The CHIMERA project, contracted by the Portuguese Environment Agency (APA) and co-funded by the EuropeanUnion Cohesion Fund (Portugal 2020 | POSEUR) intended to characterize the sedimentary record of three 10km2 areas and one 5 km2 area in the Portuguese inner shelf. Multibeam bathymetry and backscatter, parametricecho-sounder, ultra-high resolution multichannel seismics and magnetic data were acquired along high resolutionorthogonal grids. The main aim of the project was to evaluate potential borrow areas for high-magnitude beachnourishments in long term eroding stretches of the Portuguese western coast. The diversity, the large density andthe high quality of geophysical data allow for a multidisciplinary geological interpretation of the datasets.In this presentation we focus on magnetic data and its interpretation combined with acoustic data. We applieda detailed processing scheme to acquired magnetic data, which allowed retrieving several components of themagnetic spectrum and estimating some source depths. We then analyzed the geological significance of theanomalies by studying their correspondence to seismostratigraphic units mapped from seismic data. Fit betweenmagnetic signature and geologic structure was found for most of the cases, although magnetic anomalies withinthe same wavenumber spectrum may express different geological units for each study area. A correspondence wastypically found for the basement, and for recent sedimentary structures such as paleo-channels and paleo-coastalbarriers. In other cases, low wavenumber anomalies may express intra-basement geology, too deep to be observedby our high-resolution seismics. For individual anomalies we check for a relation with shallow features, eventuallyarcheological artifacts.Publication supported by FCT- project UID/GEO/50019/2019 - Instituto Dom Luiz.

The irregular variation of geomagnetic activity, caused by the solar wind interaction with the magnetosphere/ionosphere, occurs in a wide time interval (from seconds to annual and even larger periods) and amplitude ranges (from few to hundreds of nT). Major variation events (geomagnetic storms) can cause damaging effects and important perturbations to different human activities such as satellite communications, long distance radio broadcasting, navigation, surveying, etc. Furthermore, the induction of electric currents (geomagnetically induced currents – GICs) may affect all grounded conducting networks, in particular electrical power transmission systems. Useful proxies of GIC effects are still under debate; here, we identify the pros and cons of some different candidates. The intensity of geomagnetic activity is usually characterized by geomagnetic indices, among which the 3-hourly indices Kp and local K. In this study we compare 3-hour K and 1-hour K-derived local range indices, using geomagnetic time series from the mid-latitude Coimbra observatory (COI), in Portugal. We also compute smaller time-resolution geomagnetic and GIC indices such as the geomagnetic horizontal field components and their time derivatives, horizontal field magnitude and its time derivative and the LDi/LCi indices [Cid19]. We compare the computed indices with GIC simulations in the Portuguese transmission power grid, to evaluate which of them may be used to nowcast the induced currents. We suggest as a better GIC proxy, an index obtained from geomagnetic field components filtered by convolution with the uniform conductivity Earth filter (new EGIC index). Previous studies have considered the local ground conductivity to be an important factor to determine GIC amplitudes (e.g. [Tri07] and [Rib21]). We then obtain GIC estimations for power grid substations lying at different geological regions. Acknowledgements: This study is funded by national funds through FCT (Portuguese Foundation for Science and Technology, I.P.), under the project MAG-GIC (PTDC/CTA-GEO/31744/2017). FCT is also acknowledged for support through projects UIDB/50019/2020-IDL, PTDC/CTA-GEF/1666/2020 (MN) and PTDC/CTA-GEO/031885/2017 (MN). CITEUC is funded by FCT (UIDB/00611/2020 and UIDP/00611/2020). We acknowledge the collaboration with REN (Redes Energéticas Nacionais).

The SW Portuguese margin has been intensively studied, particularly for rifting, tectonic inversion and tectonic reactivation of the Atlantic passive margin. In this work we bring new data on the continental shelf, usually not acquired by the heavier geophysical methods (e.g. airborne or low resolution deep seismic-magnetic surveys). These new data allow casting a clear light bridging between the geological structures onshore and offshore. The geology of this margin went through the Variscan orogeny of Paleozoic age, the North Atlantic rifting, the Late Cretaceous alkaline magmatism (intrusive and extrusive), the Alpine tectonic inversion and the Quaternary reactivation of the passive margin. We present results from the compilation of a series of marine magnetic surveys conducted along the Portuguese nearshore from 2014 to 2019. Magnetic data were acquired with 1 nautic mile line separation, resulting in near full coverage of the nearshore along a 120 km long margin segment, from Sintra to Odeceixe. For a large part of the surveyed area, ultra-high resolution seismics and multibeam bathymetry were simultaneously acquired. Magnetic data were processed to produce high resolution mapping of magnetic anomalies, and also to enhance both shallow and deep structures, using several derivative and filtering techniques. We combine the interpretation of high-resolution magnetic mapping with the interpretation of ultra-high resolution and vintage deep penetration seismic data to infer the local and regional expression of tectonic structures and magmatic bodies. Our results allow: identifying the offshore extension of important faults, e.g. the Grândola, Pinhal Novo and Messejana faults; resolving previously blurry-imaged magmatic structures, e.g. Sines and Cabo Raso anomalies; identifying faults recycled from the Paleozoic through Present; constraining the relation between magmatic intrusions and faults; and bringing constraints to the discussion of magmatic emplacement.