Abstract
<p>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.</p>
Highlights
Heterogeneity in the Earth’s crust span a wide range of size and impedance contrast
Garcia Yeguas et al [2011] analyzed slowness and backazimuth anomalies at Deception Island volcano (Antarctica) and interpreted the results as produced by the propagation through a shallow magma chamber and shallow rigid bodies deduced by high-resolution tomography studies
Slowness and backazimuth anomalies in teleseismic signals were observed at Long Valley caldera [Steck and Prothero 1993]
Summary
Heterogeneity in the Earth’s crust span a wide range of size and impedance contrast. Beside the generation of scattered waves, they are responsible of ray path and wavefront distortion in a broad range of wavelength. In this paper we analyze local and regional earthquakes recorded at Mt. Vesuvius by a seismic array temporary deployed in 1997-1998 and observe backazimuth anomalies up to 37°. The comparison of observed backazimuth with the theoretical direction of several local and regional earthquakes shows interesting differences that are investigated by computing the wavefront propagation through heterogeneous media.
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