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Audiomagnetotelluric investigation of seawater intrusion using 2-D inversion of invariant impedances
Luján, Violeta (Centro de Investigación Científica y de Educación Superior de Ensenada, (CICESE). División de Ciencias de la Tierra)
Romo, José Manuel (Centro de Investigación Científica y de Educación Superior de Ensenada, (CICESE). División de Ciencias de la Tierra)

Date: 2010
Abstract: An audio-magnetotelluric survey was conducted to estimate the extension of the seawater intrusion in a coastal aquifer, in Ensenada, Baja California, México. The survey consisted of 134 closely spaced sites along three profiles 5 to 6 km long. The four elements of the impedance tensor were measured at every observation site and used to estimate the series and parallel (s-p) invariant impedances. 2-D resistivity models were obtained along each profile using a Gauss-Newton regularized inversion process. The seawater intrusion is clearly shown in the resulting models as highly conductive anomalies. In some places, the resistivity models show the bedrock and the basement faults in good agreement with structures interpreted from gravity and magnetic modeling. Based on the information provided by the resistivity models and using the available hydrogeologic information, we used Archie's law in an attempt to gain insights about porosity and TDS distributions in the aquifer. Porosity values between 15 and 25% near the surface reasonably predict the TDS values observed in several shallow wells in the area. TDS values range from 40 g/l typical for seawater to 1 g/l in the eastern edge of the basin, 4 km Hawai from the coastline. The best conditions were found in Profile 2, were the resistivity model predicts TDS values close to 1 g/l below 100 m depth at sites located further than 1 km from the coast. The above results show that s-p invariant impedances produced geologically plausible resistivity models. Hence, they might be a convenient set of magnetotelluric responses to be used for routine 2-D inversion of AMT data.
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Language: Anglès
Document: article ; recerca ; publishedVersion
Subject: Seawater intrusion ; Magnetotellurics ; Baja California ; México
Published in: Geologica acta, Vol. 8, Núm. 1 (Març 2010) , p. 51-66, ISSN 1696-5728

Adreça alternativa: https://www.raco.cat/index.php/GeologicaActa/article/view/188004
DOI: 10.1344/105.000001515

16 p, 2.1 MB

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Articles > Published articles > Geologica acta
Articles > Research articles

 Record created 2012-01-25, last modified 2020-08-29

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