GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 1.3 261 recorded on January 30, 2015, is a sequence of LF events. Therefore the source of such tremor must be the hydrothermal system. Conclusions. Since the level of background noise in the frequency range 0.5 – 5 Hz limits the detection of low amplitude and emergent signals like volcanic tremor and LF earthquakes, the use of array methods is necessary to detect coherent signals. Taking advantage of the array ARF, we could identify many coherent signals occurred in the area since 2010. Many of them revealed to be small LF earthquakes, while some others remained unclassified due to the very small amplitude, poor signal to noise ratio, and poor station coverage in some cases. However, the most interesting event is the tremor of hydrothermal origin occurred in January 2015 because it is the first observation of such kind of event in Campi Flegrei caldera. In the past years LF events of hydrothermal origin were located inside and at the east border of Solfatara crater (Saccorotti et al. , 2007), while the tremor described here is located more than 1 km to the SW. Therefore we conclude that the sources of such signals have similar mechanisms but different location. Further analysis about the source mechanism which generates LF earthquakes and tremor are in progress. The detection, analysis and classification of low amplitude tremor like the episode described here indicate a good performance of the current monitoring system. However, considering the very high risk of the area, further efforts are needed to detect seismic signals of volcanic origin as small as possible, and a multidisciplinary approach to their analysis and interpretation. References Chiodini G., Caliro S., De Martino P., Avino R. and Gherardi F.; 2012: Early signals of new volcanic unrest at Campi Flegrei caldera? Insights from geochemical data and physical simulations. Geology, 2012, doi:10.1130/ G33251.1. Del Pezzo E., Bianco F., Castellano M., Cusano P., Galluzzo D., La Rocca M. and Petrosino S.; 2013: Detection of Seismic Signals from Background Noise in the Area of Campi Flegrei: Limits of the Present Seismic Monitoring. Seismological Research Letters Volume 84, Number 2 March/April 2013 doi: 10.1785/0220120062. Galluzzo D., Bianco F., La Rocca M. and Zonno G.; 2016: Ground motion observations and simulation for local earthquakes in the Campi Flegrei volcanic area. Bulletin of Earthquake Engeneering, Special Issue, BEEE-D- 14-00317R1. La Rocca M. and Galluzzo D.; 2012: A seismic array in the town of Pozzuoli in Campi Flegrei (Italy). Seism. Res. Lett. 83 , n. 1, 86-96, doi: 10.1785/gssrl.83.1.86. La Rocca M. and Galluzzo D.; 2015: Seismic monitoring of Campi Flegrei and Mt. Vesuvius by stand alone instruments. Annals of Geophysics, 58, 5, S0544; doi: 10.4401/ag-6748. Saccorotti G., Petrosino S., Bianco F., Castellano M., Galluzzo D., La Rocca M., Del Pezzo E., Zaccarelli L. and Cusano P.; 2007: Seismicity associated with the 2004-2006 renewed ground uplift at Campi Flegrei Caldera, Italy. PEPI 165, 14-24, 2007. Selva J., Orsi, G., Di Vito M., Marzocchi W. and Sandri L.; 2011: Probability hazard map for future vent opening at the Campi Flegrei caldera, Italy. ����� ���������� ��� �������������������������� Bull. Volcanol., DOI 10.1007/s00445-011-0528-2. McNutt S. R.; 2005: Volcanic seismology. Annu. Rev. Earth Planet. Sci., 32, 461-491. Volcanic Tremor and Low Frequency earthquakes at Mt. Vesuvius M. La Rocca 1 , D. Galluzzo 2 1 Università della Calabria, Cosenza, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia – Osservatorio Vesuviano, Napoli, Italy Introduction. Seismic activity in volcanic environment is characterized by peculiar events not observed in tectonic regions. Beside volcano-tectonic (VT) earthquakes, low frequency (LF) earthquakes, long period events (LP) and volcanic tremor are observed at hundreds of active volcanoes worldwide (Chouet, 2003; McNutt et al. , 2005). LF events are characterized by corner