中强地震区地震烈度统计拟合因素评估

目前地震危险性综合概率分析方法中的地震动参数衰减规律一般是由研究区地震烈度和参考区地震动参数经过映射方法得出的,而烈度统计结果依赖于不同模型和不同回归方法,因此,合理评估烈度影响因素有很大现实应用价值,它直接影响地震危险性分析结果。以我国中南地区地震烈度资料,用不同回归拟合方法研究该地区地震烈度随震中距和面波震级变化的等效圆、椭圆和综合椭圆模型分布关系,考虑震级和距离因素的相关性,比较分析已有结果,评估中强地震区烈度模型和回归方法对烈度的拟合影响,结果可供该地区地震小区划和设定地震动参数参考。

Evaluation on the Factors in Statistical Fitting of Intensity in Seismic Moderate Area

The formation of intensity attenuation law is essential for traditional probabilistic seismic hazard analysis(PSHA) at a specific site to predict engineering strong ground motion for a given exceeding probabilistic level by earthquake pair mapping method,thus the rational evaluation of statistical factors determining the intensity distribution law is essentially critical to the final PSHA results,and it has economical application.This paper,focusing on the historical earthquake isoseismals in a typical seismic moderate area of Southern Central China(SCC),gives firstly an introduction of Joyner-Boore(J-B) method of LSE in intensity data fitting,then adopts different attenuation relationships of intensity in SCC over epicentral distances and magnitude of surface wave,including that of equivalent circle vs.radius,that of ellipse,and that of joint ellipse vs.long-axis or short axis.Nonlinear parameter estimation and standard deviation of above models are also tabulated by Joyner-Boore(J-B) method of LSE and ordinary least square estimation(OLSE) in intensity data fitting.Finally,comparisons of these results derived from this paper with those in previous studies in the same area and with that typical in West America are performed.Results show:(1) Different models of intensity attenuation law and intensity data applied are both crucial for statistical analysis of historical isoseismals to predict the mean earthquake intensity at a specific site,and the mean intensity predictions by various models applied in this study is fairly consistent;(2) Intensity predicted at a short distance by Joyner-Boore(J-B) method of LSE is much higher than by OLSE in SCC intensity data fitting,but the difference will dilute even reverse at a longer epicentral distance;(3) Intensity attenuation law by epicentral distances and magnitude of surface wave of joint ellipse vs.long-axis or short axis is better optimized than that of ellipse,since the former gives a congruent value at long or short-axis,while the other loses the virtue;(4) Compared with this study, traditional researches overestimated the mean intensity,but the difference will dilute with growing distance;(5) Comparisons of this study shows that the intensity prediction decayed fastest in West America,and the next is that in East China.Also,the application of this study is also confined by the distance and magnitude of the earthquake data.This study may provide a fair consideration for micro-zonation and design earthquake ground motion in seismic moderate area.