云南和四川中小地震应力降时空特征研究
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摘要
通过消除S波观测谱中的传播路径、场地响应、仪器响应、噪声等的影响,得到中小地震的震源谱。根据Brune震源模型,运用遗传算法计算了云南地区2121次ML2.0～5.3地震和四川地区323次ML3.0～5.1地震的应力降参数Δσ,分析了云南地区和四川地区中小地震应力降时空变化特征。结果表明:云南地区的地震应力降范围为0.03～47.55MPa,其中Δσ≥10.0MPa(高应力降)的地震占4.8%,Δσ的年均值在2.30～5.05MPa之间;四川地区应力降范围为0.19～47.47MPa,其中Δσ≥10.0MPa(高应力降)的地震占21.7%,Δσ的年均值在5.11～8.72MPa之间。Δσ≥10.0MPa(高应力降)的地震主要分布在滇西北至滇东北及川滇交界一带,尤其是在龙门山断裂带有较明显分布。龙门山断裂带Δσ≥10.0MPa的地震占35.8%,Δσ的年均值在5.20～12.09MPa之间,2004～2007年高应力降地震事件明显增多,反映了汶川8.0级大震前的高应力变化过程。
The observational S-waveform data are corrected by removing influential factors including the propagation route,site effects,instrument response and noise.Then,we obtained source spectra for the medium-small earthquakes.Based on Brune source model and by means of generalized inversion technique,we determined the stress drop(Δσ)of 2 121 earthquakes with ML2.0-5.3 in Yunnan region and those of 323 earthquakes with ML3.0-5.1 in Sichuan region,and we analyzed temporal and spatial features of the medium-small earthquakes in Yunnan and Sichuan Region.The results show that in Yunnan region the stress drop(Δσ)is 0.03-57.55 MPa.The earthquakes with Δσ≥10.0 MPa(higher stress drop)is 4.8% of the total,and the annual average of stress drop is 2.30-5.05 MPa.In Sichuan region,the stress drop is 0.19-47.47 MPa.The earthquakes with Δσ≥10.0MPa(higher stress drop)is 21.7%,and the annual average of stress drop is 5.11-8.72MPa.The earthquakes with Δσ≥10.0MPa(higher stress drop)mainly distribute from the Northwest to Northeast of Yunnnan region and along the boundary of Yunnan and Sichuan,especially in Longmenshan Mountain Fault Belt.The earthquakes with Δσ≥10.0 MPa in Longmenshan Mountain Fault Belt is 35.8%,and the annual average varies from 5.20 MPa to 12.09 MPa.The increase in the events with high stress drop from 2004 to 2007 reflects the high tectonic stress before the MS8.0 Wenchuan,Sichuan earthquake.
The observational S-waveform data are corrected by removing influential factors including the propagation route,site effects,instrument response and noise.Then,we obtained source spectra for the medium-small earthquakes.Based on Brune source model and by means of generalized inversion technique,we determined the stress drop(Δσ)of 2 121 earthquakes with ML2.0-5.3 in Yunnan region and those of 323 earthquakes with ML3.0-5.1 in Sichuan region,and we analyzed temporal and spatial features of the medium-small earthquakes in Yunnan and Sichuan Region.The results show that in Yunnan region the stress drop(Δσ)is 0.03-57.55 MPa.The earthquakes with Δσ≥10.0 MPa(higher stress drop)is 4.8% of the total,and the annual average of stress drop is 2.30-5.05 MPa.In Sichuan region,the stress drop is 0.19-47.47 MPa.The earthquakes with Δσ≥10.0MPa(higher stress drop)is 21.7%,and the annual average of stress drop is 5.11-8.72MPa.The earthquakes with Δσ≥10.0MPa(higher stress drop)mainly distribute from the Northwest to Northeast of Yunnnan region and along the boundary of Yunnan and Sichuan,especially in Longmenshan Mountain Fault Belt.The earthquakes with Δσ≥10.0 MPa in Longmenshan Mountain Fault Belt is 35.8%,and the annual average varies from 5.20 MPa to 12.09 MPa.The increase in the events with high stress drop from 2004 to 2007 reflects the high tectonic stress before the MS8.0 Wenchuan,Sichuan earthquake.
引文
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B ru ne J N.1970.Tectonic stress and the spectra of seismic shear wavesfrom earthquake[J].JGR,75(26):4997-5009.
Jon es L E,Helmberger D V.1998.Earthquake source parameters andfault kinematic in the eastern California shear zone[J].BSSA,88(6):1337-1352.
刘丽芳,苏有锦,刘杰,等.2007.用Moya方法反演云南数字地震台站场地响应[J].地震研究,30(1):39-42.
乔慧珍,张永久,程万正,等.2006.川西北地区介质衰减特征研究[J].地震地磁观测与研究,27(4):1-7.
秦嘉政,钱晓东,叶建庆.2005.2001年施甸MS5.9地震序列的震源参数研究[J].地震学报,27(3):250-259.
苏有锦,刘杰,郑斯华,等.2005.云南地区S波非弹性衰减Q研究[J].地震学报,28(2):1-7.
韦士忠,李玉萍.1992.大同地震前后介质Q值和小震震源参数的变化[J].地震,(2):30-38.
肖蔚文.1990.1982年卢龙地震前后的小震震源参数[J].地震学报,12(1):1-11.
张天中,马云生,黄蓉良,等.2000.1995年陡河地震前后小震震源参数及其相互关系[J].地震学报,22(3):233-240.
张永久,乔慧珍,程万正,等.2007.四川盆地地区介质衰减特征研究[J].地震研究,30(1):43-48.
B ru ne J N.1970.Tectonic stress and the spectra of seismic shear wavesfrom earthquake[J].JGR,75(26):4997-5009.
Jon es L E,Helmberger D V.1998.Earthquake source parameters andfault kinematic in the eastern California shear zone[J].BSSA,88(6):1337-1352.
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