云南武定地震余震近场尾波衰减的区域特征
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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,由此证实了地震波穿过主断层破碎带时有更强的散射
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.
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.
引文
云南省地震局 . 1996. 1995年武定 6.5级地震现场考察与研究 . 35～ 54 .
高龙生 ,华正兴 ,李瑞宣 .1987.用尾波的强度和衰减估算北京地区 S波的平均自由程 [J] .地震学报 ,9(4 ) :34 7～ 363
李白基 ,秦嘉政 ,叶建庆 ,等 .2 0 0 0 .腾冲火山区剪切波和尾波衰减初步研究 [J] .地震研究 ,2 3(2 ) :136～ 14 2
林畅彦 ,古本宗充 ,平秋良浩 ,等 .1999.兵库县南部地震引起的尾波 Q值的变化 [J] .世界地震译丛 ,(3) :4 0～ 53
秦嘉政 ,李宁 ,胡克坚 .1987.1985年云南禄劝地震余震尾波 Q值的某些研究 [J] .地震学报 ,9(3) :2 39～ 2 52
秦嘉政 .1992 .澜沧 -耿马地震前后尾波衰减的区域特征 [J] .地震学报 ,14 (1) :71～ 82
秦嘉政 ,刘祖荫 ,龙晓帆 .1995.滇西地震实验场两次中强地震前后尾波衰减的区域特征分析 [J] .中国地震 ,11(3) :2 12～ 2 2 0
张天中 ,马云生 ,黄蓉良 .1998.震源、衰减和场地因子的单台尾波解法 [J] .地震学报 ,2 0 (2 ) :137～ 14 3
Aki K,Chouet B.1975.Origin of coda waves:source,attenuation and scattering effects[J] .JGeophys Res,80 :3 32 2～ 3 34 2
Dainty A M,Toksoz M N .1981.Seismiccodason theearth and themoon:a comparison[J] .Phys Earth Planet Interiors,2 6:2 50～ 2 60
Del Pezzo E,De N atale G.1985.Qcof three- component seismm ograms of colcanic microearthquakes at Campi Flegreivolcanic area,southern Italy[J] .Pure Appl Geophys,12 3:683～ 696
Fehler M,Roberts P.1988.A temporal changesin coda wave attenuation observed during an eruption of Mount St.H elens[J] .JGeophys Res,93:4 367～ 4 373
Frankel A.1991.Mechanism s of seismic attenuation in the crust:scattering and anelasticity in N ew York state ,SouthAfrica and southern California[J] .JGeophys Res,96:62 69～ 62 89
H ough S E,Anderson J G.1988.H igh- frequency spectra observed at Anza,California:implications for structure[J] .Bull Seism Soc Am er,78:692～ 70 7
Jin A,Aki K .1986.Temporal changesin code Q before the Tangshan earthquake of 1976and the H aicheng earthquakeof1975[J] .JGeophys Res,91:91656～ 91673
Jin A,Mayeda K ,Adam s D ,et al.1994 .Separation of intrinsic and attenuation in southern California using TERRAscope data[J] .JGeophys Res,99:17835～ 1784 8
Singh S,H errmann R B.1983.Regionalization of crustal coda Q in the continental United States[J] .JGeophys Res,88:52 7～ 538
高龙生 ,华正兴 ,李瑞宣 .1987.用尾波的强度和衰减估算北京地区 S波的平均自由程 [J] .地震学报 ,9(4 ) :34 7～ 363
李白基 ,秦嘉政 ,叶建庆 ,等 .2 0 0 0 .腾冲火山区剪切波和尾波衰减初步研究 [J] .地震研究 ,2 3(2 ) :136～ 14 2
林畅彦 ,古本宗充 ,平秋良浩 ,等 .1999.兵库县南部地震引起的尾波 Q值的变化 [J] .世界地震译丛 ,(3) :4 0～ 53
秦嘉政 ,李宁 ,胡克坚 .1987.1985年云南禄劝地震余震尾波 Q值的某些研究 [J] .地震学报 ,9(3) :2 39～ 2 52
秦嘉政 .1992 .澜沧 -耿马地震前后尾波衰减的区域特征 [J] .地震学报 ,14 (1) :71～ 82
秦嘉政 ,刘祖荫 ,龙晓帆 .1995.滇西地震实验场两次中强地震前后尾波衰减的区域特征分析 [J] .中国地震 ,11(3) :2 12～ 2 2 0
张天中 ,马云生 ,黄蓉良 .1998.震源、衰减和场地因子的单台尾波解法 [J] .地震学报 ,2 0 (2 ) :137～ 14 3
Aki K,Chouet B.1975.Origin of coda waves:source,attenuation and scattering effects[J] .JGeophys Res,80 :3 32 2～ 3 34 2
Dainty A M,Toksoz M N .1981.Seismiccodason theearth and themoon:a comparison[J] .Phys Earth Planet Interiors,2 6:2 50～ 2 60
Del Pezzo E,De N atale G.1985.Qcof three- component seismm ograms of colcanic microearthquakes at Campi Flegreivolcanic area,southern Italy[J] .Pure Appl Geophys,12 3:683～ 696
Fehler M,Roberts P.1988.A temporal changesin coda wave attenuation observed during an eruption of Mount St.H elens[J] .JGeophys Res,93:4 367～ 4 373
Frankel A.1991.Mechanism s of seismic attenuation in the crust:scattering and anelasticity in N ew York state ,SouthAfrica and southern California[J] .JGeophys Res,96:62 69～ 62 89
H ough S E,Anderson J G.1988.H igh- frequency spectra observed at Anza,California:implications for structure[J] .Bull Seism Soc Am er,78:692～ 70 7
Jin A,Aki K .1986.Temporal changesin code Q before the Tangshan earthquake of 1976and the H aicheng earthquakeof1975[J] .JGeophys Res,91:91656～ 91673
Jin A,Mayeda K ,Adam s D ,et al.1994 .Separation of intrinsic and attenuation in southern California using TERRAscope data[J] .JGeophys Res,99:17835～ 1784 8
Singh S,H errmann R B.1983.Regionalization of crustal coda Q in the continental United States[J] .JGeophys Res,88:52 7～ 538
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