云南武定地震余震近场尾波衰减的区域特征  

REGIONAL FEATURES OF CODA ATTENUATION OF AFTERSHOCKS OF WUDING, YUNNAN EARTHQUAKE IN NEAR FIELD

作　　者：秦嘉政[1] 李白基[1] 钱晓东[1] 苏有锦[1] 蔡静观[1] 付虹[1] 

机构地区：[1]云南省地震局,中国昆明650041

出　　处：《地震学报》2001年第1期87-97,共11页Acta Seismologica Sinica

基　　金：国家重点基础研究发展规划<大陆强震机理与预测>项目 ;川滇西部流动实验场课题资助!(95- 13- 0 5- 0 5)

摘　　要：根据地方震尾波散射理论 ,利用云南武定 MS6.5主震后近场田心和云龙两个流动数字化台站记录的余震序列地震资料 ,以不同中心频率 (1 .5～ 2 0 Hz)取样分频研究了近场尾波振幅衰减率 β(f)的空间分布特征 .结果表明 ,两个台站给出的尾波振幅衰减率 β(f)存在明显的小区域范围非均匀性变化 .位于主发震断层两侧的云龙台 (东侧 )和田心台 (西侧 )测得的尾波振幅衰减率 β(f)值 ,当 f<6.0 Hz时基本一致 .相应的 Qc(f)值为 66～ 1 2 0的低值 ;但在高频范围 (f≥ 6.0 Hz) ,由于穿过主断层的近场尾波遭到断层破碎带强烈的吸收 ,因而云龙台测得的尾波振幅衰减率β(f )值 ,比不穿过主断层的田心台给出的β(f)降低 30 % ,并讨论了产生近场尾波振幅衰减空间分布差异的原因 .本文的研究结果还表明 ,波源因子 A0 (f)不仅与震源强度相关 ,也与频率 f 相关 ,用 1 .5～ 2 0 Hz求出的 S波平均自由程 L在主断层东侧为 30 km、西侧为 40 km。WT5BZ] According to dispersion theory of coda of local events, using near field data aftershocks recorded by two mobile digital stations at the Tianxin and Yunlong after the Wuding, Yunnan M S=6.5 main shock and sampling at different central frequencies(1.5~20 Hz), spatial distribution features of coda attenuation ratio β(f) are studied. The results show that there exists obvious non uniformity of coda attenuation ratio β(f) given by the two stations in small region. When f <6.0 Hz the coda attenuation ratio β(f) observed on both sides of earthquake generating fault are basically identical. Yunlong station is located on east side and Tianxin station on west side. The corresponding Q c (f ) is in the range of 66~120. However, in the range of high freqency( f ≥ 6.0 Hz) the coda in near field going through major fault encounters a strong absorption from the fracture zone. The β(f) going through the fault observed at Yunlong station is 30% lower than that in Tianxin station in which the seismic waves do not go through the fault. The reason for the difference in space distribution of coda attenuation is discussed. The results also show that factor A 0(f) of waves source is not only related with the source strength, but also with frequence f . The mean free path L of S wave obtained using 1.5~20 Hz is respectively 30 km on east side of the fault and 40 km on west side, from which it is verified that there is a stronger dispersion body when seismic waves go through the fracture zone.

关 键 词：尾波衰减特性 武定地震 振幅衰减率 地震尾波 地质构造 地震前兆 

分 类 号：P315.31[天文地球—地震学]