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Formisano, L. A.
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Formisano, L. A.
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- PublicationOpen AccessTopography effects in the polarization of coda waves: a comparison between surface and deep recordings(2012)
; ; ; ; ; ; ; ; ; ; ; Local and regional earthquakes recorded in 2007 by two seismic arrays at Gran Sasso (Italy), one located at surface and one at 1.4 km depth, have been analyzed. Polarization properties of the seismic wavefield have been estimated at both arrays on a short sliding window and in several frequency bands. Array methods were also applied, and the estimated slowness and backazimuth were used to compute the stacking of phase shifted signals in order to improve the signal to noise ratio. Results of polarization computed over single station and array stacked signals have been compared between the two arrays. A well defined polarization azimuth, roughly perpendicular to the main massif ridges, is evident at surface in a broad frequency band. This is observed for earthquake body waves and coda waves. On the contrary, underground the same effect is slightly visible only at very low frequency.75 34 - PublicationOpen AccessSlow earthquakes and low frequency tremor along the Apennines, Italy(2008-04)
; ; ; ; ; ; ; ;Scarpa, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Amoruso, A.; Dipartimento di Fisica, Università degli Studi di Salerno, Italy ;Crescentini, L.; Dipartimento di Fisica, Università degli Studi di Salerno, Italy ;Fischione, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Formisano, L. A.; Dipartimento di Fisica, Università degli Studi di Salerno, Italy ;La Rocca, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Tronca, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; ; ; ; ; ; This paper reviews the main observations on slow earthquakes and low frequency tremor made along the Apennines, the main seismic active zone of Italy. These observations have been made using a geodetic interferometer system operating since 1994 in the underground tunnel of Gran Sasso, central Italy, and an underground seismic array (UNDERSEIS) operating since 2002 in the same environment. The observations made in recent years indicate that both phenomena are quite rare and apparently uncorrelated. Slow earthquakes, mainly recorded in 1997 and occasionally later, have probably been caused by the activity of a shallow fault system located near the interferometers. Until now only one tremor episode characterized by low frequency content and duration of several hours has been detected in January 2004, without any correlations with the occurrence of slow or regular earthquakes. The signal to noise ratio of this event is very low, but the results of our detailed analysis show that its frequency contents and wave field characteristics are compatible with a low frequency non volcanic tremor.260 461