Seismic source dynamics at Vesuvius volcano, Italy

Abstract On October 9, 1999 an earthquake of M L =3.6 occurred about 3 km beneath the central cone of Mt. Vesuvius, near Naples, Italy. The event had the highest magnitude recorded for at least 25 years, and possibly since the last eruption of this volcano (1944), and was not accompanied by other geophysical or geochemical changes. The present paper essentially deals with the seismological data collected at Mt. Vesuvius for 29 years before the October 9 earthquake till the end of 2001, and describes the time pattern distribution of seismic slip release and the b -parameter of the Gutenberg–Richter distribution. The self-similarity of the source process is investigated through the scaling law of the seismic spectrum. Results indicate a two-fold pattern of stress release, with high values (up to 100 bar) for earthquakes occurring close to the top of the carbonate basement that underlies the volcano at 2–3 km of depth, and low values (down to 0.1 bar) for the shallow events occurring within the volcanic edifice. The scaling law of the seismic spectrum is non-self-similar, indicating that the source dimensions do not scale with the seismic moment. For this reason the low-magnitude events substantially contribute to the overall cumulative seismic slip release. The b -parameter of the Gutenberg–Richter distribution shows a variation around 1980, and a substantial constancy in the other time periods. The presence of extended aquifers, with their tops at about 1 km beneath the crater, favors the hypothesis of the triggering of the shallowest events by water-level changes. This hypothesis is in agreement with the low values of the stress drop measured for the shallowest seismic events. The existence of a carbonate basement with its top at about 2.5 km beneath the crater and the higher stress drops for the deeper events make reasonable the hypothesis that the pre-fractured carbonate basement may be the site of tectonic stress release.

[1]  G. Natale,et al.  Source parameters of microearthquakes at Phlegraean Fields (Southern Italy) volcanic area , 1987 .

[2]  J. Virieux,et al.  Seismic Evidence for a Low-Velocity Zone in the Upper Crust Beneath Mount Vesuvius , 1996, Science.

[3]  G. Ventura,et al.  Slip tendency analysis of the Vesuvius Faults: Implications for the seismotectonic and volcanic hazard assessment , 1999 .

[4]  Claudia Troise,et al.  Internal stress field at Mount Vesuvius: A model for background seismicity at a central volcano , 2000 .

[5]  P. Bruno,et al.  Seismic study of the Mesozoic carbonate basement around Mt. Somma–Vesuvius, Italy , 1998 .

[6]  F. Ferrucci,et al.  The seismic crises at Mt. Vesuvius during 1995 and 1996 , 1999 .

[7]  G. Vilardo,et al.  Seismic swarms related to diffusive processes: The case of Somma-Vesuvius volcano, Italy , 2002 .

[8]  Agustín Udías,et al.  Principles of Seismology , 2000 .

[9]  C. Buonocunto,et al.  Seismic Surveillance of Active Volcanoes: The Osservatorio Vesuviano Seismic Network (OVSN, Southern Italy) , 2002 .

[10]  Edoardo Del Pezzo,et al.  A local-magnitude scale for Mt. Vesuvius from synthetic Wood-Anderson seismograms , 2001 .

[11]  P. Gasparini,et al.  Mount Vesuvius: 2000 years of volcanological observations , 1993 .

[12]  Stuart Crampin,et al.  A review of wave motion in anisotropic and cracked elastic-media , 1981 .

[13]  G. Ventura,et al.  The Somma–Vesuvius stress field induced by regional tectonics: evidences from seismological and mesostructural data , 1998 .

[14]  Study of seismogram envelopes based on scattering by random inhomogeneities in the lithosphere: a review , 1991 .

[15]  Roberto Scarpa,et al.  Monitoring and Mitigation of Volcano Hazards , 1996 .

[16]  G. Natale,et al.  Recent geophysical investigation at Somma-Vesuvio volcanic complex , 1993 .

[17]  F. Mulargia,et al.  Confidence intervals of b values for grouped magnitudes , 1987, Bulletin of the Seismological Society of America.

[18]  J. Virieux,et al.  Seismic Evidence of an Extended Magmatic Sill Under Mt. Vesuvius , 2001, Science.

[19]  J. Ibáñez,et al.  Attenuation of short-period seismic waves at Mt Vesuvius, Italy , 1999 .

[20]  Gilberto Saccorotti,et al.  Array analyses of seismic noise at Mt. Vesuvius Volcano, Italy , 2001 .

[21]  P. Guttorp.  On least-squares estimation of b values , 1987 .

[22]  M. Rosi,et al.  Explanatory notes to the geological map , 1987 .

[23]  Warner Marzocchi,et al.  Two‐way coupling between Vesuvius eruptions and southern Apennine earthquakes, Italy, by elastic stress transfer , 1998 .

[24]  R. Santacroce.  A general model for the behavior of the Somma-Vesuvius volcanic complex , 1983 .

[25]  Michael Fehler,et al.  Seismic Wave Propagation and Scattering in the Heterogeneous Earth , 2012 .

[26]  L. Wennerberg.  Multiple-scattering interpretations of coda-Q measurements , 1993, Bulletin of the Seismological Society of America.

[27]  David Oppenheimer,et al.  FPFIT, FPPLOT and FPPAGE; Fortran computer programs for calculating and displaying earthquake fault-plane solutions , 1985 .

[28]  M. Fedi,et al.  2.5D modelling of Somma–Vesuvius structure by aeromagnetic data , 1998 .

[29]  Warner Marzocchi,et al.  Common Features and Peculiarities of the Seismic Activity at Phlegraean Fields, Long Valley, and Vesuvius , 2001 .

[30]  A. Zollo,et al.  Space and Time Behavior of Seismic Activity at Mt. Vesuvius Volcano, Southern Italy , 2002 .

[31]  Bernard A. Chouet,et al.  New Methods and Future Trends in Seismological Volcano Monitoring , 1996 .

[32]  P. Mauriello,et al.  Electric and electromagnetic outline of the Mount Somma–Vesuvius structural setting , 1998 .

[33]  T. Lay,et al.  Modern Global Seismology , 1995 .

[34]  G. Natale,et al.  The seismicity of Mt. Vesuvius , 1996 .

[35]  J. Angelier,et al.  A major geodynamic change revealed by Quaternary stress patterns in the southern Apennines (Italy) , 1994 .

[36]  F. Pingue,et al.  Eruptive history, seismic activity and ground deformations at Mt. Vesuvius, Italy , 1985 .

[37]  Jean Virieux,et al.  Precise, absolute earthquake location under Somma–Vesuvius volcano using a new three-dimensional velocity model , 2001 .