Effects of an anisotropic overburden on azimuthal amplitude analysis in horizontal transverse isotropic media     

Sonja Maultzsch  Steve Horne  Stewart Archer  Hans Burkhardt 《Geophysical Prospecting》2003,51(1):61-74

Azimuthal amplitude variation in fractured media, commonly used to characterize fracture systems, is a function not only of reflection at the target but also of transmission through the overburden. This study investigates the sensitivity of amplitudes to various anisotropic overburden effects in horizontal transverse isotropic (HTI) media. Issues considered here are geometric spreading, transmission coefficients and attenuation due to fluid flow. Their influence on the azimuthal amplitude variation is evaluated quantitatively over a wide model space.
Only the variation of transmission coefficients with azimuth proves to be negligible. Geometric spreading alters the amplitude signature significantly over a relatively narrow range of models, and its influence increases with layer thickness. The most severe effect of an anisotropic fractured overburden is attenuation due to fluid flow between the cracks or the cracks and pores in the surrounding matrix. The relative changes in amplitudes between the symmetry directions due to anisotropic absorption are of the same order of magnitude as the changes in the reflection coefficient. The effect is significant over a very wide range of petrophysical parameters. Thus it leads to considerable problems in the amplitude analysis for almost any case of an overburden that contains cracks and pores. A correct amplitude analysis at the target will not be possible unless the effect of attenuation is removed.  相似文献   

Fracture characterization from walkaround VSPs   总被引：1，自引：0，他引：1  

Steve Horne 《Geophysical Prospecting》2003,51(6):493-499

A walkaround VSP is a novel acquisition geometry comprising multiple sources azimuthally distributed around a fixed multi-component receiver at approximately the same offset. Such a configuration allows the robust measurement of fracture-induced anisotropy by the analysis of certain seismic attributes with respect to azimuth.  相似文献   

H. I. Griffiths, B. Krystufek and J. M. Reed (eds), Balkan Biodiversity: Pattern and Process in the European Hotspot     

David J. Horne 《Journal of Paleolimnology》2007,38(4):609-611

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Inversion of Time-Lapse Electric Potential Data to Estimate Fracture Connectivity in Geothermal Reservoirs     

Lilja Magnusdottir  Roland N. Horne 《Mathematical Geosciences》2015,47(1):85-104

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Effects of energy and pitch angle mixed diffusion on radiation belt electrons     

Qiuhua Zheng  Mei-Ching Fok  Jay Albert  Richard B. Horne  Nigel P. Meredith 《Journal of Atmospheric and Solar》2011,73(7-8):785-795

Understanding the dynamics of the Earth’s radiation belts is important for modeling and forecasting the intensities of energetic electrons in space. Wave diffusion processes are known to be responsible for loss and acceleration of electrons in the radiation belts. Several recent studies indicate pitch angle and energy mixed-diffusion are also important when considering the total diffusive effects. In this study, a two-dimensional Fokker Planck equation is solved numerically using the Alternating Direction Implicit method. Mixed diffusion due to whistler-mode chorus waves tends to slow down the total diffusion in the energy-pitch angle space, particularly at smaller equatorial pitch angles. We then incorporate the electron energy and pitch angle mixed diffusions due to whistler-model chorus waves into the 4-dimensional Radiation Belt Environment (RBE) model and study the effect of mixed diffusion during a storm in October 2002. The 4-D simulation results show that energy and pitch angle mixed diffusion decrease the electron fluxes in the outer belt while electron fluxes in the slot region are enhanced (up to a factor of 2) during storm time.  相似文献   

An oxygen isotope study of two contrasting orogenic vein gold systems in the Meguma Terrane, Nova Scotia, Canada, with implications for fluid sources and genetic models     

Daniel J. Kontak  Richard J. Horne  Kurt Kyser 《Mineralium Deposita》2011,46(3):289-304

Sampling of quartz vein material from two gold deposits of similar geological setting but different ages (The Ovens, 408?Ma; Dufferin, 380?Ma) in the Meguma Terrane of Nova Scotia has been done to compare and contrast their ??¹⁸O_quartz signatures. Despite different ages of formation, quartz from all vein types in each of the deposits (i.e. saddle-reef, bedding-concordant leg reefs, en echelon, discordant) shows limited intra-deposit variation with similar average ??¹⁸O values of +15.2?±?0.9?? (n?=?16) for The Ovens and +15.7?±?0.6?? (n?=?12) for Dufferin. Using an average ??¹⁸O value of +15.4?? for the two deposits, the corresponding ??¹⁸O_H2O values, calculated for 400°C and 350°C based on constraints from mineral assemblages and fluid inclusion studies, indicate averages of 11.4?±?0.2?? and +10.2?±?0.2??, respectively. The isotopic data indicate that: (1) the vein-forming fluids have a metamorphic signature, (2) all vein types in the two deposits represent formation from a single, isotopically homogeneous fluid, and (3) a fluid of similar isotopic signature was generated by two contrasting tectono-thermal events in the Meguma Terrane that were separated by 30?Ma. Integration of these results with previously published data for 14 Meguma gold deposits indicate a general stratigaphic dependence in ??¹⁸O_H2O values for deposits when arranged in their relative stratigraphic position such that ??¹⁸O_H2O values increase upwards in the stratigraphy. This apparent trend cannot be explained by models involving either fluid mixing or cooling of the vein-forming fluids, but instead is modelled using fluid/rock interaction taking into account a change in the modal mineralogy of the metasedimentary rocks upwards in the stratigraphy.  相似文献   

THE USE OF PHOTOGRAMMETRY AND REMOTE SENSING FOR FORESTRY IN GREAT BRITAIN     

K.P. Thallon  A. I. D. Horne 《The Photogrammetric Record》1984,11(64):359-370

The Forestry Commission needs information on the woodland cover of the country, both as general assessment of all ownerships for woodland census purposes and as detailed crop data on its own forest estate for management purposes. These survey requirements are outlined and the methods used for data collection are described, particular attention being given to the role of aerial survey. The development of a digital mapping system is also covered. Finally, the potential role of other remote sensing techniques and the trials currently in progress are discussed.  相似文献   

Coralline Crag Ostracoda     

J. Athersuch  D.J. Horne  J.E. Whittaker 《Proceedings of the Geologists' Association. Geologists' Association》1982,93(3):313-314

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Introduction to Special Issue on high speed solar wind streams and geospace interactions (HSS–GI)     

M.H. Denton  J.E. Borovsky  R.B. Horne  R.L. McPherron  S.K. Morley  B.T. Tsurutani 《Journal of Atmospheric and Solar》2009,71(10-11):1011-1013

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The WASP project in the era of robotic telescope networks     

D. J. Christian  D. L. Pollacco  I. Skillen  J. Irwin  W. I. Clarkson  A. Collier Cameron  N. Evans  A. Fitzsimmons  C. A. Haswell  C. Hellier  S. T. Hodgkin  K. Horne  S. R. Kane  F. P. Keenan  T. A. Lister  A. J. Norton  J. Osborne  R. Ryans  R. A. Street  R. G. West  P. J. Wheatley 《Astronomische Nachrichten》2006,327(8):800-802

We present the current status of the WASP project, a pair of wide angle photometric telescopes, individually called Super‐WASP. SuperWASP‐I is located in La Palma, and SuperWASP‐II at Sutherland in South Africa. SW‐I began operations in April 2004. SW‐II is expected to be operational in early 2006. Each SuperWASP instrument consists of up to 8 individual cameras using ultra‐wide field lenses backed by high‐quality passively cooled CCDs. Each camera covers 7.8 × 7.8 sq degrees of sky, for nearly 500 sq degrees of total sky coverage. One of the current aims of the WASP project is the search for extra‐solar planet transits with a focus on brighter stars in the magnitude range ∼8 to 13. Additionally, WASP will search for optical transients, track Near‐Earth Objects, and study many types of variable stars and extragalactic objects. The collaboration has developed a custom‐built reduction pipeline that achieves better than 1 percent photometric precision. We discuss future goals, which include: nightly on‐mountain reductions that could be used to automatically drive alerts via a small robotic telescope network, and possible roles of the WASP telescopes as providers in such a network. Additional technical details of the telescopes, data reduction, and consortium members and institutions can be found on the web site at: http://www.superwasp.org/. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献