Crustal Characterization of Portugal's mainland based on Magnetotelluric measurements. 

Abstract

<p>In the last decades, the phenomena of Geomagnetic Induced Currents (GICs) have received special attention as one of the main hazards of Space Weather and has been widely investigated. In the high and mid-latitudes, these large GICs can flow in power systems and become problematic and even severe enough to cause a complete system shutdown. Two major factors determine GICs: (1) the strength and orientation of the electric field in the power system, which depends on the ionospheric and magnetospheric currents as well as on the crust and mantle conductivity; and (2) the electric power network characteristics. The Earth's conductivity can be obtained based on geophysical measurements that give the distribution of the conductivity in-depth and laterally. A realistic model of conductivity can be built based on the interpretation of Magnetotelluric (MT) soundings. The power of this geophysical method resides in the fact that it uses a natural source of energy, which allows estimating the conductivity distribution from a dozen of meters to some kilometres in depth.</p><p>We present a 3D resistivity model of the entire Portugal mainland based on more than 40 broadband MT soundings spaced 50x50km. The present study aims to contribute to a better understanding of Portugal's crust and its main geological structures. As a more practical application, knowledge of the presence of resistivity/conductivity bodies is important to obtain more precise GICs estimations. </p><p> </p>

Toward More Accurate GIC Estimations in the Portuguese Power Network

“…The main resistivity anomalies identified in the MT inversion and shown in Figure 3 are discussed in Baltazar‐Soares et al. (2021), in the light of the geological data and tectonic models that exist for Portugal mainland.…”

“…The magnitude and orientation of the induced electric field E strongly depend on the subsurface conductivity structure (Bedrosian & Love, 2015) and, for this reason, a precise conductivity model is required. The 3D conductivity model for more accurate GIC estimations was calculated from 31 MT soundings acquired with a site spacing of approximately 50 × 50 km (Baltazar‐Soares et al., 2021) (Figure 3), and will be called B‐S conductivity model in the following. Eight MT soundings located in the south region of Portugal were acquired between 1997 and 2002 with a 03E and GMS‐06 systems (Almeida et al., 2005; Alves Ribeiro, 2018; Da Silva et al., 2007).…”

“…The most recent MT soundings were taken during 2020‐21, in the framework of the MAG‐GIC project, using GMS‐06, and GMS‐07 systems. The electric field components E x and E y were measured in the N‐S and E‐W directions with a dipole length of approximately 100 m. The two horizontal magnetic field components B x and B y were acquired along the same directions as the electric field (Baltazar‐Soares et al., 2021).…”

“…The MT method is a passive electromagnetic geophysical method that measures the variations of the natural electric and magnetic fields at the surface of the Earth (Cagniard, 1953; Tikhonov, 1950). From the gathered data set, and after selection tests were applied, an empirical 3D conductivity model for the whole territory was inverted (Baltazar‐Soares et al., 2020, 2021). In this study, we use Baltazar‐Soares et al.…”

“…In this study, we use Baltazar‐Soares et al. (2021) (B‐S) conductivity model to simulate GICs in the global Portuguese power network. Furthermore, the national transmission system operator, REN (Redes Energéticas Nacionais), has provided most of the required circuit parameters, such as the location of substations and their grounding resistances, the characterization of each transformer and information about the transmission lines regarding resistance and length values.…”