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Double-difference tomography at Mt. Etna volcano
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Abstract
Double-difference tomography at Mt Etna volcano was realized by using the tomographic
algorithm developped by Monteiller et al. (2005), in which the travel-time computation was performed using a finite-difference solution of the Eikonal equation
(Podvin and Lecomte, 1991) and a posteriori ray-tracing. The inverse problem was
solved using a probabilistic approach (Tarantola and Valette, 1982). The optimal a
priori information (correlation length and a priori model variance) was found experimentally
by performing tomographies for correlation lengths and variances varying in
large intervals. This probabilistic approach allowed us to use a sech pdf for representing
errors in differential times. Data were travel-times and time delays provided by a
set of 329 earthquakes, well-recorded by the INGV-CT seismic network (50 stations)
on the Mt Etna volcano during the seismo-volcanic crisis occurring between October
2002 and January 2003. Checkerboard tests realized with this geometry and earthquake
pairs showed that the model can be correctly reconstructed in a significant area
around Mt Etna volcano. Results of the P and S-wave double-difference tomography
clearly evidenced two concentric features: a fast central cylindrical core, probably of
intrusive origin, surrounded by a slow annealed body, which could be related to partial melting