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Journal of Asian Earth Sciences 36 (2009) 135–145
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Journal of Asian Earth Sciences
journal homepage: www.elsevier.com/locate/jseaes
Seismic velocities, density, porosity, and permeability measured at a deep hole
penetrating the Chelungpu fault in central Taiwan
Jeen-Hwa Wang a,*, Jih-Hao Hung b, Jia-Jyun Dong c
a
Institute of Earth Sciences, Academia Sinica, P.O. Box 1-55, Nangang, Taipei, 115, Taiwan, ROC
Department of Earth Sciences, National Central University, Jhongli, Taiwan, ROC
c
Graduate Institute of Applied Geology, National Central University, Jhongli, Taiwan, ROC
b
a r t i c l e
i n f o
Article history:
Received 30 June 2008
Received in revised form 11 December 2008
Accepted 5 January 2009
Keywords:
Seismic velocity
Density
Porosity
Permeability
Bulk and shear modulus
a b s t r a c t
On September 20, 1999, the Ms7.6 Chi-Chi earthquake ruptured the Chelungpu fault in central Taiwan.
After the earthquake, two deep boreholes cutting the fault were drilled. The seismic velocities (P- and
S-wave velocities denoted by vp and vs) were well-logged at a 2000-m deep hole. The values of density,
porosity and permeability of ten rock samples obtained at different depths were measured in the laboratory. Well-logged and measured results are used to study the following problems: (1) the depth variations in seismic velocities, porosity, and permeability; (2) the relationship between P- and S-wave
velocities; (3) porosity-dependence of P- and S-wave velocities and their ratio; and (4) porosity-dependence of density. Results show that the polynomial can describe the depth variations in seismic velocities.
The porosity slightly decreases with increasing depth. The permeability is depth-dependent and can be
described by a polynomial, but the functions are different for different rock types. The porosity and permeability in the fault zone cannot be evaluated from the related depth-dependent functions inferred
from wall rocks. A linear relationship, which is different from vs = 0.58 vp for the perfectly elastic materials, exists between vs and vp. Seismic velocities linearly decrease with increasing porosity. The ratio of vp
to vs slightly depends on the porosity. The porosity-dependent functions of bulk and shear modulus are
constructed and their values for dry rocks are also evaluated.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
Seismic velocities (P- and S-wave velocities, denoted by vp and
vs, respectively, hereafter) are two major parameters representing
mechanical properties of earth materials. Seismic velocities are in
terms of bulk modulus, K, shear modulus, l, and density, q, in
the individual forms: vp = [(K + 4l/3)/q]1/2 and vs = (l/q)1/2. The
ratio of P- to S-wave velocities is related to the Poisson ratio,
t (=[0.5(vp/vs)2 2]/[(vp/vs)2 1]). Hence, vp, vs, and q are three
fundamental parameters of earth materials. The values and depth
variations of the three parameters and the relationships among
them are important for (1) understanding subsurface geological
structures, geotectonics, faulting mechanism, and source properties, (2) evaluating strong ground motions, and (3) estimating seismic hazards. It is necessary to directly measure or indirectly infer
the values of the three parameters.
Not only fault zone rocks but also wall rocks are not 100% consolidated and compact. There are voids and fractures in rocks and
thus fluids can exist and flow in rocks. Presence of fluids (mainly
water) in rocks can reduce the strengths of rocks. For example,
* Corresponding author. Tel.: +886 2 27839910; fax: +886 2 27839871.
E-mail address: [email protected] (J.-H. Wang).
1367-9120/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jseaes.2009.01.010
Chen et al. (2005) observed 32% reduction in the strengths of
the saturated samples of cores relative to the corresponding dry
samples. The flow of fluids in and mechanical properties of rocks
are controlled by the effective pressure and two parameters of
rocks, i.e., porosity (/) and permeability (j). The effective pressure,
pe, is pc pw where pc and pw are the confining pressure and pore
fluid pressure, respectively. The three parameters K, l, and q are
affected by the porosity, /, and thus vp and vs vary with / (cf.
Han et al., 1986; Han and Batzle, 2004). This makes seismic velocities be influenced by the porosity (cf. Cadoret et al., 1995). Hence,
it is also significant to explore the relationships between seismic
velocities and porosity and between density and porosity. In addition, seismic velocities, porosity, and permeability are different
between fault zone and wall rocks and they are all a function of
depth (cf. Kanamori and Heaton, 2000; Japsen et al., 2007).
In the Taiwan region, the values of seismic velocities and density were mainly inferred either from controlled-source seismology
(e.g. Wang et al., 2007) or from 3-D seismic tomography (e.g. Ma
et al., 1996). There is a lack of directly-measured values of the three
parameters. Except for shallow depths, the values of porosity and
permeability are not available. On September 20, 1999, the Ms7.6
Chi-Chi earthquake ruptured the Chelungpu fault, which is a
100-km-long and east-dipping thrust fault, with a dip angle of
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J.-H. Wang et al. / Journal of Asian Earth Sciences 36 (2009) 135–145
30°, in central Taiwan (Ma et al., 1999; Shin and Teng, 2001). The
epicenter (in a solid star) and fault trace (in a solid line) are displayed in Fig. 1. To deeply investigate the physical and chemical
Fig. 1. A figure to show the epicenter (in a solid star), the Chelungpu fault (in a solid
line), and the borehole sites (inside a solid circle). The vertical and horizontal axes
represent, respectively, the north latitude and east longitude.
properties of the fault zone, the Taiwan Chelungpu-fault Drilling
Project (TCDP) sponsored by National Science Council was
launched in 2004. Two deep holes (denoted as Hole-A and HoleB hereafter) penetrating the fault plane were drilled in 2005 (cf.
Ma et al., 2006; Wang et al., 2007). The two deep holes are 40 m
apart: Hole-A with a depth of 2000 m and Hole-B with a depth of
1300 m. A smaller-sized solid circle in Fig. 1 displays the localities
of the two holes. Fig. 2 shows the structural profile across Hole-A.
Continuously coring and well-loggings were made at the two
holes. Hence, the TCDP succeeded in measuring and thus characterizing in situ rock properties and around the fault zone after
the earthquake. This was a good opportunity of directly measuring
the parameters.
Lin et al. (2007) observed that the lithostratigraphy for the
Hole-A are: (1) the lower Plio-Pleistocene Cholan Formation in
0–1013 m; (2) the Pliocene Chinshui Shale in 1013–1300 m; (3)
the Miocene Kueichulin Formation in 1300–1707 m; (4) the lower
Plio-Pleistocene Cholan Formation in 1707–2003 m. The detailed
analyses of lithology, characteristics, and structures of the fault
zone can be found in Song et al. (2007), Hung et al. (2007,
2009), Yeh et al. (2007) and Sone et al. (2007). Fault breccia
and gouge, with an increase in the degree of fracturing from
top to bottom, were found within the Chinsui shale at depths of
1105–1115 m. According to the presence of ultra-fine grained
fault gouge and a large fracture density, Ma et al. (2006) called
a 12-cm thick zone at depths of 1111.23–1111.35 m the primary
slip zone (PSZ) and named the bottom 2-cm thick sub-zone the
major slip zone (MSZ), which is least deformed and regarded as
the slip zone of this earthquake. The PSZ and MSZ are displayed
in Fig. 3. The PSZ consists of several slip sub-zones associated
with repeating past events. Each slip sub-zone has a thickness
of about 2–3 cm, with 5-mm thick ultra-fine grains at the bottom.
Hung et al. (2007) stated that the PSZ is specified with low seismic velocities, low density, high Poisson ratio, and low electric
resistivity and is specified by bedding-parallel thrust faults with
a dip angle of 30°.
Geophysical well-loggings were performed from 500 to 1750 m
at Hole-A to measure seismic velocities and other physical parameters at a 15-cm sampling space (Hung et al., 2007). The measurement error of depth is 0.01 m. In addition, laboratory experiments
Fig. 2. Structural profile across Hole A (from Hung et al. (2007)).
J.-H. Wang et al. / Journal of Asian Earth Sciences 36 (2009) 135–145
were also done on the core samples obtained from Hole-A to
measure the values of porosity and permeability by Dong et al.
(submitted for publication). Hsu (2007) measured the density on
discrete samples of sandstone and silty-shale. In addition, Hirono
et al. (2007) also measured the density values on discrete samples
of sandstone, shale, and siltstone at Hole-B. The depth variations in
seismic velocities, density, porosity, permeability, Gamma ray,
electrical resistivity etc. can represent not only the general trend
of lithology but also its finer differentiations. Wu et al. (2008)
made core-log integration studies of lithology at Hole-A. Detailed
analyses of measured values of seismic velocities, density, porosity,
and permeability will help us to quantitatively construct the relations between any two parameters.
137
In this work, the measured results of seismic velocities, density,
porosity, and permeability by Hung et al. (2007), Hsu (2007), and
Dong et al. (submitted for publication) are used to study the following problems: (1) the depth variations in seismic velocities,
porosity, and permeability; (2) the relationship between P- and
S-wave velocities; (3) the porosity-dependence of P- and S-wave
velocities and their ratio; and (4) the porosity-dependence of
density. In addition, the porosity-dependence of bulk and shear
modulus is also studied on the basis of the relationships of P- and
S-wave velocities versus porosity, thus making us able to evaluate
the bulk and shear modulus for the rocks in the dry condition.
2. Data
2.1. Seismic velocities
Fig. 3. Figure shows the traced fractures in 0.12-m thick core of PSZ drilled from
Hole A. MSZ is at the bottom 0.02 m. The arrow points to the upward direction. The
left line of MSZ displays the fault plane (reproduced from Ma et al. (2006)).
The P- and S-wave velocities, i.e., vp and vs, respectively, were
well-logged in the depth range 502.18–1868.01 m (Hung et al.,
2007), with a measurement interval of 12.5 cm when the depth
is less than 1297.23 m and 15 cm when the depth is larger than
1297.23 m. The unit for both vp and vs is km/s. The depth variations
of vp and vs in this depth range are plotted in the upper diagram of
Fig. 4a. Averages of vp and vs are, respectively, 3.87 and 1.89 km/s,
and displayed by horizontal dashed lines. Shown in the lower diagram of Fig. 3a is the depth variation of vp/vs, with an average of
2.07 which is denoted by a horizontal dashed line. The depth range
of PSZ is displayed by two vertical dotted lines which are quite
closed to each other due to a very narrow PSZ.
To display detailed information near the PSZ, the depth variations of vp, vs, and vp/vs in the depth range of 1110–1112 m are
plotted in Fig. 4b. Inside the PSZ, vp and vs were well-logged only
Fig. 4. The depth variations of vp, vs, and vp/vs: (a) for the depth range of 502.18–1868.01 m; and (b) for the depth range of 1110–1112 m;. The average values of vp, vs, and
vp/vs are denoted by horizontal dashed lines. The depth range of PSZ is displayed by two vertical dotted lines. In (a), the regression depth functions of vp and vs in four depth
ranges, i.e., 494–1013 m, 1013–1300 m, 1300–1707 m, and 1707–1866 m (separated by three vertical thin solid lines) are shown with dashed lines, and the regression depth
functions of vp = 1.68z0.12 and vs = 0.29z0.27 (z = depth) are depicted by solid lines.
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J.-H. Wang et al. / Journal of Asian Earth Sciences 36 (2009) 135–145
at a depth of 1111.305 m. The respective values of vp, vs, and vp/vs
are 3.27 km/s, 1.41 km/s, and 2.32. The differences between these
values and their individual averages are, respectively: 0.60 km/s
for vp, 0.48 km/s for vs, and 0.25 for vp/vs. The magnitude of the
difference is larger for vp than for vs. Obviously, in the PSZ vp and
vs are lower than the individual averages and vp/vs is higher than
its average.
Hsu (2007) measured the values of vp and vs under an atmosphere pressure on the discrete rock samples from which the value
of vp/vs are calculated. For some samples (e.g. R287sec1 and
R351sec2 in Table 1), he measured the values of vp and vs in two
segments with different thicknesses. Hence, we calculate the average seismic velocities, va (for vp and vs), for the three samples using
the following formulas: va = (h1 + h2)/(t1 + t2) where hi and ti
(i = 1, 2) are, respectively, the thickness of and traveling time of
seismic waves in the ith segment and ti is equal to hi/vi. Table 1
shows the values of vp, vs, and vp/vs for the samples associated with
the samples listed in Table 2. In order to compare the values of
well-logged seismic velocities and those measured in laboratory,
the values of vp, vs, and vp/vs well-logged at or very close to the
localities, where the rock samples were obtained, are taken and
listed in Table 1. The plots of the two kinds of parameters are displayed in Fig. 5: 5a for vp, 5b for vs, and 5c for vp/vs. Obviously,
well-logged vp is larger than laboratory vp for all rock samples. Except for two rock samples, the difference between well-logged vs
and laboratory vp is small. Except for one rock sample, well-logged
vp/vs is larger than laboratory vp/vs, and the difference is small for
four rock samples. In addition to the uncertainty of measuring, the
differences might be due to the effect of effective pressures on seismic velocities (cf. Fam and Santamarina, 1997; Zimmer et al.,
2007a). In the followings, the correlations between seismic velocity and porosity will be studied based only on well-logged values
of seismic velocities, because the number of data measured in lab-
oratory is smaller than that of well-loggings and the well-logged
values were mad in situ and thus they can represent elastic behavior under the related effective pressures.
2.2. Density
The density values were measured directly on discrete samples
at Hole-A under an atmosphere pressure by Hsu (2007). This density is denoted by qds. The measured values are from 2.3 to 2.7 g/
cm3 for the Cholan Formation, from 2.3 to 2.7 g/cm3 for the Chinshui Shale, and from 2.2 to 2.6 g/cm3 for the Kueichulin Formation. The density values of discrete rock samples are listed in
Table 2. The maximum difference in the density values is
0.48 g/cm3. The average density for all samples is 2.47 g/cm3. This
value is used to evaluate the upper bound confining pressure.
Hung et al. (2007) also well-logged the density values at Hole-A
using the gamma ray attenuation (GRA) method. This density is
denoted by qGRA. The values of qGRA are also listed in Table 1.
The plot of qGRA versus qds is shown in Fig. 5c. The data points
for sandstone (in solid circles) slightly depart from the bisection
line, while those for silty-shale are around the line. The difference
between the two density values, i.e., qGRA qds, range from 0.20
to 0.36 g/cm3, with a percentage error, i.e., (qGRA qds)/qds, from
7.72% to 16.51%. The difference between the two values is less
than 17%.
Fundamentally, the density values of rocks measured using different methodologies are different. Hung et al. (2007) applied the
Triple-detector Lithological Density Log (TDL) to measure the
in situ formation density (containing pore fluids) with a vertical
resolution of 5 cm and within the error of 0.01 g/cm3. The density
value has been corrected with borehole size (caliper) and mud
cake. A factor called the photoelectrical factor (Pe) was also considered to differentiate if an abnormal density value is caused by mud
Table 1
The well-logged values of seismic velocities (vp and vs) and vp/vs for ten discrete rock samples and the related values measured in laboratory for six samples. The parameter z
represents the depth of the locality where the rock samples were taken.
Sample
R261sec2-1
R261sec2-2
R307sec1
R255sec2-1
R255sec2-2
R287sec1
R351sec2
R316sec1
R390sec3
R437sec1
z (m)
Well-logged
915.24
915.24
1009.62
902.68
902.68
972.42
1114.33
1028.43
1174.24
1232.46
Measured in Laboratory
vp (km/s)
vs (km)
vp/vs
3.76
3.76
4.71
4.07
4.07
4.11
4.51
4.30
4.20
4.12
1.87
1.87
2.37
2.02
2.02
2.14
2.38
2.27
2.17
2.10
2.01
2.01
1.99
2.02
2.02
1.92
1.90
1.90
1.94
1.96
vp (km/s)
vs (km)
vp/vs
3.28
1.92
1.71
3.38
3.63
3.50
3.55
3.23
1.72
2.26
2.42
2.78
1.99
1.97
1.61
1.45
1.28
1.62
Table 2
The values of j0 and /0 under the atmospheric pressure, the exponents of the power-law functions of permeability (j) and porosity (/), and the values of density (qds and qGRA)
for 10 rock samples at different depths (z) (from Hung et al. (2007), Hsu (2007) and Dong et al. (submitted for publication)).
Sample
z (m)
qds(g/cm3)
qGRA(g/cm3)
j = j0(pe/pa)n
2
R261sec2-1
R261sec2-2
R307sec1
R255sec2-1
R255sec2-2
R287sec1
R351sec2
R316sec1
R390sec3
R437sec1
Sandstone
Sandstone
Sandstone
Silty-shale
Silty-shale
Silty-shale
Silty-shale
Silty-shale
Silty-shale
Shale
915.24
915.24
1009.62
902.68
902.68
972.42
1114.33
1028.43
1174.24
1232.46
2.21
2.21
2.18
2.59
2.59
2.58
2.59
2.60
2.66
2.58
2.45
2.45
2.54
2.45
2.45
2.62
2.39
2.64
2.51
2.64
/ ¼ /0 (pe/pa)q
j0(m )
n
/0
q
1.14 1013
2.35 1013
1.37 1013
4.91 1017
8.05 1016
6.58 1015
2.00 1017
0.112
0.305
0.143
0.817
1.357
1.594
0.830
0.2020
0.2245
0.2075
0.037
0.056
0.040
4.08 1013
2.70 1018
1.732
0.554
0.1127
0.1251
0.1023
0.1079
0.1272
0.1476
0.033
0.036
0.032
0.046
0.036
0.014
J.-H. Wang et al. / Journal of Asian Earth Sciences 36 (2009) 135–145
139
Fig. 5. The plot of well-logged vp, vs, and vp/vs versus those measured in laboratory: (a) for vp, (b) for vs, and (c) for vp/vs. In (d), the GRA density, qGRA, versus discrete-sample
density, qds, is plotted. In each plot, the thin solid line displays the bisection line and the symbols are: a circle for sandstone and a square for silty-shale.
infiltration or minerals inside the formation. Hsu (2007) measured
the density value from the weight and volume of dry core samples.
The equipment used by Hirono et al. (2007) applied a similar methodology in well loggings as Hung et al. (2007) except that their
samples had no mud and essentially dry. So, the three types of
measurements are different either in methodology or environmental conditions. Thereby, the resolution and the value will be different in the three methods. At Hole-B, Hirono et al. (2007) not only
well-logged the GRA density but also measured the density, with
high accuracy of less than 0.01 g/cm3, on discrete rock samples.
From a comparison between the density values obtained from
the two methods, they found the data points of the GRA and discrete-sample densities are scattering and the GRA density is generally 0.1 g/cm3 higher than the discrete-sample density. In this
study the discrete-sample density values measured by Hsu
(2007) will be used, because she made the measurements on the
same rock samples as Dong et al. (submitted for publication).
The measured permeability values are 101 to 102 md
(1 md = 1015 m2) for sandstones and 104 to 101 md for siltyshale. They also found that the power-law function is better than
the exponential-law function to describe confining pressuredependence of the two parameters. The power-law function is
j = j0(pe/pa)n for permeability and / ¼ /0 (pe/pa)q for porosity.
In the two expressions, j0 and /0 are the values under an atmospheric pressure, pa (0.1 MPa), and n and q are the exponents.
The values of j0, /0 , n, and q for ten samples obtained at different
depths are shown in Table 2. Among the ten samples, three are for
sandstones, seven for siltsty-shale. The permeability of sample
R316sec1 with a depth of 1028.43 m and the porosity of sample
R255sec2-2 with a depth of 902.68 m are not measured.
2.3. Porosity and permeability
Fig. 4a shows that the depth variations in the P- and S-waves.
The plot can be separated into four depth ranges: 494–1013 m
(in the Cholan Formation), 1013–1300 m (in the Chinshui Shale),
1300–1707 m (in the Kueichulin Formation), and 1707–1866 m
(in the repeated Cholan Formation). The four ranges are separated
by three vertical thin lines in Fig. 4a. In each depth range, velocities
are almost linearly related to the depth, z, as suggested by Slotnick
(1936) in the following form: v = (a ± da)+(b ± db)z, where v is vp or
vs, a and b are two coefficients, and da and db are the standard errors of a and b, respectively. The values of a, da, b, and db of the
regression linear equations are shown in Table 3 and the equations
are depicted in Fig. 4a with dashed line segments.
On the other hand, Faust (1951) first proposed a polynomial to
describe the depth variation in seismic velocity. Boore and Joyner
(1997) took the following first-order polynomial:
Dong et al. (submitted for publication) used an integrated permeability/porosity measurement system (called YOYK2) to measure the porosity and permeability of ten discrete core samples
in the depth range 900–1235 m at Hole-A under the confining
pressures from 3 to 120 MPa. The two parameters were measured
in the laboratory using gas flow through the samples, and thus the
measured values are actually the gas porosity and permeability at
the dry condition. The gas porosity at the dry condition is similar to
the porosity measured at the wet condition using fluid flow
through the samples. The gas permeability might be 1–2 orders
higher than the fluid permeability. Results show confining pressure-dependence of the two parameters. The measured porosity
values are (15–19%) for sandstones and (8–14%) for silty-shale.
3. Results
3.1. Depth variations in
vp, vs, and vp/vs
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J.-H. Wang et al. / Journal of Asian Earth Sciences 36 (2009) 135–145
Table 3
The values of a ± da and b ± db of the regression linear equations of vp versus z and
versus z for four depth ranges (in meters).
vs
502–1013
1013–1300
1300–1707
1707–1868
vp
a ± da
b ± db
2.838 ± 0.026
0.001 ± 0.000
4.446 ± 0.083
0.000 ± 0.000
2.664 ± 0.084
0.001 ± 0.000
1.226 ± 0.420
0.001 ± 0.000
vs
a ± da
b ± db
0.891 ± 0.017
0.001 ± 0.000
1.957 ± 0.005
0.000 ± 0.000
0.893 ± 0.056
0.001 ± 0.000
0.815 ± 0.277
0.001 ± 0.000
v ðzÞ ¼ czd ;
ð1Þ
where c and d are two coefficients, to describe seismic velocitydepth relation. Brocher (2008) considered a forth-order polynomial
and a second-order polynomial to describe the depth functions,
respectively, for vp and vs for Holocene and Plio-Quaternary deposits in northern California. Huang et al. (2007) studied the depth
function of vs using the well-logging data at Hole-A on the basis
of Eq. (1). But, they did not clearly show the depth functions.
Here, the depth functions of vp and vs are determined from the
well-logging data at Hole-A on the basis of Eq. (1). However, the
depth functions are inferred only from the data in the first three
depth range, i.e., from 494 to 1707 m, because Fig. 4a shows that
the plot in the forth depth range remarkably departs from the general trend of data in the first three depth ranges. Results are
v p ðzÞ ¼ 1:68z0:12
ð2Þ
for vp and
v s ðzÞ ¼ 0:29z0:27
ð3Þ
for vs. The two depth functions are displayed in Fig. 4a with solid
lines. Except for the depth range 1707–1866 m, the solid lines are
close to the dashed lines. This means that in the first three depth
ranges, the depth variations in vp and vs can be approximated by
a set of three linear functions or a first-order polynomial.
Dividing Eq. (2) by Eq. (3) results in the depth-dependent function of vp/vs:
v p =v s ¼ 5:71z0:15 :
ð4Þ
Eq. (4) is shown by a solid line in the depth range 494–1707 m in
the lower diagram of Fig. 4a for vp/vs.
3.2. Correlation between
vs and vp
To study the correlation between vs and vp, well-logged values
of the two parameters are plotted in Fig. 6. Although the data
points are somewhat dispersed, the S-wave velocity still correlates
linearly with the P-wave velocity. Using the least-squared regression method, the linear relation is
v s ¼ ð0:91 0:02Þ þ ð0:72 0:01Þv p :
ð5Þ
This equation is displayed a solid line in Fig. 6.
3.3. Depth variation in porosity and permeability
On the basis of the power-law functions obtained by Dong et al.
(submitted for publication), the values of / are calculated from the
effective confining pressure, pe, from 0.3 MPa to an upper bound.
This upper bound is taken to be qgz where q is the density of rocks,
g is the gravity acceleration, and z is the depth at which the sample
was located. As mentioned above, q is taken to be qds.
Fig. 7a shows the depth variation in / with depth. In this figure,
for a certain rock sample the values of / in the confining pressure
range are displayed by a vertical line segment. For the present
study, the confining pressure pc is the lithostatic pressure. Hence,
pc = qgz and pw = qwgz where qw is the density of fluids. The pore
fluid pressure pw can be written as cqgz, where c is the pore-fluid
factor (cf. Sibson, 1992). At shallow depths, where the fluid gradient is hydrostatic, c is the ratio of fluid to rock density, typically
0.4. At depths, where the fluid pressure may become suprahydrostatic, c is larger than 0.4. The effective pressure can be re-written
as pe = (1 c)qgz. It is significant to study the values of porosity
and permeability at the hydrostatic state with pw = 0.4 pc and thus
pe = 0.6, pc = 0.6 qgh due to c = 0.4. The porosity value at this state
is denoted by a solid symbol in Fig. 7a: a circle for sandstone and a
square for siltsty-shale. The average values for all sandstone samples and for all siltstone samples are, respectively, 17.3% and 12.5%
and depicted by horizontal dashed lines in Fig. 7a. Except for the
depth of 1232.46 m, the data points for silty-shale are below the
horizontal dashed line of 12.5%. Excluding the data point for the
depth of 1232.46 m, the average is 9.7% which is depicted by a horizontal dashed-dotted line in Fig. 7a. This line seems more appropriate to describe the data points with a depth less than
1232.46 m than the dashed line.
Like the porosity, the values of j are calculated from the effective confining pressure in the range from 0.3 MPa to an upper
bound on the basis of the power-law functions obtained by Dong
et al. (submitted for publication). Fig. 7b shows the depth variation
in j. Permeability ranges from 104 to 102 md. In this figure for a
certain rock sample the values of j in the individual confining
pressure range are displayed by a vertical line segment and the value at the hydrostatic state is denoted by the solid symbol: a circle
for sandstone, a square for silty-shale, and a triangle for shale.
3.4. Correlation between velocities and porosity
To construct the relationships between vp as well as vs and /,
the values of vp and vs at or near the depths associated with the discrete rock samples, on which Dong et al. (submitted for publication) measured the values of porosity and permeability, are taken
from well-logging data and shown in Table 1 as mentioned above.
The plots of vp and vs versus / are displayed in Fig. 7c. In general, vp
and vs decrease with increasing /. From the values of vp and vs and
the averages of /, the linear regression equations are:
v p ¼ ð4:49 0:13Þ ð2:54 3:07Þ/
ð6Þ
for the P-waves and
Fig. 6. The plot of vp versus vs. The regression linear function of this study is:
vs = 0.91+0.72vp. The dashed line shows vs = 0.58vp for commonly-used crustal
rocks. The dashed-dotted line shows Castagna mudrock equation: vs = 1.66 + 0.9vp
(Castagna et al., 1985). The thin solid line demonstrates Eq. (15): vs = 0.7858 1.2344vp + 0.7949v 2p 0:1238v 3p þ 0:0064v 4p inferred by Brocher (2005).
v s ¼ ð2:42 0:09Þ ð2:31 1:88Þ/
ð7Þ
for the S-waves. The standard error of the slope value is higher for
vp than for vs.
J.-H. Wang et al. / Journal of Asian Earth Sciences 36 (2009) 135–145
141
Fig. 7. Figure shows (a) the plot of porosity (/) versus depth; (b) the permeability (j) versus depth; (c) the plots of vp and vs versus /; and (d) the plot of vp/vs versus / for the
discrete rock samples. In the four diagrams, the short vertical and horizontal line segments display the values of related parameter in the individual confining pressure range
and solid symbols denote the values at the hydrostatic state for rock samples: a circle for sandstone and a square for silty-shale. In (a) and (b), the vertical dotted lines denote
the PSZ. In (a), the horizontal dashed lines display the averages. In (b) the solid and dashed lines display the relationships of log(j) versus log(z). In (c) the solid lines
demonstrate the regression equations.
Fig. 7d shows the plot of vp/vs versus / for the ten discrete rock
samples. The values of vp/vs are shown in Table 3. Dividing Eq. (6)
by Eq. (7) leads to the porosity-dependent function of vp/vs:
v p =v s ¼ ð4:49 2:54/Þ=ð2:42 2:31/Þ:
ð8Þ
Eq. (8) is depicted by a solid line in Fig. 7d.
4. Discussion
In this section, we will discuss the following issues: (1) the
depth variations in vp, vs, and vp/vs; (2) the correlation between
vs and vp; (3) the depth variations in porosity and permeability;
(4) the correlation between seismic velocity and porosity; and
(5) evaluations of bulk and shear modulus.
4.1. Depth variations in
vp, vs, and vp/vs
Table 3 shows a similar increasing rate with depth for the P- and
S-wave velocities in the first, third, and fourth depth ranges. The
rate is 0.001 km/s per meter or 0.1 km/s per hundred meters.
Fig. 2 displays that the normal geological structures on the footwall side follow the sequence: the Tokoushan formation, the Cholan formation, the Chinshui formation, and the Kueichulin formation. Basically, seismic velocities increase with depth along this
sequence. As mentioned above, the first and forth depth ranges
are composed of the Cholan Formation. There should be a similar
trend in the plot of vp as well as vs versus depth in the two depth
ranges. However, the fourth depth range lies in the footwall of the
Chelungpu thrust fault. This is a repeated section as it in the first
depth range in the hanging-wall. The remarkable changes in burial
depth and lithology from Miocene Kueichuklin Formation to Plio-
cene Cholan Formation are the primary reasons for the drastic decrease in porosity and velocity across the formation boundary. In
the second depth range, which belongs to the Chinshui Shale, the
data points vary around an average. This means that vp and vs of
the Chinshui Shale are almost depth-independent. Japsen et al.
(2007) also observed that the degree of change of velocity with
depth is smaller for shale than for sandstone.
Huang et al. (2007) compared the depth function of well-logging vs with those of the velocities inferred by Chen et al. (2001)
and Satoh et al. (2001) from earthquake data underneath eight
seismic stations inside a circle, with a radius 13 km, centered at
the TCDP’s deep hole. Except for a station (coded TCU067), welllogged velocities are about 0.3 km/s smaller than the inferred ones.
While at Station TCU067, the average well-logged velocity is about
0.73 km/s larger than the inferred one. Among the 8 stations, this
station is to the south of and has the largest distance to the
deep-hole site. Their results seem to suggest that seismic velocities
inferred from earthquake data are acceptable for constructing a
subsurface velocity model.
Fig. 4a shows that the one-variable polynomial function can
well describe the data points of seismic velocities versus depth.
The reason of the existence of such a one-variable polynomial
function is elucidated below. Wyllie et al. (1958) first observed that
seismic velocities depend upon the effective pressure, pe. Fam and
Santamarina (1997) reviewed numerous empirical forms relating
vs to pe, and then they suggested the following form: vs = OkS(pe/
pa)a to be a correlation function between vs and pe. In this equation,
the parameters O, S, and pa are, respectively, the overconsolidation
ratio, a proportionality constant that is related to intrinsic anisotropy, and the atmospheric pressure, and k and a are the exponents
of the scaling relations. Zimmer et al. (2007a) proposed a similar
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J.-H. Wang et al. / Journal of Asian Earth Sciences 36 (2009) 135–145
form for vp: vp = vpo + OkS(pe/pa)a where vpo is the P-wave velocity
for dry rocks (it is noted that a was denoted by n/2 in Zimmer
et al. (2007a)). For the present study, the confining pressure pc in
the two equations is the lithostatic pressure, that is, pc = qgz. As
mentioned above, the effective pressure is pe = (1 c)qgz due to
the existence of pore fluid pressures. Inserting this expression into
the two equations results in vs za and vp za when c is only
slightly dependent on z. This leads to depth-dependence of seismic
velocities in a one-variable polynomial function.
From laboratory work, Zimmer et al. (2007a) measured the values of a for different rocks: from 0.200 ± 0.06 to 0.600 ± 0.200 for
vp and from 0.181 ± 0.005 to 0.332 ± 0.008 for vs. Eqs. (2) and (3)
give, respectively, a = 0.12 for vp and 0.27 for vs. Obviously, the
present value of a is outside the range of Zimmer et al. (2007a)
for vp and inside it for vs. The rocks used by Zimmer et al.
(2007a) (shown in their Table 4) are different from those of the
Chelungpu fault area, even though the value of a for vs is comparable with theirs. It is noted that for sandstone Japsen et al. (2007)
also observed an increase in seismic velocity with depth, with an
exponent <1.
Eq. (4) for vp/vs is depicted in the lower diagram of Fig. 4a with a
solid line. Obviously, this line can well describe the plot in the first
three depth ranges. Results show that vp/vs decreases with increasing z in a one-variable polynomial function, with a negative exponent. Zimmer et al. (2007b) also observed a decrease of vp/vs with
the effective confining pressure (also the depth). The decreasing
rate is higher for saturated rocks than for dry rocks.
4.2. Correlation between
vs and vp
For dry, perfectly elastic crustal materials, vs is related to vp in
the following expression: vs = 0.58vp. This expression is also plotted in Fig. 6 with a dashed line. It can be seen that most of data
points are below the dashed line for vs = 0.58vp. In other words,
vs cannot be calculated from vp on the basis of this commonly used
formula. This might be due to a reason that rocks are porous and
wet. Castagna et al. (1985) proposed a relation between vs and vp
for porous and wet rocks in the following form: vs = 1.17 + 0.86vp,
which is called the Castagna mudrock equation. Obviously, this
equation is slightly different from Eq. (5). For all lithologies except
calcium-rich and magmatic rocks, gabbros, and serpentinities, Brocher (2005) obtained an empirical equation for vs as a function of
vp:
v s ¼ 0:7858 1:2344v p þ 0:7949v 2p 0:1238v 3p þ 0:0064v 4p ;
ð9Þ
which is depicted by a thin solid curve in Fig. 6. Obviously, most of
data points are below this curve. Hence, Eq. (9) is not appropriate to
describe the relation between vs and vp for the study area.
4.3. Depth variations in porosity and permeability
Fig. 7a shows that the porosity is higher for sandstone than for
silty-shale. Although there is a lack of remarkable depth-dependence of porosity for a single rock type, there is somewhat a
decreasing trend with depth for all rock samples. Although the
two much closed vertical dotted lines to represent the PSZ are close
to the rock sample R351sec2 with / ¼ ð8:5—9:8Þ%, we cannot take
these values to be the porosity of the PSZ due to the following reason: Hirono et al. (2007) measured, with accuracy of 0.1%, the
porosity inside the FZB1136 fault zone at Hole-B (at depths
1134–1137 m), which is equivalent to the FZA1111 fault zone at
Hole-A. Their results are >30% and 10% inside and outside this
zone, respectively. The values inside and outside the fault zone
are, respectively, higher and almost close to the present values.
This means that the porosity is higher in fault rocks than in wall
rocks. Results suggest a higher degree of fracturing inside than outside the fault zone.
Fig. 7b shows that like the porosity, the permeability is higher
for sandstone than for silty-shale. A comparison between Fig. 7a
and b shows that the depth variation for silty-shale is higher for
permeability than for porosity. This might suggest a fact that the
permeability is more sensitive to the sample size, lithology, layering (including bioturbation), and degree of fracturing than the
porosity. By analyzing more than 90 case histories of induce seismicity, Talwani et al. (2007) found that the permeability values
are in the range 5 101 to 5 101 md. Hence, the present permeability values are smaller than those inferred by Talwani et al.
(2007). In Fig. 7b, there is only low dependence of permeability
with depth for sandstone, and there are abnormally large permeability values for silty-shale at a depth of 1174.24 m. According
to core samples obtained from Cajon Pass, Morrow and Byerlee
(1992) observed that permeability decreases with increasing depth
at shallow depths, but they are abnormally high permeability values, departing from the decreasing trend, at depths. From a large
number of data, Sibson and Rowland (2003) proposed that the permeability of fault zone gouge ranges from 107 to 102 md. Except
for the data point at z = 1174.24 m, our results are comparable with
theirs.
From the laboratory results for 18 samples from 482 m to
1316 m at Hole-A, Takahashi et al. (2005) observed that j decreases logarithmically with increasing pe under pe = 10–30 MPa.
However, they took all data into account, ignoring the behavior
of individual rock types. Manning and Ingebritsen (1999) proposed
a quasi-exponential decay of permeability with depth of
log(j) = 14.0 3.2 log(z). This equation is displayed by a solid
line in Fig. 7b. This equation cannot interpret the observations. If
the solid line is shifted upward and downward with the same
exponent yet with different intercepts to form two equations, i.e.,
log(j) = 13.0 3.2 log(z) and log(j) = 18.0 3.2 log(z).
The two equations are shown by dashed lines in Fig. 7b. The upper
dashed line can describe the data points for sandstone, while except for the values of j at z = 1174.24 m, the lower dashed seems
able to describe the data points for silty-shale. Excluding the data
points with z = 1232.46 m, a one- variable polynomial function of j
in term of z, with a positive exponent, is more appropriate to describe the plot than a log–log function. From experimental results
of j versus pe, Lockner et al. (2007) proposed log(j) z0.074.
The PSZ is displayed by two much closed vertical dotted lines in
Fig. 7b. The two dashed lines are close to the rock sample
R351sec2. It is significant to examine how high the permeability
in the PSZ is. Lockner et al. (2005) measured whole core permeability values at the effective confining pressure of 15.5 MPa. Their values range from (0.4 to 7) 105 md with the lowest value in the
PSZ. The lowest value of 0.4 105 md is smaller than all values
of j shown in Fig. 7b. From the hydraulic test on the Chelungpu
fault, Doan et al. (2006) inferred the permeability values 101 to
103 md of fault rocks from hydraulic diffusivity values under
some assumptions. Their maximum value is at most one hundred
times larger than those obtained on core samples from wall rocks
and higher than those obtained by Lockner et al. (2005) and
slightly larger than those 103 to 104 md of country rock samples
with a depth of 837 m at effective pressures of 5–40 MPa measured
from siltstone reference samples (Chen et al., 2005). There is inconsistency between the values of Doan et al. (2006) and those of
Lockner et al. (2005) and Chen et al. (2005). Since Doan et al.
(2006) pumped water at Hole-A and monitored water level at
Hole-B, their inferred values or permeability should represent
those of the fault zone between the two hole. Hence, it is more
appropriate to use the values obtained by Lockner et al. (2005)
than from those by Doan et al. (2006). In addition, the values measured by Lockner et al. (2005) in the PSZ are much less than those
143
J.-H. Wang et al. / Journal of Asian Earth Sciences 36 (2009) 135–145
by Chen et al. (2005) for wall rocks. Sibson and Rowland (2003) observed that in New Zealand the permeability is lower in fault zone
rocks than in wall rocks. Hence, we assume that the permeability
values in the PSZ could be lower than those of wall rocks in its
surroundings.
4.4. Correlation between seismic velocity and porosity
In Fig. 7c, there is not any correlation between seismic velocity
and porosity for a single type rock due to limited data. In spite of
rock type, seismic velocities remarkably decrease from silty-shale
to sandstone as shown in the figure. Eqs. (6) and (7) show such a
decrease in vp as well as vs with increasing /. For 18 rock samples,
Kitamura et al. (2005) observed decreases of seismic velocities
from siltstone to sandstone at low pore fluid pressure. For laboratory experiments for different rocks, Castagna et al. (1985) observed a decrease in vp as well as vs with increasing /. They also
constructed the relationships between seismic velocities and
porosity. Eqs. (6) and (7) are close to the relationships for elastic
silicate obtained by Castagna et al. (1985): vp = 5.819.42/ and
vs = 3.89–7.07/. Eqs. (6) and (7) show that a small difference in
the decreasing rates of velocity versus porosity for vp and vs. This
indicates that a change of porosity can make a similar effect on
both vp and vs. It is noted that the standard error of the decreasing
rate is higher for vp than for vs. The two equations also lead to that
the seismic velocities for dry rocks with / ¼ 0 are vp = 4.49 km/s
and vs = 2.42 km/s. This gives vp/vs = 1.85 when / ¼ 0.
From the values of vp and vs inside the PSZ as mentioned above,
the values of / can be calculated from Eqs. (6) and (7). Results are
0.48 from vp and 0.44 from vs. The value calculated from vp is 0.04
higher than that from vs. These computed values are higher than
the lower bound of / ¼ 0:30 of the fault zone measured by Hirono
et al. (2007). This indicates that the porosity of the fault zone
seems unable be evaluated from the relationships between seismic
velocities versus porosity for wall rocks.
Inserting Eq. (6) into Eq. (7) leads to vs = 1.66 + 0.91vp. This inferred relationship is displayed in Fig. 7c with a dashed-dotted line.
The dashed-dotted line is somewhat close to the solid line associated with Eq. (5) obtained from all well-logged data. Fig. 7d demonstrates that vp/vs slightly increases with /. The solid line
associated with Eq. (8) is able to describe the data points. Tatham
(1982) also observed the increasing trend of vp/vs with / from laboratory results.
The plot of seismic velocities versus depth for the discrete rock
samples in use is depicted in Fig. 8a. As mentioned above, the seismic velocities were the well-logging values at or near the depths
associated with the discrete rock samples. Plotted also in Fig. 8a
with dashed lines are the linear regression equations of seismic
velocities in terms of depth. Results show that for vp, the data
points are above and around the dashed line for vp versus z when
z < 1013 m and when z > 1013 m, respectively; while for vs all data
points are still above the dashed line for vs versus z. This indicates
that most of the values of vp and vs of the rocks samples in use are
slightly higher than the individual statistical averages for the
whole well-logging range. This makes the data points of vp/vs be
below the solid line related to Eq. (4) as shown in Fig. 8b. This
would cause a small bias on the inferred equation of vp versus
porosity, /, and that of vs versus /. However, the inferred equation
of vp/vs versus porosity can interpret the observations very well as
displayed in Fig. 7d. This implies that the inferred equations of vp
versus / and vs versus / are acceptable.
4.5. Evaluations of bulk and shear modulus
The bulk modulus and shear modulus of saturated rocks can be
written as:
K ¼ q v 2p 4v 2s =3 ;
ð10Þ
l ¼ qv
ð11Þ
2
s:
Since vp and vs are both a function of /, K, and l are also dependent
on /. To evaluate K and l, in addition to the need of porosity-dependent seismic velocities as described by Eqs. (6) and (7) it also demands the porosity-dependent density (cf. Han and Batzle, 2004).
In order to construct the correlation between density and porosity,
the linear correlation between density and porosity must be first
established. The data points of density versus porosity are depicted
in Fig. 8c. Actually, the number of data is small and the data points
do not distribute very well. Nevertheless, the data points are distributed almost around a linear function and show a porositydependent decreasing function of density. This fits the general form
of the density-porosity functions inferred by other researchers (cf.
Han and Batzle, 2004). In addition, the values of bulk modulus
and shear modulus calculated from the inferred equations are in
the reasonable range as mentioned below. This makes us able to accept the inferred density-porosity function. Of course, the densityporosity correlation must be re-examined when more values of
density and porosity are measured from discrete samples in laboratory. The linear relationship is
q ¼ ð3:22 0:12Þ ð5:99 0:90Þ/:
ð12Þ
This equation gives q = 3.22(1 1.86/), which is different from the
simplified correlation: q = q0(1 /) proposed by Han and Batzle
(2004).
Inserting Eqs. (6), (8), and (12) into Eqs. (10) and (11) leads to
K ¼ 40:89 1 1:77/ þ 0:81/2 þ 0:10/3 ðin GPaÞ;
l ¼ 19:18 1 3:77/ þ 4:46/2 1:69/3 ðin GPaÞ:
ð13Þ
ð14Þ
Eqs. (13) and (14) give K0 = 40.89 GPa and l0 = 19.18 GPa which are,
respectively, the values of K and l at / ¼ 0 and represent the average bulk and shear modulus of the rocks in the dry state. The value
of l0 is about two third of the commonly used value, i.e., 30 GPa, for
crustal materials. The two equations also show that the effect of the
/3 term is positive for K and negative for l, and the magnitude of
such an effect is lower on K than on l. They are depicted by a solid
line and a dashed line, respectively, in Fig. 8d. The bulk and shear
modulus both decrease monotonously with increasing /.
Han and Batzle (2004) proposed that the following Gassmann’s
equations offer a simple model for estimating the fluid-saturation
effect on the bulk and shear modulus:
K s ¼ K d þ DK d ;
ls ¼ ld :
ð15Þ
ð16Þ
In Eq. (15), Ks and Kd are, respectively, the bulk modulus of the saturated rock frame and dry rock, DKd is the increasing quantity of
bulk modulus caused by saturation. In Eq. (16), ls and ld are,
respectively, the shear modulus of the saturated rock frame and
dry rock. DKd can be expressed by
DK d ¼ K g ð1 K d =K g Þ2
.
1 / K d =K g þ /K g =K f ;
ð17Þ
where Kg and Kf are, respectively, the bulk modulus of the mineral
grain and fluid. When / ¼ 0, Eq. (17) yields DKd = Kg Kd, thus
resulting in Ks = Kg. Hence, Ko = 40.89 GPa and lo = 19.18 GPa are
also, respectively, the average bulk and shear modulus of mineral
grain. The value of Ko = 40.89 GPa is close to those of shale sands
in a pressure range 10–40 MPa obtained by Han and Batzle (2004)
in the laboratory. On the other hand, the value of lo = 19.18 GPa
is smaller than those obtained by Han and Batzle (2004).
Han and Batzle (2004) observed that the grain bulk and shear
modulus decrease with increasing fractional clay content. From
X-ray diffraction (XRD) Song et al. (2007) observed that the
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J.-H. Wang et al. / Journal of Asian Earth Sciences 36 (2009) 135–145
Fig. 8. (a) The data points of vp and vs versus depth for the discrete rock samples in use and the upper and lower solid lines represent Eqs. (8) and (9), respectively; (b) the data
points of vp/vs versus depth for the rock samples in use and the solid line represents Eq. (10); (c) the plot of q versus /; and (d) the plots of K and l versus / from Eqs. (19) and
(20), respectively. In (a), (b), and (c) the symbols are the same as those in Fig. 6.
contents of other clay minerals (illite, chlorite, and kaolinite) are
rich in the PSZ. From XRD, Ma et al. (2006) also found that the minerals in the MSZ are composed of about 70% of quartz, 5% of feldspar, and 25% of clay minerals. Hence, the bulk and shear
modulus of the PSZ at depths 1111.29–1111.35 m should be,
respectively, less than K0 = 40.89 GPa and lo = 19.18 GPa.
The density decreases with increasing porosity. From the porosity-dependent functions of seismic velocities and density, the
functions of bulk and shear modulus in terms of porosity are
constructed. The bulk and shear modulus at the dry condition
are 40.89 GPa and 19.18 GPa, respectively.
Acknowledgements
5. Conclusions
Seismic velocities (P- and S-wave velocities), density, porosity,
and permeability were measured directly on the discrete core
samples or through well-loggings in a deep borehole penetrating
the Chelungpu fault drilled after the 1999 Ms7.6 Chi-Chi earthquake in central Taiwan. The measured values are applied to
study the following problems: (1) the depth variations in seismic
velocities, porosity, and permeability; (2) the relationship between vp and vs; (3) porosity-dependence of P- and S-wave
velocities and their ratio; and (4) porosity-dependence of density. Results show that a one-variable polynomial function can
describe the depth variations in vp and vs. The porosity is only
slightly dependent on the depth. The one-variable polynomial
function can interpret the depth dependence of permeability.
However, such depth functions are different for sandstone and
silty-shale. The values of porosity and permeability in the PSZ
cannot be estimated from the depth functions of the two parameters inferred from wall rocks. The S-wave velocity linearly increases with the P-wave velocity. However, the inferred
relationship of vs versus vp is different from the equation:
vs = 0.58vp for the perfectly elastic material. Seismic velocities
linearly decrease with increasing porosity. The effects on vp
and vs caused by a change of porosity are almost similar. The ratio of P- and S-wave velocities slightly increases with porosity.
The authors would like to thank Prof. Ando (Associated Editor)
and two reviewers for valuable comments. The study was financially supported by Academia Sinica (Taipei) and the National Sciences Council under Grant No. NSC94-2119-M-001-016.
References
Boore, D.M., Joyner, W.B., 1997. Site amplifications for generic rock sites. Bull.
Seismol. Soc. Am. 87, 327–341.
Brocher, T.M., 2005. Empirical relations between elastic wavespeeds and density in
the Earth’s crust. Bull. Seismol. Soc. Am. 95, 2081–2092.
Brocher, T.M., 2008. Compressional and shear-wave velocity versus depth relations
for common rock types in northern California. Bull. Seismol. Soc. Am. 98, 950–
968.
Cadoret, T., Marion, D., Zinszner, B., 1995. Influence of frequency and fluid
distribution on elastic wave velocities in partially saturated limestones. J.
Geophys. Res. 100 (B6), 9789–9803.
Castagna, J.P., Batzle, M.L., Eastwood, R.L., 1985. Relationships between
compressional-wave and shear-wave velocities in elastic silicate rocks.
Geophysics 50, 571–581.
Chen, C.-H., Wang, W.-H., Teng, T.-L., 2001. 3D velocity structures around the source
area of the 1999 Chi-Chi, Taiwan, earthquake: Before and after the mainshock.
Bull. Seismol. Soc. Am. 91 (5), 1013–1027.
Chen, N., Zhu, W., Wang, T.F., Song, S., 2005a. Hydromechanical behavior of country
rock samples from the Taiwan Chelungpu Drilling Project, Eos Trans. AGU
86(52), Fall Meet. Suppl., Abstract T51A-1324.
Chen, T.-M., Zhu, W., Wong, T.-f., Song, S.-R., 2005b. Hydromechanical behavior of
country rock samples from the Taiwan Chelungpu-Fault Drilling Project, Eos,
Trans. AGU 86(52), Fall Meet. Suppl., Abstract T51A-1324, F1833.
J.-H. Wang et al. / Journal of Asian Earth Sciences 36 (2009) 135–145
Doan, M.L., Brodsky, E.E., Kano, Y., Ma, K.-F., 2006. In situ measurement of the
hydraulic diffusivity of the active Chelungpu fault, Taiwan. Geophys. Res. Lett.
33, L16317. doi:10.1029/2006GL026889.
Dong, J.-J., Hsu, J.-Y., Shimamoto, T., Hung, J.-H., Yeh, E.-C., Wu, Y.-H., submitted for
publication. Elucidating the relation between confining pressure and fluid flow
properties of young sedimentary rocks retrieved from a 2 km deep hole-TCDP
Hole-A. Am Assoc. Petrol. Geol.
Fam, M., Santamarina, J.C., 1997. A study of consolidation using mechanical and
electromagnetic waves. Geotechnique 47, 203–219.
Faust, L.Y., 1951. Seismic velocity as a function of depth and geological time.
Geophysics 16, 192–206.
Han, D.-h., Batzle, M., 2004. Gassmann’s equation and fluid-saturation effects on
seismic velocities. Geophysics 69, 398–405.
Han, D.-h., Nur, A., Morgan, D., 1986. Effects of porosity and clay content on wave
velocities in sandstones. Geophysics 51 (11), 2093–2107.
Hirono, T., Yeh, E.-C., Lin, W., Sone, H., Mishima, T., Soh, W., Hashimoto, Y.,
Matsubayashi, O., Aoike, K., Ito, H., Kinoshita, M., Murayama, M., Song, S.-R., Ma,
K.-F., Hung, J.-H., Wang, C.-Y., Tsai, Y.-B., Kono, T., Nishimura, M., Moriya, S.,
Tanaka, T., Fujiki, T., Maeda, L., Muraki, H., Kuramoto, T., Sugiyama, K.,
Sugawara, T., 2007. Nondestructive continuous physical property
measurements of core samples recovered from hole B, Taiwan, ChelungpuFault Drilling Project. J. Geophys. Res. 112 B07404. doi:10.1029/2006JB004738.
Hsu, R.-Y., 2007. Stress-dependent fluid flow properties of sedimentary rocks and
overpressure generation. MS Thesis, Graduate Inst. Appl. Geol., Natl. Central
Univ., p. 73.
Huang, M.-W., Wang, J.-H., Ma, K.-F., Wang, C.-Y., Hung, J.H., Wen, K.-L., 2007.
Frequency-dependent site amplifications with f P 0.01 Hz evaluated from the
velocity and density models in Central Taiwan. Bull. Seismol. Soc. Am. 97 (2),
624–637.
Hung, J.-H., Wu, Y.-H., Yeh, E.-C., TCDP Scientific Party, 2007. Subsurface structure,
physical properties, and fault zone characteristics in the scientific drill holes of
Taiwan Chelungpu Fault Drilling Project. Terr. Atmos. Ocean Sci. 18, 271–293.
Hung, J.-H., Ma, K.-F., Wang, C.-Y., Ito, H., Lin, W., Yeh, E.-C., 2009. Subsurface
structure, physical properties, fault zone characteristics and stress state in the
scientific drill holes of Taiwan Chelungpu Fault Drilling Project. Tectonophysics
466, 307–321.
Japsen, P., Mukerji, T., Mavko, G., 2007. Constraint on velocity-depth trends from
rock physics models. Geophys. Prosp. 55, 135–154.
Kanamori, H., Heaton, T.H., 2000. Microscopic and macroscopic physics of
earthquakes, in geocomplexity and physics of earthquakes. In: Rundle, J.B.,
Turcotte, D.L., Klein, W. (Eds.), Geophys. Monog., vol. 120, AGU, Washington, DC,
pp. 147–163.
Kitamura, K., Takahashi, M., Masuda, K., Ito, H., Song, S.-R., Wang, C.-Y., 2005.
The relationship between pore-pressure and the elastic-wave velocities of
TCDP-cores, Eos, Trans., AGU, 86(52), Fall Meet. Suppl., Abstract T51A-1326,
F1833.
Lin, A.T.-S., Wang, S.-M., Hung, J.-H., Wu, M.-S., Liu, C.-S., 2007. Lithostratigraphy of
the Taiwan Chelungpu-Fault Drilling Project-A borehole and its neighboring
region, central Taiwan. Terr. Atmos. Ocean Sci. 18 (2), 223–241.
Lockner, D.A., Morrow, C., Song, S.-R., Tembe, S., Wong, T.-f., 2005. Permeability of
whole core samples of Chelungpu faulr, Taiwan TCDP scientific drillhole, Eos,
Trans., AGU, 86(52), Fall Meet. Suppl., Abstract T43D-04, F1825.
Lockner, D.A., Morrow, C., Song, S.-R., 2007. Effect of brine composition and
concentration on physical properties of clay and shale and strength, velocity
and permeability of TCDP Hole-A whole core samples, Lecture Notes presented
in TCDP Workshop, May 15, 2007, USGS.
Ma, K.-F., Wang, J.H., Zhao, D., 1996. Three-dimensional seismic velocity structure of
the crust and uppermost mantle beneath Taiwan. J. Phys. Earth 44, 85–105.
145
Ma, K.-F., Lee, C.-T., Tsai, Y.-B., Shin, T.-C., Mori, J., 1999. The Chi-Chi, Taiwan
earthquake: large surface displacements on an inland thrust fault. Eos,
Transaction, AGU 80, 605–611.
Ma, K.-F., Song, S.-R., Tanaka, H., Wang, C.-Y., Hung, J.-H., Tsai, Y.-B., Mori, J., Song, Y.F., Yeh, E.-C., Sone, H., Kuo, L.-W., Wu, H.-Y., 2006. Slip zone and energetics of a
large earthquake from the Taiwan Chelungpu-fault Drilling Project (TCDP).
Nature 444, 473–476.
Manning, C.E., Ingebritsen, S.E., 1999. Permeability of the continental crust:
Implications of geothermal data and metamorphic systems. Rev. Geophys. 37
(1), 127–150.
Morrow, C.A., Byerlee, J.D., 1992. Permeability of core samples from Cajon Pass
scientific drill hole: results from 2100 to 3500 m depth. J. Geophys. Res. 97,
5145–5151.
Satoh, T., Kawase, H., Iwata, T., Higashi, S., Sato, T., Irikura, K., Huang, H.C., 2001. Swave velocity structure of the Taichung basin, Taiwan, estimated from array
and single-station records of microtremors. Bull. Seismol. Soc. Am. 91 (5),
1255–1266.
Shin, T.-C., Teng, T.-L., 2001. An overview of the 1999 Chi-Chi, Taiwan. Earthquake
Bull. Seismol. Soc. Am. 91, 895–913.
Sibson, R.H., 1992. Implications of fault-valve behavior for rupture nucleation and
recurrence. Tectonophysics 211, 283–293.
Sibson, R.H., Rowland, J.V., 2003. Stress, fluid pressure and structural permeability
in seismogenic crust, North Island, New Zealand. Geophys. J. Int. 154, 584–594.
Slotnick, M.M., 1936. On seismic computations, with applications, II. Geophysics 1,
299–305.
Sone, H., Yeh, E.-C., Nakaya, T., Hung, J.-H., Ma, K.-F., Wang, C.-Y., Song, S.-R.,
Shimamoto, T., 2007. Mesoscopic structural observations of cores from the
Chelungpu fault system, Taiwan Chelungpu-fault Drilling Project Hole-A,
Taiwan. Terr. Atmos. Ocean Sci. 18 (2), 359–377.
Song, S.-R., Kuo, L-W., Yeh, E.-C., Wang, C.-Y., Hung, J.-H., Ma, K.-F., 2007.
Characteristics of the lithology, fault-related rocks and fault zone structures
in TCDP Hole-A. Terr. Atmos. Ocean Sci. 18, 243–270.
Takahashi, M., Kitamura, K., Masuda, K., Ito, H., Song, S.-R., Wang, C.-Y., 2005.
Pressurization effect on bulk properties and pore connection of sedimentary
rock specimens from TCDP-cores, Eos, Trans., AGU, 86(52), Fall Meet. Suppl.,
Abstract T51A-1325, F1833.
Talwani, P., Chen, L., Gahalaut, K., 2007. Seismogenic permeability, js. J. Geophys.
Res. 112, B07309. doi:10.1029/2006JB004665.
Tatham, R.H., 1982. Vp/Vs and lithology. Geophysics 47 (3), 336–344.
Wang, C.-Y., Lee, C.-L., Wu, M.-C., Ger, M.-L., 2007. Investigating the TCDP drill site
using deep and shallow reflection seismics. Terr. Atmos. Ocean Sci. 18 (2), 129–
141.
Wu, Y.-H., Yeh, E.-C., Dong, J.-J., Kuo, L.-W., Hsu, J.-Y., Hung, J.-H., 2008. Core-log
integration studies in Hole-A of Taiwan Chelungpu-fault Drilling Project.
Geophys. J. Int. 174, 949–965.
Wyllie, M.R.J., Gregory, A.R., Gardner, G.H.F., 1958. An experimental investigation of
factors affecting elastic wave velocities in porous media. Geophysics 23, 459–
493.
Yeh, E.-C., Sone, H., Nakaya, T., Ian, K.H., Song, S.-R., Hung, J.-H., Lin, W., Hirono, T.,
Wang, C.-Y., Ma, K.-F., Soh, W., Kinoshita, M., 2007. Core description and
characteristics of fault zones from Hole-A of the Taiwan Chelungpu-Fault
Drilling Project. Terr. Atmos. Ocean Sci. 18, 327–358.
Zimmer, M.A., Prasad, M., Mavko, G., Nur, A., 2007a. Seismic velocities of
unconsolidated sands: Part 1 – Pressure trends from 0.1 to 20 MPa.
Geophysics 72 (1), E1–E13.
Zimmer, M.A., Prasad, M., Mavko, G., Nur, A., 2007b. Seismic velocities of
unconsolidated sands: Part 2 – Influence of sorting- and compaction-induced
porosity variation. Geophysics 72 (1), E15–E25.