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|Authors: ||Del Pezzo, E.*|
|Editors: ||Sato, H:|
|Title: ||Seismic wave scattering in volcanoes|
|Issue Date: ||2008|
|Keywords: ||seismic scattering|
|Abstract: ||Volcano-tectonic (VT) earthquakes produce high-frequency seismograms characterized by impulsive shear mech-
anism; their seismogram coda re ects the random inhomogeneity of the volcano structure. Consequently, this
inhomogeneity can be investigated through the analysis of the coda wave envelopes of the VT events. In this
chapter, I will review the main observational results obtained from volcanoes around the World, with the aim
of quantifying the scattering and attenuation properties of the volcanic areas. First, I will review the coda-Q
observations and their frequency dependence, then I will report on attempts that have been made to sepa-
rate the intrinsic from the scattering attenuation using multiple scattering and di¤usion models, and nally,
I will report on the interpretations based on these results. The results show that the coda-Q absolute values
characteristic of volcanoes are slightly smaller than those measured in non-volcanic zones, and that sometimes
their frequency dependence is di¤erent. It is impossible to deduce by coda-Q observations only whether this
di¤erence is controlled more by the intrinsic or the scattering attenuation. The application of multiple scatter-
ing models allows separate estimates of the intrinsic and the scattering attenuation coe¢ cients. Results show
that volcanoes are highly heterogeneous structures, with a mechanism of seismic wave energy dissipation that
tends to be controlled by the scattering phenomena with increasing frequency. For Mt. Vesuvius, Mt. Merapi
and Deception island volcano scattering attenuation prevails at frequencies higher than 2-3 Hz. At Mt. Etna,
intrinsic dissipation prevails or is comparable with scattering attenuation for frequencies lower than 8 Hz.
At high frequencies, di¤usion approximation is appropriate to describe the energy seismogram envelope.
The intrinsic dissipation of shear waves [possibly connected with magma reservoirs, which should decrease the
intrinsic Q values for shear waves] only has an important role at low frequencies.
Key words: Seismic scattering, coda waves, volcanoes|
|Appears in Collections:||04.06.09. Waves and wave analysis|
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