以空间光滑的地震活动性模型为空间分布函数的地震危险性分析方法

Seismic hazard estimate using spatially smoothed seismicity model as spatial distribution function

根据华北地区的地震目录,建立了4个空间光滑的地震活动性模型,并以这些模型为空间分布函数,将华北地震区每个地震带的地震年发生率分配到空间格点中,计算这一地区的地震危险性.结果表明,采用仪器记录地震计算得到的地震活动性模型和地震危险性结果能够反映华北地区现今的地震活动水平和地震危险性水平,符合人们对现今华北地区地震危险性的认识;采用历史破坏性地震(M≥4.7)计算的地震活动性模型和地震危险性结果,较好地反映了华北地区中强地震活动区的地震危险性水平;以地震应变计算地震活动率,并根据点椭圆模型和线椭圆模型计算得到的地震活动性模型,能够较好地反映大地震的活动水平和空间构造特征.将根据4个模型计算得到的50年超越概率10%峰值加速度(PGA)分布加权平均,得到综合的华北地区PGA分布,并将该PGA分布与根据《中国地震动参数区划图》中综合潜源方案计算得到的50年超越概率10%的PGA分布做了比较,发现二者无本质差别,均能反映华北地震区的地震危险性水平.当然,二者也具有一定的差异:前者计算得到的符合PGA≥100cm/s2条件的区域面积明显要比后者的大,而符合PGA≥250cm/s2条件的区域面积则比后者的要小.这主要是由于潜在震源区类型和空间分布函数不同造成的.

In this study, we established four based on the earthquake catalog of North spatially smoothed seismieity models China. Taking these models as the spatial distribution function, we distributed the seismic annual rates into grid cells of every seismic belt in North China seismic area, and calculated the seismic hazard in this region. The result shows that, first, the seismic activity model and seismic hazard result both calculated by using instrumental earth- quake catalog, can reflect the contemporary seismic activity level and seismic hazard level of North China area; second, the seismic activity model and seismic hazard result, both calculated by using historical earthquakes （M≥4.7）, represent the seismic hazard level of moderate earthquakes in North China quite well; third, the seismic activity, which is based on the calculation using point-ellipse model and linear-ellipse model involving seismic activity rate derived from seismic strain, can fairly well exhibit strong earthquakes＇ activity level and relevant tectonic characteristics. The PGA distribution in North China region is the average with an equal weight of four PGA values obtained from four seismicity models for 10% P. E. in 50 a. Comparing this PGA distribution with another PGA distribution for 10% P.E. in 50 a, which is calculated by combined potential seismic sources according to ＂National Seismic Zoning Map＂, we find that there is no essential difference between them, and both of them can reflect the seismic hazard level of North China seismic region. Admittedly, there are still some differences between these two distributions： the area satisfying the condition of PGA~ 100 cm/s2 calculated from the former is obviously larger than that calculated from the latter; nevertheless, the area satisfying PGA≥100 cm/s^2 calculated from the former is smaller than the one calculated from the latter. It is principally due to the differences of potential seismic sources and spatial distribution functions.