J. Miquel Torta

Geomagnetically induced currents in a power grid of northeastern Spain

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.

Regional modeling of the geomagnetic field in Europe from 6000 to 1000 B.C.

We have developed a first low-degree regional geomagnetic model for the European continent valid for the period 6000–1000 B.C. from a selected compilation of sedimentary and archeomagnetic data (the SCHA.DIF.8K model). This model provides information about both direction (declination and inclination) and intensity of the Earths magnetic field. By connecting it with our previous model, SCHA.DIF.3K, valid from 1000 B.C. to 1900 A.D., and the IGRF, we furnish continuous geomagnetic field information for the last 8000 years in Europe. It has been developed using the Revised Spherical Cap Harmonic Analysis in 2 Dimensions technique (R-SCHA2D) and using the norm of the Earths magnetic field to constrain the inversion problem. The size of the cap is 22°, and the maximum degree of the expansion is 2. The linearization problem was solved by using the truncated Taylors series applied to the expressions representing the relationship between the declination, inclination, and intensity data and the Cartesian components of the geomagnetic field. We used the geocentric axial dipole (GAD) field as our initial or reference field. For time, we used the classical sliding overlapping window method. The size of the window was set to 100 years shifted by 50 years. We compared the models prediction with the input data, with the global CALS7K.2 model, and with new independent data. The regional model shows a better fit to the input and to the independent data than the global model, especially in terms of intensity, and agrees with the virtual axial dipole moment given by other studies. For the last 8000 years, the European geomagnetic field has recorded rapid changes or archeomagnetic jerks. The average field for the last 8000 years in Europe is indistinguishable from the GAD field.

Analysis and modelling of the aeromagnetic anomalies of Gran Canaria (Canary Islands)

Abstract In this paper we present a crustal magnetic model of the volcanic island of Gran Canaria based on aeromagnetic data. This magnetic study has made it possible to constrain the location and geometry of: (1) the mafic core of Gran Canaria, built as the result of the crystallization of magmas which rose from the mantle during the submarine and shield basaltic stages of its evolution. The most intense magnetic high, displayed over the NW part of the island likely shows the main feeding system of the shield volcano; (2) the residual syenitic shallow magma chamber which fed the salic volcanic activity in the center of the island, linked to the formation of the Tejeda caldera and to the intrusion of felsic rocks which made up a cone sheet; (3) a reversely magnetized linear intrusion located in the marine area to the NW of the island, which could be related to the magmatic source of the submarine volcanism between Gran Canaria and Tenerife. Most of these magnetic sources show a linear pattern with trends that are in close agreement with the orientations of previously identified fractures. The magmatic intrusion to the NW of the island could be related with a WSW–ENE active fault between Gran Canaria and Tenerife, while the main trend and location of the mafic core agree with a NW–SE fault suggested by geological studies. This means that these magnetic sources are the result of the ascent and intrusion of magma along regional fractures. Therefore, this study provides fresh data which demonstrate the influence of regional tectonics on the growth of Gran Canaria during its entire evolution. Finally, the spectral analysis of the magnetic anomaly map suggests that it is possible that rocks located at mantle-like depths (from the Moho to about 23 km) behave as magnetic sources, a fact that can be related with the magmatic underplating detected by other geophysical techniques.

Evidence for a new geomagnetic jerk in 2014

The production of quasi-definitive data at Ebre observatory has enabled us to detect a new geomagnetic jerk in early 2014. This has been confirmed by analyzing data at several observatories in the European-African and Western Pacific-Australian sectors in the classical fashion of looking for the characteristic V shape of the geomagnetic secular variation trend. A global model produced with the latest available satellite and observatory data supports these findings, giving a global perspective on both the jerk and a related secular acceleration pulse at the core-mantle boundary. We conclude that the jerk was most visible in the Atlantic and European sectors.