Wavefront distortion across Mt. Vesuvius observed by a seismic array

Abstract

Local and regional earthquakes recorded at Mt. Vesuvius in 1997 and 1998 by a temporary seismic array have been analyzed with array methods to estimate slowness and backazimuth of correlated phases. The backazimuth observed for the direct P-wave has been compared with the expected direction, and results show surprising large differences in most of the cases. Since the observed difference is not systematic but depends on the epicenter backazimuth, we ascribe it to a wavefront distortion produced by the propagation through a non-homogenous velocity structure. To check this hypothesis we computed synthetic wavefront propagation in two different velocity models by applying a finite-difference method. The first model was homogeneous, while the second one was heterogeneous, with 2D symmetry in the horizontal plane given by a positive velocity anomaly centered at the volcano crater. We observe that the heterogeneous model gives results in good qualitative agreement with the observations. Such model is supported by the results of tomographic studies carried out for Mt. Vesuvius.