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Time-lapse waveform analysis for elastic and anelastic structural changes of transducer-transducer active seismic experiments' data during triaxial deformation of granitic rock
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  • Ssu-Ting Lai,
  • Nobuaki FUJI,
  • Ikuo Katayama,
  • Luis Fabian Bonilla,
  • Yann Capdeville
Ssu-Ting Lai
Institut De Physique Du Globe De Paris

Corresponding Author:[email protected]

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Nobuaki FUJI
Institut De Physique Du Globe De Paris
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Ikuo Katayama
Hiroshima University
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Luis Fabian Bonilla
Université Gustave Eiffel
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Yann Capdeville
Université de Nantes
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Abstract

We quantitatively evaluate transducer-transducer one-source one-station active seismic waveform data, in order to monitor time-lapse changes of elastic and anelastic structure during deformation experiments in laboratory. The experiment data of dry and water-saturated sample are provided by Zaima and Katayama (2018, https://doi.org/10.1029/2018JB016377). A transducer receiver, at the mid-point of cylindrical rock sample, is located on the antipodal position of the transducer source, emitting compressional and shear waves. Due to the extremely underdetermined nature of inverse problem, we limit the number of unknowns to be four: global P- and S- wave velocities and their corresponding anelastic attenuation factors, which can represent the micro-cracks nucleation during the loading and before the appearance of the largest crack that causes the fracture. We first performed a trial-and-error search for a realistic boundary condition in three-dimensional seismic waveform modeling using spectral-element method, in order to fit the synthetic data with the observed waveforms. We then generated synthetic data for 6000 combinations of elastic and anelastic parameters, in order to conduct Monte-Carlo waveform inversion based on the cost functions using waveform misfit and zero-lag cross-correlation. We obtained the time-lapse changes in velocity and attenuation during the deformation, which are then linked to crack development. Compared with the wet experiment, the dry experiment has a larger change in both the velocity and attenuation. However, regardless of the configuration, global seismic wave speeds rise first and then decrease during the experiments. The quality factor shows roughly the same trend.