Abstract
The integration of geophysical methods, together with the previous information of the Vallès basin area, has resulted in the creation of a new conceptual model that explains La Garriga-Samalús geothermal system. The integration of complementary geophysical methods seems to be a good option for the preliminary stages of a geothermal system exploration, especially in urban areas.An integrated seismic ambient noise, magnetotellurics, and gravity methods were used to determine the geological units and structures which control the La Garriga-Samalús geothermal system. The 2D resistivity and density models have allowed the identification of the four main units which regulate the geothermal system: the Miocene basin, the Prelitoral Range unit, the Vallès Faut Zone, and the Paleozoic basement. The interpretation of our models set the Vallès Fault Zone, which is characterized by an anomalous low resistivity and low density, as the main path for the hot fluids. Moreover, the geophysical characterization established a new geometry for the Miocene basin. The Miocene basin presents a stepwise morphology, with the minor thickness towards the fault and an increasing thickness towards the center of the basin. This geometry seems to be related to synthetic normal faults.These results have evidenced that, although, in some geothermal systems, the warm water may create an insufficient physical contrast; the appropriate use of some techniques can still be useful for the exploration of medium and low-temperature geothermal systems.
Highlights
We have considered the compiled values of density and electrical resistivity (Manger and Nolan, 1963; Schon, 2015; Tenzer et al, 2011; Wald et al, 2013), as well as the geological map (Fig. 2), to assign the following geological units to our models: the Miocene basin, the Prelitoral range unit, the Valles Fault Zone, and the Paleozoic basement (Table 2)
The present integrated geophysical study demonstrates that the combination of different geophysical methods, based on different physical properties, are an efficient option during the preliminary phase of the geothermal exploration
We have presented a multi-physics characterization of the La Gar riga-Samalús geothermal system to create a new conceptual model
Summary
The role of geophysics in the exploration of geothermal resources has been discussed in several review papers (Banwell, 1973, 1970; Bod varsson, 1970; Manzella, 1973; Meidav and Tonani, 1976; Palmason, 1976; Shah et al, 2015), and it has been definitely set among the main disciplines which allows the characterization and monitoring of a geothermal system (Abdelfettah et al, 2018; Chambefort et al, 2016; Hermans et al, 2014; Hunt et al, 2009; Kana et al, 2015; Peacock et al, 2013).Geophysical exploration involves taking measurements at or near the Earth’s surface that are influenced by the internal distribution of phys ical properties. (Di et al, 2006; Lüschen et al, 2014; Moeck et al, 2015; Yousefi et al, 2019; Zhang et al, 2012) This renewable energy has an enormous potential in populated regions, where the demand is contin uously growing and there is a need of reducing the reliance on highly polluting energies (Kraft et al, 2009; Schiel et al, 2016). In this geographical context, the development of geophysical surveying, prop erly applied, can optimize exploration programs by maximizing the rate of ground coverage and minimizing the drilling requirement (Kearey et al, 2002). The physical property contrast in the subsurface of the study area would condition the quality of the geophysical results (Benson et al, 2003)
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