The Deep Structure of the Larderello-travale Geothermal Field (Italy) from Integrated, Passive Seismic Investigations

Abstract

We report the preliminary results from a project (GAPSS-Geothermal Area Passive Seismic Sources), aimed at testing the resolving capabilities of passive exploration methods on a well-known geothermal area, namely the Larderello-Travale Geothermal Field (LTGF). Located in the western part of Tuscany (Italy), LTGF is the most ancient geothermal power field of the world. GAPSS consisted of up to 20 seismic stations deployed over an area of about 50 x 50 Km. During the first 12 months of measurements, we located more than 2000 earthquakes, with a peak rate of up to 40 shocks/day. Preliminary results from analysis of these signals include: (i) analysis of Shear-Wave-Splitting from local earthquake data, from which we determined the areal distribution of the most anisotropic regions; (ii) local-earthquake travel-time tomography for both P-and S-wave velocities; (iii) telesismic receiver function aimed at determining the high-resolution (<0.5km) S-velocity structure over the 0-20km depth range, and seismic anisotropy using the decomposition of the angular harmonics of the RF data-set; (iv) S-wave velocity profiling through inversion of the dispersive characteristics of Rayleigh waves from earthquakes recorded at regional distances. After presenting results from these different analyses, we eventually discuss their potential application to the characterisation and exploration of the investigated area.

Regional thermo-rheological field related to granite emplacement in the upper crust: implications for the Larderello area (Tuscany, Italy)

“…Moreover, from the evolution of 2D strength profiles of the upper crust, it emerges that the BD 1 transition is timedependent and that its pronounced culmination progressively fades out during magma cooling. Throughout this migration there is a time interval (up to 300 kyr) when it coincides with the pluton roof, conforming to the interpretation of the K-horizon provided by and more recently by Saccorotti et al (2014), on the basis of local earthquake tomography. Therefore, from our results it emerges that the interpretations proposed of the K-horizon, i.e.…”

“…Here, the magmatic source, invoked in all studies, is still poorly defined, despite the importance of the related geothermal field, the most ancient in the world (e.g. Saccorotti et al, 2014).…”

Tectonic and Anthropogenic Microseismic Activity While Drilling Toward Supercritical Conditions in the Larderello‐Travale Geothermal Field, Italy

“…The model refines the initial velocity model by introducing (or removing) layers and recalibrating the velocity of the existing ones. The inversion process added four new layers (0.5, 1.5, 2.0, and 4.0 km depth) and removed the 3.7 km depth layer from the original model derived from De Matteis et al (), Saccorotti et al (), and Rabbel et al (). Velocities were reduced until 1.5 km depth and increased until 4.5 km depth.…”

“…A starting 1‐D wave velocity model was built considering velocity models obtained in different studies and with different methods (De Matteis et al, ; Rabbel et al, ; Saccorotti et al, ). The first location of each event was calculated using HYPOCENTER, an algorithm based on the Geiger's method (Lienert, ).…”

“…Initial and final 1‐D wave velocity models used to locate and relocate the recorded seismic events. The starting velocity model obtained from the literature (Saccorotti et al, ; De Matteis et al, ; Rabbel et al, ) is shown in gray, and the velocity model for the Lago area obtained by simultaneously inverting for hypocenters and velocity model is shown in black.…”