Three-dimensional tomography and rock properties of the Larderello-Travale

In a geothermal area, a detailed knowledge of the three-dimensional velocity structures aids the managementof
the field and the further development of the geothermal source. Here,we present a high-resolution
study of the three-dimensional S-wave velocity structures from microearthquake travel times for the
Larderello-Travale geothermal field, Italy.We have also deduced the Vp/Vs and Vp ×Vs parameters for this
area toemphasize the deep variations in the physical rock properties due to fluid content and porosity. Furthermore,
effective porousmedium modelling has been performed for site-relevant lithologies, to improve
our interpretation of the results in terms of rock physics signatures. This has allowed us to estimate the
variation range of the seismological parameters investigated, as well as their sensitivity for suitable rock
under specific physical conditions. LowVp/Vs anomalies, arising froma lower Vp compared to Vs, dominate
the geothermal field of Larderello-Travale. These have been interpreted as due to steam-bearing formations.
On the contrary, analysis of Vp ×Vs images provides information on the relative changes in rock
porosity at depth. Comparison of tomographic section images with previously interpreted seismic lines
suggests that the reflective ‘K-horizon’ delineates a transition between zones that have different porosities
or crack gatherings. The ‘K-horizon’ also lies on low Vp/Vs anomalies, which suggests a steam saturation
zone, despite the reduced porosity at this depth.

Abbate, E., Bortolotti, V., Passerini, P., Sagri, M., 1970. Introduction to the geology
of the Northern Apennines in Development of the Northern Apennines geosyncline.
Sedimen. Geol. 4, 207–642.
Barelli, A., Bertini, G., Buonasorte, G., Cappetti, G., Fiordelisi, A., 2000. Recent deep
exploration results at the margins of the Larderello-Travale geothermal system.
In: Proceedings 2000World Geothermal Congress, Kyushu, Tohoku, Japan.
Batini, F., Burgassi, P.D., Cameli, G.M., Nicolich, R., Squarci, P., 1978. Contribution
to the study of the deep lithospheric profiles: deep reflecting horizons in
Larderello-Travale Geothermal field. Mem. Soc. Geol. Ital. 19, 477– 484.
Batini, F., Bertini, G., Giannelli, G., Pandeli, E., Puxeddu, M., Villa, I., 1985. Deep structure,
age and evolution of the Larderello-Travale geothermal field. Geotherm.
Res., Commun. Trans. 9, 253–259.
Batini, F., Nicolich, R., 1985. P and S reflection seismic profiling and well logging in
the Travale geothermal field. Geothermics 14, 731–747.
Batzle, M., Wang, Z., 1992. Seismic properties of pore fluids. Geophysics 57,
1396–1408.
Benz, H.M., Chouet, B.A., Dawson, P.B., Lahr, J.C., Page, R.A., Hole, J.A., 1996. Threedimensional
P and S wave velocity structure of Redoubt Volcano, Alaska. J.
Geophys. Res. 101, 8111–8128.
Birch, F., 1960. The velocity of compressional waves in rocks to 10 kilobars Part I. J.
Geophys. Res. 65, 1083–1102.
Brogi, A., Lazzarotto, A., Liotta, D., Ranalli, G., 2003. Extensional shear zones as
imaged by reflection seismic lines: the Larderello geothermal field (central Italy).
Tectonophysics 363 (1/2), 127–139.
Cameli, G., Ceccarelli, A., Dini, I., Mazzotti, A., 2000. Contribution of the seismic
reflection method to the location of Deep fractured levels in the geothermal
fields of southern Tuscany (central Italy). In: Proceedings 2000World Geothermal
Congress, Kyushu, Tohoku, Japan.
Cappetti, G., Passaleva, G., Sabatelli, F., 2000. Italy country update report 1995–1999.
In: Proceedings 2000World Geothermal Congress, Kyushu, Tohoku, Japan.
Cappetti, G., Ceppatelli, L., 2005. Geothermal power generation in Italy: 2000–2004
update report. In: Proceedings 2005 World Geothermal Congress, Antalia,
Turkey.
Cappetti, G., Fiordelisi, A., Casini, M., Ciuffi, S., Mazzotti, A., 2005. A new deep
exploration program and preliminary results of a 3D seismic survey in the
Larderello-Travale Geothermal field (Italy). In: Proceedings 2005World Geothermal
Congress, Antalia, Turkey.
Chatterjee, S.N., Pitt, A.M., Iyer, H.M., 1985. Vp/Vs ratios in the Yellowstone National
Park region, Wyoming. J. Volc. Geoth. Res. 26 (3/4), 213–230.
Christensen, N.I., 1985. Measurements of dynamic properties of rocks at elevated
temperatures and pressures. In: Pincus, H.J., Hoskins, E.R. (Eds.), Measurements
of Rock Properties at Elevated Pressures and Temperatures. Spec. Tech.
Publ.—ASTM, 869, 93–107.Christensen, N.I., Mooney, W.D., 1995. Seismic velocity structure and composition
of the continental crust: a global view. J. Geophys. Res. 100 (B6), 9761–9788.
Dvorkin, J., Prasad, M., Sakai, A., Lavoie, D., 1999. Elasticity of marine sediments: rock
physics modeling. Geophys. Res. Lett. 26 (12), 1781–1784.
Ito, H., DeVilbiss, J., Nur, A., 1979. Compressional and shear waves in saturated rock
during water-steam transition. J. Geophys. Res. 84, 4731–4735.
Iverson, W.P., Fahmy, B.A., Smithson, S.B., 1989. VpVs from mode-converted P–S
reflections. Geophysics 54, 843–852.
Mavko, G., Mukerjy, T., Dvorkin, J., 1998. Rock Physics Handbook. Cambridge University
Press.
Mindlin, R.D., 1949. Compliance of elastic bodies in contact. Trans. ASME 71, A-259.
Minissale, A., Aug 1991. The Larderello Geothermal Field: a review 1991. Earth-Sci.
Rev. 31 (2), 133–151.
Monna, S., Filippi, L., Beranzoli, L., Favali, P., 2003. Rock properties of the uppercrust
in Central Apennines (Italy) derived fromhigh-resolution 3D tomography.
Geophys. Res. Lett. 30, 7, doi:10.1029/2002GL016780.
Murase, T.,McBirney, A.R., 1973. Properties of some common igneous rocks and their
melts at high temperature. Bull. Geol. Soc. Am. 84, 3563–3592.
Nur, A., Mavko, G., Dvorkin, J., Galmudi, D., 1998. Critical porosity: a key to relating
physical properties to porosity in rocks. The Leading Edge 17 (3), 357–362.
Nur, A., Wang, Z. (Eds.), 1989. Seismic and Acoustic Velocities in Reservoir Rocks:
Experimental Studies, vol. 1. Society of Exploration Geophysicists, Tulsa, p. 405.
O’Connell, R.J., Budiansky, B., 1974. Seismic velocities in dry and saturated cracked
solids. J. Geophys. Res. 79, 5412–5426.
Okubo, P.G., Benz, H.M., Chouet, B.A., 1997. Imaging the crustal magma sources
beneath Mauna Loa and Kilauea volcanoes, Hawaii. Geology 25 (10), 867–
870.
Paige, C.C., Saunders, M.A., 1982. LSQR: an algorithm for sparse linear equations and
sparse least squares. ACM Trans. Math. Software 8, 43–71.
Podvin, P., Lecomte, I., 1991. Finite difference computation of traveltimes in very
contrasted velocity models: a massively parallel approach and its associated
tools. Geophys. J. Int. 105, 271–284.
Prasad, M., 2002. Acoustic measurements in sands at low effective pressure: overpressure
detection in sands. Geophysics 67 (2), 405–412.
Puxeddu, M., 1984. Structure and late Cenozoic evolution of the upper lithosphere
in Southwest Tuscany (Italy). Tectonophysics 101 (3/4), 357–382.
Raffaele, R., Langer, H., Gresta, S., Moia, F., 2006. Tomographic inversion of local earthquake
data fromthe Gioia Tauro basin (south-western Calabria, Italy). Geophys.
J. Int. 165, 167–179, doi:10.1111/j.1365-246X.2006.02872.x.
Sanders, C.O., Ponko, S.C., Nixon, L.D., Schwartz, E.A., 1995. Seismological evidence
for magmatic and hydrothermal structure in Long Valley caldera from local
earthquake attenuation and velocity tomography. J. Geophys. Res. 100, 8311–
8326.
Spencer Jr., J.W.,Nur, A.M., 1976. The effects of pressure, temperature, and porewater
on velocities inWesterly Granite. J. Geophys. Res. 81 (5), 899–904.
Tatham, R.H., 1982. Vp/Vs and Lithology. In: Proceedings of the 50th Annual International
Meeting, R35, Society of Exploration Geophysicists, pp. 2401–2414,
Reprints.
Toks ¨ oz, M.N., Cheng, C.H., Timur,A., 1976. Velocities of seismicwaves in porous rocks.
Geophysics 41, 621–645.
Vanorio, T., De Matteis, R., Zollo, A., Batini, F., Fiordelisi, A., Ciulli, B., 2004. The deep
structure of the Larderello-Travale geothermal field from 3D microearthquake
traveltime tomography. Geophys. Res. Lett. 32, doi:10.1029/2004GL019432.
Villasenor, A., Benz, H.M., Filippi, L., De Luca, G., Scarpa, R., Patane, G., Vinciguerra, S.,
1998. Three-dimensional P wave velocity structure of Mt. Etna, Italy. Geophys.
Res. Lett. 25 (11), 1975–1978.
Wang, Z., Nur, A. (Eds.), 1992. Seismic and Acoustic Velocities in Reservoir Rocks:
Theoretical and Model Studies, vol. 2. Society of Exploration Geophysicists, Tulsa,
p. 457.
Zollo, A., Judenherc, S., Auger, E., D’Auria, L., Virieux, J., Capuano, P., Chiarabba, C., de
Franco, R., Makris, J., Michelini, A., Musacchio, G., 2003. Evidence for the buried
rim of Campi Flegrei caldera from3D active seismic imaging. Geophys. Res. Lett.
30, 19, doi:10.1029/2003GL018173.