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Authors: Murru, Maura* 
Montuori, Caterina* 
Console, Rodolfo* 
Lisi, Arianna* 
Title: Mapping of the b value anomalies beneath Mt. Etna, Italy, during July–August 2001 lateral eruption
Issue Date: 12-Mar-2005
Series/Report no.: /32 (2005)
DOI: 10.1029/2004GL021545
Keywords: Mt Etna, bvalue, eruption
Abstract: The pattern of b value of the frequency-magnitude relation, or mean magnitude, has been analyzed as function of space beneath Mt. Etna during the intense lateral eruption of July–August 2001. The data used (August 1999–August 2001), subdivided in the pre-eruptive and eruption period, show significant space variations in the b value. For each of the two periods, a volume of anomalously high b value can be observed in the southeastern flank of the volcano. The anomalies located at 3 ± 1 km (b = 1.84 ± 0.20), and at about 1 ± 1 km (b = 2.11 ± 0.29) depth are interpreted as two different steps of a magma migration process ended with the July–August 2001 eruption. All the available geophysical evidences such as geodetic deformation measurements, focal mechanism and tomographic studies support this interpretation
Description: the spatial variations of the b value in the area studied are real circumstances, linked to the magmatic processes ongoing in that period of time and leading to the eruptive phenomena. Our detailed b value tomography appears to be a good example in which an intrusion activity may be also documented by increased b values. Our analysis demonstrates clearly that the parameter b is a sensitive and accurate indicator of the magmatic processes that occurred during the investigation period at Etna volcano. In summary, the anomalies observed during the two period analyzed (August 1999–June 2001 and July–August 2001) appear to be the result of a fundamental process connected to the magma ascending, ending with a high velocity vertical dike emplacement, which heralded to the July–August 2001 eruption.
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