3D Scattering Image of Mt. Vesuvius

Abstract

In this article we apply a passive scattering-imaging method, derived from the method developed by Nishigami (1991) to data from the coda of the local volcano-tectonic (VT) earthquakes of Mt. Vesuvius. This method provides the space distribution of the strong scatterers together with a rough estimate of their strength. In the development of our method we use a realistic raytracing calculated with a raybending approach in the 3D velocity model of Mt. Vesuvius structure obtained with travel-time inversion. The inversion procedure adopted for the scattering imaging in the present study is based on the conjugate gradient method (CGM). The volume under study is divided into cubic cells with different dimensions in a multiscale approach. We obtain the best resolution (900 m cubic cell size) in the central part of the volume under study (roughly in a radius of 4 km centered in the crater) within a depth of 5 km. We analyzed the coda signals after filtering in two frequency bands, the first centered at 12 Hz and the second at 18 Hz, where most of the seismic energy is concentrated. Results show that most of the strong scatterers are located in the depth range between the surface and 3000 m below the sea level, in correspondence with the crater axis where most of the seismicity occurs. Part of the scatterers are located in the zones characterized by the maximum velocity contrasts.