自相似型各向异性自组织介质中地震波场动力学响应
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摘要
地下岩石结构/构造和矿物组成在小尺度上存在的不均匀性和各向异性会导致地震波速度的分形分布,进而衍生出自组织介质模型.本文针对地球内部岩浆垂向侵入及横向溢流为特征的岩浆作用,开展自相似型各向异性自组织介质的地震波动力学响应研究.基于二维自组织介质模型和声波方程,本文利用有限差分法模拟了不同强度岩浆侵入和溢流作用形成的自组织介质中地震波场,并进行了波场特征分析.研究结果表明:(1)在横向溢流作用为主的自组织介质中,横向相关长度小于地震波波长的条件下,聚焦效应随着横向相关长度的增大而增强,地震波能量随之增强;反之,在横向相关长度大于地震波波长的条件下,散射效应随横向相关长度的增大而增强,地震波能量随之减弱.(2)在垂向侵入作用为主的自组织介质中,随着垂向相关长度增大,散射效应增强,地震波的能量也随之迅速减弱.(3)岩浆作用的自组织强度增强,地震波的能量增大,而中心频率无变化.(4)自组织介质具有相同的小尺度扰动,其速度梯度背景越小,地震波能量在炮点附近越集中.(5)当多层自组织介质共存,特征层位的波场特征仍以各自的自组织特性为主,因此利用实际资料中不同层位的地震反射特征可推测地下介质的自组织性质.
The multi-scale variation in composition and anisotropy in rocks and minerals may cause corresponding fractal variations of seismic velocity hence lead to self-organized models.Based on 2-D self-organized models with three layers and the acoustic finite difference method,we investigate the seismic sounding in the anisotropic self-similar medium to explain the volcano vertical or transverse intrusion in the earth.We find some interesting phenomena.In the horizontal intrusion medium,the diffraction and refraction of waves at randomly distributed inhomogeneities results in a random focusing and defocusing of wave energy and consequently results in an increase of the amplitude fluctuation with increasing propagation distances.When the lateral correlation length increases within the wavelength,focusing of energy will be enhanced.While it continues to increase beyond the wavelength,defocusing will play a main role and wave energy decreases greatly.In the self-similar media dominated by vertical intrusion,diffraction of seismic waves becomes noticeable.Moreover,the random amplitudes fortify the reflection energy and the large-scale velocity backgrounds influence the assembling of waves.We also investigated two-layer random medium like the crust,the result shows that seismic recordings from different layers carry selforganized characteristics of corresponding layer.Therefore,we can detect the characteristics of the earth in the field data.
The multi-scale variation in composition and anisotropy in rocks and minerals may cause corresponding fractal variations of seismic velocity hence lead to self-organized models.Based on 2-D self-organized models with three layers and the acoustic finite difference method,we investigate the seismic sounding in the anisotropic self-similar medium to explain the volcano vertical or transverse intrusion in the earth.We find some interesting phenomena.In the horizontal intrusion medium,the diffraction and refraction of waves at randomly distributed inhomogeneities results in a random focusing and defocusing of wave energy and consequently results in an increase of the amplitude fluctuation with increasing propagation distances.When the lateral correlation length increases within the wavelength,focusing of energy will be enhanced.While it continues to increase beyond the wavelength,defocusing will play a main role and wave energy decreases greatly.In the self-similar media dominated by vertical intrusion,diffraction of seismic waves becomes noticeable.Moreover,the random amplitudes fortify the reflection energy and the large-scale velocity backgrounds influence the assembling of waves.We also investigated two-layer random medium like the crust,the result shows that seismic recordings from different layers carry selforganized characteristics of corresponding layer.Therefore,we can detect the characteristics of the earth in the field data.
引文
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[15]Tittgemeyer M,Wnzel F,Ryberg T,et al.Scales of heterogeneitiesin the continental crust and upper mantle.Pure Appl.Geophys.,1999,156(1):29-52
[16]Nielsen L,Thybo H,Morozov I B,et al.Teleseismic Pn arrivals:influence of mantle velocity gradient and crustal scattering.Geophys.J.Int.,2003,152(2):F1-F7
[17]Jannaud L R,Adler P M,Jacquin C G.Spectral analysis andinversion of codas.J.Geophys.Res.,1991,96(B11):18215-18231
[18]Frankel A,Clayton R W.Finite difference simulations of seismicscattering:implications for the propagation of short-period seismicwaves in the crust and models of crustal heterogeneity.J.Geophys.Res.,1986,91(B6):6465-6489
[19]Xu T,Xu G,Gao E,et al.Block modeling and segmentally iterativeray tracing in complex 3-D media.Geophysics,2006,71(3):T41-T51,doi:10.1190/1.2192948
[20]Ikelle L T,Yung S K,Daube F.2-D random media with ellipsoidalautocorrelation functions.Geophysics,1993,58(9):1359-1372
[21]Klimes L.Correlation functions of random media.Pure Appl.Geophys.,2002,159(8):1811-1831
[22]Iooss B.Seismic reflection traveltimes in two-demensional statisticallyanisotropic random media.Geophys.J.Int.,1998,135(3):999-1010
[23]Ojo S B,Mereu R F.The effect of random velocity function on thetravel times and amplitudes of seismic waves.J.Geophys.Res.Astr.Soc.,1986,84:607-618
[24]Wu R S.Attenuation of short period seismic waves due to scattering.Geophys.Res.Lett.,1982,9(1):9-12
[25]Kneib G,Kerner C.Accurate and efficient seismic modeling inrandom media.Geophysics,1993,58(4):576-588
[26]Clayton J F,Enquist B.Absorbing boundary conditions for acousticand elastic wave equations.Bull.Seism.Soc.Am.,1977,67:1529-1540
[27]Yang D H,Wang S Q,Zhang Z J,et al.N-times absorbingboundary conditions for compact finite difference modeling of acousticand elastic propagation in the 2D TI medium.Bull.Seism.Soc.Am.,2003,93:2389-2401
[28]Muller T M,Shapiro S A.Amplitude fluctuations due to diffractionand refraction in anisotropic random media:implications for seismicscattering attenuation estimates.Geophys.J.Int.,2003(1),155:139-148
[29]Morozov I B,Smithson S B,Morozova E A,et al.A database ofdeep seismic sounding peaceful nuclear explosion recordings forseismic monitoring of northern Eurasia.23rdSeismic Research Review:Worldwide Monitoring ofNuclear Explosions,2001,2-5:570-579
[30]Ross A R,Brown L D,Pananont P,et al.Deep reflection surveyingin central Tibet:lower-crustal layering and crustal flow.Geophys.J.Int.,2004,156(1):115-128
[31]Zhang Z J,He Q D,Teng J W,et al.Simulation of 3-componentseismic records in a 2-dimensional transversely isotropic media withfinite-difference.Can.J.Expl.Geophys.,1993,29:51-58
[32]Levander A R,Gibson B S.Wide-angle seismic reflections from two-dimensional random target zones.J.Geophys.Res.,1991,96(B6):10251-10260
[33]Zhang Z J,Wang G J,Harris J M.Multi-component wavefieldsimulation in viscous extensively dilatancy anisotropic media.Phys.Earth Planet Inter.,1999,114(1):25-38
[34]杨顶辉.双相各向异性介质中弹性波方程的有限元解法及波场模拟.地球物理学报,2002,45(4):575-583Yang D H.Finite element method of the elastic wave equation andwavefield simulation in two-phase anisotropic media.Chinese J.Geophys.(in Chinese),2002,45(4):575-583
[35]张智,赵兵,张晰等.云南思茅-中甸地震剖面的地壳结构.地球物理学报,2006,49(5):1377-1384Zhang Z,Zhao B,Zhang X,et al.Crustal structure beneath thewide-angle seismic profile between Simao and Zhongdian in Yunnan.Chinese J.Geophys.(in Chinese),2006,49(5):1377-1384
[36]Levander A R,Holliger K.Small-scale heterogeneity and large-scalevelocity structure of the continental crust.J.Geophys.Res.,1992,97(B6):8797-8840
[2]Zhao W,Nelson K D.The Project INDEPTH Team.Deep seismicreflection evidence for continental underthrusting beneath south Tibet.Nature,1993,366:557-559
[3]滕吉文.柴达木盆地的深层地震反射波和地壳构造.地球物理学报,1974,17(2):121-134Teng J W.Deep reflected waves and the structure of the earth crust ofthe eastern part of Qaidam Basin.Chinese J.Geophys.(inChinese),1974,17(2):121-134
[4]Yang B J,Tang J R,Li Q X,et al.Crustal reflection structure inthe uplifting zone of Songliao basin and disconnecting Moho interface.Science in China(Series D),2004,47(6):514-521
[5]Zhang Z J,Teng J W,Li Y K,et al.Crustal structure of seismicvelocity in southern Tibet and east-westward escape of the crustalmaterial.Science in China(Series D),2004,47(6):500-506
[6]高锐,成湘洲,丁谦.格尔木-额济纳旗地学断面地球动力学模型初探.地球物理学报,1995,38(增):3-14Gao R,Cheng X Z,Ding Q.Preliminary geodynamic model ofGolmud-Ejin Qi geoscience transect.Chinese J.Geophys.(inChinese),1995,38(Suppl.):3-14
[7]王椿镛,韩渭宾,吴建平等.松潘-甘孜造山带地壳速度结构.地震学报,2003,25(3):229-241Wang C Y,Han W B,Wu J P,et al.Crust structure beneath theSongpan-Garze orogenic belt.Acta Seismologica Sinica(in Chinese),2003,25(3):229-241
[8]高恩源.喜马拉雅山北麓-雅鲁藏布江地区人工爆炸地震测深地壳结构.见:西藏地球物理文集.北京:地质出版社,1990.1-14Gao E Y.Crustal structure in northern Himalaya-Yarlung Zangbu byartificial deep seismic explosion.In:Tibet Geophysical Corpus(inChinese).Beijing:Geological Publishing House,1990.1-14
[9]国家地震局科技监测司编.中国大陆深部构造的研究与进展.北京:地震出版社,1988China Earthquake Administration.Research and Progress of DeepStructure in China(in Chinese).Beijing:Seismological Press,1988
[10]陈运泰,滕吉文,张中杰.地球物理学的回顾与展望.地球科学进展,2001,16(5):634-642Chen Y T,Teng J W,Zhang Z J.Geophysics:The 20thcentury inretrospect and the 21stcentury in prospect.Advance in Earth Sciences(in Chinese),2001,16(5):634-642
[11]Zhang Z J,Klemperer S.West-east variation in crustal thickness innorthern Lhasa block,central Tibet,from deep seismic soundingdata.J.Geophys.Res.,2005,110,doi:10.1029/2004JB003139
[12]胡家富,丛连理,苏有锦等.云南及周边地区Lg尾波Q值的分布特征.地球物理学报,2003,46(6):809-813Hu J F,Cong L L,Su Y J,et al.Distribution characteristics ofQvalue of the Lg coda in Yunnan and its adjacent regions.Chinese J.Geophys.(in Chinese),2003,46(6):809-813
[13]张智,刘财,邵志刚等.伪谱法在常Q粘弹介质地震波场模拟中的应用效果.地球物理学进展,2005,20(4):945-949Zhang Z,Liu C,Shao Z G,et al.The application of pseudo-spectralforward modeling of seismic wave field in constantQviscoelasticmedium.Prog.Geophys.(in Chinese),2005,20(4):945-949
[14]Crossley D J,Jensen O G.Fractal velocity models in refractionseismology.Pure Appl.Geophys.,1989,131(1):61-76
[15]Tittgemeyer M,Wnzel F,Ryberg T,et al.Scales of heterogeneitiesin the continental crust and upper mantle.Pure Appl.Geophys.,1999,156(1):29-52
[16]Nielsen L,Thybo H,Morozov I B,et al.Teleseismic Pn arrivals:influence of mantle velocity gradient and crustal scattering.Geophys.J.Int.,2003,152(2):F1-F7
[17]Jannaud L R,Adler P M,Jacquin C G.Spectral analysis andinversion of codas.J.Geophys.Res.,1991,96(B11):18215-18231
[18]Frankel A,Clayton R W.Finite difference simulations of seismicscattering:implications for the propagation of short-period seismicwaves in the crust and models of crustal heterogeneity.J.Geophys.Res.,1986,91(B6):6465-6489
[19]Xu T,Xu G,Gao E,et al.Block modeling and segmentally iterativeray tracing in complex 3-D media.Geophysics,2006,71(3):T41-T51,doi:10.1190/1.2192948
[20]Ikelle L T,Yung S K,Daube F.2-D random media with ellipsoidalautocorrelation functions.Geophysics,1993,58(9):1359-1372
[21]Klimes L.Correlation functions of random media.Pure Appl.Geophys.,2002,159(8):1811-1831
[22]Iooss B.Seismic reflection traveltimes in two-demensional statisticallyanisotropic random media.Geophys.J.Int.,1998,135(3):999-1010
[23]Ojo S B,Mereu R F.The effect of random velocity function on thetravel times and amplitudes of seismic waves.J.Geophys.Res.Astr.Soc.,1986,84:607-618
[24]Wu R S.Attenuation of short period seismic waves due to scattering.Geophys.Res.Lett.,1982,9(1):9-12
[25]Kneib G,Kerner C.Accurate and efficient seismic modeling inrandom media.Geophysics,1993,58(4):576-588
[26]Clayton J F,Enquist B.Absorbing boundary conditions for acousticand elastic wave equations.Bull.Seism.Soc.Am.,1977,67:1529-1540
[27]Yang D H,Wang S Q,Zhang Z J,et al.N-times absorbingboundary conditions for compact finite difference modeling of acousticand elastic propagation in the 2D TI medium.Bull.Seism.Soc.Am.,2003,93:2389-2401
[28]Muller T M,Shapiro S A.Amplitude fluctuations due to diffractionand refraction in anisotropic random media:implications for seismicscattering attenuation estimates.Geophys.J.Int.,2003(1),155:139-148
[29]Morozov I B,Smithson S B,Morozova E A,et al.A database ofdeep seismic sounding peaceful nuclear explosion recordings forseismic monitoring of northern Eurasia.23rdSeismic Research Review:Worldwide Monitoring ofNuclear Explosions,2001,2-5:570-579
[30]Ross A R,Brown L D,Pananont P,et al.Deep reflection surveyingin central Tibet:lower-crustal layering and crustal flow.Geophys.J.Int.,2004,156(1):115-128
[31]Zhang Z J,He Q D,Teng J W,et al.Simulation of 3-componentseismic records in a 2-dimensional transversely isotropic media withfinite-difference.Can.J.Expl.Geophys.,1993,29:51-58
[32]Levander A R,Gibson B S.Wide-angle seismic reflections from two-dimensional random target zones.J.Geophys.Res.,1991,96(B6):10251-10260
[33]Zhang Z J,Wang G J,Harris J M.Multi-component wavefieldsimulation in viscous extensively dilatancy anisotropic media.Phys.Earth Planet Inter.,1999,114(1):25-38
[34]杨顶辉.双相各向异性介质中弹性波方程的有限元解法及波场模拟.地球物理学报,2002,45(4):575-583Yang D H.Finite element method of the elastic wave equation andwavefield simulation in two-phase anisotropic media.Chinese J.Geophys.(in Chinese),2002,45(4):575-583
[35]张智,赵兵,张晰等.云南思茅-中甸地震剖面的地壳结构.地球物理学报,2006,49(5):1377-1384Zhang Z,Zhao B,Zhang X,et al.Crustal structure beneath thewide-angle seismic profile between Simao and Zhongdian in Yunnan.Chinese J.Geophys.(in Chinese),2006,49(5):1377-1384
[36]Levander A R,Holliger K.Small-scale heterogeneity and large-scalevelocity structure of the continental crust.J.Geophys.Res.,1992,97(B6):8797-8840
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