GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 1.3 265 properties at depth below 5 km bsl (roughly corresponding to Ts-Tp = 1.2 s) would explain the lower frequency contents of tremor and LFVTs in terms of lower stress drop compared with the VT located at shallower depth. Moreover the lack of any sources located deeper than about 6.5 km bsl suggests a further increase of temperature below that depth, in good agreement with the presence of melt material inferred to lay below 8 km bsl. The corner frequency of seismic waves radiated by a shear failure depends by several parameters. Low frequency may be caused by very low rupture velocity or by very low stress drop. Weak fault subject to low normal stress in a rock volume with temperature not much lower than the brittle failure limit seems the best candidate for the source of tremor and LFVTs at Vesuvius. Unfortunately a reliable estimation of such physical parameters is not possible at the moment. Attempts to estimate the rupture velocity and stress drop from the analysis of available signals are in progress, but preliminary results are not encouraging. In fact our LFVTs and tremor are characterized by low signal to noise ratio, which makes difficult some analysis and the interpretation of results. On the other hand, considering the current seismicity rate we have to wait many years to collect a sufficient number of good quality events for a better estimation of the source parameters. References Chouet, B.A., 1996. Long-period volcano seismicity: its source and use in eruption forecasting. ������� ���� ���� ��� Nature, vol. 380, pp. 309-316, 1996. Chouet, B.A., 2003. Volcano seismology. Pure Appl. ��������� ���� �������� ����� Geophys., 160, 739-788, 2003. Cusano P., Petrosino, S., Bianco, F., Del Pezzo, E., 2013. The first Long Period earthquake detected in the background seismicity at Mt. Vesuvius. Annals of Geophysics, 56, 4, 2013, S0440; doi:10.4401/ag-6447. D’Auria, L., Esposito, A.M., Lo Bascio, D., Ricciolino, P., Giudicepietro, F., Martini, M., Caputo, T., De Cesare, W., Orazi, M., Peluso, R., Scarpato, G., Buonocunto, C., Capello, M., Caputo, A., 2013. The recent seismicity of Mt. Ves������ ��������� �� ����������� ���������� ������ �� ����������� ��� �� ������ ���� ���������������� uvius: inference on seismogenic processes. Annals of Geophysics, 56, 4, S0442; doi: 10.4401/ag-6448. Del Pezzo, E., Bianco, F., Saccorotti, G., 2004. ������� ������ �������� �� �������� �������� ������ �� ����� ������ Seismic source dynamics at Vesuvius volcano, Italy. �� ����� ������ J. Volc. Geoth. Res., 133, 23-29. Konstantinou, K. I., Schlindwein, V., 2002. Nature, wavefield properties and source mechanism of volcanic tremor: a review. J. Volc. Geoth. Res. 119, 161-187, 2002. La Rocca M., D. Galluzzo (2016). Volcanic tremor at Mt Vesuvius associated with low frequency shear failures. Earth Planet. Sci. Lett., 442, 32-38, doi: 10.1016/j.epsl.2016.02.048. La Rocca, M., 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. La Rocca, M., Galluzzo, D., 2014. ������� ���������� �� ��� �������� �� ����� �������� ������ ���� ������ ��� ��� Seismic monitoring of Mt. Vesuvius by array methods. Seism. Res. Lett., ��� ��� vol 85, n 4, 809-816, doi: 10.1785/0220130216. McNutt, S.R., 2005. Volcanic seismology. Annu. Rev. Earth Planet. Sci., 32, 461-491. Fig. 3 – ������ ��������� ������ ����� �� ������� ������ Corner frequency versus Ts-Tp of tremor, LFVTs, and VT earthquakes. The existence of two groups of results without a smooth transition from one to the other is the most important result of our analysis.