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Departamento De Quımica y Fısica, Canana de San Urbano, University of Almerıa, E-04071 Almerıa, Spain
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- PublicationRestrictedSpatial distribution of intrinsic and scattering seismic attenuation in active volcanic islands – II: Deception Island images(2013)
; ; ; ; ; ;Prudencio, I.; Instituto Andaluz de Geofısica, Campus de Cartuja, University of Granada, E-18071 Granada, Spain ;Ibanez, J.; Instituto Andaluz de Geof´ısica, Campus de Cartuja, University of Granada, E-18071 Granada, Spain ;Garcia-Yeguas, A.; Instituto Andaluz de Geofısica, Campus de Cartuja, University of Granada, E-18071 Granada, Spain ;Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Posadas, A. M.; Departamento De Quımica y Fısica, Canana de San Urbano, University of Almerıa, E-04071 Almerıa, Spain; ; ; ; In this work, we present regional maps of the inverse intrinsic quality factor (Qi −1), the inverse scattering quality factor (Qs −1) and total inverse quality factor (Qt −1) for the volcanic environment of Deception Island (Antarctica). Our attenuation study is based on diffusion approximation, which permits us to obtain the attenuation coefficients for every single couple source-receiver separately. The data set used in this research is derived from an active seismic experiment using more than 5200 offshore shots (air guns) recorded at 32 onshore seismic stations and four ocean bottom seismometers. To arrive at a regional distribution of these values, we used a new mapping technique based on a Gaussian space probability function. This approach led us to create ‘2-D probabilistic maps’ of values of intrinsic and scattering seismic attenuation. The 2-D tomographic images confirm the existence of a high attenuation body below an inner bay of Deception Island. This structure, previously observed in 2-D and 3-D velocity tomography of the region, is associated with a massive magma reservoir. Magnetotelluric studies reach a similar interpretation of this strong anomaly. Additionally, we observed areas with lower attenuation effects that bear correlation with consolidated structures described in other studies and associated with the crystalline basement of the area. Our calculations of the transport mean-free path and absorption length for intrinsic attenuation gave respective values of ≈950 m and 5 km, which are lower than the values obtained in tectonic regions or volcanic areas such as Tenerife Island. However, as observed in other volcanic regions, our results indicate that scattering effects dominate strongly over the intrinsic attenuation.247 50 - PublicationRestrictedAnalysis of the seismic wavefield properties of volcanic explosions at Volc ´an de Colima,Mexico: insights into the source mechanism(2009)
; ; ; ; ; ; ; ; ;Palo, M.; Universit´a degli Studio di Salerno, Dipartimento di Matematica e Informatica, Italy ;Ibanez, J. M.; Instituto Andaluz de Geofısica, Universidad de Granada, Spain. 3Departamento de F´ısica Te´orica y del Cosmos, Universidad de Granada. ;Cisneros, M.; Observatorio Vulcanologico, Universidad de Colima, Colima, Mexico ;Breton, M.; Observatorio Vulcanologico, Universidad de Colima, Colima, Mexico ;Del Pezzo, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Ocana, E.; Instituto Andaluz de Geof´ısica, Universidad de Granada, Spain. ;Orozco-Rojas, J.; Observatorio Vulcanol´ogico, Universidad de Colima, Colima, Mexico ;Posadas, A. M.; Departamento de Fısica Aplicada, Universidad de Almerıa, Spain; ; ; ; ; ; ; We have investigated thewavefield properties of the seismic signals generated by the explosions of Volc´an de Colima (M´exico). We have analysed these properties to understand the initial mechanism that triggered the explosive events. Our study is focused on the direct waves coming from the crater area. Thus, we have analysed a set of moderate volcanic explosions at Volc´an de Colima that was recorded by a small aperture seismic array over two periods: October 2005 and April 2006. We can distinguish two types of explosions, Vulcanian and ash-free events. Both types of explosions share the same characteristics, that is a long-period signal (not related to any type of emission) before the arrival of high frequency phases, and a later high frequency signal directly related to ash or gas emission. We have applied the Zero Lag Cross Correlation technique to obtain backazimuth and apparent slowness of the incoming waves. We have also applied polarization analysis to the record of every detected volcanic explosion. By comparing the results of both of these analyses, we have been able to identify the dominant wave types that comprise the seismic wavefield and infer in time and space a possible primary source mechanism that would trigger the volcanic explosions. We have observed an apparent slowness variation of the first onset of the long-period (LP) signal with a possible upward migration of the source; the depth of the source has been identified at a range between 2.6 and 3.3 km below the crater, associated with the range of measured apparent velocities relative to the first onset of the LP signal.246 29