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| Titel |
Boundary conditions in the stochastic description of the scattered wave-field: checking tomographic structures in an active caldera. |
| VerfasserIn |
L. De Siena, E. Del Pezzo, C. Thomas, A. Curtis, L. Margerin |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250059616
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| Zusammenfassung |
| The mixing between coherent and incoherent signals in volcanic seismic recordings is
continuous. To highlight the actual limit between these two means discerning the soil at
which a deterministic or stochastic approach can be applied, as well as providing a better
image of a volcanic structure. In order to model volcano-tectonic envelopes in a caldera we
show the importance of including in the usual stochastic approach (i. e. Monte Carlo
simulations based on the Radiative Transfer Theory) the effects induced by a drastic change
in the scattering properties of the medium. Even if caused by a deterministic boundary, these
effects are still stochastic in their mathematical and physical form, and can be modeled by
using a second set of transport equations. In our approach, coda envelopes in the caldera
are ruled by three different length scales: the mean free path, the transport mean
free path, and the distance between the source and a large scale boundary - as the
caldera rim. We use this model for a first order check of large scale tomographic
anomalies in the caldera, giving important markers on the minimum frequency at
which a deterministic approach (e. g. a ray approximation) can be used. We compare
velocity, attenuation, and scattering tomography images of the caldera, as well
as the recorded data envelopes, with the synthetic envelopes obtained by using
our 2D codes. The result is a first order model which fits data only in case of a
large scale change into the heterogeneity distribution - like the one induced by a
caldera rim. We recognize that a 3D model is necessary to discern between the
presence of a vertical and/or of a horizontal anomaly, as well as to fit smaller scale
envelopes changes and tomography anomalies. We proved anyway that, in the range
between 1 and 20 Hz, the exclusive application of a deterministic or stochastic
approximation to interpret seismic data provides unfeasible results. A mixed approach can
account for the correct values of quantities which are currently employed to obtain
attenuation and scattering tomography images - like envelope broadening and coda decay. |
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