, 定量评估

Abstract: Based on the results of quantitative research on active faults,and especially the detailed investigation and systematic summary on paleoearthquakes in the basin-and-range province,northwest of Beijng by Ran Yongkang et al., a catalog of strong earthquakes since 25ka B.P. (including historical earthquakes) has been compiled for the 15 individual segments of 7 active faults in this area. Furthermore,this catalog is used to estimate the strong earthquake recurrence interval (T),average strong earthquake recurrence interval (T_a) and value of normalized function (T/T_a) for all specific fault segments in the light of the thought of the NB model.In these estimations,the recurrence intervals of strong earthquakes on 2 specific segments are estimated separately for longer-interval and shorter-interval,and correspondingly their T_a and T_a/T values are estimated in the same manner.The reason is that we found that the recurrence of characteristic earthquakes follows a fractal-law,i.e. the recurrence of characteristic earthquake follows a quasi-periodic model with longer quiet and active periods,while within the active period it follows a quasi-periodic model with shorter interval.Moreover,the recurrence of small earthquakes within the relatively short active period may follow a clustering model. As the 15 fault segments have a similar tectonic environment,it is considered that they have a similar recurrence model of strong earthquakes.Therefore, the obtained 35 T/T_a values are treated as an equal basis for the statistical analysis.The result of statistic analysis shows that the distribution of normalized strong earthquake recurrence internal follows a normal distribution with mean (μ) equal to 1.000 3 and standard deviation (σ) of 0.246 4,and we call it the Northwest Beijing model.Using this model and also comparing with the NB model,we have estimated the probabilities of strong earthquake occurrence on 25 segments of 15 faults in the basin-and-range province,northwest of Beijing.The results indicate that the potential fault segments for the occurrence of future strong earthquake should be the North marginal fault of the Tiznzhen-Yanggao basin,the South marginal fault of the Yangyuan basin,the Xingwei segment of the North marginal fault of the Yanqing basin,the Yanshui segment of the North marginal fault of the Fanshan basin,and the South marginal fault of the Xuanhua basin.

Key words: Earthquake, Probability distribution, Model of northwest Beijing, Quantitative estimates