Abstract
Unconsolidated soft sediments deform and mix complexly by seismically induced fluidization. Such geological soft-sediment deformation structures (SSDSs) recorded in boring cores were imaged by X-ray computed tomography (CT), which enables visualization of the inhomogeneous spatial distribution of iron-bearing mineral grains as strong X-ray absorbers in the deformed strata. Multifractal analysis was applied to the two-dimensional (2D) CT images with various degrees of deformation and mixing. The results show that the distribution of the iron-bearing mineral grains is multifractal for less deformed/mixed strata and almost monofractal for fully mixed (i.e. almost homogenized) strata. Computer simulations of deformation of real and synthetic digital images were performed using the egg-beater flow model. The simulations successfully reproduced the transformation from the multifractal spectra into almost monofractal spectra (i.e. almost convergence on a single point) with an increase in deformation/mixing intensity. The present study demonstrates that multifractal analysis coupled with X-ray CT and the mixing flow model is useful to quantify the complexity of seismically induced SSDSs, standing as a novel method for the evaluation of cores for seismic risk assessment.
Highlights
The present study demonstrates that multifractal analysis coupled with X-ray computed tomography (CT) and the mixing flow model is useful to quantify the complexity of seismically induced soft-sediment deformation structures (SSDSs), standing as a novel method for the evaluation of cores for seismic risk assessment
The wavy pattern suggests that the observed deformation of the soft and watersaturated sediments is conceivably related to vibration triggered by earthquakes
Multifractal analysis coupled with X-ray CT and the mixing flow model described here could represent a novel method for the quantitative evaluation of cores in terms of seismic risk assessment
Summary
Multifractal analysis is a useful technique to quantify the complex deformation/mixing processes of fluids.[11,12,13,14,40] X-ray computed tomography (CT) provides quantitative two-dimensional (2D) images of geological samples with SSDSs.[15] The spatial distribution of iron-bearing minerals (strong X-ray absorbers) as marker particles is recorded in the CT images. Multifractal analysis was applied to CT images of boring cores with various degrees of SSDSs to reveal the effects of the deformation/mixing intensity on the degree of multifractality (i.e. shape of f (α) spectra). Mixing simulations of sediment digital images were performed using the egg-beater flow model[14,16] to reproduce the effects of the deformation/mixing intensity on the multifractality
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