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Titre du document / Document title

Hydrogeologic assessment of the Amchitka Island nuclear test site (Alaska) with magnetotellurics

Auteur(s) / Author(s)

UNSWORTH Martyn (1) ; SOYER Wolfgang (2) ; TUNCER Volkan (1) ; WAGNER Anna (3) ; BARNES David (3) ;

Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)

(1) University of Alberta, Department of Physics, Edmonton, Alberta, CANADA
(2) Geosystem SRL, Via Clericetti, Milano, ITALIE
(3) University of Alaska, Water and Environmental Research Center, Civil and Environmental Engineering Department, Fairbanks, Alaska, ETATS-UNIS

Résumé / Abstract

Amchitka Island, in Alaska, was used for underground nuclear testing from 1965 to 1971. Since the test program concluded, there have been concerns about the possible release of radionuclides into the marine environment of the Aleutian Islands. The hydrogeology of islands such as Amchitka is characterized by a layer of freshwater overlying a saltwater layer, with the salinity increasing across a transition zone (TZ). Hydrogeologic modeling can provide an estimate of the timing and amount of radionuclide release from the explosions beneath Amchitka Island. This modeling is inconclusive because of a lack of information regarding subsurface structure. To address this problem, magnetotelluric (MT) data were collected on Amchitka Island in 2004. Broadband MT data were recorded on profiles passing through three explosion sites to give information about subsurface porosity and salinity. A 2D MT inversion produced models of subsurface electrical resistivity and showed a pattern of increasing, decreasing, and increasing resistivity with depth at each test site. The depth at which resistivity begins to decrease defines the top of the TZ. The deeper increase in resistivity approximates the base of the TZ. The depths of the top and bottom of the TZ were determined as follows: Cannikin 900-2500 m; Long Shot 600-1700 m; Milrow 900-1700 m. Uncertainties were estimated for these depths. Effective porosities were also estimated and ranged from 10%-20% at the surface to 1%-3% at 3-km depth. These porosities are higher than those assumed in several hydrogeologic models, and give longer transit times from the explosion to the marine environment. Subject to the limits of the analysis, it appears that each of the cavities resulting from underground nuclear explosions is located in the TZ from fresh to saltwater. This implies shorter transit times to the marine environment than if the detonations had been located in the saltwater layer.

Revue / Journal Title

Geophysics    ISSN  0016-8033   CODEN GPYSA7 

Source / Source

2007, vol. 72, no3, [Note(s): B47-B57] (3/4 p.)

Langue / Language

Anglais

Editeur / Publisher

Society of Exploration Geophysicists, Tulsa, OK, ETATS-UNIS  (1936) (Revue)

Mots-clés anglais / English Keywords

North America

;

United States

;

Pacific Ocean

;

North Pacific

;

Aleutian Islands

;

Alaska

;

Amchitka Island

;

depth

;

electrical resistivity

;

models

;

inverse problem

;

porosity

;

nuclear explosions

;

transition zones

;

salinity

;

hydrogeology

;

marine environment

;

radionucleids

;

programs

;

testing

;

Mots-clés français / French Keywords

Amérique du Nord

;

Etats Unis

;

Océan Pacifique

;

Océan Pacifique Nord

;

Iles Aléoutiennes

;

Alaska

;

Ile Amchitka

;

Profondeur

;

Résistivité électrique

;

Modèle

;

Problème inverse

;

Porosité

;

Explosion nucléaire

;

Zone transition

;

Salinité

;

Hydrogéologie

;

Milieu marin

;

Radionucléide

;

Programme

;

Expérimentation

;

Mots-clés espagnols / Spanish Keywords

America del norte

;

Estados Unidos

;

Océano Pacífico

;

Islas Aleutianas

;

Alaska

;

Isla Amchitka

;

Profundidad

;

Resistividad eléctrica

;

Modelo

;

Problema inverso

;

Porosidad

;

Explosión nuclear

;

Zona transición

;

Salinidad

;

Hidrogeología

;

Medio marino

;

Radionucleido

;

Programa

;

Localisation / Location

INIST-CNRS, Cote INIST : 3126, 35400014963434.0040

Nº notice refdoc (ud4) : 18787533



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