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Resistivity imaging in steep and weathered terrains

Mendoza, Alfredo LU and Dahlin, Torleif LU (2008) In Near Surface Geophysics 6(2). p.105-112
Abstract
In areas where tectonics and weathering have hydrogeological significance, electrical methods can assist in mapping the subsurface. In this work, resistivity imaging was used to map fractures, faults and quartz veins emplaced in strongly weathered volcanic rocks. The aim was to map geological units related to the formation of groundwater systems in the Rio Artiguas basin, Nicaragua. Eight 2D resistivity surveys selected from two sites with characteristic geological features are discussed in this article. The resistivity lines were carried out with a multi-electrode system together with different electrode geometries. The data inversion was done by applying the robust (L-i-norm) method and a finite element grid to accommodate the steep... (More)
In areas where tectonics and weathering have hydrogeological significance, electrical methods can assist in mapping the subsurface. In this work, resistivity imaging was used to map fractures, faults and quartz veins emplaced in strongly weathered volcanic rocks. The aim was to map geological units related to the formation of groundwater systems in the Rio Artiguas basin, Nicaragua. Eight 2D resistivity surveys selected from two sites with characteristic geological features are discussed in this article. The resistivity lines were carried out with a multi-electrode system together with different electrode geometries. The data inversion was done by applying the robust (L-i-norm) method and a finite element grid to accommodate the steep topography. The data interpretation included numerical modelling to assess the suitability of all used electrode arrays in relation to the expected geological settings. The results indicated a top high resistive layer consisting of colluviums with laterite (>50 Omega m), underlain by conductive clay weathered layers (10-50 Omega m). Below the conductive layer less weathered or fresh rock can be found with higher values (50-600 Omega m). The quartz veins and dykes stand out as the highest resistive bodies (100-4000 Omega m). The results indicated an overall weathering thickness of 10-30 m or more. In conclusion, the extensive resistivity imaging surveys allowed delineation of geological structures and weathering layers throughout the study area. Furthermore, the vertical extension of weathering was examined at all locations. A finite element grid in the inversion prevented distortions arising from topography regardless of the steep slope observed at the survey locations. The numerical modelling results revealed the strengths of different arrays for the particular cases of a fault and a quartz vein in irregular terrains. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Near Surface Geophysics
volume
6
issue
2
pages
105 - 112
publisher
EAGE
external identifiers
  • wos:000254795600004
  • scopus:41849111629
ISSN
1873-0604
language
English
LU publication?
yes
id
dfb2954d-797f-4b31-a317-64a6b0cef6c9 (old id 1207192)
date added to LUP
2008-08-28 13:05:25
date last changed
2017-01-01 04:27:17
@article{dfb2954d-797f-4b31-a317-64a6b0cef6c9,
  abstract     = {In areas where tectonics and weathering have hydrogeological significance, electrical methods can assist in mapping the subsurface. In this work, resistivity imaging was used to map fractures, faults and quartz veins emplaced in strongly weathered volcanic rocks. The aim was to map geological units related to the formation of groundwater systems in the Rio Artiguas basin, Nicaragua. Eight 2D resistivity surveys selected from two sites with characteristic geological features are discussed in this article. The resistivity lines were carried out with a multi-electrode system together with different electrode geometries. The data inversion was done by applying the robust (L-i-norm) method and a finite element grid to accommodate the steep topography. The data interpretation included numerical modelling to assess the suitability of all used electrode arrays in relation to the expected geological settings. The results indicated a top high resistive layer consisting of colluviums with laterite (>50 Omega m), underlain by conductive clay weathered layers (10-50 Omega m). Below the conductive layer less weathered or fresh rock can be found with higher values (50-600 Omega m). The quartz veins and dykes stand out as the highest resistive bodies (100-4000 Omega m). The results indicated an overall weathering thickness of 10-30 m or more. In conclusion, the extensive resistivity imaging surveys allowed delineation of geological structures and weathering layers throughout the study area. Furthermore, the vertical extension of weathering was examined at all locations. A finite element grid in the inversion prevented distortions arising from topography regardless of the steep slope observed at the survey locations. The numerical modelling results revealed the strengths of different arrays for the particular cases of a fault and a quartz vein in irregular terrains.},
  author       = {Mendoza, Alfredo and Dahlin, Torleif},
  issn         = {1873-0604},
  language     = {eng},
  number       = {2},
  pages        = {105--112},
  publisher    = {EAGE},
  series       = {Near Surface Geophysics},
  title        = {Resistivity imaging in steep and weathered terrains},
  volume       = {6},
  year         = {2008},
}