TY - JOUR A1 - Vales, Dina A1 - Dias, Nuno A. A1 - Rio, Ines A1 - Matias, Luis A1 - Silveira, Graca A1 - Madeira, Jose A1 - Weber, Michael H. A1 - Carrilho, Fernando A1 - Haberland, Christian T1 - Intraplate seismicity across the Cape Verde swell: A contribution from a temporary seismic network JF - Tectonophysics : international journal of geotectonics and the geology and physics of the interior of the earth N2 - We present an analysis and characterization of the regional seismicity recorded by a temporary broadband seismic network deployed in the Cape Verde archipelago between November 2007 and September 2008. The detection of earthquakes was based on spectrograms, allowing the discrimination from low-frequency volcanic signals, resulting in 358 events of which 265 were located, the magnitudes usually being smaller than 3. For the location, a new 1-D P-velocity model was derived for the region showing a crust consistent with an oceanic crustal structure. The seismicity is located mostly offshore the westernmost and geologically youngest areas of the archipelago, near the islands of Santo Antao and Sao Vicente in the NW and Brava and Fogo in the SW. The SW cluster has a lower occurrence rate and corresponds to seismicity concentrated mainly along an alignment between Brava and the Cadamosto seamount presenting normal faulting mechanisms. The existence of the NW cluster, located offshore SW of Santo Antao, was so far unknown and concentrates around a recently recognized submarine cone field; this cluster presents focal depths extending from the crust to the upper mantle and suggests volcanic unrest No evident temporal behaviour could be perceived, although the events tend to occur in bursts of activity lasting a few days. In this recording period, no significant activity was detected at Fogo volcano, the most active volcanic edifice in Cape Verde. The seismicity characteristics point mainly to a volcanic origin. The correlation of the recorded seismicity with active volcanic structures agrees with the tendency for a westward migration of volcanic activity in the archipelago as indicated by the geologic record. (C) 2014 Elsevier B.V. All rights reserved. KW - Intraplate seismicity KW - Clustering KW - Local magnitude scale KW - Active volcanism KW - Cape Verde KW - Atlantic Ocean Y1 - 2014 U6 - https://doi.org/10.1016/j.tecto.2014.09.014 SN - 0040-1951 SN - 1879-3266 VL - 636 SP - 325 EP - 337 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Matos, Catarina A1 - Silveira, Graca A1 - Matias, Luis A1 - Caldeira, Rita A1 - Ribeiro, M. Luisa A1 - Dias, Nuno A. A1 - Krüger, Frank A1 - Bento dos Santos, Telmo T1 - Upper crustal structure of Madeira Island revealed from ambient noise tomography JF - Journal of volcanology and geothermal research N2 - We present the first image of the Madeira upper crustal structure, using ambient seismic noise tomography. 16 months of ambient noise, recorded in a dense network of 26 seismometers deployed across Madeira, allowed reconstructing Rayleigh wave Green's functions between receivers. Dispersion analysis was performed in the short period band from 1.0 to 4.0 s. Group velocity measurements were regionalized to obtain 20 tomographic images, with a lateral resolution of 2.0 km in central Madeira. Afterwards, the dispersion curves, extracted from each cell of the 2D group velocity maps, were inverted as a function of depth to obtain a 3D shear wave velocity model of the upper crust, from the surface to a depth of 2.0 km. The obtained 3D velocity model reveals features throughout the island that correlates well with surface geology and island evolution. (C) 2015 Elsevier B.V. All rights reserved. KW - Madeira island KW - Volcanic rift zone KW - Crustal structure KW - Ambient noise tomography Y1 - 2015 U6 - https://doi.org/10.1016/j.jvolgeores.2015.03.017 SN - 0377-0273 SN - 1872-6097 VL - 298 SP - 136 EP - 145 PB - Elsevier CY - Amsterdam ER -