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Susceptibility assessments of shallow earthflows triggered by heavy rainfall at three catchments by logistic regression analyses 总被引：11，自引：3，他引：11
Tolga Can Hakan A. Nefeslioglu Candan Gokceoglu Harun Sonmez Tamer Y. Duman 《Geomorphology》2005,72(1-4):250-271
Sometimes regional meteorological anomalies trigger different types of mass movements. In May 1998, the western Black Sea region of Turkey experienced such a meteorological anomaly. Numerous residential and agricultural areas and engineering lifelines were buried under the flood waters. Besides the reactivation of many previously delineated landslides, thousands of small-scale landslides (mostly the earthflow type) occurred all over the region. The earthflows were mainly developed in flysch-type units, which have already presented high landslide concentrations. In this study, three different catchments — namely Agustu, Egerci, and Kelemen — were selected because they have the most landslide-prone geological units of the region. The purposes of the present study are to put forward the spatial distributions of the shallow earthflows triggered, to describe the possible factors conditioning the earthflows, and to produce the shallow earthflow susceptibility maps of the three catchments. The unique condition units (UCU) were employed during the production of susceptibility maps and during statistical analyses. The unique condition units numbered 4052 for the Agustu catchment, 13,241 for the Egerci catchment and 12,314 for the Kelemen catchment. The earthflow intensity is the highest in the Agustu catchment (0.038 flow/UCU) and lowest in the Egerci catchment (0.0035 flow/UCU). Logistic regression analyses were also employed. However, during the analyses, some difficulties were encountered. To overcome the difficulties, a series of sensitivity analyses were performed based on some decision rules introduced in the present study. Considering the decision rules, the proper ratios of UCU free from earthflow (0) / UCU including the earthflow (1) for the Agustu, Egerci and Kelemen catchments were obtained as 3, 6, and 5, respectively. Also, a chart for the proper ratio selection was developed. The regression equations from the selected ratios were then applied to the entire catchment and the earthflow susceptibility maps were produced. The landslide susceptibility maps revealed that 15% of the Agustu catchment, 8% of the Egerci catchment, and 7% of the Kelemen catchment have very high earthflow susceptibility; and most of the earthflows triggered by the May 1998 meteorological event were found in the very high susceptibility zones. 相似文献
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Summary. A problem in modelling electromagnetic fields used in exploration geophysics is treated mathematically. Analytical expressions are obtained for the electric field due to a harmonic current in a horizontal loop on or above a conducting ground in which is buried a conductive and permeable sphere (ore body). The loop is coaxial with the sphere. For a general time-varying current in the loop, the analysis is carried to the stage where a Fourier inversion can be used to obtain readily the electric field in the time-domain. A new relationship between spherical and cylindrical wave functions is obtained as a transformation of local elements.
Solution of this problem has not been presented before in this form. Lee's solution of 1975 which uses an integral-equation formulation treats a similar problem without taking account of differences in magnetic permeability. The effects of magnetic permeability may have important and useful implications for geophysical explorations. 相似文献
Solution of this problem has not been presented before in this form. Lee's solution of 1975 which uses an integral-equation formulation treats a similar problem without taking account of differences in magnetic permeability. The effects of magnetic permeability may have important and useful implications for geophysical explorations. 相似文献
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Jean-Claude Mareschal 《Geophysical Journal International》1981,66(3):535-552
Summary. If one can measure the anomalous horizontal magnetic field associated with a (locally bounded) two-dimensional conductivity anomaly, the transfer function which results from correlating the vertical with the anomalous horizontal magnetic field directly indicates the depth to an equivalent line-current. A. numerical model can be used to illustrate this. If three-dimensional effects (including current channelling) produce the current anomaly, interpretation in terms of conductive structure would be less clear. It has been claimed (Babour & Mosnier etc.) that such three-dimensional effects are experimentally observed in the highly coherent transfer functions determined from differential geomagnetic sounding experiments. These effects are, specifically, the 'linear polarization' of the anomalous fields, and the invariance of the phase of the measured anomalous field across the anomaly. It is suggested in this present paper that both these effects can be explained in terms of simple local induction models.
If the embedded two-dimensional anomaly is sufficiently close to the Earth's surface, the transfer function (between the vertical and the total horizontal field) contains more information than is usually interpreted. With this in mind, the magnetovariational data collected by Rooney & Hutton in the Kenyan Rift is re-examined. 相似文献
If the embedded two-dimensional anomaly is sufficiently close to the Earth's surface, the transfer function (between the vertical and the total horizontal field) contains more information than is usually interpreted. With this in mind, the magnetovariational data collected by Rooney & Hutton in the Kenyan Rift is re-examined. 相似文献
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Wilfred H. Theakstone Frank M. Jacobsen & N. Tvis Knudsen 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):767-776
The most labour-intensive and time-consuming part of many mass balance programmes is the acquisition of snow depth data. The standard technique, which involves probing the snow cover at intervals along a series of profiles, generally by an individual on skis, may involve more than 300 discrete measurements along a total of more than 20 km of profiling at a single glacier. Kinematic surveying with a global positioning system (GPS) in differential mode provides much more information about changes of glacier surface level and snow thickness between surveys. The positions of a large number of points can be fixed in a relatively short time by GPS surveying, and the technique is usable in adverse weather conditions. With real-time kinematic GPS surveying, it is possible to return to the same positions (longitude, latitude) during successive field programmes, and a previously followed route can be retraced precisely. GPS surveying facilitates the production of accurate glacier maps for mass balance programmes. Data obtained by snow depth probing and GPS surveying in 1995 at Austre Okstindbreen, the largest glacier of the Okstindan area, Norway (66°N), indicate that repeated GPS surveys are likely to provide a large amount of information on withinyear and between-year changes of surface topography and are not subject to the errors in mass balance calculations which arise from probing snow depths along selected profiles. Kinematic GPS surveying of several glaciers within an area would overcome the difficulties arising when mass balance studies are confined to a single glacier within a particular area. 相似文献
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Generation of Pseudotachylyte by Ancient Seismic Faulting 总被引：21，自引：0，他引：21
Richard H. Sibson 《Geophysical Journal International》1975,43(3):775-794
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Determination of source parameters by wavefield extrapolation 总被引：3，自引：0，他引：3
George A. McMechan 《Geophysical Journal International》1982,71(3):613-628
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