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Seismotectonic analysis of a complex fault system in Italy: the "Garfagnana-North" (Northern Tuscany) line
Author(s)
Language
English
Obiettivo Specifico
3.2. Tettonica attiva
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
2 / 5 (2007)
Pages (printed)
131-133
Issued date
2007
Abstract
We present the results obtained combining different techniques to determine the seismotectonic character of the Garfagnana region (northern Tuscany). There, the existence of a rather complex fault system is acknowledged and somewhat mapped, but apart from the geological evidences, very little is known about its extension with depth and the regime.
The seismic potential of the system is also well known. The area was characterized, in the past, by destructive earthquakes; in particular a major event (Ms=6.4) struck the Lunigiana-Garfagnana area in September 1920, but many others have been reported. Therefore, the seismicity is under constant monitoring by the national seismic network (RSNC – National Central Seismic Network) and a pool of local stations, belonging to a regional network (RSLG – Regional Seimic network of Lunigiana and Garfagnana). These additional stations account for the lower magnitude seismicity.
Such a concentration of seismic stations, and the consequent availability of several seismograms, makes likely to record and localize earthquakes down to a very low magnitude threshold (inferior to Ml = 2.0) with extremely narrow hypocentral parameter errors .
Making use of the resulting databases, several analyses were conducted to determine the shape, size, extension with depth of the fault and the associated seismicity. The methodology consists in seismic tomography (1D and 3D velocity models), precise location algorithms NonLinLoc and HypoDD (very constrained and reliable locations) and computation of focal mechanisms (fault orientation and source), all combined with the constraints provided by the geology.
The main findings of the study are that the concentration of the recent seismic activity is close to the likely location of the most relevant historical events. In particular the earthquakes are distributed along a plane in the range 0 – 20 km depth dipping 30° NE. All focal mechanisms show a transtensive character.
The seismic potential of the system is also well known. The area was characterized, in the past, by destructive earthquakes; in particular a major event (Ms=6.4) struck the Lunigiana-Garfagnana area in September 1920, but many others have been reported. Therefore, the seismicity is under constant monitoring by the national seismic network (RSNC – National Central Seismic Network) and a pool of local stations, belonging to a regional network (RSLG – Regional Seimic network of Lunigiana and Garfagnana). These additional stations account for the lower magnitude seismicity.
Such a concentration of seismic stations, and the consequent availability of several seismograms, makes likely to record and localize earthquakes down to a very low magnitude threshold (inferior to Ml = 2.0) with extremely narrow hypocentral parameter errors .
Making use of the resulting databases, several analyses were conducted to determine the shape, size, extension with depth of the fault and the associated seismicity. The methodology consists in seismic tomography (1D and 3D velocity models), precise location algorithms NonLinLoc and HypoDD (very constrained and reliable locations) and computation of focal mechanisms (fault orientation and source), all combined with the constraints provided by the geology.
The main findings of the study are that the concentration of the recent seismic activity is close to the likely location of the most relevant historical events. In particular the earthquakes are distributed along a plane in the range 0 – 20 km depth dipping 30° NE. All focal mechanisms show a transtensive character.
References
Ameri G., 2005. Simulazione numerica del terremoto di scenario per la Lunigiana-Garfagnana. Tesi di laurea, Università di Genova, 156 pp.
Chiarabba C., Jovane L., Di Stefano R., 2005. A new view of italian seismicity using 20
years of instrumental recordings. Tectonophysics, 395, 3-4, 251-268.
Ellsworth W. L., 1977. Three dimensional structure of the crust and mantle beneath the island of Hawaii. Ph.D. thesis (Massachusetts Institute of Tecnology), 327 pp.
Eva E., Ferretti G. and Solarino S., 2005. Superposition of different stress orientations in
the western sector of the northern Apennines (Italy). Journ. Seism.,9, 413-430.
Kissling E., 1988. Geotomography with local earthquake data. Rev. Geophys., 26,659-698.
Lomax A., Zollo A., Capuano P. and Virieux J., 2001. Precise, absolute earthquake location under Somma-Vesuvius volcano using a new 3D velocity model. Geophys. J. Int., 146, 313-331.
Solarino S., 2002. The September 7, 1920 earthquake in Lunigiana-Garfagnana (Tuscany, Italy): can instrumental data provide a reliable location? Proceedings of the XXVIII Assembly of ESC, CD Rom.
Solarino S., 2005. The role of instrumental versus macroseismic locations for earthquakes of the last century: a discussion based on the seismicity of the North-Western Apennines (Italy). Annals of Geophysics, 48, 6, 923-936.
Solarino S., Hill D.P. and Ellsworth W.L., 1996. Eastern California seismicity beginning
from 1927 and its relations to the post-1980 unrest in Long Valley Caldera. Agu Fall meeting, Book of abstracts, 206.
Thurber C.H., 1983. Earthquake locations and three dimensional crustal structure in the Copyote Lake area, central California. J. Geophys. Res., 88, 1548-1560.
Waldhauser F. and Ellsworth W.L.,2000. A Double Difference earthquake location algorithm: method and application to the Northern Hayward Fault,California. Bull. Seism. Soc. Am., 90, 6, 1353-1368
Chiarabba C., Jovane L., Di Stefano R., 2005. A new view of italian seismicity using 20
years of instrumental recordings. Tectonophysics, 395, 3-4, 251-268.
Ellsworth W. L., 1977. Three dimensional structure of the crust and mantle beneath the island of Hawaii. Ph.D. thesis (Massachusetts Institute of Tecnology), 327 pp.
Eva E., Ferretti G. and Solarino S., 2005. Superposition of different stress orientations in
the western sector of the northern Apennines (Italy). Journ. Seism.,9, 413-430.
Kissling E., 1988. Geotomography with local earthquake data. Rev. Geophys., 26,659-698.
Lomax A., Zollo A., Capuano P. and Virieux J., 2001. Precise, absolute earthquake location under Somma-Vesuvius volcano using a new 3D velocity model. Geophys. J. Int., 146, 313-331.
Solarino S., 2002. The September 7, 1920 earthquake in Lunigiana-Garfagnana (Tuscany, Italy): can instrumental data provide a reliable location? Proceedings of the XXVIII Assembly of ESC, CD Rom.
Solarino S., 2005. The role of instrumental versus macroseismic locations for earthquakes of the last century: a discussion based on the seismicity of the North-Western Apennines (Italy). Annals of Geophysics, 48, 6, 923-936.
Solarino S., Hill D.P. and Ellsworth W.L., 1996. Eastern California seismicity beginning
from 1927 and its relations to the post-1980 unrest in Long Valley Caldera. Agu Fall meeting, Book of abstracts, 206.
Thurber C.H., 1983. Earthquake locations and three dimensional crustal structure in the Copyote Lake area, central California. J. Geophys. Res., 88, 1548-1560.
Waldhauser F. and Ellsworth W.L.,2000. A Double Difference earthquake location algorithm: method and application to the Northern Hayward Fault,California. Bull. Seism. Soc. Am., 90, 6, 1353-1368
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