多震相层析成像与在介质中的多波型射线跟踪
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摘要
本文介绍了多震相的层析成像的思路和算法，通过穿透和反射走时可以同时作出２维和３维慢度（速度的倒数）重建。我们分析了在穿透和反射数据中确定速度和深度的不确定性，并认识到深度扰动对反射走时异常比慢度扰动更敏感。由不同波类型所提供的对速度和深度的约束，这个算法实际上减少了在一般反射层析成像在速度和深度之间的不确定性，并且也避免了在穿透层析成像中的不确定问题。线性化反演是通过从反射界面深度由分离速度参数迭代进行的。使用一个快速的２－Ｄ和３－Ｄ射线跟踪算法来计算穿透和反射走时和对幔度及反射界面深度的偏导数。深度和速度都用立方Ｂ样条函数来进行参数化。合成例子表明，当同时考虑穿透和反射时间，层析成像的结果得到改进。这个方法也应用到英国煤炭测量局（ＢｒｉｔｉｓｈＣｏａｌＭｅａｓｕｒｅｓ）沿跨线排列所记录的逆ＶＳＰ数据组。通过使用波形配合技术，用同时确定时间延迟和叠加权，可以自动拾取旅行时间。所观察到的逆ＶＳＰ层析成像可比周围介质具有较低速度的两个断层区域成像。断层的位置由附近的反射测线所确定。本文还讨论了在复杂２－Ｄ和３－Ｄ非均匀各向同性介质中地震射线跟踪方法。界面的几何形状和水平速度场都通过使用非均匀步长立方Ｂ－样条节点?
A multi phase tomographic algorithm and idea is presented which allows 2 D and 3 D slowness(inverse of velocity) and variable reflector depth to be reconstructed simultaneously from both transmission and reflection travel times,analyze the ambiguity in the determination of velocity and depth in transmission and reflection data and realize that depth perturbation is more sensitive to reflection traveltime anomalies than slowness perturbation,whereas the reverse is true of transmission traveltime anomalies. Because of the constraints on velocity and depth provided by the different wave types,this algorithm substantially reduces the ambiguity between velocity and depth prevalent in reflection tomography, and also avoids the undetermined problem in transmission tomography. The linearized inversion was undertaken by de coupling velocity parameters from reflector depths. A rapid 2 D and 3 D ray tracing algorithm is used to compute transmission and reflection traveltimes and partial derivatives with respect to slowness and reflector depth. Both depth and velocity are parameterized in terms of cubic B spline functions.The method has been applied to a reverse VSP dataset recorded on the British Coal Measures along a crossed linear array. Treveltimes were picked automatically by the simultaneous determination of time delays and stacking weights using a waveform matching technique. The tomographic inversion of the observed reverse VSP images two fault zones of lower velocity than the sur rounding media. The location of the faults was comfirmed by near by reflection lines. The detailed imaging process will be described in another paper.
A multi phase tomographic algorithm and idea is presented which allows 2 D and 3 D slowness(inverse of velocity) and variable reflector depth to be reconstructed simultaneously from both transmission and reflection travel times,analyze the ambiguity in the determination of velocity and depth in transmission and reflection data and realize that depth perturbation is more sensitive to reflection traveltime anomalies than slowness perturbation,whereas the reverse is true of transmission traveltime anomalies. Because of the constraints on velocity and depth provided by the different wave types,this algorithm substantially reduces the ambiguity between velocity and depth prevalent in reflection tomography, and also avoids the undetermined problem in transmission tomography. The linearized inversion was undertaken by de coupling velocity parameters from reflector depths. A rapid 2 D and 3 D ray tracing algorithm is used to compute transmission and reflection traveltimes and partial derivatives with respect to slowness and reflector depth. Both depth and velocity are parameterized in terms of cubic B spline functions.The method has been applied to a reverse VSP dataset recorded on the British Coal Measures along a crossed linear array. Treveltimes were picked automatically by the simultaneous determination of time delays and stacking weights using a waveform matching technique. The tomographic inversion of the observed reverse VSP images two fault zones of lower velocity than the sur rounding media. The location of the faults was comfirmed by near by reflection lines. The detailed imaging process will be described in another paper.
引文
1deBoor，C．，1962，Bicubicspineinterpolation：J．Math．andPhys．，41，212～218．2Cerveny，V．andPsencik，I．，1979，Rayamplitudesofseismicbodywavesinlateralyinhomogeneousmedia；Geophys．J．R．astr．Soc．，57，97～106．3Chiu，S．K．，andKanasewich，E．R．andPhadka，S．，1986，Three－dimensionaldeterminationofstructureandvelocitybyseismictomography．Geophysics，51，1559～1571．4Farra，V．，Virieux，J．andmadariaga，R．，1989，Rayperturbatontheoryforinterfaces：Geophys．J．Int．，9，377～390．5Julian，B．R．，andGubbins，D．，1977，Three－dimensionalseismicraytracing：J．Geophys．．，4395～113．6Koch，M．，1994，Simultaneousinversionfor3－Dcrustalstructureandhypocentresincludingdirect，refractedandfeflectedphassesGeophys．J．Int．，112，385～412．7Langan，R．T．，Lerche，I．m，andCutler，R．T．，1985，Tracingofraysthrougthheterogeneousme－dia：Anaccurateandeficientprocedure；Geohysics，50，1456～1465．8Lines，L．R．，andTreitel，S．，1984，Tutorial：Areviewofleast－squaresinversionaditsapplicationtogeophysicalproblems：Geophys．Prosp．，32，159～186．9Mao，W．J．，andStart，G．W．，1995，Transmissionreflectiontomography：applicationtoareverseVSPdata，submittedtoGeophysics．10Snieder，R．andSpencer，C．，1993，Aunifiedapproachtoraybending，rayperturbation，paraxialraytheories：Geophys．J．Int．，115，456～470．11Thurber，C．H．，1993，Localearthquaketomography：velocitiesandVp．Vstheory，inIyer，H．M．andHirahara，K．Ed．，SeismicTomography：TheoryandPractice：ChapmanandHal，563～583．12Um，J．andThurber，C．H．，1987，Afastalgorithmfortwo－pointseismicraytracing：Bul．Seism．Soc．Am．，77，972～986．13Vidale，J．M．，1988，Finite－diferencecalculationoftraveltimes：Bul．Seism．Soc．Am．，78，2062～2076．14Virieux，J．，1991，AfastandaccurateraytracingbyHamiltionianperturbation：J．Geophys．Res．，96，579～594．
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