Seismic energy envelopes in volcanic media

in need of boundary conditions

L. De Siena*, E. Del Pezzo, C. Thomas, A. Curtis, L. Margerin

*Corresponding author for this work

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Seismogram envelopes recorded at Campi Flegrei caldera show diffusive characteristics as well as steep amplitude increases in the intermediate and late coda, which can be related to the presence of a non-uniformly scattering medium. In this paper, we first show the results of a simulation with a statistical model considering anisotropic scattering interactions, in order to match coda-envelope duration and shape. We consider as realistic parameters for a volcanic caldera the presence of large square root velocity fluctuations (10 per cent) and two typical correlation lengths for such an heterogeneous crust, a = 0.1 and 1 km. Then, we propose the inclusion of a diffusive boundary condition in the stochastic description of multiple scattering, in order to model intermediate and late coda intensities, and particularly the sharp intensity peaks at some stations in the caldera. Finally, we show that a reliable 2-D synthetic model of the envelopes produced by earthquakes vertically sampling a small region can be obtained including a single drastic change of the scattering properties of the volcano, that is, a caldera rim of radius 3 km, and sections varying between 2 and 3 km. These boundary conditions are diffusive, which signifies that the rim must have more scattering potential than the rest of the medium, with its diffusivity 2-3 orders of magnitude lower than the one of the background medium, so that the secondary sources on its interface(s) could enhance coda intensities. We achieve a good first-order model of high-frequency (18 Hz) envelope broadening adding to the Monte Carlo solution for the incident flux the secondary source effects produced by a closed annular boundary, designed on the caldera rim signature at 1.5 km depth. At lower frequencies (3 Hz) the annular boundary controls the intermediate and late coda envelope behaviour, in a way similar to an extended diffusive source. In our interpretation, the anomalous intensities observed at several stations and predicted by the final Monte Carlo solutions are mainly due to the diffusive transmission reflection from a scattering object of increased scattering power, and are controlled by its varying thickness.

Original languageEnglish
Pages (from-to)1102-1119
Number of pages18
JournalGeophysical Journal International
Volume195
Issue number2
Early online date7 Aug 2013
DOIs
Publication statusPublished - Nov 2013

Keywords

  • numerical solutions
  • seismic anisotropy
  • seismic attenuation
  • seismic tomography
  • wave scattering and diffraction
  • calderas
  • campi-flegrei caldera
  • Monte-Carlo-simulation
  • multiple-scattering
  • elastic-waves
  • diffusion

Cite this

De Siena, L., Del Pezzo, E., Thomas, C., Curtis, A., & Margerin, L. (2013). Seismic energy envelopes in volcanic media: in need of boundary conditions. Geophysical Journal International, 195(2), 1102-1119. https://doi.org/10.1093/gji/ggt273

Seismic energy envelopes in volcanic media : in need of boundary conditions. / De Siena, L.; Del Pezzo, E.; Thomas, C.; Curtis, A.; Margerin, L.

In: Geophysical Journal International, Vol. 195, No. 2, 11.2013, p. 1102-1119.

Research output: Contribution to journalArticle

De Siena, L, Del Pezzo, E, Thomas, C, Curtis, A & Margerin, L 2013, 'Seismic energy envelopes in volcanic media: in need of boundary conditions', Geophysical Journal International, vol. 195, no. 2, pp. 1102-1119. https://doi.org/10.1093/gji/ggt273
De Siena, L. ; Del Pezzo, E. ; Thomas, C. ; Curtis, A. ; Margerin, L. / Seismic energy envelopes in volcanic media : in need of boundary conditions. In: Geophysical Journal International. 2013 ; Vol. 195, No. 2. pp. 1102-1119.
@article{ee3364a108aa4503bb96ae3af4cf03e5,
title = "Seismic energy envelopes in volcanic media: in need of boundary conditions",
abstract = "Seismogram envelopes recorded at Campi Flegrei caldera show diffusive characteristics as well as steep amplitude increases in the intermediate and late coda, which can be related to the presence of a non-uniformly scattering medium. In this paper, we first show the results of a simulation with a statistical model considering anisotropic scattering interactions, in order to match coda-envelope duration and shape. We consider as realistic parameters for a volcanic caldera the presence of large square root velocity fluctuations (10 per cent) and two typical correlation lengths for such an heterogeneous crust, a = 0.1 and 1 km. Then, we propose the inclusion of a diffusive boundary condition in the stochastic description of multiple scattering, in order to model intermediate and late coda intensities, and particularly the sharp intensity peaks at some stations in the caldera. Finally, we show that a reliable 2-D synthetic model of the envelopes produced by earthquakes vertically sampling a small region can be obtained including a single drastic change of the scattering properties of the volcano, that is, a caldera rim of radius 3 km, and sections varying between 2 and 3 km. These boundary conditions are diffusive, which signifies that the rim must have more scattering potential than the rest of the medium, with its diffusivity 2-3 orders of magnitude lower than the one of the background medium, so that the secondary sources on its interface(s) could enhance coda intensities. We achieve a good first-order model of high-frequency (18 Hz) envelope broadening adding to the Monte Carlo solution for the incident flux the secondary source effects produced by a closed annular boundary, designed on the caldera rim signature at 1.5 km depth. At lower frequencies (3 Hz) the annular boundary controls the intermediate and late coda envelope behaviour, in a way similar to an extended diffusive source. In our interpretation, the anomalous intensities observed at several stations and predicted by the final Monte Carlo solutions are mainly due to the diffusive transmission reflection from a scattering object of increased scattering power, and are controlled by its varying thickness.",
keywords = "numerical solutions, seismic anisotropy, seismic attenuation, seismic tomography, wave scattering and diffraction, calderas, campi-flegrei caldera, Monte-Carlo-simulation, multiple-scattering, elastic-waves, diffusion",
author = "{De Siena}, L. and {Del Pezzo}, E. and C. Thomas and A. Curtis and L. Margerin",
year = "2013",
month = "11",
doi = "10.1093/gji/ggt273",
language = "English",
volume = "195",
pages = "1102--1119",
journal = "Geophysical Journal International",
issn = "0956-540X",
publisher = "Wiley-Blackwell",
number = "2",

}

TY - JOUR

T1 - Seismic energy envelopes in volcanic media

T2 - in need of boundary conditions

AU - De Siena, L.

AU - Del Pezzo, E.

AU - Thomas, C.

AU - Curtis, A.

AU - Margerin, L.

PY - 2013/11

Y1 - 2013/11

N2 - Seismogram envelopes recorded at Campi Flegrei caldera show diffusive characteristics as well as steep amplitude increases in the intermediate and late coda, which can be related to the presence of a non-uniformly scattering medium. In this paper, we first show the results of a simulation with a statistical model considering anisotropic scattering interactions, in order to match coda-envelope duration and shape. We consider as realistic parameters for a volcanic caldera the presence of large square root velocity fluctuations (10 per cent) and two typical correlation lengths for such an heterogeneous crust, a = 0.1 and 1 km. Then, we propose the inclusion of a diffusive boundary condition in the stochastic description of multiple scattering, in order to model intermediate and late coda intensities, and particularly the sharp intensity peaks at some stations in the caldera. Finally, we show that a reliable 2-D synthetic model of the envelopes produced by earthquakes vertically sampling a small region can be obtained including a single drastic change of the scattering properties of the volcano, that is, a caldera rim of radius 3 km, and sections varying between 2 and 3 km. These boundary conditions are diffusive, which signifies that the rim must have more scattering potential than the rest of the medium, with its diffusivity 2-3 orders of magnitude lower than the one of the background medium, so that the secondary sources on its interface(s) could enhance coda intensities. We achieve a good first-order model of high-frequency (18 Hz) envelope broadening adding to the Monte Carlo solution for the incident flux the secondary source effects produced by a closed annular boundary, designed on the caldera rim signature at 1.5 km depth. At lower frequencies (3 Hz) the annular boundary controls the intermediate and late coda envelope behaviour, in a way similar to an extended diffusive source. In our interpretation, the anomalous intensities observed at several stations and predicted by the final Monte Carlo solutions are mainly due to the diffusive transmission reflection from a scattering object of increased scattering power, and are controlled by its varying thickness.

AB - Seismogram envelopes recorded at Campi Flegrei caldera show diffusive characteristics as well as steep amplitude increases in the intermediate and late coda, which can be related to the presence of a non-uniformly scattering medium. In this paper, we first show the results of a simulation with a statistical model considering anisotropic scattering interactions, in order to match coda-envelope duration and shape. We consider as realistic parameters for a volcanic caldera the presence of large square root velocity fluctuations (10 per cent) and two typical correlation lengths for such an heterogeneous crust, a = 0.1 and 1 km. Then, we propose the inclusion of a diffusive boundary condition in the stochastic description of multiple scattering, in order to model intermediate and late coda intensities, and particularly the sharp intensity peaks at some stations in the caldera. Finally, we show that a reliable 2-D synthetic model of the envelopes produced by earthquakes vertically sampling a small region can be obtained including a single drastic change of the scattering properties of the volcano, that is, a caldera rim of radius 3 km, and sections varying between 2 and 3 km. These boundary conditions are diffusive, which signifies that the rim must have more scattering potential than the rest of the medium, with its diffusivity 2-3 orders of magnitude lower than the one of the background medium, so that the secondary sources on its interface(s) could enhance coda intensities. We achieve a good first-order model of high-frequency (18 Hz) envelope broadening adding to the Monte Carlo solution for the incident flux the secondary source effects produced by a closed annular boundary, designed on the caldera rim signature at 1.5 km depth. At lower frequencies (3 Hz) the annular boundary controls the intermediate and late coda envelope behaviour, in a way similar to an extended diffusive source. In our interpretation, the anomalous intensities observed at several stations and predicted by the final Monte Carlo solutions are mainly due to the diffusive transmission reflection from a scattering object of increased scattering power, and are controlled by its varying thickness.

KW - numerical solutions

KW - seismic anisotropy

KW - seismic attenuation

KW - seismic tomography

KW - wave scattering and diffraction

KW - calderas

KW - campi-flegrei caldera

KW - Monte-Carlo-simulation

KW - multiple-scattering

KW - elastic-waves

KW - diffusion

U2 - 10.1093/gji/ggt273

DO - 10.1093/gji/ggt273

M3 - Article

VL - 195

SP - 1102

EP - 1119

JO - Geophysical Journal International

JF - Geophysical Journal International

SN - 0956-540X

IS - 2

ER -