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García, Alicia
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García, Alicia
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- PublicationRestrictedNew evidence about the structure and growth of ocean island volcanoes from aeromagnetic data: The case of Tenerife, Canary Islands(2011)
; ; ; ; ; ;Blanco Montenegro, I.; Departamento de Física, Universidad de Burgos, Burgos, Spain. ;Nicolosi, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Pignatelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;García, A.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain. ;Chiappini, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; ; ; ; We present 3-D magnetic models of Tenerife based on a high-resolution aeromagnetic survey carried out in 2006. Two different inverse modeling techniques have been applied: (1) a linear method aimed at imaging lateral magnetization contacts and (2) a nonlinear method aimed at obtaining a 3-D description of deep intrusive bodies, in which a constant magnetization value characterizes the main sources. Magnetic models show that deep intrusive structures are located beneath the northern part of the island and aligned along the E-W direction. This arrangement of intrusive bodies does not support the hypothesis of a three‐armed rift system that has been present since the early formation of the island. The shallow portion of the intrusive structures shows a round geometry that agrees with the previously proposed location of some of the landslide headwalls, suggesting that collapse scars have acted as preferential sites for magma upwelling. Our magnetic model probably provides the first geophysical evidence of the location of the headwall of the Icod landslide beneath the Teide‐Pico Viejo complex, thus supporting the vertical collapse hypothesis for the origin of the Cañadas caldera. The largest intrusive complex is located to the northwest of Teide and Pico Viejo, revealing the presence of a very high dike density in this area. This complex probably resulted from the intrusion of magma over the span of millions of years, beginning with the early phases of basaltic shield volcanism in central Tenerife and lasting until the building of Teide and Pico Viejo stratovolcanoes.446 26 - PublicationOpen AccessHigh resolution magnetic anomaly map of Tenerife, Canary Islands(2007-10)
; ; ; ; ; ; ; ; ; ; ;García, A.; Dep. Volcanologìa, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Chiappini, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Blanco-Montenegro, I.; Dep. Fisica, Universidad de Burgos, Burgos, Spain ;Carluccio, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;D’Ajello Caracciolo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;De Ritis, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Nicolosi, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Pignatelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Sánchez, N.; Dep. Volcanologìa, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Boschi, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione AC, Roma, Italia; ; ; ; ; ; ; ; ; This study presents magnetic anomaly data from a new high-resolution, low-altitude helicopter-borne magnetic survey recently collected on and offshore Tenerife in the Canary Archipelago. The Italian Istituto Nazionale di Geofisica e Vulcanologia (INGV) in collaboration with the Museo Nacional de Ciencias Naturales of the CSIC of Spain conducted the survey in 2006. The data for Tenerife and surrounding marine areas were processed into digital total intensity magnetic anomalies for geomagnetic epoch 2006.4. Relative to previously available higher altitude magnetic survey data, the new survey mapped higher resolution anomalies with significantly improved spatial details, especially over the Las Cañadas caldera and Teide-Pico Viejo complex in the central part of the island. A good correlation is evident between known structural geology and the magnetic anomalies, where the new shorter wavelength anomalies facilitate more detailed and comprehensive geologic interpretations.2506 39687 - PublicationRestrictedSeismovolcanic signals at Deception Island volcano,Antarctica: Wave field analysis and source modeling(2000-06-10)
; ; ; ; ; ; ; ;Ibanez, J.; University of Granada, Spain ;Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Almendros, J.; University of Granada, Spain ;La Rocca, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Alguacil, G.; University of Granada, Spain ;Ortiz, R.; CSIC, Madrid ;Garcia, A.; CSIC, Madrid; ; ; ; ; ; Island (Antarctica), recorded during three Antarctic summers (1994- 1995, 1995-1996 and 1996-1997), are analyzed using a dense small-aperture (500 m) seismic array. The visual and spectral classification of the seismic events shows the existence of long-period and hybrid isolated seismic events, and of low-frequency, quasi-monochromatic and spasmodic continuous tremors, All spectra have the highest amplitudes in the frequency band between 1 and 4 Hz, while hybrids and spasmodic tremors have also significant amplitudes in the high-frequency band (4-10 Hz). The array analysis indicates that almost all the well-correlated low-frequency signals share similar array parameters (slowness and back azimuth) and have the same source area, close to the array site. The polarization analysis shows that phases at high-frequency are mostly composed of P waves, and those phases dominated by low frequencies can be interpreted as surface waves. No clear shear waves are evidenced. From the energy evaluation, we have found that the reduced displacement values for surface and body waves are confined in a narrow interval. Volcano-tectonic seismicity is located close to the array, at a depth shallower than 1 km. The wave-field properties of the seismovolcanic signals allow us to assume a unique source model, a shallow resonating fluid-filled crack system at a depth of some hundreds of meters. All of the seismic activity is interpreted as the response of a reasonably stable stationary geothermal process. The differences observed in the back azimuth between low and high frequencies are a near-field effect. A few episodes of the degassification process in an open conduit were observed and modeled with a simple organ pipe.249 28 - PublicationOpen AccessMagnetic study of the Furnas caldera (Azores)(1997-03)
; ; ; ;Blanco, I.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Garcìa, A.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Torta, J. M.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain; ; A local ground magnetic study of the Furnas caldera (S. Miguel Island, Azores) has provided new insight into the magnetic structure of this volcano. Analysis of the data comprised removal of the IGRF, reduction to the pole, pseudogravity integration and upward continuation. Also, a spectral method was applied to estimate the depth to the magnetic sources, as well as a 2.5D forward modelling technique. Magnetic properties obtained at the laboratory for some representative sample rocks were considered in the modelling process. The most relevant features are the existence of an important negative anomaly inside the caldera and of an intense positive anomaly to the south of the coast. The former points out a decrease in the magnetization of the caldera filling materials with respect to the surrounding rocks, which could be explained as the result of post-eruption processes such as hydrothermal alteration. This is expected as Furnas has an active hydrothermal system probably related with a magmatic reservoir at high temperature. The positive anomaly suggests the existence of a strongly-magnetized body beneath the south coast.271 766 - PublicationOpen AccessHigh-resolution aeromagnetic survey of the Teide volcano (Canary Islands): a preliminary analysis(1997-03)
; ; ; ; ;Garcìa, A.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Blanco, I.; Instituto Geográfico Nacional, Madrid, Spain ;Torta, J. M.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Socías, I.; Instituto Geográfico Nacional, Madrid, Spain; ; ; To contribute to our understanding of the structure of the Teide volcano, a detailed aeromagnetic survey was carried out covering the area of Las Cañadas caldera and the Teide-Pico Viejo complex. Taking into account the rugged relief of the area (altitude ranges from sea level to almost 4000 m), a terrain correction has been applied. As a first approximation, the topography has been characterized by a uniform magnetization of 5 Am-1 (based on field and laboratory rock magnetic data). Several enhancement techniques have been applied to the residual map (original map minus topographic effect), such as reduction to the pole, pseudogravity integration and upward continuation. In the reduced-to-the-pole map the large positive anomaly that appears centered to the north of Pico Viejo is noteworthy and could be caused by a basaltic intrusion responsible for the last eruptions in this area. Also, a small magnetic low appears over Teide peak, which should be related to slightly-magnetized shallow phonolitic materials. The main tectonic direction of Tenerife, SW-NE, is also clearly reflected on the magnetic anomaly map. The comparison between the pseudogravity and the Bouguer anomaly maps indicates a good correlation between magnetic and gravimetric sources.244 698 - PublicationOpen AccessA search for the volcanomagnetic signal at Deception volcano (South Shetland I., Antarctica)(1997-03)
; ; ; ; ; ; ;Garcìa, A.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Blanco, I.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Torta, J. M.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain ;Astiz, M. M.; E.T.S. Arquitectura, Universidad Politécnica de Madrid, Spain ;Ibáñez, J. M.; Instituto Andaluz de Geofísica, Granada, Spain ;Ortiz, R.; Departamento de Volcanología, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain; ; ; ; ; After the increase in seismic activity detected during the 1991-1992 summer survey at Deception Island, the continuous measurement of total magnetic intensity was included among the different techniques used to monitor this active volcano. The Polish geomagnetic observatory Arctowski, located on King George Island, served as a reference station, and changes in the differences between the daily mean values at both stations were interpreted as indicators of volcanomagnetic effects at Deception. A magnetic station in continuous recording mode was also installed during the 1993-1994 and 1994-1995 surveys. During the latter, a second magnetometer was deployed on Deception Island, and a third one in the vicinity of the Spanish Antarctic Station on Livingston Island (at a distance of 35 km) and was used as a reference station. The results from the first survey suggest that a small magma injection, responsible for the seismic re-activation, could produce a volcanomagnetic effect, detected as a slight change in the difference between Deception and Arctowski. On the other hand, a long term variation starting at that moment seems to indicate a thermomagnetic effect. However the short register period of only two stations do not allow the sources to be modelled. The future deployment of a magnetic array during the austral summer surveys, throughout the volcano, and of a permanent geomagnetic observatory at Livingston I. is aimed at further observations of magnetic transients of volcanic origin at Deception Island.234 203