HR: 1340h
AN: S13A-1031    [Abstracts]
TI: Mapping of the B-Value Anomalies in Colfiorito Tectonic Zone (Central Italy) and beneath Mt. Etna Volcano (Sicily, Italy)
AU: * Murru, M
EM: murru@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, Rome, I 00143 Italy
AU: Console, R
EM: console@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, Rome, I 00143 Italy
AU: Lisi, A
EM: lisi@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, Rome, I 00143 Italy
AU: Montuori, C
EM: montuori@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata, 605, Rome, I 00143 Italy
AB: We show an example of seismicity and mean magnitude variations correlated to the strongest earthquakes of the 1997 Colfiorito sequence, occurred in Central Italy. Moreover we review the results obtained by mapping of the b-value anomalies beneath Mt. Etna volcano (Sicily, Italy). Analyzing the seismicity in Central Italy from 1987 to 2001 we have shown how the a and b parameters of the Gutenberg-Richter relationship change significantly in space and time, at short scale, in relation with the 1997 Colfiorito sequence. In particular, comparing the frequency-magnitude distribution before and after the strongest main shocks of the sequence, we found after Colfiorito main shocks (M$_{w }$5.7 and 6.0) an increase of seismicity rate within 40-50 km of the epicenters and a strong decrease of b-value in an area at 12 km SE from the epicenters, where the third larger event (M$_{w }$5.6) of the sequence occurred. In the same area the combined effects of the changed a and b-values resulted in high values for the theoretical rate of M$_{L }$$>$=5.0 events. On the basis of these observations we postulate that spatial-temporal variations in both a and b-values can indicate a probable causal connection between large earthquakes and can help to identify location where large earthquakes are more probable. We have mapped the b-values in 3D under Mt. Etna defining high b-value anomalies by the data recorded from the Sicilian network (1990-1997). These anomalies were interpreted as due to active magma reservoirs, one located WSW of the summit at $3\pm2$ km b.s.l., the other 2 km E of the summit at $10\pm3$ km b.s.l. Our results supported the previously published estimates of magma chambers based on crustal deformation data. The data collected during the pre-eruptive (August 1999-June 2001) and intense eruption period (July-August 2001) of Mt. Etna were also analyzed by a detailed b-value tomography. The spatial variations of the b-value in this area have been correlated to a process of magma uprising, ending with a high velocity vertical dike emplacement, which heralded to the 2001 lateral eruption. All the available geophysical evidences such as geodetic deformation measurements, focal mechanism and tomographic studies support this interpretation.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting