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Three-Dimensional Geophysical Mapping: Providing New Constraints for Understanding Hydrogeogical and Geological Processes

English title Three-Dimensional Geophysical Mapping: Providing New Constraints for Understanding Hydrogeogical and Geological Processes
Applicant Green Alan G.
Number 137603
Funding scheme Project funding
Research institution Institut für Geophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geophysics
Start/End 01.10.2011 - 28.02.2014
Approved amount 557'070.32
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All Disciplines (2)

Discipline
Geophysics
Geology

Keywords (3)

High-resolution-geophysics; Okavango Delta; hydrology

Lay Summary (English)

Lead
The juxtaposition of the Makgadikgadi Basin, the world’s largest saltpancomplex, with the Okavango Delta, one of the planet’s largest inland deltas, has intrigued explorers and scientists since the middle of the 19 thcentury. It was clear from early observations that the Makgadikgadi Basin once containeda huge lake, Paleo-Lake Makgadikgadi. Several authors speculated that thislake also covered wide regions to the north and west of the Makgadikgadi Basin. Our interpretationof high-quality helicopter time-domain electromagnetic (HTEM) data indicates that Paleo-Lake Makgadikgadi extended northwestward at least into the region presently occupied by the Okavango Delta. The total area of Paleo-Lake Makgadikgadi exceeded 90,000 square km, larger than Earth’s most extensive freshwater body today, Lake Superior. Our HTEM data, constrained by ground-based geophysical and borehole information, also provide evidence for a paleo-megafan underlying Paleo-Lake Makgadikgadi sediments.
Lay summary
Integration of information from the following sources have been used to produce a better constrained and more complete four-unit model of the Okavango Delta: (i) a 3D resistivity model determined from helicopter electromagnetic data, (ii) 2D models and images derived from ground-based electrical resistance, electromagnetic, and high resolution seismic reflection/refraction  data, and (iii) geological details extracted from boreholes. The upper heterogeneous unit is the modern delta, comprising extensive dry and freshwater-saturated sand and lesser amounts of clay and salt. It has moderate to high electrical resistivities and very low to low P-wave velocities. Except for images of buried abandoned river channels, it is non-reflective. The laterally extensive underlying unit of low resistivities, low P-wave velocity, and subhorizontal reflectors contains saline-water-saturated sands and clays deposited in the huge Paleo Makgadikgadi Lake (PLM), which once covered a 90,000 km2. Examples of PLM sediments are intersected in many of the boreholes. Low permeability clay within the PLM unit seems to be a barrier to the downward flow of the saline water. Below the PLM unit, freshwater-saturated sand of the Paleo Okavango Megafan (POM) unit is distinguished by moderate to high resistivities, low P-wave velocity, and numerous subhorizontal reflectors. It is interpreted to be the remnants of a megafan based on the arcuate nature of its front and the semi-conical shape of its upper surface. Moderate to high resistivity subhorizontal layers are consistent with this interpretation. The deepest unit is the basement with very high resistivity, high P wave velocity, and low or complex reflectivity. The interface between POM sediments and basement is a prominent reflector.
Direct link to Lay Summary Last update: 28.07.2014

Responsible applicant and co-applicants

Employees

Publications

Publication
A hybrid boundary element-finite element approach to modeling plane wave 3D electromagnetic induction responses in the Earth
Zhengyong Ren Kalscheuer T. Greenhalgh S. and Maurer H.R. (2014), A hybrid boundary element-finite element approach to modeling plane wave 3D electromagnetic induction responses in the Earth, in Journal of Computational Physics, 258, 705-717.
Characterizing sagging and collapse sinkholes in a mantled karst by means of Ground Penetrating Radar (GPR)
Rodríguez V. Gutiérrez F. Green A.G. Carbonel D. Horstmeyer H. and Schmelzbach C. (2014), Characterizing sagging and collapse sinkholes in a mantled karst by means of Ground Penetrating Radar (GPR), in Environmental & Engineering Geoscience, XX, 109-132.
Constraining helicopter electromagnetic models of the Okavango Delta with seismic-refraction and seismic-reflection data
Reiser F. Podgorski J.E. Schmelzbach C. Horstmeyer H. Green A. Kalscheuer T Maurer H.R. (2014), Constraining helicopter electromagnetic models of the Okavango Delta with seismic-refraction and seismic-reflection data, in Geophysics, 79(B123), B134.
Crustal structure beneath southern Norway imaged by magnetotellurics
Cherevatova M ...... Kalscheuer T. (2014), Crustal structure beneath southern Norway imaged by magnetotellurics, in Tectonophysics, 628, 55-70.
The Use of Geophysics for Sensitive Clay Investigations
Donohue S. Long M. L'Heureux J.-S Solberg I.-L Sauvin G. Rømoen M. Kalscheuer T. (2014), The Use of Geophysics for Sensitive Clay Investigations, in Advances in Natural and Technological Hazards Research, 36(159), 178.
Two-dimensional probabilistic inversion of radio magnetotelluric data: Methodology, model constraints and joint inversion with electrical resistivity data
Carbajal R. Linde N. Kalscheuer T. Vrugt J. (2014), Two-dimensional probabilistic inversion of radio magnetotelluric data: Methodology, model constraints and joint inversion with electrical resistivity data, in Geophysical Journal Internationa, 196, 1508-1524.
Seismic imaging of the Alpine Fault near Inchbonnie, New Zealand.
Carpentier S.F.A. Green A.G. Langridge R. Hurter F. Kaiser A. Horstmeyer H. (2013), Seismic imaging of the Alpine Fault near Inchbonnie, New Zealand., in Journal Geophysical Research, 118, 1-16.
A combined approach of remote sensing and airborne electromagnetics to determine the volume of polynya sea ice in the Laptev Sea.
Rabenstein L. Krumpen T. Hendricks S. Koeberle C. Haas C Hoelemann J.A. (2013), A combined approach of remote sensing and airborne electromagnetics to determine the volume of polynya sea ice in the Laptev Sea., in The Cryosphere, 7, 947-959.
A goal-oriented adaptive finite-element approach for 3D electromagnetic modeling
Zhengyong Ren Kalscheuer T. Greenhalgh S. and Maurer H.R. (2013), A goal-oriented adaptive finite-element approach for 3D electromagnetic modeling, in Geophysical Journal International, 194, 700-718.
Boundary element solutions for broad-band 3-D geo-electromagnetic problems accelerated by an adaptive multilevel fast multipole method
Zhengyong Ren Kalscheuer T. Greenhalgh S. and Maurer H.R. (2013), Boundary element solutions for broad-band 3-D geo-electromagnetic problems accelerated by an adaptive multilevel fast multipole method, in Geophysical Journal International, 192, 473-499.
Delineation of a quick clay zone at Smørgrav, Norway, with electromagnetic methods under geotechnical constraints
Kalscheuer T. Bastani M. Donohue S. Persson L. Pfaffhuber A.A. Reiser F. and Zhengyong Re (2013), Delineation of a quick clay zone at Smørgrav, Norway, with electromagnetic methods under geotechnical constraints, in Journal of Applied Geophysics, 92, 121-136.
Determining hydrological and soil mechanical parameters from multichannel surface wave analysis across the Alpine Fault at Inchbonnie, New Zealand
Konstantaki L.A. Carpentier S. Garofalo F. Bergamo P. and Socco L.V. (2013), Determining hydrological and soil mechanical parameters from multichannel surface wave analysis across the Alpine Fault at Inchbonnie, New Zealand, in Near Surface Geophysics, 11, 435-448.
Paleo megalake and paleo megafan in southern Africa
Podgorski J.E. Green A.G. Kgotlhang L. Kinzelbach W. Kalscheuer T. Auken E Ngwisanyi T. (2013), Paleo megalake and paleo megafan in southern Africa, in Geology, 41, 1155-1158.
Processing and inversion of commercial helicopter time-domain electromagnetic data for environmental assessments and geological and hydrological mapping
Podgorski J.E. Auken E. Schamper C. Christiansen A.V. Kalscheuer T. Green A.G. (2013), Processing and inversion of commercial helicopter time-domain electromagnetic data for environmental assessments and geological and hydrological mapping, in Geophysics., 78, E149-E159.
Water content estimates of a first-year sea-ice pressure ridge keel from surface-nuclear magnetic resonance tomography
Nuber A. Rabenstein L. Lehmann-Horn J.A. Hertrich M. Hendricks S. Mahoney A. Eicken H. (2013), Water content estimates of a first-year sea-ice pressure ridge keel from surface-nuclear magnetic resonance tomography, in Annals of Glaciology, 54, 33-43.
Seismic monitoring of radioactive waste repositories
Manukyan E. Maurer H.R. Marelli S. Greenhalgh. S.A. and Green A.G. (2012), Seismic monitoring of radioactive waste repositories, in Geophysics, 77, EN73-EN83.
Hydrogeophysical investigations in the western and northern Okavango Delta (Botswana) using electrical resistance tomography (ERT) and transient electromagnetic (TEM) techniques.
Meier P. Kalscheuer T. Podgorski J. Green A. Greenhalgh S. Rabenstein L. Doetsch J., Hydrogeophysical investigations in the western and northern Okavango Delta (Botswana) using electrical resistance tomography (ERT) and transient electromagnetic (TEM) techniques., in Geophysics.

Collaboration

Group / person Country
Types of collaboration
Dr. Lesego Kgotlhang, Botswana Department of Water Affairs Botswana (Africa)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Dr. Hudson Ngwisanyi, Dr. Gomotsang Tshoso and colleagues, Botswana Department of Geological Survey Botswana (Africa)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel
Dr. Robert Langridge and colleagues at GNS Science New Zealand (Oceania)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Professor Wolfgang Kinzelback ETH Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Exchange of personnel
Professor Esben Auken and colleagues, University of Aarhus Denmark (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel

Awards

Title Year
Honorary Mention for "Best Paper in Geophysics", the top applied geophysics journal 2014

Associated projects

Number Title Start Funding scheme
126981 Three-Dimensional Geophysical Mapping: Providing New Constraints for Understanding Hydrogeogical and Geological Processes 01.10.2009 Project funding
126981 Three-Dimensional Geophysical Mapping: Providing New Constraints for Understanding Hydrogeogical and Geological Processes 01.10.2009 Project funding

Abstract

We have been developing fast and accurate high-resolution 3-D geophysical techniques as non-destructive means for studying the shallow subsurface. The proposed research involves the application of these techniques to a region in New Zealand that was recently hit by a highly damaging magnitude 7.1 earthquake and numerous aftershocks and a region in Africa of enormous hydrogeological importance. Both aspects of the proposed research represent completions of projects described in our previous two-year grant applications.
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