浅层地震资料解释陷阱(英文)
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摘要
高分辨率浅层地震方法是在近地表调查中使用最为广泛的方法。然而,在许多情况下,地震资料的解释经常会出现错误。在本文中,我们介绍了三个例子,分析了造成P波,SH波,多道的面波(MASW)地震资料解释的错误原因,大都是由于在表面或地下条件约束不确当引起的。第一个例子是P波反射剖面上的一个波的特征被解释为浅层断裂带,但后来证实它是由高水平的背景噪音引起的,因为采集测线通过了一个公路交叉口。第二个例子是SH波反射地震剖面上一个波特征被解释为是逆倾向滑断层,但有针对性的钻探表明,它是一个侵入到基岩面的一个深层局部侵蚀。最后,第三个例子,MASW调查剖面上,一个陡倾特征一开始被解释为基岩谷。然而,后来的钻探表明这是一个非常软的湖泊沉积物,后者严重损坏了应用面波频段。虽然最初的解释是不正确的,但这刺激地球物理学家和地质学家之间的讨论,并强调地球物理数据采集的时候,采集之前以及采集之后需要科学家之间有意义的合作与讨论。
High-resolution shallow seismic methods are the most widely used geophysical methods in near surface characterization. However, in many cases interpreting the seismic images can be misleading. In this article, we present three case studies where results from P-wave seismic re? ection, SH-wave seismic re? ection, and multi-channel analysis of surface wave (MASW) surveys were incorrectly interpreted because of inadequate constraints on either the surveyed sites surface or subsurface conditions. A P-wave reflection survey feature was first interpreted as a shallow fault zone but it was later determined to result from a high level of background noise as the acquisition passed through a road intersection. A SH-wave seismic re? ection survey feature was interpreted to be a reverse dip-slip fault but targeted drilling showed it was deep local erosion into the bedrock surface. Finally, in an MASW survey, a steeply dipping feature was first interpreted as a bedrock valley. However, later exploratory drilling showed the feature to be a shallow layer of very soft lake sediment that severely damped most of the applied surface wave frequency band. Although initial interpretations were incorrect, they stimulated discussions among geophysicists and geologists and underscored the need for meaningful cooperation and discourse between the scientists before, during, and after geophysical data acquisition.
High-resolution shallow seismic methods are the most widely used geophysical methods in near surface characterization. However, in many cases interpreting the seismic images can be misleading. In this article, we present three case studies where results from P-wave seismic re? ection, SH-wave seismic re? ection, and multi-channel analysis of surface wave (MASW) surveys were incorrectly interpreted because of inadequate constraints on either the surveyed sites surface or subsurface conditions. A P-wave reflection survey feature was first interpreted as a shallow fault zone but it was later determined to result from a high level of background noise as the acquisition passed through a road intersection. A SH-wave seismic re? ection survey feature was interpreted to be a reverse dip-slip fault but targeted drilling showed it was deep local erosion into the bedrock surface. Finally, in an MASW survey, a steeply dipping feature was first interpreted as a bedrock valley. However, later exploratory drilling showed the feature to be a shallow layer of very soft lake sediment that severely damped most of the applied surface wave frequency band. Although initial interpretations were incorrect, they stimulated discussions among geophysicists and geologists and underscored the need for meaningful cooperation and discourse between the scientists before, during, and after geophysical data acquisition.
引文
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Pugin, A., Larson, T., and Phillips, A., 2002, Shallow high-resolution shear-wave seismic reflection acquisition using a land-streamer in the Mississippi River ? oodplain: Potential for engineering and hydrogeologic applications: SAGEEP 2002, Las Vegas, Nevada, CD-ROM edition, 7 p.
Sheriff, R. E., and Geldart, L. P., 1995, Exploration seismology: Cambridge University Press, Cambridge.
U.S. Department of Agriculture, Soil Conservation Service, 1978, Soil survey of Kendall County, Illinois: Washington, D. C., 77 p.
Xia, J., Miller, R. D., and Park, C. B., 1999, Estimation of near-surface shear-wave velocity by inversion of Rayleigh waves: Geophysics, 64 (3), 691-700.
Zimmer, M. A., 2003, Seismic velocities in unconsolidated sands: Measurements of pressure, sorting and compaction effects: PhD Dissertation, Stanford University, 204 p.
Curry, B. B. (Ed.), 2008, The glacial history andpaleoenvironments of northeastern Illinois: Illinois State Geological Survey, Open File Series 2008 – 1, 175 p.
Hansel, A. K., and McKay, E. D. III, 2010, Quaternary period: in Kolata, D. R., and Nimz, C. K., Eds., Geology of Illinois, Illinois State Geological Survey, 216 – 247.
Larson, D. R., Herzog, B. L., and Larson, T. H., 2003, Groundwater geology of Dewitt, Piatt, and northern Macon Counties, Illinois: Illinois State Geological Survey, Environmental Geology Report 155, 35 pages.
Nelson, W. J., 2005, Bedrock geology of Freeburg Quad?rangle, St. Clair County: Illinois State Geological Survey, Illinois Preliminary Geologic Map, IPGM Freeburg-BR, 2 sheets, 1:24,000.
Park, C. B., Ivanov, J., Miller, R. D., Xia, J., and Ryden, N., 2001, Seismic investigation of pavements by MASW method-geophone approach: SAGEEP 2001, Denver, Colorado, RBA – 6.
Phillips, A. C., 2005, Surficial geology of Freeburg Quad?rangle, St. Clair County: Illinois State Geological Survey, STATEMAP deliverable, 2 sheets, 1:24,000.
Pugin, A. J., Larson, T. H., Sargent, S. L., McBride, J. H., and Bexf ield, C. E. 2004, Near-surface mapping using SH-wave and P-wave seismic land-streamer data acquisition in Illinois: The Leading Edge, 23(7), 677 – 682.
Pugin, A., Larson, T., and Phillips, A., 2002, Shallow high-resolution shear-wave seismic reflection acquisition using a land-streamer in the Mississippi River ? oodplain: Potential for engineering and hydrogeologic applications: SAGEEP 2002, Las Vegas, Nevada, CD-ROM edition, 7 p.
Sheriff, R. E., and Geldart, L. P., 1995, Exploration seismology: Cambridge University Press, Cambridge.
U.S. Department of Agriculture, Soil Conservation Service, 1978, Soil survey of Kendall County, Illinois: Washington, D. C., 77 p.
Xia, J., Miller, R. D., and Park, C. B., 1999, Estimation of near-surface shear-wave velocity by inversion of Rayleigh waves: Geophysics, 64 (3), 691-700.
Zimmer, M. A., 2003, Seismic velocities in unconsolidated sands: Measurements of pressure, sorting and compaction effects: PhD Dissertation, Stanford University, 204 p.
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