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Analysis of gravimetric anomalies in Furnas caldera (Sao Miguel, Azores)

Camacho, Antonio and González Montesinos, Fuensanta and Vieira, Ricardo (1999) Analysis of gravimetric anomalies in Furnas caldera (Sao Miguel, Azores). Journal of Geophysical Research-Solid Earth, 102 (B4). pp. 7717-7730. ISSN 0148-0227

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Abstract

Gravimetric studies are becoming more and more widely acknowledged as a useful tool for studying and modeling the distributions of subsurface masses that are associated with volcanic activity. In this paper, new gravimetric data for the volcanic island of Sao Miguel (Azores) were analyzed and interpreted by a stabilized linear inversion methodology. An inversion model of higher resolution was calculated for the Caldera of Furnas, which has a larger density of data. In order to filter out the noncorrelatable anomalies, least squares prediction was used, resulting in a correlated gravimetric signal model with an accuracy of the order of 0.9 mGal. The gravimetric inversion technique is based on the adjustment of a three-dimensional (3-D) model of cubes of unknown density that represents the island's subsurface. The problem of non-uniqueness is solved by minimization with appropriate covariance matrices of the data (resulting from the least squares prediction) and of the unknowns. We also propose a criterion for choosing a balance between the data fit (which in this case corresponds to residues with rms of the order of 0.6 mGal) and the smoothness of the solution. The global model of the island includes a low-density zone in a WNW-ESE direction and a depth of the order of 20 km, associated with the Terceira rift spreading center. The minimums located at a depth of 4 km may be associated with shallow magmatic chambers beneath the main volcanoes of the island. The main high-density area is related to the Nordeste basaltic shield. With regard to the Caldera Furnas, in addition to the minimum that can be associated with a magmatic chamber, there are other shallow minimums that correspond to eruptive processes.


Item Type:Article
Subjects:Sciences > Geology > Seismology
ID Code:16012
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Deposited On:19 Jul 2012 11:10
Last Modified:06 Feb 2014 10:36

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