Time-lapse waveform analysis for elastic and anelastic structural
changes of transducer-transducer active seismic experiments' data during
triaxial deformation of granitic rock
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.