Browsing by Author "Perez-Estay, N."

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    Reactivation of Fault Systems by Compartmentalized Hydrothermal Fluids in the Southern Andes Revealed by Magnetotelluric and Seismic Data
    (2020) Pearce, R. K.; Sanchez de la Muela, A.; Moorkamp, M.; Hammond, J. O. S.; Mitchell, T. M.; Cembrano, J.; Araya Vargas, J.; Meredith, P. G.; Iturrieta, P.; Perez-Estay, N.; Marshall, N. R.; Smith, J.; Yanez, G.; Ashley Griffith, W.; Marquardt, C.; Stanton-Yonge, A.; Nunez, R.
    In active volcanic arcs such as the Andean volcanic mountain belt, magmatically sourced fluids are channeled through the brittle crust by faults and fracture networks. In the Andes, volcanoes, geothermal springs, and major mineral deposits have a spatial and genetic relationship with NNE trending, margin-parallel faults and margin-oblique, NW trending Andean Transverse Faults (ATF). The Tinguiririca and Planchon-Peteroa volcanoes in the Andean Southern Volcanic Zone (SVZ) demonstrate this relationship, as their spatially associated thermal springs show strike alignment to the NNE oriented El Fierro Thrust Fault System. We constrain the fault system architecture and its interaction with volcanically sourced hydrothermal fluids using a combined magnetotelluric (MT) and seismic survey that was deployed for 20 months. High-conductivity zones are located along the axis of the active volcanic chain, delineating fluids and/or melt. A distinct WNW trending cluster of seismicity correlates with resistivity contrasts, considered to be a reactivated ATF. Seismicity occurs below 4 km, suggesting activity is limited to basement rocks, and the cessation of seismicity at 9 km delineates the local brittle-ductile transition. As seismicity is not seen west of the El Fierro fault, we hypothesize that this structure plays a key role in compartmentalizing magmatically derived hydrothermal fluids to the east, where the fault zone acts as a barrier to cross-fault fluid migration and channels fault-parallel fluid flow to the surface from depth. Increases in fluid pressure above hydrostatic may facilitate reactivation. This site-specific case study provides the first three-dimensional seismic and MT observations of the mechanics behind the reactivation of an ATF.
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    Shallow anatomy of hydrothermal systems controlled by the Liquin?e-Ofqui Fault System and the Andean Transverse Faults: Geophysical imaging of fluid pathways and practical implications for geothermal exploration
    (PERGAMON-ELSEVIER SCIENCE LTD, 2022) Perez-Estay, N.; Molina-Piernas, E.; Roquer, T.; Aravena, D.; Vargas, J. Araya; Morata, D.; Arancibia, G.; Valdenegro, P.; Garcia, K.; Elizalde, D.
    We combined geoelectric and seismic ambient noise methods to image the shallow depth (<30 m) distribution of thermal waters in two fault-controlled hydrothermal systems located in southern Chile. The bedrock depth was constrained with seismics, while hotsprings and mapped faults were imaged by low-electrical-resistivity domains (<160 omega m) defined with electrical resistivity tomographies (ERT). The distribution and shape of low-resistivitydomains suggest that thermal fluids follow complex pathways, including deep vertical conduits hosted in fractured rock and shallow horizontal bodies hosted in sediments. These results indicate that the studied hydrothermal systems are at least twice longer within the sediments than the superficial area covered by hotsprings.
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    Soil electrical resistivity monitoring as a practical tool for evaluating irrigation systems efficiency at the orchard scale: a case study in a vineyard in Central Chile
    (2021) Vargas, J. Araya; Gil, P. M.; Meza, F. J.; Yanez, G.; Menanno, G.; Garcia-Gutierrez, V; Luque, A. J.; Poblete, F.; Figueroa, R.; Maringue, J.; Perez-Estay, N.; Sanhueza, J.
    In many orchards, irrigation scheduling is designed based on data from meteorological networks and considering homogeneous soil properties. Such assumptions may result in inefficient irrigation, which is difficult to constrain without expensive or invasive techniques. Here we have evaluated the ability of the electrical resistivity tomography (ERT) for detecting meter-scale irrigation uniformity and deep percolation during irrigation. The spatiotemporal variability of soil volumetric water content (VWC) in a vineyard located near Santiago (Chile) was inferred using ERT monitoring of two irrigation cycles. The electrical resistivity structure up to 4 m depth was estimated using two-dimensional inversion of ERT data. ERT results were verified by comparing resistivity models with VWC measured with soil moisture sensors, soil properties mapped in a 2 m-depth soil pit, and the spatiotemporal evolution of VWC obtained by solving numerically Richards equation. Largest temporal variations of resistivity were observed within the root depth (1 m) and are consistent with expected relative changes in VWC during irrigation. ERT images exhibit lateral changes in resistivity at these depths, likely indicating non-uniform infiltration of water controlled by observed soil texture variations. Resistivity changes were also observed below the root zone, suggesting that a fraction of the irrigation water percolates downward. These findings can be explained by an excess of irrigation water applied during the monitoring, which was planned considering regional evapotranspiration (ET) data that overestimated the actual ET measured at the vineyard. Altogether, our results suggest that ERT monitoring during irrigation is a cost-effective tool to constrain the performance of irrigation systems.