起算震级与衰减不确定性校正  

Threshold Magnitude and Correction of Attenuation Uncertainty

作　　者：沈建文[1] 蔡长青[1] 

机构地区：[1]上海市地震局

出　　处：《中国地震》1998年第4期36-43,共8页Earthquake Research in China

摘　　要：分析表明，起算震级Ｍ０对危险性分析结果的影响表现为当Ｍ０取值不够低时，场地的危险性将被低估。此种低估影响与场地的地震危险性高低、潜源距场地的距离及衰减公式的形式和标准差有关。场地的危险性越低，潜源距场地越近，衰减公式的标准差越大，则Ｍ０的影响越大。粗略地说，在７度及７度以上地区，且主要影响潜源距场地有一定距离，对５０年超越概率１０％和３％的结果，Ｍ０取４级大体中满足要求；但对５０年６３％的结果，Ｍ０的影响相当严重。为使这种低估误差不超过１０％，Ｍ０应控制到３级甚至更低。对地震危险性较低的地区，或主要影响潜源距场地较近，Ｍ０取４级可能低估５０年１０％的危险性。从所得结果看，Ｍ０的取值宜根据具体情况适当降低，尽管此时由于低震级部分衰减不确定性增大也不是理想的方法。据所得结果，把５０年６３％的地震动作为强度抗震设防标准存在较大的不确定性，用５０年１０％的地震动据结构性质折算得到强度设防标准应更为合理。It is pointed out in this paper that the effect of threshold magnitude M 0 to the result of seismic hazard analysis may be expressed as underestimating the hazard when M 0 is not small enough.Such underestimate is related to the hazard level of the site,the distances of the site to the main potential source and the attenuation law.The effect of M 0 grows with the rising of the hazard,the distance between site and main potential source,and the standard error of the attenuation law.Roughly speaking,for regions of basic intensities 7 or above 7,and main potential source is at a distance from the site, M 0 takes 4.0 can meet the cases for results of the probabilities of exceedance 10% and 3% in 50 years.But for 63% in 50 years,the effect of M 0 is large.To let the underestimate error be smaller than 10%, M 0 should take magnitude 3.0 or lower.For regions with lower seismic hazard,or the main potential source is near to the site, M 0 takes magnitude 4.0 may underestimate the seismic hazard of 10% in 50 years.From the results obtained in this paper, M 0 should take suitable low magnitude according to practical circumstances,even if the method is not perfect,the uncertainty is large at the low magnitude part of the attenuation law.According to this paper,there are large uncertainty taking the acceleration of 63% in 50 years as earthquake resistant level for strength.It is more reasonable setting the earthquake resistance level of strength by discounting the acceleration of 10% in 50 years according to structure quality.

关 键 词：危险性分析 不确定性校正 起算震级 地震 

分 类 号：P315.9[天文地球—地震学]