Abstract

The hydric resource coming from groundwater has a strategic nature at global scale, within a context of overpopulation and over exploitation of the resource and climate change. Chile doesn’t scape to it, where climate models predict a drought for most of the country, including partially, the agriculture region of the Central Valley between Santiago and Puerto Montt. The adaption process to global change demands the exploration new sources of provisions of this resource, being strategic the one coming from aquifers. To date, the knowledge of these resources is limited to depths below 200 m in each aquifer. However, in the Central Valley between Santiago and Chiloé, the geophysical evidences allow to infer the existence of a thick volcano-sedimentary basin growing in thickness southward well above 500m, with good potential for occurrence of large groundwater resources. 
 The characterization of deep aquifers, 200-1,000 m of depth, demands to have an exploration tool economic, non-invasive, and reliable, able to be applied in semi-urban and rural environments, where the water resource need is higher.
 The geophysical methodologies meet these characteristics and have been applied in Chile and elsewhere as an exploration tool of ground water resources. However, its application have not been described in Andean environments, of large population and/or agro-industrial activity. In consequence, the present work raises a methodological strategy for the characterization of groundwater resources, in particular for the detection of deep resources. We propose the application of a combination of complementary geophysical techniques, including electrical, electromagnetic, and gravimetric methods (to determine the aquifer geometry) along with complementary techniques, like magnetometry, to reduce interpretation ambiguity and , constrained by hydrogeological information and petrophysics of rocks and sediments of the basin and basement. Complementary, we include an analysis of the potential effects of cultural noise and its effects on geophysical observations, given the focus of exploration in semi-urban and rural places.
 With the aim to validate the proposed methodology we use as a case study the aquifer of Ñuble river, in the Ñuble region, Chile. This aquifer properly represents an Andean forearc environment in rural and semi-urban condition, and potentially hosting a deep seated aquifer. The results allow the characterization of an aquifer with hydrogeological potential between 50 and 300-500 depth, overlying a sedimentary basin of more than 1,000 m thickness. The application of the proposed methodology for the exploration of groundwater resources will provide, in consequence, the recognition of a vital relevance resource for the sustainability of Chile during the following decades.

Highlights

  • R siendo estratégico el proveniente de acuíferos

  • We propose the application of a combination of complementary geophysical techniques, including electrical, electromagnetic, and gravimetric methods along with complementary techniques, like magnetometry, to reduce interpretation ambiguity and, S constrained by hydrogeological information and petrophysics of rocks and sediments of the basin and basement

  • Yáñez G.; Perez-Estay, N.; Araya-Vargas, J.A.; Sanhueza, J.; Figueroa, R.; Maringue, J.; Rojas, T

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Summary

Introducción

Existe un amplio consenso en que el recurso hídrico es una necesidad de primer orden a nivel global, tanto para la vida humana como para los ecosistemas del planeta. Dadas las ventajas y desventajas que son inherentes a cada una de las técnicas geofísicas utilizadas para determinar la resistividad eléctrica del subsuelo en este trabajo metodológico se experimentó con ambas aproximaciones, Corriente Continua y Alterna. Las técnicas geofísicas más utilizadas y aceptadas y que permiten identificar esta transición son los métodos gravimétricos, geo-eléctricos, y sísmico (Telford y Sheriff, 1990). Nuestra estrategia para la estimación del amplio espectro de profundidades de basamento, utiliza métodos combinados, esencialmente mediante prospecciones geo-eléctricas (TEM y MT) y gravimétricas (ver caso de estudio en sección 4), complementándose en menor medida con prospecciones aeromagnéticas y de CC. Diversas estrategias se pueden aplicar para determinar este campo regional, por ejemplo, contar con información de sondajes y/o filtro de bajas frecuencias (utilizar un filtro pasa-bajo que elimine las longitudes de onda de decenas de kilómetros, asumiendo que están asociadas a fuentes gravimétricas profundas, e.g. Yáñez et al, 2015). P información complementaria (por ejemplo magnética regional, terrestre o aérea, teniendo en IN consideración que la magnetización de la cobertura sedimentaria debería ser en general solo marginalmente magnética comparada con el basamento)

Área de Estudio: cuenca hidrogeológica del Ñuble
Estudio geofísico
Perfil Hidrogeológico
E ND-0801-7134
Discusión
Conclusiones
Full Text
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