Electrical resistivity model of the crust and upper mantle from a magnetotelluric survey through the central Pyrenees

Pous, J.; Ledo, Juanjo; Marcuello, Álex; Daignières, M.

doi:10.1111/j.1365-246x.1995.tb06436.x

Cited by 43 publications

(43 citation statements)

References 29 publications

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“…Sénéchal et al (1996), for instance, through coupled shear wave splitting measurements and magnetotelluric soundings along a transect in the Canadian shield, retrieved similar directions of anisotropy from both datasets and, considering that the measured electrical anisotropy originates between 50 and 150 km, they concluded that the seismic anisotropy also originates from a well-defined fabric in the lithospheric upper mantle fabric. Similar preliminary results have been obtained in the Appalachians (Wannamaker et al, 1996) and the Pyrenees (Pous et al, 1995;M. Daignières, pers.…”

Section: Tectonic Fabric Of the Continental Lithospheric Mantlesupporting

confidence: 74%

“…(f) Magnetotelluric soundings in the Pyrenees (Pous et al, 1995) have imaged a steeply dipping boundary that penetrates into the upper mantle beneath the North Pyrenean fault, suggesting that the fault crosscuts the Moho. Electrical anisotropy measurements in the Canadian shield (Sénéchal et al, 1996) and the eastern US (Wannamaker et al, 1996) show a very good agreement between the directions of conductivity anisotropy in the upper mantle and the crustal tectonic fabric, suggesting that the mantle and the crustal fabrics are similar.…”

Section: Rheology Of the Lithospherementioning

confidence: 99%

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Rheological heterogeneity, mechanical anisotropy and deformation of the continental lithosphere

1998

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This paper aims to present an overview on the influence of rheological heterogeneity and mechanical anisotropy on the deformation of continents. After briefly recapping the concept of rheological stratification of the lithosphere, we discuss two specific issues: (1) as supported by a growing body of geophysical and geological observations, crust=mantle mechanical coupling is usually efficient, especially beneath major transcurrent faults which probably crosscut the lithosphere and root within the sublithospheric mantle; and (2) in most geodynamic environments, mechanical properties of the mantle govern the tectonic behaviour of the lithosphere. Lateral rheological heterogeneity of the continental lithosphere may result from various sources, with variations in geothermal gradient being the principal one. The oldest domains of continents, the cratonic nuclei, are characterized by a relatively cold, thick, and consequently stiff lithosphere. On the other hand, rifting may also modify the thermal structure of the lithosphere. Depending on the relative stretching of the crust and upper mantle, a stiff or a weak heterogeneity may develop. Observations from rift domains suggest that rifting usually results in a larger thinning of the lithospheric mantle than of the crust, and therefore tends to generate a weak heterogeneity. Numerical models show that during continental collision, the presence of both stiff and weak rheological heterogeneities significantly influences the large-scale deformation of the continental lithosphere. They especially favour the development of lithospheric-scale strike-slip faults, which allow strain to be transferred between the heterogeneities. An heterogeneous strain partition occurs: cratons largely escape deformation, and strain tends to localize within or at the boundary of the rift basins provided compressional deformation starts before the thermal heterogeneity induced by rifting are compensated. Seismic and electrical conductivity anisotropies consistently point towards the existence of a coherent fabric in the lithospheric mantle beneath continental domains. Analysis of naturally deformed peridotites, experimental deformations and numerical simulations suggest that this fabric is developed during orogenic events and subsequently frozen in the lithospheric mantle. Because the mechanical properties of single-crystal olivine are anisotropic, i.e. dependent on the orientation of the applied forces relative to the dominant slip systems, a pervasive fabric frozen in the mantle may induce a significant mechanical anisotropy of the whole lithospheric mantle. It is suggested that this mechanical anisotropy is the source of the so-called tectonic inheritance, i.e. the systematic reactivation of ancient tectonic directions; it may especially explain preferential rift propagation and continental break-up along pre-existing orogenic belts. Thus, the deformation of continents during orogenic events results from a trade-off between tectonic forces applied at plate boundaries, plate geometry,...

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Section: Tectonic Fabric Of the Continental Lithospheric Mantlesupporting

confidence: 74%

Section: Rheology Of the Lithospherementioning

confidence: 99%

Rheological heterogeneity, mechanical anisotropy and deformation of the continental lithosphere

1998

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“…We practiced either with a uniform ground conductivity of σ = 0.001 S/m (as in Torta et al 2012) or with different layered conductivity models. For the latter, we chose either the electrical resistivity model given by Pous et al (1995) for the Ebre basin or the 1-D ground model of the #29 block in Figure 2 by Viljanen et al (2012). In Table 4, we give the linear correlation coefficients for each case, but in our opinion, this measure is not always the best indicator for quantifying the goodness of such model performances.…”

Section: Comparisons With Gic Measurementsmentioning

confidence: 99%

“…The measured GIC is in red. The results are from analyses that used either a uniform ground conductivity set to 0.001 S/m (blue), a layered conductivity structure according to Pous et al (1995) (green), a layered conductivity structure according to Viljanen et al (2012) (black), or a uniform ground conductivity under the condition where the Vandellòs-Pierola transmission line was switched off (pink). one lies in the fact that Torta et al (2012) used the timedomain integral approach to infer the electric field from the geomagnetic variation data by setting M equal to just 30 min.…”

Section: Comparisons With Gic Measurementsmentioning

confidence: 99%

Assessing the hazard from geomagnetically induced currents to the entire high-voltage power network in Spain

2014

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After the good results obtained from an assessment of geomagnetically induced currents (GICs) in a relatively small subset of the Spanish power transmission network, we now present the first attempt to assess vulnerability across the entire Spanish system. At this stage, we have only included the power grid at the voltage level of 400 kV, which contains 173 substations along with their corresponding single or multiple transformers and almost 300 transmission lines; this type of analysis could be extended to include the 220-kV grid, and even the 110-kV lines, if more detailed information becomes available. The geoelectric field that drives the GICs can be derived with the assumption of plane wave geomagnetic variations and a homogeneous or layered conductivity structure. To assess the maximum expected GICs in each transformer as a consequence of extreme geomagnetic storms, a post-event analysis of data from the Ebre Geomagnetic Observatory (EBR) during the 2003 Halloween storm was performed, although other episodes coincident with very abrupt storm onsets, which have proven to be more hazardous at these mid-latitudes, were analyzed as well. Preferred geomagnetic/geoelectric field directions in which the maximum GICs occur are automatically given from the grid model. In addition, EBR digital geomagnetic data were used to infer statistical occurrence probability values and derive the GIC risk at 100-year or 200-year return period scenarios. Comparisons with GIC measurements at one of the transformers allowed us to evaluate the model uncertainties.

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“…Based on a model of electrical resistivity from magnetotelluric measurements, which includes a NS profile from the Pyrenees to near the Mediterranean coast along about the meridian 1 E [Pous et al, 1995], it can be observed that it varies strongly with depth and, specially, below a depth of 30 km, with the latitude as well. Due to the relatively low frequency of the phenomena under concern, small-scale conductivity anomalies near the surface are not important when calculating the geoelectric field that causes the GIC, as these fields penetrate to a certain depth.…”

Section: Gic Modelingmentioning

confidence: 99%

Geomagnetically induced currents in a power grid of northeastern Spain

et al. 2012

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[1] Using the geomagnetic records of Ebro geomagnetic observatory and taking the plane wave assumption for the external current source and a homogeneous Earth conductivity, a prediction of the effects of the geomagnetic activity on the Catalonian (northeastern Spain) power transmission system has been developed. Although the area is located at midlatitudes, determination of the geoelectric field on the occasion of the largest geomagnetic storms during the last solar cycles indicates amplitudes that are higher than those recorded in southern Africa, where some transformer failures on large transmission systems have been reported. A DC network model of the grid has been constructed, and the geomagnetically induced current (GIC) flows in the power network have been calculated for such extreme events using the electric field at Ebro as a regional proxy. In addition, GICs have been measured at one transformer neutral earthing of the power grid, so that there the accuracy of the model has been assessed. Although the agreement is quite satisfactory, results indicate that better knowledge of the ground conductivity structure is needed. This represents the first attempt to study and measure GICs in southern European power grids, a region considered to have low GIC-risk up to the present.

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Electrical resistivity model of the crust and upper mantle from a magnetotelluric survey through the central Pyrenees

Cited by 43 publications

References 29 publications

Rheological heterogeneity, mechanical anisotropy and deformation of the continental lithosphere

Rheological heterogeneity, mechanical anisotropy and deformation of the continental lithosphere

Assessing the hazard from geomagnetically induced currents to the entire high-voltage power network in Spain

Geomagnetically induced currents in a power grid of northeastern Spain

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