Publication
A utilização do método de resistividade eléctrica num meio granítico fracturado : aproximações e ratoeiras
| datacite.subject.fos | Ciências Naturais::Ciências da Terra e do Ambiente | |
| dc.contributor.author | Alte da Veiga, Nuno | |
| dc.date.accessioned | 2025-07-01T14:05:50Z | |
| dc.date.available | 2025-07-01T14:05:50Z | |
| dc.date.issued | 2025-04 | |
| dc.description.abstract | RESUMO: O método de resistividade eléctrica teve, durante um longo período do séc. XX, um amplo uso nas suas variantes de sondagem eléctrica e perfil de resistividade. Mais recentemente, conheceu uma evolução no sentido da utilização de dispositivos com eléctrodos múltiplos, com possibilidades de aquisição 2D e 3D. A interpretação de sondagens eléctricas esteve desde sempre associada basicamente a um modelo de terreno com camadas horizontais; em terrenos graníticos, esta situação pode condicionar a forma como o terreno é concebido, o que pode levar a interpretações desfasadas da realidade. Nos casos considerados, numa zona de falha em granitos, a curva de sondagem obtida tem um ajustamento mais próximo da realidade usando um modelo com limites verticais. Numa aquisição 2D, num terreno granítico com uma estruturação quer horizontal quer vertical bastante marcada, a secção obtida com Wenner-Schlumberger apresenta um artefacto, tendo o dipolo-dipolo mostrado uma melhor capacidade de diferenciação do terreno. | por |
| dc.description.abstract | ABSTRACT: For most of the last century, the electrical resistivity method was used in the two basic techniques of the electrical resistivity sounding and the resistivity profiling. Further development led to the multielectrode devices now in use, with 2D and 3D capabilities. Traditionally, the electrical resistivity sounding requires for its interpretation the assumption of a stratified earth parallel to the surface; the translation of such an earth to the situation of a granitic terrain may affect the way in which the terrain is conceived. Specific situations considered in this work concern a granitic terrain in centre-northern Portugal. In such a geological context, the sounding curve obtained over a 130 m wide fault zone is better interpreted using a model with vertical limits. 2D acquisition and interpretation techniques have brought the capability to overcome the 1D limitations of electrical soundings and to better address terrain lateral heterogeneity; however, even in a 2D survey some issues may arise. A 235 m long 2D acquisition with Wenner-Schlumberger (WS) and dipole-dipole (DD) arrays (in the same place and in sequence) led to inverse model resistivity sections with partially different results: a vertical discontinuity centred at 150 m in the DD section is displaced to 120 m in the WS section. To gain some insight on this issue, apparent resistivity pseudo-sections with WS and DD arrays were obtained from a dike and a bloc models with the same resistivity. WS results for these models put in evidence higher overall apparent resistivity for the bloc case, but apparent resistivity data structure is basically the same for the two models. In the DD case, even though the apparent resistivity sections have a similar geometry, data structure is different: the apparent resistivities in the lower part of the sections, compared to the ones in the side areas, are, respectively, similar/significantly lower for the bloc/dike cases; and the observable oblique bands show an almost homogeneous symmetric cross-section (bloc) but an heterogeneous character and asymmetric cross-section (dike). A final situation, concerning a field case over a simpler structured horizontally stratified terrain (alluvium) puts in evidence that the inversion algorithm creates a high/low resistivity pair in the zone concerning a surface high apparent resistivity patch. In the above concerned 2D survey, the combined effect data structure/inversion algorithm led to the creation of an artifact in the case of the WS section; the dipole-dipole showed a better capacity for terrain differentiation. | eng |
| dc.identifier.citation | Alte da Veiga, N. (2025). A utilização do método de resistividade eléctrica num meio granítico fracturado : aproximações e ratoeiras. In: Comunicações Geológicas, 2025, vol. 112, Fascículo Especial I, pp. 395-399. https://doi.org/10.34637/3v1a-1102 | |
| dc.identifier.doi | 10.34637/3v1a-1102 | |
| dc.identifier.eissn | 1647-581X | |
| dc.identifier.issn | 0873-948X | |
| dc.identifier.uri | http://hdl.handle.net/10400.9/5906 | |
| dc.language.iso | por | |
| dc.peerreviewed | yes | |
| dc.publisher | LNEG - Laboratório Nacional de Energia e Geologia | |
| dc.relation.hasversion | https://www.lneg.pt/wp-content/uploads/2025/04/79_Alte-da-Veiga.pdf | |
| dc.rights.uri | http://creativecommons.org/licenses/by/4.0/ | |
| dc.subject | Resistividade eléctrica | |
| dc.subject | Secção de resistividade | |
| dc.subject | Sondagem eléctrica | |
| dc.subject | Granito | |
| dc.subject | Rocha cristalina | |
| dc.subject | Electrical resistivity | |
| dc.subject | Electrical sounding | |
| dc.subject | Granite | |
| dc.subject | Crystalline rock | |
| dc.title | A utilização do método de resistividade eléctrica num meio granítico fracturado : aproximações e ratoeiras | por |
| dc.title.alternative | Using the electrical resistivity method in a fractured granitic environment : approaches and pitfalls | eng |
| dc.type | journal article | |
| dspace.entity.type | Publication | |
| oaire.citation.endPage | 399 | |
| oaire.citation.issue | Especial I | |
| oaire.citation.startPage | 395 | |
| oaire.citation.title | Comunicações Geológicas | |
| oaire.citation.volume | 112 | |
| oaire.version | http://purl.org/coar/version/c_970fb48d4fbd8a85 | |
| person.familyName | Alte da Veiga | |
| person.givenName | Nuno | |
| person.identifier.orcid | 0009-0000-3083-0943 | |
| relation.isAuthorOfPublication | 95501dd3-f1f1-436f-ac1c-e5f6672dfe94 | |
| relation.isAuthorOfPublication.latestForDiscovery | 95501dd3-f1f1-436f-ac1c-e5f6672dfe94 |