scholarly journals 3D Characterization of a Coastal Freshwater Aquifer in SE Malta (Mediterranean Sea) by Time-Domain Electromagnetics

Water ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 1566 ◽  
Author(s):  
Potpreecha Pondthai ◽  
Mark E. Everett ◽  
Aaron Micallef ◽  
Bradley A. Weymer ◽  
Zahra Faghih ◽  
...  
Keyword(s):  
Sea Level ◽  
Time Domain ◽  
Geophysical Methods ◽  
High Resistivity ◽  
Mean Sea Level ◽  
Time Domain Electromagnetics ◽  
Time Domain Electromagnetic ◽  
Saturated Formations ◽  
Water Saturated ◽  
Subsurface Geometry

Electromagnetic (EM) geophysical methods are well equipped to distinguish electrical resistivity contrasts between freshwater-saturated and seawater-saturated formations. Beneath the semi-arid, rapidly urbanizing island of Malta, offshore groundwater is an important potential resource but it is not known whether the regional mean sea-level aquifer (MSLA) extends offshore. To address this uncertainty, land-based alongshore and across-shore time-domain electromagnetic (TDEM) responses were acquired with the G-TEM instrument (Geonics Ltd., Mississauga, ON, Canada) and used to map the onshore structure of the aquifer. 1-D inversion results suggest that the onshore freshwater aquifer resides at 4–24 m depth, underlain by seawater-saturated formations. The freshwater aquifer thickens with distance from the coastline. We present 2D and 3D electromagnetic forward modeling based on finite-element (FE) analysis to further constrain the subsurface geometry of the onshore freshwater body. We interpret the high resistivity zones that as brackish water-saturated bodies are associated with the mean sea-level aquifer. Generally, time-domain electromagnetic (TDEM) results provide valuable onshore hydrogeological information, which can be augmented with marine and coastal transition-zone measurements to assess potential hydraulic continuity of terrestrial aquifers extending offshore.

Subsurface Resistivity Imaging of Nasudake (Chausudake) Volcano Determined from Time Domain Electromagnetic Survey (TDEM)

2020 ◽  
Vol 15 (6) ◽  
pp. 735-744
Author(s):  
Toshikazu Tanada ◽  
Yoichi Nakamura ◽  
◽  
Keyword(s):  
Time Domain ◽  
Hot Spring ◽  
Geological Structure ◽  
High Resistivity ◽  
Volcanic Gas ◽  
Layer Structures ◽  
Spring Area ◽  
Time Domain Electromagnetic ◽  
Subsurface Resistivity ◽  
East West

A time domain electromagnetic survey (TDEM method) was conducted to investigate the resistivity structure of the crater, fumarole, and hot spring area of the Nasudake (Chausudake) volcano. The findings of this survey are as follows: (1) Under the crater area, a thin low-resistivity layer (approximately 50 m) was found on the surface, and lens-shaped high-resistivity areas continued to a depth of 800 m below it. The lens-shaped high-resistivity areas are believed to correspond to a thermal volcanic gas region. (2) From the east-west direction survey line crossing the foot of the Nasudake, two or three horizontal resistivity layer structures, which are considered to be caused by the geological structure and surface water, were observed.

Study of Thermal Water Resources in Sri Lanka Using Time Domain Electromagnetics (TDEM)

2014 ◽  
Vol 955-959 ◽  
pp. 3198-3201 ◽  
Author(s):  
Nalaka Deepal Subasinghe ◽  
Thusitha Bandara Nimalsiri ◽  
Nuwan Buddhika Suriyaarachchi ◽  
Bruce Hobbs ◽  
Morrel Fonseka ◽  
...  
Keyword(s):  
Sri Lanka ◽  
Time Domain ◽  
Thermal Springs ◽  
Geothermal Exploration ◽  
Near Surface ◽  
Environmental Friendly ◽  
Major Cation ◽  
Structural Relationships ◽  
Time Domain Electromagnetics ◽  
Time Domain Electromagnetic

Thermal springs can be utilized as an environmental friendly source of renewable energy, as well as for other purposes. Time domain electromagnetic (TDEM) method is used as an accessory tool in geothermal exploration to investigate the local heterogeneities in geology. The study consists of two of the thermal springs in Sri Lanka, Wahawa and Mahaoya, both in the same crustal unit. Major structural discontinuities of the area vary between two peculiar fracture sets striking ENE and NW. Close relationships between these individual springs have been witnessed by their approximate major cation chemistries, which provoke the idea of geochemical provinces. Survey reveals the pathways of the heated water to the surface, at Wahawa, although the path is not clear at Mahaoya. Near surface resistivity diagrams can be used only to interpret the immediate depths of the springs. The expected structural relationships may be identified with a grid of TDEM soundings encompassing both the spring systems.

scholarly journals Characterisation of subglacial water using a constrained transdimensional Bayesian Time Domain Electromagnetic Inversion

2019 ◽  
Author(s):  
Siobhan F. Killingbeck ◽  
Adam D. Booth ◽  
Philip W. Livermore ◽  
Charles R. Bates ◽  
Landis J. West
Keyword(s):  
Electrical Resistivity ◽  
Time Domain ◽  
Saline Water ◽  
Radar Data ◽  
High Resistivity ◽  
Fractured Bedrock ◽  
Geological Interpretation ◽  
Seismic Shear ◽  
Time Domain Electromagnetics ◽  
Ground Penetrating

Abstract. Subglacial water influences the dynamics of ice masses. The state of subglacial pore water, whether liquid or frozen, is associated with differences in electrical resistivity that span several orders of magnitude, hence liquid water can be inferred from electrical resistivity depth profiles. Such profiles can be obtained from inversions of time domain electromagnetics (TEM) soundings, but these are often non-unique. Here, we adapt an existing Bayesian transdimensional algorithm (MuLTI) to the inversion of TEM data constrained by independent depth constraints, to provide statistical properties and uncertainty analysis of the resistivity profile with depth. The method was applied to ground-based TEM data acquired on the terminus of the Norwegian glacier Midtdalsbreen, with depth constraints provided by co-located ground penetrating radar data. Our inversion shows that the glacier bed is directly underlain by material of resistivity 102 Ωm ± 100 %, with thickness 5–40 m, in turn underlain by a highly conductive basement (100 Ωm ± 15 %). High resistivity material, 5 × 104 Ωm ± 25 %, exists at the front of the glacier. All uncertainties are defined by the interquartile range of the posterior resistivity distribution. Combining these resistivity profiles with co-located seismic shear-wave velocity inversions to further reduce ambiguity in the hydro-geological interpretation of the subsurface, we propose a new 3D interpretation of the Midtdalsbreen subglacial material partitioned into partially frozen sediment, frozen sediment/permafrost and weathered/fractured bedrock with saline water.

Inversion of airborne geophysics over the DO-27/DO-18 kimberlites — Part 3: Induced polarization

2017 ◽  
Vol 5 (3) ◽  
pp. T327-T340 ◽  
Author(s):  
Seogi Kang ◽  
Dominique Fournier ◽  
Douglas W. Oldenburg
Keyword(s):  
Time Domain ◽  
Geophysical Methods ◽  
Induced Polarization ◽  
Three Dimensions ◽  
Data Set ◽  
Time Constants ◽  
Airborne Geophysics ◽  
Petrophysical Model ◽  
Time Domain Electromagnetic ◽  
Conductivity Models

The geologically distinct DO-27 and DO-18 kimberlites, often called the Tli Kwi Cho (TKC) kimberlites, have been used as a testbed for airborne geophysical methods applied to kimberlite exploration. This paper focuses on extracting chargeability information from time-domain electromagnetic (TEM) data. Three different TEM surveys, having similar coincident-loop geometry, have been carried out over TKC. Each records negative transients over the main kimberlite units and this is a signature of induced polarization (IP) effects. By applying a TEM-IP inversion workflow to a versatile time domain EM (VTEM) data set we decouple the EM and IP responses in the observations and then recover 3D pseudo-chargeability models at multiple times. A subsequent analysis is used to recover Cole-Cole parameters. Our models demonstrate that both DO-18 and DO-27 pipes are chargeable, but they have different Cole-Cole time constants: 110 and 1160 μs, respectively. At DO-27, we also distinguish between two adjacent kimberlite units based on their respective Cole-Cole time constants. Our chargeability models are combined with the density, magnetic susceptibility and conductivity models to build a 3D petrophysical model of TKC using only information obtained from airborne geophysics. Comparison of this final petrophysical model to a 3D geological model derived from the extensive drilling program demonstrates that we can characterize the three main kimberlite units at TKC: HK, VK, and PK in three dimensions by using airborne geophysics.

Helicopter time-domain electromagnetics — Newmont and the NEWTEM experience

Geophysics ◽  
2013 ◽  
Vol 78 (6) ◽  
pp. W45-W56 ◽  
Author(s):  
Perry A. Eaton ◽  
Robert G. Anderson ◽  
Steven V. Queen ◽  
Bruno Y. Nilsson ◽  
Eric Lauritsen ◽  
...  
Keyword(s):  
Time Domain ◽  
Original System ◽  
Geologic Mapping ◽  
Use Of Time ◽  
Different Types ◽  
Time Domain Electromagnetics ◽  
Time Domain Electromagnetic ◽  
Airborne Em ◽  
Mapping Information ◽  
Gold Bearing

Over the past two decades, the use of time-domain electromagnetic (EM) surveying systems, designed for an airborne helicopter-based platform, has risen in popularity. One of the first of these systems was developed and has been operated by Newmont Mining Corporation. The original system (NEWTEM I) and its more capable successor (NEWTEM II) were created to help our company explore for different types of mineral deposits, primarily gold bearing, as well as to provide general geologic mapping information in parts of the world that are often very difficult or expensive to explore otherwise. The NEWTEM system has some characteristics that have proven to be advantageous in terms of safety, cost of operation, spatial resolution, and the ability to map effectively at both ends of the resistivity scale. Our approach to the acquisition, processing, and interpretation of airborne EM data is specific to this system and to the goals of our gold-focused exploration programs. Using what is most often a locally derived helicopter, we are able to carry out a survey of whatever size our exploration program dictates and on a schedule that meets our company’s needs. Results from NEWTEM surveys have been used to identify conductive and resistive targets but more importantly to advance our general understanding of an area’s potential to host mineralization of interest to this company. We intended to provide a brief written account of the NEWTEM story for the scientific and exploration communities, including information about its design and capabilities, as well as how we process this type of data. Hopefully, this documentation will serve to inspire future developers, explorers, geoscientists, and airborne EM enthusiasts.

Note on Selection of Coordinate Systems for Geodynamics

1975 ◽  
Vol 26 ◽  
pp. 395-407
Author(s):  
S. Henriksen
Keyword(s):  
Sea Level ◽  
The Other ◽  
Coordinate Systems ◽  
Mean Sea Level ◽  
The Earth ◽  
The One ◽  
Static Systems ◽  
Selection Of

The first question to be answered, in seeking coordinate systems for geodynamics, is: what is geodynamics? The answer is, of course, that geodynamics is that part of geophysics which is concerned with movements of the Earth, as opposed to geostatics which is the physics of the stationary Earth. But as far as we know, there is no stationary Earth – epur sic monere. So geodynamics is actually coextensive with geophysics, and coordinate systems suitable for the one should be suitable for the other. At the present time, there are not many coordinate systems, if any, that can be identified with a static Earth. Certainly the only coordinate of aeronomic (atmospheric) interest is the height, and this is usually either as geodynamic height or as pressure. In oceanology, the most important coordinate is depth, and this, like heights in the atmosphere, is expressed as metric depth from mean sea level, as geodynamic depth, or as pressure. Only for the earth do we find “static” systems in use, ana even here there is real question as to whether the systems are dynamic or static. So it would seem that our answer to the question, of what kind, of coordinate systems are we seeking, must be that we are looking for the same systems as are used in geophysics, and these systems are dynamic in nature already – that is, their definition involvestime.

scholarly journals Deterministic approach for multiple-source tsunami hazard assessment for Sines, Portugal

2015 ◽  
Vol 15 (11) ◽  
pp. 2557-2568 ◽  
Author(s):  
M. Wronna ◽  
R. Omira ◽  
M. A. Baptista
Keyword(s):  
Sea Level ◽  
Wave Height ◽  
Hazard Assessment ◽  
Test Site ◽  
Tsunami Hazard ◽  
Deterministic Approach ◽  
Flow Depth ◽  
Mean Sea Level ◽  
Tsunami Hazard Assessment ◽  
The Impact

Abstract. In this paper, we present a deterministic approach to tsunami hazard assessment for the city and harbour of Sines, Portugal, one of the test sites of project ASTARTE (Assessment, STrategy And Risk Reduction for Tsunamis in Europe). Sines has one of the most important deep-water ports, which has oil-bearing, petrochemical, liquid-bulk, coal, and container terminals. The port and its industrial infrastructures face the ocean southwest towards the main seismogenic sources. This work considers two different seismic zones: the Southwest Iberian Margin and the Gloria Fault. Within these two regions, we selected a total of six scenarios to assess the tsunami impact at the test site. The tsunami simulations are computed using NSWING, a Non-linear Shallow Water model wIth Nested Grids. In this study, the static effect of tides is analysed for three different tidal stages: MLLW (mean lower low water), MSL (mean sea level), and MHHW (mean higher high water). For each scenario, the tsunami hazard is described by maximum values of wave height, flow depth, drawback, maximum inundation area and run-up. Synthetic waveforms are computed at virtual tide gauges at specific locations outside and inside the harbour. The final results describe the impact at the Sines test site considering the single scenarios at mean sea level, the aggregate scenario, and the influence of the tide on the aggregate scenario. The results confirm the composite source of Horseshoe and Marques de Pombal faults as the worst-case scenario, with wave heights of over 10 m, which reach the coast approximately 22 min after the rupture. It dominates the aggregate scenario by about 60 % of the impact area at the test site, considering maximum wave height and maximum flow depth. The HSMPF scenario inundates a total area of 3.5 km2.

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