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| Titel |
Simulation of seismic waves in the brittle-ductile transition (BDT) using a Burgers model |
| VerfasserIn |
Flavio Poletto, Biancamaria Farina, José Maria Carcione |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250089815
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| Publikation (Nr.) |
 EGU/EGU2014-4027.pdf |
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| Zusammenfassung |
| The seismic characterization of the brittle-ductile transition (BDT) in the Earth’s crust is of
great importance for the study of high-enthalpy geothermal fields in the proximity of
magmatic zones. It is well known that the BDT can be viewed as the transition between zones
with viscoelastic and plastic behavior, i.e., the transition between the upper, cooler, brittle
crustal zone, and the deeper ductile zone. Depending on stress and temperature conditions,
the BDT behavior is basically determined by the viscosity of the crustal rocks, which acts as a
key factor. In situ shear stress and temperature are related to shear viscosity and steady-state
creep flow through the Arrhenius equation, and deviatory stress by octahedral stress
criterion.
We present a numerical approach to simulate the propagation of P-S and SH seismic
waves in a 2D model of the heterogeneous Earth’s crust. The full-waveform simulation code
is based on a Burgers mechanical model (Carcione, 2007), which enables us to describe both
the seismic attenuation effects and the steady-state creep flow (Carcione and Poletto, 2013;
Carcione et al. 2013). The differential equations of motion are calculated for the Burgers
model, and recast in the velocity-stress formulation. Equations are solved in the
time domain using memory variables. The approach uses a direct method based
on the Runge-Kutta technique, and the Fourier pseudo-spectral methods, for time
integration and for spatial derivation, respectively. In this simulation we assume isotropic
models.
To test the code, the signals generated by the full-waveform simulation algorithm are
compared with success to analytic solutions obtained with different shear viscosities.
Moreover, synthetic results are calculated to simulate surface and VSP seismograms in a
realistic rheological model with a dramatic temperature change, to study the observability of
BDT by seismic reflection methods. The medium corresponds to a selected rheology of the
Iceland scenario (Violay et al. 2012), with steep velocity gradient, and assuming
deep basaltic rock with low content of glass. The analysis shows the importance of
the assessment of the Arrhenius parameters for the characterization and definition
of the rheological models in the simulation of wave propagation in geothermal
areas.
References
Carcione JM. Wave fields in real media: Wave propagation in anisotropic, anelastic,
porous and electromagnetic media. Handbook of Geophysical Exploration, vol. 38, Elsevier
(2nd edition, revised and extended), 2007.
Carcione JM, Poletto F. Seismic rheological model and reflection coefficients of the
brittle-ductile transition. Pure and Applied Geophysics, DOI 10.1007/s00024-013-0643-4,
2013.
Carcione JM, Poletto F., Farina B., Craglietto, A. Simulation of seismic waves at the
Earth crust (brittle-ductile transition) based on the Burgers model. Submitted to Solid Earth ,
2013.
Violay M, Gibert B, Mainprice D, Evans B, Dautria JM, Azais P, Pezard PA. An
experimental study of the brittle-ductile transition of basalt at oceanic crust pressure and
temperature conditions. Geophys. Res. 117:1-23, 2012. |
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