Resistivity monitoring of an active volcano using the controlled-source electromagnetic technique: Kilauea, Hawaii

This study characterises high-fluoride groundwater in the aquifer system on the flanks of Mount Meru, focusing on parts of the flanks that were only partially or not at all covered by previous research. Additionally, we analyse the impact of rainwater recharge on groundwater chemistry by monitoring spring discharges during water sampling. The results show that the main groundwater type in the study area is NaHCO3 alkaline groundwater (average pH = 7.8). High F− values were recorded: in 175 groundwater samples, the concentrations range from 0.15 to 301 mg/L (mean: 21.89 mg/L, median: 9.67 mg/L), with 91% of the samples containing F− values above the WHO health-based guideline for drinking water (1.5 mg/L), whereas 39% of the samples have Na+ concentrations above the WHO taste-based guideline of 200 mg/L. The temporal variability in F− concentrations between different seasons is due to the impact of the local groundwater recharge. We recommend that a detailed ecohydrological study should be carried out for the low-fluoride springs from the high-altitude recharge areas on the eastern and northwestern flanks of Mount Meru inside Arusha National Park. These springs are extracted for drinking purposes. An ecohydrological study is required for the management of these springs and their potential enhanced exploitation to ensure the sustainability of this water extraction practice. Another strategy for obtaining safe drinking water could be to use a large-scale filtering system to remove F− from the groundwater.

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Probabilistic Tsunami Hazard Analysis of Inundated Buildings Following a Subaqueous Volcanic Explosion Based on the 1716 Tsunami Scenario in Taal Lake, Philippines

Geosciences ◽

10.3390/geosciences11020092 ◽

2021 ◽

Vol 11 (2) ◽

pp. 92

Author(s):

Kwanchai Pakoksung ◽

Anawat Suppasri ◽

Fumihiko Imamura

Keyword(s):

Hazard Analysis ◽

Active Volcano ◽

The Philippines ◽

Tsunami Hazard ◽

Initial Water ◽

Volcanic Explosion ◽

Inundation Depth ◽

Tsunami Mitigation ◽

Probabilistic Tsunami Hazard Analysis ◽

Tunami N2

A probabilistic hazard analysis of a tsunami generated by a subaqueous volcanic explosion was performed for Taal Lake in the Philippines. The Taal volcano at Taal Lake is an active volcano on Luzon Island in the Philippines, and its eruption would potentially generate tsunamis in the lake. This study aimed to analyze a probabilistic tsunami hazard of inundated buildings for tsunami mitigation in future scenarios. To determine the probabilistic tsunami hazard, different explosion diameters were used to generate tsunamis of different magnitudes in the TUNAMI-N2 model. The initial water level in the tsunami model was estimated based on the explosion energy. The tsunami-induced inundation from the TUNAMI-N2 model was overlaid on the distribution of buildings. The tsunami hazard analysis of inundated buildings was performed by using the maximum inundation depth in each explosion case. These products were used to calculate the probability of the inundated building given the occurrence of a subaqueous explosion. The results from this study can be used for future tsunami mitigation if a tsunami is generated by a subaqueous volcanic explosion.

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Three-dimensional inversion of controlled-source audio-frequency magnetotelluric data based on unstructured finite-element method

Applied Geophysics ◽

10.1007/s11770-020-0812-z ◽

2020 ◽

Vol 17 (3) ◽

pp. 349-360

Author(s):

Xiang-Zhong Chen ◽

Yun-He Liu ◽

Chang-Chun Yin ◽

Chang-Kai Qiu ◽

Jie Zhang ◽

...

Keyword(s):

Finite Element Method ◽

Finite Element ◽

Three Dimensional ◽

Audio Frequency ◽

Magnetotelluric Data ◽

Controlled Source ◽

Element Method

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Research on the forward modeling of controlled-source audio-frequency magnetotelluric in three-dimensional electrical conductivity and magnetic permeability heterogeneity media

Arabian Journal of Geosciences ◽

10.1007/s12517-021-07001-w ◽

2021 ◽

Vol 14 (9) ◽

Author(s):

Huadong Song ◽

Shengjun Liang

Keyword(s):

Electrical Conductivity ◽

Magnetic Permeability ◽

Three Dimensional ◽

Forward Modeling ◽

Audio Frequency ◽

Controlled Source ◽

Permeability Heterogeneity

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Source modification for efficiency enhancement of marine controlled-source electromagnetic method

Journal of Geophysics and Engineering ◽

10.1093/jge/gxab011 ◽

2021 ◽

Vol 18 (2) ◽

Author(s):

Amir Rostami ◽

Noorhana Yahaya ◽

Hassan Soleimani ◽

Muhammad Rauf ◽

Tadiwa E Nyamasvisva ◽

...

Keyword(s):

Electromagnetic Wave ◽

Shallow Water ◽

Method Of Moments ◽

Experimental Setup ◽

Efficiency Enhancement ◽

Shooting Methods ◽

Detection Capability ◽

Controlled Source ◽

Element Simulation ◽

Electromagnetic Source

Abstract Controlled-source electromagnetics is a strongly efficient technique to explore deep-water marine hydrocarbon reservoirs. However, the shallow-water unsolved limitations of electromagnetic shooting methods still exist. In this regard, this work aims to alter the existing conventional electromagnetic source such that it can converge the down-going electromagnetic wave while simultaneously dispersing the up-going electromagnetic energy to minimise the airwave in shallow water. This work presents computed electric current distribution inside a modified transmitter, using a method of moments. Simulation and an experiment-based methodology are applied to this work. Finite element simulation of the response of the modified transmitter displayed the capability of the new transmitter in dispersing the airwave, by 15%. The experimental setup confirmed a better performance of the new transmitter, showing hydrocarbon delineation of up to 48%, compared to the existing conventional transmitter, with 25% oil delineation at the same depths in the same environment. Modification of the electromagnetic source to unbalance the up-down signals may have the potential to enhance the delineation magnitude of the target signal and, as a result, significantly improve oil detection capability.

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Mineral exploration with 3-D controlled-source electromagnetic method: a synthetic study of Sukhoi Log gold deposit

Geophysical Journal International ◽

10.1093/gji/ggz390 ◽

2019 ◽

Vol 219 (3) ◽

pp. 1698-1716 ◽

Cited By ~ 3

Author(s):

M Malovichko ◽

A V Tarasov ◽

N Yavich ◽

M S Zhdanov

Keyword(s):

Finite Difference ◽

Gold Deposit ◽

Large Scale ◽

Mineral Exploration ◽

Mineral Deposit ◽

Hydrocarbon Exploration ◽

Contraction Operator ◽

Inversion Algorithm ◽

Controlled Source ◽

Regularized Inversion

SUMMARY This paper presents a feasibility study of using the controlled-source frequency-domain electromagnetic (CSEM) method in mineral exploration. The method has been widely applied for offshore hydrocarbon exploration; however, nowadays this method is rarely used on land. In order to conduct this study, we have developed a fully parallelized forward modelling finite-difference (FD) code based on the iterative solver with contraction-operator preconditioner. The regularized inversion algorithm uses the Gauss–Newton method to minimize the Tikhonov parametric functional with the Laplacian-type stabilizer. A 3-D parallel inversion code, based on the iterative finite-difference solver with the contraction-operator preconditioner, has been evaluated for the solution of the large-scale inverse problems. Using the computer simulation for a synthetic model of Sukhoi Log gold deposit, we have compared the CSEM method with the conventional direct current sounding and the CSEM survey with a single remote transmitter. Our results suggest that, a properly designed electromagnetic survey together with modern 3-D inversion could provide detailed information about the geoelectrical structure of the mineral deposit.

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