Article,
Three-dimensional tomography and rock properties of the Larderello-Travale geothermal area, Italy
Physics of the Earth and Planetary Interiors, 168 (1-2): 37--48 (May 2008)
DOI: 10.1016/j.pepi.2008.04.019
Abstract
In a geothermal area, a detailed knowledge of the three-dimensional
velocity structures aids the management of 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 VpxVs parameters for this area
to emphasize the deep variations in the physical rock properties
due to fluid content and porosity. Furthermore, effective porous
medium 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. Low Vp/Vs anomalies,
arising from a 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 x 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.
