长白山天池火山区介质非均匀性
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摘要
高频S波随着传播距离的增大其均方根(RMS)包络逐渐变宽,我们把这种现象称为S波包络展宽现象.S波传播路径上随机分布的非均匀体对S波的多次前向散射和绕射作用是导致S波包络展宽现象的主要原因,因此可用S波包络展宽现象来研究介质非均匀性.本文采用S波包络峰值延时来对S波包络展宽现象进行量化.S波包络峰值延时定义为S波初至与其均方根包络峰值最大值之间的时间差.本文选用长白山天池火山区的小震记录,运用S波包络峰值延时对长白山天池火山口地区的介质非均匀性进行了评价.结果发现长白山天池火山区呈现强烈的介质非均匀性,在0-2 km深度范围内介质非均匀性表现出南部强北部弱的空间分布特征;在2-5 km深度范围内介质非均匀性的空间分布特征与频率具有相关性;天池火山区介质非均匀性具有明显的多尺度特性;强弱非均匀性接触带,往往是地震频发地带.根据地震与非均匀体在空间分布的相对位置,我们认为火山区介质非均匀性可能反映了火山早期喷发堆积物介质结构的差异.
High-frequency S-wave seismogram envelopes of microearthquakes are broadened with increasing travel distance, which is called S-wave envelope broadening. Multiple forward scattering and diffraction induced by random inhomogeneities along seismic ray path are the main reasons to cause the S-wave envelope broadening, so the phenomena of S-wave envelope broadening can be used to study the medium inhomogeneity. The peak delay time of S-wave, which is defined as the time lag from the direct S-wave onset to the maximum amplitude arrival of its envelope, was accepted to quantify the phenomena of S-wave envelope broadening. The medium inhomogeneity of crust in Changbaishan Tianchi volcano area, based on analyzing small local earthquakes waveform, was studied by the peak delay time of S-wave envelope broadening method. The results show that the medium of Changbaishan Tianchi volcano area presents strong inhomogeneity, the spatial distribution characters of inhomogeneous medium in the south are stronger than that in the north region of Changbaishan Tianchi volcano area at the depth of 0-2 km, and the spatial distribution characters of inhomogeneous medium at the depth of 2 - 5 km depend on frequency. The medium inhomogeneity in Changbaishan Tianchi volcano area presents multi-scale character. Earthquakes usually occur around the contact band of the strong and the weak inhomogeneity. We believe that the medium inhomogeneity of crust in Changbaishan Tianchi volcano area may reveal the difference of early erupted material properties according to the relative spatial position of earthquakes and inhomogeneities.
High-frequency S-wave seismogram envelopes of microearthquakes are broadened with increasing travel distance, which is called S-wave envelope broadening. Multiple forward scattering and diffraction induced by random inhomogeneities along seismic ray path are the main reasons to cause the S-wave envelope broadening, so the phenomena of S-wave envelope broadening can be used to study the medium inhomogeneity. The peak delay time of S-wave, which is defined as the time lag from the direct S-wave onset to the maximum amplitude arrival of its envelope, was accepted to quantify the phenomena of S-wave envelope broadening. The medium inhomogeneity of crust in Changbaishan Tianchi volcano area, based on analyzing small local earthquakes waveform, was studied by the peak delay time of S-wave envelope broadening method. The results show that the medium of Changbaishan Tianchi volcano area presents strong inhomogeneity, the spatial distribution characters of inhomogeneous medium in the south are stronger than that in the north region of Changbaishan Tianchi volcano area at the depth of 0-2 km, and the spatial distribution characters of inhomogeneous medium at the depth of 2 - 5 km depend on frequency. The medium inhomogeneity in Changbaishan Tianchi volcano area presents multi-scale character. Earthquakes usually occur around the contact band of the strong and the weak inhomogeneity. We believe that the medium inhomogeneity of crust in Changbaishan Tianchi volcano area may reveal the difference of early erupted material properties according to the relative spatial position of earthquakes and inhomogeneities.
引文
[1] Sato H, Fehler M C. Seismic Wave Propagation and Scattering in the Heterogeneous Earth. Springer. American,1998． 1-3
[2] Sato H. Broadening of seismogram envelops in the randomly inhomogeneous lithosphere based on the parabolic approximation Southeast Honshu, Japan. J. Geophys Res. ,1989,94:17735-17747
[3] Saito T, Sato H, Ohtake M. Envelope broadening of spherically outgoing wave in three-dimensional media having power law spectra. J. Geophys. Res. ,2002,107:3-1-316
[4] Scherbaum F, Sato H. Inversion of full seismogram envelopes based on the parabolic approximation; Estimation of randomness and attenuation in southeast Honshu, Japan. J. Geophys. Res., 1991,96:2223-2232
[5] Takahashi T, Sato H, Nishimura T, Obara K. Strong inhomogeneity beneath Quaternary volcanoes revealed from the peak delay analysis of S-wave seismograms of microearthquakes in northeastern Japan. Geophys. J. Int. , 2007,168:90-99
[6] Gusev A, Abubakirov I R. Vertical profile of effective turbidity reconstructed from broadening of incoherent bodywave pulses-Ⅱ. General approach and the inversion procedure. Geophys. J. Int. ,1999,136:295-308
[7] Gusev A , Abubakirov T R. Vertical profile of effective turbidity reconstructed from broadening of incoherent body-wave pulses-Ⅱ. Application ot Kamchatka data. Geophys. J.Int. ,1999,136:309-323
[8] Obara K, Sato H. Regional differences of random inhomogeneities around the volcanic front in the Kanto-Tokai area, Japan, revealed frome the broadening of S wave seismogram envelopes. J. Geophys Res. , 1995, 100:2103-2121
[9] 刘若新.李继泰,魏海泉等.长白山天池火山-一座具有潜在喷发危险的近代火山.地球物理学报,1992． 35(5) :661-665 Liu R X, Li J T, W H Q, et al. Volcano at Tianchi lake, Changbaishan MT-a modern volcano with potential danger of eruption. Chinese J . Geophys. (in Chinese) , 1992 ,35(5) : 661-665
[10] 吴建平,明跃红,刘一鸣等.2002年8月20日长白山天池火山小震震群研究.地震地磁观测与研究,2003,24(4) :1-8 Wu J P, Ming Y H, Liu Y M, et al . A study on the microearthquake swarm occurred on Aug. 20 ,2002 in Changbaishan Tianchi volcano. Seisrnological and Geomagnetic Observation and Research (in Chinese) ,2003,24(4) :1-8
[11] 吴建平,明跃红,苏伟.长白山天池火山的深部结构及地震活动特征研究.见:中国大陆地球深部结构与动力学研究.北京:科学出版社,2004． 859-871 Wu J P, Ming Y H, Su W. Study on the deep velocity structures and seismicity in Changbai Shan Tianchi volcano region. In :The Deep Structure and Dynamics of the Chinese Mainland ( in Chinese ) . Beijing:Science Press, 2004． 859-871
[12] 吴建平,明跃红,张恒荣等.2002年夏季长白山天池火山区的地震活动研究.地球物理学报,2005,48(3) :621-628 Wu J P, Ming Y H, Zhang H R, et al. Seismic activity at the Changbaishan Tianchi volcano in the summer of 2002． Chinese J. Geophys. (in Chinese), 2005 ,48(3) : 621-628
[13] 吴建平,明跃红,张恒荣等.长白山天池火山区的震群活动研究.地球物理学报,2007,50(4) :1089-1096 Wu J P, Ming Y H, Zhang H R, et al. Earthquake swarm activity in Changbaishan Tianchi volcano. Chinese J. Geophys. (in Chinese) ,2007,50(4) :1089-1096
[14] 张先康,张成科,赵金仁等.长白山天池火山岩浆系统的深地震测深研究.地震学报,2002,24(2) :135-143 Zhang X K, Zhang C K, Zhao J R, et al. Deep seismic sounding investigation into the deep structure of the magma system in Changbaishan-Tianchi volcano region. Acta SeismoLogica Simca ,2002,15(2) :143-151
[15] 赵金仁,张先康,杨卓欣等.长白山天池火山区上地壳三维速度层析成像.地球物理学报,2003,46(6) :796-802 Zhao J R , Zhang X K, Yang Z X, et al . 3D tomography of velocity structure in upper crust beneath the Changbaishan Tianchi volcanic region. Chinese J . Geophys. (in Chinese), 2003,46(6) :796-802
[16] 刘志,张先康,王夫运等.用地震走时反演计算长白山天池火山区二维地壳泊松比.地震学报,2005,27(3) :324-331 Liu Z, Zhang X K, Wang F Y, et al. 2-D crustal Poisson's ratio from seismic travel time inversion in Changbaishan Tianchi volcanic region. Acta Seismologica Sinica ( in Chinese) ,2005,27(3) :324-331
[17] 汤吉,邓前辉,赵国泽等.长白山天池火山区电性结构和岩浆系统.地震地质,2001,23(2) :191-200 Tang J,Deng Q H,Zhao G Z,et al. Electric conductivity and magma chamber at the Tianchi volcano area in Changbaishan Mountain. Seismology and Geology (in Chinese), 2001,23(2) :191-200
[18] 张元生,周民都,荣代潞等.祁连山中东段地区三维速度结构研究.地震学报,2004,26(3) :247-255 Zhang Y S, Zhou M D, Rong D L, et al. 3-D Velocity structure in the central eastern part of Qilian shan. Acta Seismologica Sinica (in Chinese) ,2004,26(3) :247-255
[19] 高尔根,徐国明,蒋先艺等.三维结构下逐段迭代射线追踪方法.石油地球物理勘探,2002,37(1) :11-16 Gao E G, Xu G M, Jiang X Y, et al. Iterative ray-tracing method segment by segment under 3D construction. OGP, 2002,37(l):11-16
[20] 杨卓欣,张先康,赵金仁等.长白山天池火山区三维地壳结构层析成像.地球物理学报,2005,48(1) :107-115 Yang Z X,Zhang X K,Zhao J R, et al. Tomographic imaging of 3-D crustal structure beneath Changbaishan-Tianchi Volcano region. Chinese J. Geophys. (in Chinese),2005,48(1) :107-115
[2] Sato H. Broadening of seismogram envelops in the randomly inhomogeneous lithosphere based on the parabolic approximation Southeast Honshu, Japan. J. Geophys Res. ,1989,94:17735-17747
[3] Saito T, Sato H, Ohtake M. Envelope broadening of spherically outgoing wave in three-dimensional media having power law spectra. J. Geophys. Res. ,2002,107:3-1-316
[4] Scherbaum F, Sato H. Inversion of full seismogram envelopes based on the parabolic approximation; Estimation of randomness and attenuation in southeast Honshu, Japan. J. Geophys. Res., 1991,96:2223-2232
[5] Takahashi T, Sato H, Nishimura T, Obara K. Strong inhomogeneity beneath Quaternary volcanoes revealed from the peak delay analysis of S-wave seismograms of microearthquakes in northeastern Japan. Geophys. J. Int. , 2007,168:90-99
[6] Gusev A, Abubakirov I R. Vertical profile of effective turbidity reconstructed from broadening of incoherent bodywave pulses-Ⅱ. General approach and the inversion procedure. Geophys. J. Int. ,1999,136:295-308
[7] Gusev A , Abubakirov T R. Vertical profile of effective turbidity reconstructed from broadening of incoherent body-wave pulses-Ⅱ. Application ot Kamchatka data. Geophys. J.Int. ,1999,136:309-323
[8] Obara K, Sato H. Regional differences of random inhomogeneities around the volcanic front in the Kanto-Tokai area, Japan, revealed frome the broadening of S wave seismogram envelopes. J. Geophys Res. , 1995, 100:2103-2121
[9] 刘若新.李继泰,魏海泉等.长白山天池火山-一座具有潜在喷发危险的近代火山.地球物理学报,1992． 35(5) :661-665 Liu R X, Li J T, W H Q, et al. Volcano at Tianchi lake, Changbaishan MT-a modern volcano with potential danger of eruption. Chinese J . Geophys. (in Chinese) , 1992 ,35(5) : 661-665
[10] 吴建平,明跃红,刘一鸣等.2002年8月20日长白山天池火山小震震群研究.地震地磁观测与研究,2003,24(4) :1-8 Wu J P, Ming Y H, Liu Y M, et al . A study on the microearthquake swarm occurred on Aug. 20 ,2002 in Changbaishan Tianchi volcano. Seisrnological and Geomagnetic Observation and Research (in Chinese) ,2003,24(4) :1-8
[11] 吴建平,明跃红,苏伟.长白山天池火山的深部结构及地震活动特征研究.见:中国大陆地球深部结构与动力学研究.北京:科学出版社,2004． 859-871 Wu J P, Ming Y H, Su W. Study on the deep velocity structures and seismicity in Changbai Shan Tianchi volcano region. In :The Deep Structure and Dynamics of the Chinese Mainland ( in Chinese ) . Beijing:Science Press, 2004． 859-871
[12] 吴建平,明跃红,张恒荣等.2002年夏季长白山天池火山区的地震活动研究.地球物理学报,2005,48(3) :621-628 Wu J P, Ming Y H, Zhang H R, et al. Seismic activity at the Changbaishan Tianchi volcano in the summer of 2002． Chinese J. Geophys. (in Chinese), 2005 ,48(3) : 621-628
[13] 吴建平,明跃红,张恒荣等.长白山天池火山区的震群活动研究.地球物理学报,2007,50(4) :1089-1096 Wu J P, Ming Y H, Zhang H R, et al. Earthquake swarm activity in Changbaishan Tianchi volcano. Chinese J. Geophys. (in Chinese) ,2007,50(4) :1089-1096
[14] 张先康,张成科,赵金仁等.长白山天池火山岩浆系统的深地震测深研究.地震学报,2002,24(2) :135-143 Zhang X K, Zhang C K, Zhao J R, et al. Deep seismic sounding investigation into the deep structure of the magma system in Changbaishan-Tianchi volcano region. Acta SeismoLogica Simca ,2002,15(2) :143-151
[15] 赵金仁,张先康,杨卓欣等.长白山天池火山区上地壳三维速度层析成像.地球物理学报,2003,46(6) :796-802 Zhao J R , Zhang X K, Yang Z X, et al . 3D tomography of velocity structure in upper crust beneath the Changbaishan Tianchi volcanic region. Chinese J . Geophys. (in Chinese), 2003,46(6) :796-802
[16] 刘志,张先康,王夫运等.用地震走时反演计算长白山天池火山区二维地壳泊松比.地震学报,2005,27(3) :324-331 Liu Z, Zhang X K, Wang F Y, et al. 2-D crustal Poisson's ratio from seismic travel time inversion in Changbaishan Tianchi volcanic region. Acta Seismologica Sinica ( in Chinese) ,2005,27(3) :324-331
[17] 汤吉,邓前辉,赵国泽等.长白山天池火山区电性结构和岩浆系统.地震地质,2001,23(2) :191-200 Tang J,Deng Q H,Zhao G Z,et al. Electric conductivity and magma chamber at the Tianchi volcano area in Changbaishan Mountain. Seismology and Geology (in Chinese), 2001,23(2) :191-200
[18] 张元生,周民都,荣代潞等.祁连山中东段地区三维速度结构研究.地震学报,2004,26(3) :247-255 Zhang Y S, Zhou M D, Rong D L, et al. 3-D Velocity structure in the central eastern part of Qilian shan. Acta Seismologica Sinica (in Chinese) ,2004,26(3) :247-255
[19] 高尔根,徐国明,蒋先艺等.三维结构下逐段迭代射线追踪方法.石油地球物理勘探,2002,37(1) :11-16 Gao E G, Xu G M, Jiang X Y, et al. Iterative ray-tracing method segment by segment under 3D construction. OGP, 2002,37(l):11-16
[20] 杨卓欣,张先康,赵金仁等.长白山天池火山区三维地壳结构层析成像.地球物理学报,2005,48(1) :107-115 Yang Z X,Zhang X K,Zhao J R, et al. Tomographic imaging of 3-D crustal structure beneath Changbaishan-Tianchi Volcano region. Chinese J. Geophys. (in Chinese),2005,48(1) :107-115
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