CHINESE JOURNAL OF GEOPHYSICS Vol. 50, No. 1 Jan., 2007,,..,2007,50 (1) : Liu Y X,Xu T, Zhao B,et al. Seismic sounding of anisotrop

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1 CHINESE JOURNAL OF GEOPHYSICS Vol 50 No 1 Jan (1) : Liu Y X Xu T Zhao B et al Seismic sounding of anisotropic self2similar self2organized medium Chinese J Geophys (in Chinese) (1) : Π : (1) ; (2) (3) (4) (5) (2007) P Seismic sounding of anisotropic self2similar self2organized medium LIU Yong2Xia 1 XU Tao 1 ZHAO Bing 1 LIU Chun2Cheng State Key Laboratory of Lithosphere Evolution Institute of Geology and Geophysics Chinese Academy of Sciences Beijing China 2 China National Offshore Oil Corporation Tianjin China Abstract The multi2scale variation in composition and anisotropy in rocks and minerals may cause corresponding fractal variations of seismic velocity hence lead to self2organized models Based on 2-D self2 organized models with three layers and the acoustic finite difference method we investigate the seismic sounding in the anisotropic self2similar 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 self2similar media dominated by vertical intrusion diffraction of seismic waves becomes ( ) 973 (2002CB412604) E2mail : com cn

2 222 (Chinese J Geophys ) 50 noticeable Moreover the random amplitudes fortify the reflection energy and the large2scale velocity backgrounds influence the assembling of waves We also investigated two2layer random medium like the crust the result shows that seismic recordings from different layers carry self2organized characteristics of corresponding layer Therefore we can detect the characteristics of the earth in the field data Keywords 2-D self2organized models Anisotropy Lateral intrusion Vertical intrusion [1 10 ] [17 18 ] : (1) v ( x z) = v 0 ( x z) + v ( x z) (1) v 0 ( x z) v 0 ( x z) = v 0 + v ( z - z j ) v z j j [5 8 v ( x z) Π ] (2) CMP v ( x z) = k ( x z) [ v 0 + v ( x z) ] (2) ( 1 km) k k = 1 s [2 3 ] 011 ( x z) ( ) CMP : : < ( x z) > = 0 (3) : 1 s 2 : < 2 ( x z) > = 2 (4)? :? c ( x z) = < ( x + x 1 z + z 1 ) ( x z) > = 2 ( x z) (5) ( ) ( x z) ( x z) ( x z) ( x z) [11 16 ] [19 20] [1 3 ] 212 ( ) [21 ]

3 1 : 223 [22 24 ] [25 ] Ricker 1 20 Hz 2 ( 15 Hz a b) [22 ] m 5000 m d x = d z = 10 m d t = 1 ms 315 s ; m v 1 [22 ] ( z - z 1 ) ; m v 3 = 4000 mπs Table 1 1- D and 2- D autocorrelation functions and power spectrum expression m 4000 m K 0 ( rπa) ( a k 2 ) - 1Π2 K 0 ( x 2 Πa 2 + z 2 Πb 2 ) (1 + a 2 k 2 x + b 2 k 2 z) : m mπs ; m 2500 mπs ; m 3000 mπs : (1) w ( x z) ^W ( k x k z ) ; (2) ^f ( k x k z ) ^U ( k x k z ) = ^f ( k x k z ) ^W ( k x k z ) ; (3) ^U ( k x k z ) u ( x z) ; (4) u ( x z) ; 50 m [21 ] : (1) 400 ; (2) ; (3) [25 ] 2000 mπs ; m 11 4 [26 27 ] v 2

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5 1 : 225 ( 1a ) a = 30 m b = 10 m d 1 = (b d) E ( 2) ( 3) ( A ) [28 31 ] Fig th record spectral chart of different variations [28 ] 400 ( 6) Fig th record spectral chart of different lateral relative length 413 a = 30 m d 1 = 0 2 = m 7(a c) ( 8) ( 7d) b = 10 m d 1 = 0 2 = 011 a = 30 m m b = 10 m d 1 = 0 2 = 011 ( 4) ( 9 (a c) ) [ ] ( 10 d v ( 5) ) ; ( a = 100 m) ( 9d) Muller [28 ]

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7 1 : 227

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9 1 : Fig 2 Energy residual with different variation of model 1 Fig 5 Comparison of energy residuals for model 1 with different lateral relative length Fig 8 Comparison of relative energy residual for model 1 Fig 10 Comparison of relative energy residual with different vertical relative length with changeable velocity grads Fig 12 Based on model 2 Comparison of energy residual with lateral relative length 100 m and vertical relative length 10 m in second layer ;Velocity and seismograms with lateral length 10 m and vertical length 30 m in third layer and both media in two layers

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11 1 : ( 100 m 10 m) 3 ( 10 m 30 m) ( References) 11 (a c) [ 1 ] : : ( 12) [ 3 ] (2) : ( Teng J W Deep reflected waves and the structure of the earth crust of 11d) 5 : [28 ] ; [30 ] ; ( 115 ) [34 36 ] : (1) (3) : ; (2) (3) (4) (5) Teng J W Zhang Z J Bai W M et al Lithosphere Physics ( in Chinese ) Beijing : Science Press 2003 [ 2 ] Zhao W Nelson K D The Project INDEPTH Team Deep seismic reflection evidence for continental underthrusting beneath south Tibet Nature : the eastern part of Qaidam Basin Chinese J Geophys ( in Chinese) (2) : [ 4 ] Yang B J Tang J R Li Q X et al Crustal reflection structure in the uplifting zone of Songliao basin and disconnecting Moho interface Science in China (Series D) (6) : [ 5 ] Zhang Z J Teng J W Li Y K et al Crustal structure of seismic velocity in southern Tibet and east-westward escape of the crustal material Science in China (Series D) (6) : [ 6 ] ( ) : 3 14 Gao R Cheng X Z Ding Q Preliminary geodynamic model of Golmud- Ejin Qi geoscience transect Chinese J Geophys ( in Chinese) (Suppl ) : 3 14 [ 7 ] (3) : Wang C Y Han W B Wu J P et al Crust structure beneath the Songpan- Garze orogenic belt Acta Seismologica Sinica (in Chinese) [ 8 ] - : : Gao E Y Crustal structure in northern Himalaya- Yarlung Zangbu by artificial deep seismic explosion In : Tibet Geophysical Corpus ( in Chinese) Beijing : Geological Publishing House [ 9 ] : 1988 China Earthquake Administration Research and Progress of Deep Structure in China (in Chinese) Beijing : Seismological Press 1988 [10 ] (5) : Chen Y T Teng J W Zhang Z J Geophysics : The 20 th century in

12 232 (Chinese J Geophys ) 50 retrospect and the 21 st century in prospect Advance in Earth Sciences (in Chinese) (5) : [11 ] Zhang Z J Klemperer S West-east variation in crustal thickness in northern Lhasa block central Tibet from deep seismic sounding data J Geophys Res doi : Π2004JB [12 ] Lg Q (6) : Hu J F Cong L L Su YJ et al Distribution characteristics of Q value of the Lg coda in Yunnan and its adjacent regions Chinese J Geophys (in Chinese) (6) : [13 ] Q Am : (4) : Zhang Z Liu C Shao Z G et al The application of pseudo- spectral forward modeling of seismic wave field in constant Q viscoelastic medium Prog Geophys (in Chinese) (4) : [14 ] Crossley D J Jensen O G Fractal velocity models in refraction seismology Pure Appl Geophys (1) : [15 ] Tittgemeyer M Wnzel F Ryberg T et al Scales of heterogeneities in the continental crust and upper mantle Pure Appl Geophys (1) : [16 ] Nielsen L Thybo H Morozov I B et al Teleseismic Pn arrivals : influence of mantle velocity gradient and crustal scattering Geophys J Int (2) : F1 F7 [17 ] Jannaud L R Adler P M Jacquin C G Spectral analysis and inversion of codas J Geophys Res (B11) : [18 ] Frankel A Clayton R W Finite difference simulations of seismic scattering : implications for the propagation of short-period seismic waves in the crust and models of crustal heterogeneity J Geophys Res (B6) : [19 ] Xu T Xu G Gao E et al Block modeling and segmentally iterative ray tracing in complex 3-D media Geophysics ( 3 ) : T41 T51 doi : Π [20 ] Ikelle L T Yung S K Daube F 2-D random media with ellipsoidal autocorrelation functions Geophysics (9) : [21 ] Klimes L Correlation functions of random media Pure Appl Geophys (8) : [22 ] Iooss B Seismic reflection traveltimes in two- demensional statistically anisotropic random media Geophys J Int ( 3) : [23 ] Ojo S B Mereu R F The effect of random velocity function on the travel times and amplitudes of seismic waves J Geophys Res Astr Soc : [24 ] Wu R S Attenuation of short period seismic waves due to scattering Geophys Res Lett (1) : 9 12 [25 ] Kneib G Kerner C Accurate and efficient seismic modeling in random media Geophysics (4) : [26 ] Clayton J F Enquist B Absorbing boundary conditions for acoustic and elastic wave equations Bull Seism Soc Am : [27 ] Yang D H Wang S Q Zhang Z J et al N-times absorbing boundary conditions for compact finite difference modeling of acoustic and elastic propagation in the 2D TI medium Bull Seism Soc [28 ] Muller T M Shapiro S A Amplitude fluctuations due to diffraction and refraction in anisotropic random media : implications for seismic scattering attenuation estimates Geophys J Int 2003(1) 155 : [29 ] Morozov I B Smithson S B Morozova E A et al A database of deep seismic sounding peaceful nuclear explosion recordings for seismic monitoring of northern Eurasia 23 rd Seismic Research Review : Worldwide Monitoring of Nuclear Explosions : [30 ] Ross A R Brown L D Pananont P et al Deep reflection surveying in central Tibet : lower2crustal layering and crustal flow J Int (1) : Geophys [31 ] Zhang Z J He Q D Teng J W et al Simulation of 3-component seismic records in a 2- dimensional transversely isotropic media with finite-difference Can J Expl Geophys : [32 ] Levander A R Gibson B S Wide2angle seismic reflections from two2 dimensional random target zones J Geophys Res (B6) : [33 ] Zhang Z J Wang G J Harris J M Multi2component wavefield simulation in viscous extensively dilatancy anisotropic media Earth Planet Inter (1) : Phys [34 ] (4) : Yang D H Finite element method of the elastic wave equation and wavefield simulation in two-phase anisotropic media Chinese J Geophys (in Chinese) (4) : [35 ] (5) : Zhang Z Zhao B Zhang X et al Crustal structure beneath the wide-angle seismic profile between Simao and Zhongdian in Yunnan Chinese J Geophys (in Chinese) (5) : [36 ] Levander A R Holliger K Small- scale heterogeneity and large- scale velocity structure of the continental crust J Geophys Res (B6) : ( )