Geophysical study of viability for a new geomagnetic observatory at São Marcos (Portugal)

Abstract

<p>The magnetic observatory of Coimbra (IAGA code COI) measures the geomagnetic field components since 1866. These long time series were disturbed by the urban expansion in Coimbra city, causing anthropogenic perturbations in particular to the high frequency spectral band of the vertical Z component.</p><p>We plan to move the observatory to another site with less magnetic disturbances. The new site is about 15 km west of Coimbra over limestone Cretaceous terrains, in São Marcos (SMC). It is far from important industrial facilities, high voltage lines, and DC electrified railways. This farm is under administration of the University of Coimbra and is surrounded by walls.  </p><p>Both magnetic surveys and electrical soundings were carried out at SMC. Results show low values for the magnetic gradients and resistivity profiles of relatively low to moderate values (~ 10-1000 ohm.m), typical of the studied lithological types (sandstone, marl and limestone). In this study we characterize the geomagnetic field as measured at SMC, in comparison with COI and SPT (San Pablo/Toledo) in Spain, the nearest observatory in the INTERMAGNET network of magnetic observatories.</p>