{"id":21,"date":"2018-12-04T08:36:18","date_gmt":"2018-12-04T08:36:18","guid":{"rendered":"https:\/\/emttarge.com\/site\/?page_id=21"},"modified":"2023-12-30T17:58:50","modified_gmt":"2023-12-30T17:58:50","slug":"ves","status":"publish","type":"page","link":"https:\/\/emttarge.com\/site\/en\/ves\/","title":{"rendered":"VES"},"content":{"rendered":"

Method<\/strong><\/span><\/h3>\n
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Direct current resistivity method gathers data via injecting electric current\u00a0<\/span>into ground<\/span>\u00a0with two electrodes (stainless steel bars) and measuring voltage differences occurs at two different points. The distance between the current electrodes and the electrical resistivities of the geological units determine the depth of investigation. The measured data are first converted to the apparent resistivity data,<\/span><\/span>\n

\u00a0<\/p>\n

\u03c1a<\/sub>=k \u2206V\/I,<\/span><\/p>\n

here, \u03c1a is a value that\u00a0 the combination of the resistivities of all subsurface geological units . A and B electrodes where current injected, M and N are the electrodes where voltage difference measured. The AB interval defines the depth of investigation.<\/span><\/p>\n<\/td>\n

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\"DC
vertical electrical survey<\/span><\/figcaption><\/figure>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
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Field work<\/strong><\/span><\/h3>\n\n\n\n
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In the field;<\/span><\/p>\n

\u2022 The lower the potential difference occurs, the worse the signal\/noise becomes.<\/span><\/p>\n

If 1D inversion is the tool;<\/span><\/p>\n

\u2022 Selecting\u00a0 large interval for MN is a simple but dangerous approach. ,<\/span><\/p>\n

\u2022 The large MN interval in Schlumberger array makes\u00a0 easier to measure the voltage difference but the measured value deviates from what it should be!<\/span><\/p>\n

suggested ratio MN < ~AB\/10<\/span><\/p>\n

in the field condition, one must comply with this ratio , at least for first few measurement then the ratio can be changed as much as required.<\/span><\/p>\n<\/div>\n

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The measurements made with large MN\u00a0 do not cause problems in 2D or 3D inversion since the MN is also utilised in codes.<\/span><\/p>\n

The survey data with different MN\u00a0 is shifted to the first MN curve prior to the modeling steps. In other words, all curve segments are shifted to overlap with the curve obtained for the first MN (blue).<\/span><\/p>\n<\/div>\n<\/td>\n

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\"Raw
Segmented curves due to MN variation<\/span><\/figcaption><\/figure>\n

\u00a0<\/p>\n

\u00a0<\/p>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

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Survey<\/strong><\/span><\/h3>\n\n\n\n
A minimum of 3 measurements are recommended for each survey. Overlapping measurements along the profile always provide control over each other.<\/span><\/td>\n\n
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\"VES
Overlapping schlumberger arrays along the profile<\/span><\/figcaption><\/figure>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
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Orientation<\/strong><\/span><\/h3>\n\n\n\n\n
\u00a0The AB expansion is directly related to the approach to be used in the data processing. If one is going to do 1D modeling, survey lines should be taken parallel to possible discontinuity (fracture, contact etc.). “Jumps” in curves is prevented . The F-distance is important,\u00a0 a fictitious\u00a0 layer at depth F should be expected\u00a0in the 1D layered model.<\/span><\/td>\n\n
\"1D
Survey line parallel to fault zone<\/span><\/figcaption><\/figure>\n<\/td>\n<\/tr>\n
If one is going to do 2D modeling, the lines should be taken perpendicular to the potential discontinuity (fracture, contact etc.). “Jumps” on the curve should be left as is.<\/span><\/td>\n\n
\"survey
VES data set for 2D inversion<\/span><\/figcaption><\/figure>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n
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Depth of investigation<\/strong><\/span><\/h3>\n\n\n\n
For the\u00a0 survey design;\u00a0 max(AB \/ 2) should be selected\u00a0 3 (three) times or more of the targeted depth of investigation.\u00a0 The figures show the relation between max(AB\/2) and basement depth.\u00a0 The resistivity of the basement can only be determined accurately with measurements larger than max(AB \/ 2) ~ 300m<\/span><\/td>\n\n
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\"depth
Depth of investigation and max(AB\/2)<\/span><\/figcaption><\/figure>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
\u00a0<\/div>\n
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1D vs. 2D Inversion<\/strong><\/span><\/h3>\n\n\n\n
The result is always different w<\/span>hen\u00a0 1D and 2D inversion applied to the same data set. In geophysical surveys, lateral geological changes, which are the targets in many survey, cannot be \u0131maged correctly\u00a0 in 1D modeling studies.<\/span><\/td>\n\n
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2D inversion of VES data<\/figcaption><\/figure>\n<\/td>\n
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result of 1D inversion<\/figcaption><\/figure>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\u00a0<\/div>\n<\/div>\n\n\n

References<\/p>\n\n\n\n

Ertekin,C., and Ulugergerli, E. U. <\/strong>Geoelectrical survey over perched aquifers in the northern part of Upper Sakarya River Basin, T\u00fcrkiye. Journal of Groundwater Science and Engineering, 2022, 10(4): 335-352. https:\/\/doi.org\/10.19637\/j.cnki.2305-7068.2022.04.003<\/p>\n\n\n\n

Ulugergerli, E. U. <\/strong>(2017).Marine effects on vertical electrical soundings along shorelines. Turkish Journal of Earth Sciences, 26(1), 57-72.<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"

Method Direct current resistivity method gathers data via injecting electric current\u00a0into ground\u00a0with two electrodes (stainless steel bars) and measuring voltage differences occurs at two different points. The distance between the current electrodes and the electrical resistivities of the geological units determine the depth of investigation. The measured data are first converted to the apparent resistivity … <\/p>\n

Okumaya devam et “VES”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-21","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/emttarge.com\/site\/wp-json\/wp\/v2\/pages\/21","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/emttarge.com\/site\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/emttarge.com\/site\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/emttarge.com\/site\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/emttarge.com\/site\/wp-json\/wp\/v2\/comments?post=21"}],"version-history":[{"count":21,"href":"https:\/\/emttarge.com\/site\/wp-json\/wp\/v2\/pages\/21\/revisions"}],"predecessor-version":[{"id":599,"href":"https:\/\/emttarge.com\/site\/wp-json\/wp\/v2\/pages\/21\/revisions\/599"}],"wp:attachment":[{"href":"https:\/\/emttarge.com\/site\/wp-json\/wp\/v2\/media?parent=21"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}