Seismic evidence for a low-velocity zone in the upper crust beneath mount vesuvius

Science

Volumn 274, Issue 5287, 1996, Pages 592-594

  Zollo, A ^a   Gasparini, P ^a   Virieux, J ^b   Le Meur, H ^a   De Natale, G ^c   Biella, G ^d   Boschi, E ^e   Capuano, P ^c   De Franco, R ^d   Dell'Aversana, P ^a   De Matteis, R ^a   Guerra, I ^f   Lannaccone, G ^a   Mirabile, L ^g   Vilardo, G ^c  

^a UNIVERSITY OF NAPLES FEDERICO II   (Italy)

^b Institut de Geodynamique   (France)

^c OSSERVATORIO VESUVIANO   (Italy)

^d CNR   (Italy)

^e ISTITUTO NAZIONALE DI GEOFISICA E VULCANOLOGIA   (Italy)

^f UNIVERSITY OF CALABRIA   (Italy)

^g Instituto di Oceanologia   (Italy)

Author keywords

[No Author keywords available]

Indexed keywords

ARTICLE; GEOLOGY; ITALY; PHYSICAL PHENOMENA; PHYSICS; PRIORITY JOURNAL; VELOCITY; VOLCANO;

CRUST (UPPER); LOW VELOCITY ZONE; MELTING ZONE; SEISMIC EXPERIMENT;

ITALY, CAMPANIA, VESUVIUS;

EID: 0029659761     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.274.5287.592     Document Type: Article

References (30)

1. V. Arnò et al., in Somma-Vesuvius, R. Santacroce, Ed. (Quaderni de La Ricerca Scientifica, Rome, 1987), pp. 53-103.
2. F. Barberi et al., Bull. Volcanol. 44, 295 (1981); L. Civetta, R. Galati, R. Santacroce, ibid. 53, 517 (1991).
3. F. Barberi et al., Bull. Volcanol. 44, 295 (1981); L. Civetta, R. Galati, R. Santacroce, ibid. 53, 517 (1991).
4. H. E. Belkin and B. De Vivo, J. Volcanol. Geotherm. Res. 58, 89 (1993).
5. H. Sigurdsson, S. Carey, W. Cornell, T. Pescatore. Natl. Geogr. Res. 1, 332 (1985).
6. P. Papale and F. Dobran, J. Volcanol. Geotherm. Res. 58, 101 (1993).
7. P. Gasparini, M. S. M. Mantovani, R. Scandone, Bull. Volcanol. 44, 317 (1981).
8. R. Santacroce, A. Bertagnini, L. Civetta, P. Landi, A. Sbrana, J. Petrol. 34, 383 (1993); H. E. Belkin, C. J. Kilburn, B. De Vivo, J. Volcanol. Geotherm. Res. 58, 273(1993).
9. R. Santacroce, A. Bertagnini, L. Civetta, P. Landi, A. Sbrana, J. Petrol. 34, 383 (1993); H. E. Belkin, C. J. Kilburn, B. De Vivo, J. Volcanol. Geotherm. Res. 58, 273(1993).
10. I. Finetti and C. Morelli, Boll. Geofis. Teor. Appl. 16, 175(1974).
11. C. Principe, M. Rosi, R. Santacroce, A. Sbrana, in Somma-Vesuvius, R. Santacroce, Ed. (Quaderni de La Ricerca Scientifica, Rome, 1987), pp. 11-52.
12. E. Cassano and P. La Torre, ibid., pp. 175-196.
13. F. Ferrucci et al., Geophys. Res. Lett. 16, 1317 (1989).
14. The seismic stations (60 of the 82 were three-component digital recorders) deployed along the profile were spaced 250 m apart in the center of the profile (as far as 5 km northwest and southeast of the crater) and 500 m apart at the outer parts. Shot S1 was located on the carbonates of the Sorrento Peninsula, shot S2 was on the southeast slope of the volcano near the Trecase well, and shot S3 was on the south edge of the Mount Somma caldera rim.
15. L < 3) shallower than 5 to 6 km and concentrated beneath Gran Cono, as monitored by the permanent seismic network of Osservatorio Vesuviano. The data from shots S2 and S3 were integrated with arrival times from a selected set of 40 well-located microearthquakes, which provide additional constraints on the deeper part of the volcano edifice. The local earthquakes were preliminarily located in a structure that approximated the 2D initial model used for the tomographic inversion.
16. Methods for travel-time inversion and delay-time tomography were applied to direct P-wave arrival times read on the seismic records of shots S2 and S3 at the stations located along the volcano slope. We estimated preliminary 1D velocity profiles for the shallow part of the volcano by using a revised version of the tau-p inversion method (20, 21), The 2D shallow structure of Somma-Vesuvius has been determined with a tomographic method in which the propagating medium is described by continuous functions interpolating linearly the velocities assigned to nonregular grid points (21). The ray paths were approximated by an arc of circles, and the solution was obtained by iterative, damped least squares. Space resolution was inferred from ad hoc tests using synthetic data from spike anomalies centered at different positions within the investigated section (21). Resolution is the highest (1.0 km laterally and 0.5 km vertically) at the center of the profile down to a depth of about 4 km and deteriorates laterally and downward.
17. J. Virieux, V. Farra, R. Madariaga, J. Geophys. Res. 93, 6585 (1988); J. Virieux, ibid. 96, 579 (1991).
18. J. Virieux, V. Farra, R. Madariaga, J. Geophys. Res. 93, 6585 (1988); J. Virieux, ibid. 96, 579 (1991).
19. A. Bernasconi, P. Bruni, L. Gorla, C. Principe, A. Sbrana, Rend. Soc. Geol. Ital. 4, 237 (1981).
20. S ratio has been assumed to be homogeneous (1.73) for the whole investigated structure.
21. J. Virieux, Geophysics 51,889 (1986). The equations of motion for elastic velocities and stresses were approximated by FD formulas based on a staggered-grid scheme for space and time steps. Earth's surface was approximated by a discontinuous topography above which stress was assumed to be zero. In our FD simulations, a discretized 2D medium with a grid of points equally spaced in the x and z directions (Δx = Δz= 50m) was used. At each grid point, P- and S-wave velocity were assigned according to the velocity model used for ray-tracing analysis except that an average velocity profile was used to simulate the velocity variation in shallow volcanic sediments.
22. A. R. Sanford, O. Altepkin, T. R. Toppozada, Bull. Seismol. Soc. Am. 63, 2021 (1973); M. Mizoue, I. Nakamura, T. Yokota, Bull. Earthquake Res. Inst. 57, 653 (1982); S. Matsumoto and A. Hasegawa, J. Geophys. Res. 101, 3067 (1996).
23. A. R. Sanford, O. Altepkin, T. R. Toppozada, Bull. Seismol. Soc. Am. 63, 2021 (1973); M. Mizoue, I. Nakamura, T. Yokota, Bull. Earthquake Res. Inst. 57, 653 (1982); S. Matsumoto and A. Hasegawa, J. Geophys. Res. 101, 3067 (1996).
24. A. R. Sanford, O. Altepkin, T. R. Toppozada, Bull. Seismol. Soc. Am. 63, 2021 (1973); M. Mizoue, I. Nakamura, T. Yokota, Bull. Earthquake Res. Inst. 57, 653 (1982); S. Matsumoto and A. Hasegawa, J. Geophys. Res. 101, 3067 (1996).
25. E. N. Bessonova, V. M. Fishman, V. Z. Ryaboyl, G. A. Sitnikova, Geophys. J. P. Astron. Soc. 36, 377 (1974).
26. C. H. Thurber, J. Geophys. Res. 88, 8226 (1983).
27. R. De Matteis, A. Zollo, J. Virieux, in preparation; A. Zollo, et al., Ann. Geofis., in press; H. Le Meur, A. Zollo, G. De Natale, J. Virieux, in preparation.
28. R. De Matteis, A. Zollo, J. Virieux, in preparation; A. Zollo, et al., Ann. Geofis., in press; H. Le Meur, A. Zollo, G. De Natale, J. Virieux, in preparation.
29. R. De Matteis, A. Zollo, J. Virieux, in preparation; A. Zollo, et al., Ann. Geofis., in press; H. Le Meur, A. Zollo, G. De Natale, J. Virieux, in preparation.
30. We acknowledge two anonymous reviewers for their helpful and critical comments on the manuscript. The seismic tomography of Vesuvius is supported by the Gruppo Nazionale di Vulcanologia, CNR, Italy. This research was cosponsored by the Instituto Italiano di Studi Filosofici, Naples, Conferenza Permanente dei Rettori (Progetto Galileo), and the French embassy in Italy. It was also financially supported through the Ministero per I'Università e la Ricerca Scientifica e Tecnologica (40%) (P.G.).