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- Recent Macaronesian kinematics from GNSS ground displacement analysisPublication . Barbero, Ignacio; Torrecillas, Cristina; Paez, Raul; Prates, Gonçalo; Berrocoso, ManuelMacaronesia is a complex oceanic region spanning three tectonic plates in the northeast Atlantic ocean. It is composed of four archipelagos, widely distributed and limited to the east by the Iberian Peninsula and north-western coast of Africa. This study aims to clarify recent Macaronesian kinematics from 19 GNSS stations located on the four archipelagos and the Iberian and African coastlines. The analysis is based on nearly 15 years of common data acquisition and aimed to detect new effects of intraplate tectonics or similar local/regional events consistent with calculated ground displacements. Evaluating the GNSS stations residual velocities relative to those expected from the NNR-MORVEL56 model, higher residuals were found at continental coastal stations (Africa) than at oceanic ones (Canaries and Madeira). From the computed strain rate map, the possible existence of a shear zone connecting the Gloria and Transmoroccan fault systems, already mentioned by other authors, was depicted. Cluster statistical analysis of the horizontal residual velocities helped to identify tectonic boundaries in Macaronesia and four groups of analogous intraplate residual velocities within this region. Three of four groups were identified in the Azores, highlighting the African-Nubian-Eurasian diffuse plate boundary in this region. Furthermore, in the Canary Islands, two distinct kinematic behaviours were detected, possibly due to the activity along a previously detected tectonic fault between Tenerife and Gran Canaria, where some stations have similar intraplate residuals to those at Madeira and Cape Verde stations, while others have similar intraplate residuals to those of continental stations. Finally, all stations on oceanic crust, except Cape Verde, present recent ground subsidence which may be attributed to isostatic adjustment.
- Deception Island 1967–1970 volcano eruptions from historical aerial frames and satellite imagery (Antarctic Peninsula)Publication . Prates, Gonçalo; Torrecillas, Cristina; Berrocoso, Manuel; Goyanes, Gabriel; Vieira, GonçaloAerial frames and satellite imagery are widely recognized data sources from which to produce maps. For volcanoes, maps enable the quantification of erupted ash and the destruction caused. The last eruptive sequence on Deception Island was endured from 1967 to 1970. Analogue maps were produced via classical photogrammetric methods with a high degree of human intervention mainly to analyse the volcanic-centres areas only. However, historical aerial frames cover the whole of Deception Island. Structure from motion photogrammetry, a near-automated compilation of digital image processing strategies, minimizes the degree of human intervention to produce orthographic mosaics and digital elevation models from digital aerial frames. Orthographic mosaics were produced from historical aerial frames of 1956 and 1968, and a Kompsat-3 image of 2020. Their shared rootmean-square deviation was 1.8 m and 1.7 m in easting and northing, respectively, at ground control points measured with phase-differential global navigation satellite systems. The digital elevation models were processed with a root-mean-square deviation of 2.3 m and 3.6 m from 1956 and 1968 aerial frames, respectively. As the first application, erupted ashfall and the subsequent destruction, mainly at the former Chilean and British bases, were identified, and the volume of erupted ash was assessed to be over 0.16 km3 within the area mapped by these new digital cartographic products.
- The time lag between deformation process and seismic activity in El Hierro Island during the eruptive process (2011–2014): a functional phased approachPublication . Pérez-Plaza, Sonia; Berrocoso, Manuel; Rosado, Belén; Prates, Gonçalo; Fernández-Palacín, FernandoOn 10 October 2011, a submarine eruption occurred in El Hierro island. Thus, the eruptive process in the Canary islands was reactivated after 40 years of inactivity. The main objective of this work is to evaluate, using Functional Data Analysis, how the surface deformation phenomenon explains the seismic–volcanic activity in the island. The GNSS-GPS data are from the FRON (GRAFCAN) station, located in Frontera. These data measure, each 4 h, the distance between the FRON station and the reference station LPAL (La Palma island) from August, 2010 to December, 2013. In this study a functional correlation measure is employed to establish the relation between the deformation curve and the curve of cumulative energy released. The period of time analysed has been divided into four phases to avoid the mix of phenomena. For each phase, the correlation measure and the time lag between deformation curve and the curve of cumulative energy released have been estimated. These values show a strong relation between these curves. With respect to time lag period, the only signifcant lag, of about 1 month, occurred in Phase 1, which was after a long period without seismic activity. The later phases had very short, insignifcant, lags. After a long period without seismic and volcanic activity in El Hierro island, the time lag between the deformation process and the beginning of the seismic activity takes approximately 1 month. In a similar situation a method to predict in real time the beginning of the seismic activity is proposed. This method, based on the changes produced in the derivative curves when there is a rapid descent in the deformation curve, could activate a warning system approximately 13 days before the beginning of seismicity.