Supplementary Material to: Slip Zone and Energetics of a Large Earthquake: Results
from the Taiwan Chelungpu-fault Drilling Project (TCDP)
Determination of Particle Size Distribution in the Major Slip Zone (MSZ):
Several images from MSZ were observed through optical, scanning electron
microscope (SEM), and transmission electron microscope (TEM) (Supplementary Fig.
1a-1c). The observations were made in the same area with different magnifications,
following the method described by Sammis et al. (1987) with careful measurements to
avoid overestimation of the grain size. Clasts were fragmented in grains. The
observations of the grains in every clast were taken from at least three images with the
same magnification. The grain counting of each clast was the average value from the
three observations. The original concept described in Mandelbrot (1983) and
techniques in Takayasu (1986), similar to Chester et al. (2005), were used to
determine the particle size distribution.
For each image, the grains were counted and measured one by one by eyes and
by a software for grain counting developed by National Institute of Health (USA).
The numbers of grains in each grain size is listed in Supplementary Table 1.
According to the observation area, the number of grains were normalized to the
number of grains per mm square (N(D), #/mm2) assuming homogeneous distribution
of the grains. The particle size distribution shows a distribution with a power law of
N(D)=0.0045D-2.3. According to the number of each grain size from the power law
distribution, and consider the ratio of the surface area to volume for spheres of
3/radius, the total surface area of the grains in a unit volume of meters cubic is
obtained. The corresponding values of each grain size are listed in Supplementary
Table 1. The total number of grains is 1409. The total surface area per meters cubic
volume is 3.23x107 m2/m3. For the 2cm major slip zone, the total surface area, SMSZ,
is 6.46x105 m2 per meters squared area.
The fractal dimension observed in this major slip zone has the value of 2.3,
which is larger than other observations as the values of equal or less than 2.0 (e.g.
Sammis et al., 1987, Chester et al., 2005). However, recent observations in Nojima
fault (e.g. Otsuki et al., 2003) obtained the fractal dimension of larger than 2.0 similar
to our value of 2.3 for the ultrafine, and homogeneous fault gouge. This value is also
similar to the fractal dimension generally observed in hypervelocity impact
fragmentation (Kadono et al. 2006). The observation of Otsuki et al. (2003) suggests
that if the gouge is fluidized, the fragmentation process may not follow the
constrained comminution with fractal dimension of two or less. However, the
mechanism of the fractal dimension as greater than 2 in these observations is still not
well understood.
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