Numerical Simulations of Terrestrial Heat Flow in the Beiras Region, Mainland Portugal

Duque, Maria Rosa Alves

doi:10.31214/ijthfa.v3i1.48

Cited by 4 publications

(3 citation statements)

References 11 publications

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“…The location of data can be seen in Figure 1 with borehole location in black and wells location in sedimentary basins in brown. Due to the lack of data in the northern and central part of the territory, numerical models were made [5][6] [7] to obtain more heat flow values in these regions. and using numerical models (red).…”

Section: Heat Flow Density Data In Mainland Portugalmentioning

confidence: 99%

“…Due to scarcity of data in some regions it was very difficult to build maps, define regions with identical properties and obtain statistical values that can characterize them. More heat flow values were obtained in recent years [5][6] [7] using numerical models based in some characteristics of the region obtained from seismological data [8], heat production by radioactivity [9] [10], fault location and tectonics of the region. The method assumes that the heat flow value at the surface is the result of adding to the heat flowing from the deeper zones and arriving at the base of the crust as heat flowing from the mantle , Qm, the heat flow generated by crustal heat sources, Qc.…”

Section: Introductionmentioning

confidence: 99%

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Geotermalny przepływ ciepła w Portugalii kontynentalnej

Duque

2024

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Heat flow density measurements in Portugal were made in boreholes used for mining prospecting. Heat flow density values in the sedimentary basins of the western and southern margins of the country were obtained using data from oil or gas prospecting works. Due to the scarcity of data in the central and northern regions of the country, numerical models based on some characteristics of the region were used to obtain more heat flow values. The total of heat flow values used in this work is 69, with 17 values obtained using numerical models, 36 obtained in boreholes and 16 obtained from oil/gas prospecting wells data. The analysis and location of these data allows to define different regions in the territory and characterize them using average values of heat flow density, temperature gradient and thermal conductivity. Statistical values with all the data in the territory are also presented.

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Section: Heat Flow Density Data In Mainland Portugalmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Geotermalny przepływ ciepła w Portugalii kontynentalnej

Duque

2024

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“…Thus, a higher geothermal gradient would reduce its thickness. Heat flow data in the specific area are heterogeneously distributed, showing important variations across strike (Duque, 2020; Fernández et al., 1998; Marzán, 2000) (Figure 1b). In general terms, NW Iberia reaches 60–80 mW/m 2 in the southwest of the region decreasing toward the east to 50 mW/m 2 in the Cantabrian Mountains.…”

Section: Introductionmentioning

confidence: 99%

New Insights into the Lateral‐Strength Variations and Depth to the Brittle‐Ductile Transition Zone in NW Iberia

2021

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The mechanism of faulting is controlled by pressure, temperature, fluid pressure, and strain-rate leading to brittle fracture and frictional slip in the upper levels of the continental crust, and ductile flow at greater depths (Pollard & Fletcher, 2005; Tullis & Yund, 1977). The transition from one domain to the other is defined by the brittle-ductile transition zone (BDTZ), which also represents the transition between the rheological changes from cataclasis to crystal plasticity (e.g., Stewart et al., 2000). This boundary demarcates the limit of the seismogenic zone (with 95% of all seismicity, Magistrale, 2002). This sharp level correlates to the depth to which earthquakes occur in the continental interiors due to the rapid reduction of resistance to shearing (e.g., Long & Zelt, 1991; Sibson, 2007). This boundary is controlled by factors affecting the deformation mechanisms, such as temperature, pressure, strain rate, composition, pore fluid pressure, and tectonic stress (Stewart et al., 2000; Tullis & Yund, 1977). Variations in these factors are responsible for changes of the BDTZ depth and therefore the thickness of the seismogenic crust (Figure 1a). In most tectonic regions, earthquakes are occurring in the shallow part of the lithosphere (C. Scholz, 1988), where rock strength is mostly controlled by thermo-mechanical properties (i.e., rheology and thermal gradient), crustal thickness and rock composition (Maggi et al., 2000; Watts & Burov, 2003). Early observations of brittle-plastic transition provide evidence of increasing plastic flow with depth and the progressive change in the physical factors that control rock deformation (Sibson, 1977). The BDTZ represents a transition in which semi-brittle deformation dominates (C. H. Scholz, 2002). This shift constrains the maximum depth at which earthquakes can occur and represents a mixture of brittle and plastic processes at the microscale, while the rheology is macroscopically ductile (Karato, 2012; C. Scholz, 1988).

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Heat Flow in SW of Galicia And NW of Portugal. The Interpretation of a Seismic Anomaly

Duque

2020

IOP Conf. Ser.: Earth Environ. Sci.

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Four heat flow density values and five temperature-depth profiles were obtained in a heterogeneous region considering heat flow by conduction in the vertical direction, and heat sources in the crust due to radioactivity decay. The heat produced in the upper layers of the crust was obtained based on gamma-ray charts and published data of laboratory radioactivity measurements on samples taken from the region. Seismic data were used to obtain the thickness of the different layers of the upper and middle crust and the depth of the Moho discontinuity considered coincident with the crust/mantle boundary. The heat flow at the surface is obtained by adding the heat flow from the mantle with the heat generated by the radioactive sources in the crust. The method was applied to a region with one measured heat flow density value (Ourense) and four points without any heat flow density measurement. A heat flow value from the mantle was obtained with Ourense data. Special attention was given to a region (A) with a seismic anomaly near the surface. The anomaly was explained by mass deficit near the surface that gives rise to an abnormal density value and an increase in seismic wave velocity values. The decrease in density is due to the presence of water in the region forming an aquifer. Geothermometer values obtained from samples of water in the thermal springs of Tuy (Spain) and Monção (Portugal) were used as the water temperature at the bottom of the aquifer. Isostatic balance in the region was considered to obtain density values and the amount of water in the region. Thermal conductivity and radioactivity heat source values in the region were obtained considering the amount of water in the region. Values from 86 to 97 mW/m2 were obtained using the same value of heat flow from the mantle. This is due to different values of heat produced in the crust due to different thickness layer values or/and to different heat production values.

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Numerical Simulations of Terrestrial Heat Flow in the Beiras Region, Mainland Portugal

Cited by 4 publications

References 11 publications

Geotermalny przepływ ciepła w Portugalii kontynentalnej

Geotermalny przepływ ciepła w Portugalii kontynentalnej

New Insights into the Lateral‐Strength Variations and Depth to the Brittle‐Ductile Transition Zone in NW Iberia

Heat Flow in SW of Galicia And NW of Portugal. The Interpretation of a Seismic Anomaly

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