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Use of spectral gamma ray as a lithology guide for fault rocks: A case study
from the Wenchuan Earthquake Fault Scientific Drilling project Borehole 4
(WFSD-4)

Article in Applied Radiation and Isotopes · June 2017

DOI: 10.1016/j.apradiso.2017.06.038

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 Applied Radiation and Isotopes 128 (2017) 75–85

Contents lists available at ScienceDirect

Applied Radiation and Isotopes

journal homepage: www.elsevier.com/locate/apradiso

Use of spectral gamma ray as a lithology guide for fault rocks: A case study MARK
from the Wenchuan Earthquake Fault Scientific Drilling project Borehole 4
(WFSD-4)
Ahmed Amara Konatéa,e, , Heping Pana, , Huolin Maa, Zhen Qina, Bo Guoa,
⁎ ⁎⁎

Yao Yevenyo Ziggahc, Claude Ernest Moussounda Koungad, Nasir Khana, Fodé Tounkarab
a
Institute of Geophysics and Geomatics, China University of Geosciences (Wuhan), Lumo Road 388, Postal code, 430074 Wuhan, Hubei, China
b
Faculty of Earth Resource, China University of Geosciences (Wuhan), Lumo Road 388, Postal code, 430074 Wuhan, Hubei, China
c
Faculty of Information Engineering, China University of Geosciences (Wuhan), Lumo Road 388, Postal code, 430074 Wuhan, Hubei, China
d
Resources Planning & Developing Dept., Baosteel Resource Co., Ltd, No. 568, East Dongdaming ing Road, Hongkou District, Postcode, 200080 Shanghai, China
e
Institut Supérieur des Mines et Géologie de Boké, BP, 84, Boké, République de Guinée

H I G H L I G H T S

• Lithology and fault rocks show a variability of SGR logs responses and clay minerals.
• SGR
The cross plot and statistical multi log analysis are effective in characterizing lithology and fault rock.
• log together with others logs would help understand earthquake mechanism.

A R T I C L E I N F O A B S T R A C T

Keywords: The main purpose of the Wenchuan Earthquake Fault Scientific drilling project (WFSD) was to produce an in-
Spectral gamma-ray logs depth borehole into the Yingxiu–Beichuan (YBF) and Anxian–Guanxian faults in order to gain a much better
Wenchuan earthquake understanding of the physical and chemical properties as well as the mechanical faulting involved. Five bore-
Well log interpretation holes, namely WFSD-1, WFSD-2, WFSD-3P, WFSD-3 and WFSD-4, were drilled during the project entirety. This
Fault rocks
study, therefore, presents first-hand WFSD-4 data on the lithology (original rocks) and fault rocks that have been
Clay minerals
Lithology
obtained from the WFSD project. In an attempt to determine the physical properties and the clay minerals of the
lithology and fault rocks, this study analyzed the spectral gamma ray logs (Total gamma ray, Potassium,
Thorium and Uranium) recorded in WFSD-4 borehole on the Northern segment of the YBF. The obtained results
are presented as cross-plots and statistical multi log analysis. Both lithology and fault rocks show a variability of
spectral gamma ray (SGR) logs responses and clay minerals. This study has shown the capabilities of the SGR
logs for well-logging of earthquake faults and proves that SGR logs together with others logs in combination with
drill hole core description is a useful method of lithology and fault rocks characterization.

1. Introduction Gamma rays and Neutrons. The former is our concern here to study the
Spectral gamma ray (SGR) log responses of the Wenchuan Earthquake
In deep drilling, borehole logging has long played a significant part Fault Scientific Drilling project borehole 4 (WFSD-4).
in the evaluation of the drilled rock (Engell-Jensen et al., 1984). Log- Access to the interior of active faults is of fundamental importance
ging data are processed and interpreted to provide a variety of in- to the understanding of earthquake slip (Kinoshita et al., 2014). Over
formation for geoscience research. Borehole logging includes acous- the years there has been a continuous research interest in Earthquake
tical, electrical, and nuclear methods. A complete set of logs have been science. Studies have shown that geophysical logs and drill well core
used in scientific drilling research to provide information on lithology description in active faults can provide reliable evidence for under-
and rock properties. Well logs exploit two kinds of nuclear radiation, standing earthquake physical properties (e.g. Li et al., 2013, 2014,

⁎
Corresponding author at: Institute of Geophysics and Geomatics, China University of Geosciences (Wuhan), Lumo Road 388, Postal code, 430074 Wuhan, Hubei, China.
⁎⁎
Corresponding author.
E-mail addresses: konate77@yahoo.fr (A. Amara Konaté), panpinge@163.com (H. Pan).

http://dx.doi.org/10.1016/j.apradiso.2017.06.038

Available online 28 June 2017

Received 14 January 2017; Received in revised form 23 June 2017; Accepted 24 June 2017

0969-8043/ © 2017 Elsevier Ltd. All rights reserved.

A. Amara Konaté et al. Applied Radiation and Isotopes 128 (2017) 75–85

Fig. 1. Well site schema of WFSD, modified from Nie et al.

(2013). Wenchuan earthquake surface rupture zone (red line).
WFSD-1 drill hole and WFSD-2 drill hole are located in the
southern segment of Yingxiu-Beichuan fault; WFSD-3 drill hole
and WFSD-3P drill hole are sited in the Guanxian-Anxian fault;
WFSD-4 drill hole situated in the northern segment of Yingxiu-
Beichuan fault. (For interpretation of the references to color in
this figure legend, the reader is referred to the web version of this
article.)

Fig. 2. Lithological profile (original rock) and fault rock distribution of the WFSD-4 cores, with depth being the well depth.

2015; Wu et al., 2008). Understanding the complex physics of earth- motion (Sibson, 1977). Fault rocks have therefore been extensively
quakes is among the major remaining unsolved problems in the geos- investigated in earthquake studies (e.g. Solum et al., 2006; Song et al.,
ciences (Tobin et al., 2007). 2007; Li et al., 2013, 2014, 2015; Si et al., 2014; Yang et al., 2013) to
Fault rocks (Sibson, 1977) are important geologic rocks in earth- better comprehend their development and their physical and chemical
quake science as they symbolize the only physical evidence for seismic properties. Despite the aforementioned existing research, so far, the
activity. The laborious analysis of these rocks is essential to under- SGR log signature has not yet been thoroughly exploited. Therefore, the
standing the nature of earthquakes. Fault rocks record major episodes WFSD drill hole offers a unique opportunity to characterize the Total
of fault movement, being one of the most significant subjects for un- Gamma Ray (GR), Potassium (K), Thorium (Th) and Uranium (U) log
derstanding the fault zones nature as well as the whole history of fault signature of fault rocks (and lithology). These radioactive logs resulting

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A. Amara Konaté et al. Applied Radiation and Isotopes 128 (2017) 75–85

Fig. 2. (continued)

from the SGR tool are therefore a useful physical property since it mineral contains by far the greatest concentration, whereas kaolinite
provides an indication of the lithology or, more specifically, the rock has very little (Serra, 1979). (U) and (Th) may be originated in such
mineralogy in wells. Variations of the concentration of (K), (Th), and materials as phosphates, clays, feldspars, organic matter, and heavy
(U) are related to specific clay minerals. In active faults studies, one of minerals (Engell-Jensen et al., 1984). The (232Th) isotope decays to
the major goals is to obtain an indication of the clay minerals and (208Pb) through a decay series including many intermediate products
hence, fault quality. Clay minerals play a significant mechanical part in and the half-life of the isotope is 14 billion years (Luthi, 2001). (Th) has
active faults, because they are fairly weak and their existence impacts its origin principally in acidic and intermediate igneous rocks and may
permeability with consequences for fluid pressure evolution and shear contribute to the radioactivity of a rock either as a structural compo-
strength (Schleichera et al., 2015). nent of resistate heavy minerals, or adsorbed onto the surfaces of clay
SGR measurements became available in the 1980s, and they are minerals (Rider, 2002). The (Th) content correlated with the clay mi-
highly sensitive to the lithological composition of the rock (Luthi, nerals (Hassan et al., 1976). Pure clay samples ordinarily comprise
2001). The SGR tool measures the gamma ray (GR) spectrum that is the 5–30 ppm (Th) (Adams and Weaver, 1958). The 238U isotope decays in
GR energy distribution produced as natural radioactivity by the for- an even more complex radioactive series to (206Pb), with a half-life of
mation (Fabricius et al., 2003). The GR originates from the isotopes of 4.4 billion years. The (238U) isotope constitutes more than 99% of all
Thorium (232Th), Uranium (238U), Potassium (40K), and their daughter naturally occurring (U) (Luthi, 2001). Acidic igneous rocks are the
products (e.g., Hearst et al., 2000). These radioisotopes produce (GR) major original source for the element. (U) behaves as an independent
that have characteristic energy levels. The quantity and energy of these constituent thus; it is not chemically combined in the principal mole-
(GR) can be measured in a scintillation detector. The measured energy cules of rocks like (K), but is loosely associated with secondary com-
spectrum is converted into concentrations of (K), (Th) and (U) ponents (Rider, 2002). (U) species may also be adsorbed onto clay
(Schlumberger, 1982). A SGR log is usually presented as a GR log (GR minerals. (U) is much more soluble than (K) or (Th), therefore it is
(API) = 4 Th (ppm) + 8 U (ppm) + 16 K (%)) and the weight fraction commonly observed in fractures. (U) is also linked with organic matter.
of (Th) (ppm), (U) (ppm) and (K) (%). (K) is both chemically active and The principles of SGR tools and the geochemical behavior of (K), (Th)
volumetrically common in several naturally occurring rock-forming and (U), and natural radioactivity can be found in Rider (2002) and
minerals (Rider, 2002). The radioactive isotope (40K) constitutes about Serra (1979).
0.012% of all (K) present in a mineral and it decays to (40Ar) by This study is part of a larger effort to make available detailed log-
emitting beta and gamma rays with a single spectral peak at 1.46 MeV ging response information on Wenchuan earthquakes. Here, the aim is
(Luthi, 2001). The (GR) signal from the radioactive decay is a sig- to characterize the lithological unit, and fault rocks using SGR logs data
nificant indicator of mineralogical composition (Fabricius et al., 2003). from borehole WFSD-4. As is so often the case in log analysis, crossplots
(K) is associated with numerous minerals in sedimentary formations, and statistical multi log analysis are used. This study focused on in-
including some clays and feldspars. The (K) content of clay mineral terpretation of the insitu logging data from WFSD-4 for the reason that
species varies considerably. Illite, a non-expanding clay crystalline the data have not been reported and investigated by geoscientists.

77
A. Amara Konaté et al. Applied Radiation and Isotopes 128 (2017) 75–85

Fig. 2. (continued)

Therefore, this study constitutes a good foundation for future research WFSD-4 drilling site is located in Pingwu Nanba Village at latitude
in this borehole. 32° 13'0.91 "N, longitude 104° 49'45.69"E, and elevation of 700 m.
Initiated on August 2012, the drilling of WFSD-4 hole was completed to
the depth of 2273 m on February 2014. WFSD-4 geophysical mea-
2. Wenchuan earthquake
surements were carried out using advanced equipment of ECLIPS-5700
type and Halliburton EXCELL-2000 imaging logging system to ensure
Wenchuan earthquake is one of the world's most destructive
accurate and reliable variety of geophysical logging data. All logging
earthquakes that caused severe loss of life on 25 August 2008. It was
operations were undertaken by Shengli logging of the SINOPEC well
recorded that there were 69,226 deaths, 374,643 injured, and 17,923
logging corporation. The lithological profile of WFSD-4 core consists
missing (Yong and Booth, 2011). Many urban and rural constructions
mainly of carbonaceous slate, slate, sandstone, carbonaceous sand-
were devastated. Some towns, including Beichuan, Yingxiu, and a large
stone, argillaceous sandstone and sandy mudstone rocks (Fig. 2).
number of villages were destroyed (Yong and Booth, 2011). The Mw 7.9
Moreover, from the inspection of the WFSD-4 cores (Fig. 2), the depth
Wenchuan earthquake generated coseismic surface ruptures of 270 km
interval 2012–2265 m consists of a continuous fault zone with fault
and 80 km in length along the Yingxiu–Beichuan (YBF) and Guanxian-
breccia of different scale and very few fault gouges. For that reason, this
Anxian (GAF) fault, respectively (Si et al., 2014). The former rupture
study agrees that the depth interval 2012–2265 m represent a large
zone, YBF, has thrust along with dextral strike-slip motion with the
scale fault zone. WFSD is a great opportunity to improve the logging
main movement of Southern section being thrust. In contrast, the main
technology in China as well as to clarify the logging characteristic of the
movement of Northern section is strike-slip motion. The GAF rupture
active faults.
zone, on the other hand, is a pure thrust fault (Li et al., 2015). In order
to explore the fault zones physical, chemical and mechanical properties,
the Wenchuan Earthquake Fault Scientific Drilling project (WFSD) 2.1. Data and methodology
which includes five boreholes (that is WFSD-1, WFSD-2, WFSD-3P,
WFSD-3 and WFSD-4) situated in the YBF and GAF faults was initiated This study analyzed the SGR logs and other logs recorded in WFSD-4
in China (Duan et al., 2015). WFSD-1 drill hole and WFSD-2 drill hole borehole on Northern segment of the YBF (Fig. 3). In an attempt to
are sited on Southern section of the YBF while WFSD-4 drill hole is sited determine the physical properties and the clay minerals of the lithology
on Northern segment of the YBF, which has a strong strike-slip fault. and fault rocks, crossplot and statistical multi log analysis were used.
WFSD-3P drill hole and WFSD-3 drill hole are situated on the thrust Explanation on crossplot and multilog analysis can be found in Rider
GAF (Fig. 1). (2002).

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A. Amara Konaté et al. Applied Radiation and Isotopes 128 (2017) 75–85

Fig. 3. Spectral gamma ray logs and others logs re-

sponses from 23 to 2273 m depth in WFSD-4 drill
hole. Shadow zone show the location of Yingxiu-
Beichuan fault (YBF) (2012–2265 m) which is char-
acterized by the lowest resistivity log values and the
highest Total Gamma ray(GR), Potassium(K),
Thorium(Th), Uranium(U), Spontaneous potential
(SP), and Photoelectric index(Pe) log values as
compared to other sections in the borehole.
Additionally, YBF has significant high Neutron por-
osity (CNL) and Acoustic transit time (AC) while it
has low Density (DEN) values.

3. Log characterization and interpretation Table 1, slates are characterized by moderate mean values of GR
(116.170 API), (K) (2.3406%), (Th) (9.123 ppm) and (U) (6.370 ppm).
3.1. Lithology (original rocks) Argillaceous sandstones are characterized by relatively high mean va-
lues of GR (136.701 API), and moderate mean values of (K) (2.6204%),
Lithology is one of the most significant geological characteristics of (Th) (9.605 ppm) and (U) (7.5056 ppm). Both Slates and argillaceous
rocks. Lithologies cored through the WFSD-4 consist mainly of carbo- sandstones are showing comparable log responses. Consequently (GR),
naceous slate, slate, sandstone, carbonaceous sandstone, argillaceous (K), (Th) and (U) showed inconsistent log curve to differentiate slates
sandstone and sandy mudstone rocks. The SGR logs and others logs from argillaceous sandstones. Again from Table 1, the log responses
signatures from 23 to 2273 m depth in WFSD-4 drill hole are illustrated ((K), (Th)) are comparable in fault rocks (fault breccia, fault gouge) and
in Fig. 3. The mean values, standard deviations, minimums and max- indicating that (K) and (Th) are not reliable log parameters to differ-
imums of SGR log for each lithological unit were calculated for intervals entiate fault breccia from fault gouge.
matched with the rock type recognized from the description of drill A crossplot was used to find the relationship between log para-
core. Table 1. displays statistic summaries of SGR log signature in the meters. Fig. 4a-c show the crossplot of (GR) vs. (K), (Th) and (U) re-
lithological units. From Table 1, carbonaceous slates and carbonaceous spectively. As can be seen from the crossplots, overall, a positive cor-
sandstones are characterized by the overall highest mean values of relation between GR and (K), (Th) and (U) respectively are observed
(GR), (K), (Th) and (U) due to the highest percentage of clay content. In which possibly reflects the increase in clay content (Keys, 1979). Note
contrast, Sandstones and Sandy mudstones exhibit the lowest con- that the average clay has a (K) content of about 2–3% of potassium,
centrations of radioactive material, and thus give low GR readings. Low 8–18 ppm of thorium and 2–6 ppm of Uranium (Myers, 1987). Fur-
GR with sandstones has been observed in WFSD-1 drill hole (Li et al., thermore, Rider (2002) has stated that ‫״‬as clay content identification,
2014) and in WFSD-3 drill hole (Li et al., 2015). Therefore, GR, (K), (Th) may be used in most cases, (K) may be used in many cases but (U)
(Th) and (U) are reliable parameters to differentiate carbonaceous should not be used at all‫״‬. With Rider's (2002) assertion in mind, it can
slates (as well carbonaceous sandstones) from Sandstones. Again from be said that the increase in GR vs (K), (Th) and (U) as observed in

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A. Amara Konaté et al. Applied Radiation and Isotopes 128 (2017) 75–85

Table 1
Min-Max, Mean values and standard deviations of log properties for each rock type, WSDF-4. Log values statistics were obtained by applying the electrofacies method. The
minimum, maximum, means values and standard deviation are showed for each electrofacies. An electrofacies characterizes a rock type by a specific set of log responses. By using core-
log-correlation, the in situ log data were allocated to the different rock types.

GR (API) K (%) Th (ppm)

Rock type N Min Max Mean Std. Dev. Min Max Mean Std. Dev. Min Max Mean Std. Dev.

Argillaceous sandstone 3419 83.712 219.114 130.701 14.825 1.292 4.047 2.6204 0.514 3.221 18.723 9.605 2.104
Carbonaceous slate 1559 122.518 221.475 174.393 18.801 2.065 4.461 3.309 0.382 7.457 17.416 12.045 1.813
Carbonaceous sandstone 142 99.045 228.716 159.470 29.0352 2.482 3.864 3.0581 0.322 5.849 15.116 11.483 2.357
Sandstone 9204 44.781 208.592 99.812 26.171 0.604 3.904 2.125 0.601 2.647 15.302 7.688 2.113
Sandy mudstone 56 78.093 114.332 98.815 9.287 1.636 2.726 2.356 0.251 6.726 11.810 9.321 1.279
Slate 14,692 45.891 221.62 116.170 30.189 0.586 4.077 2.340 0.544 3.020 17.639 9.123 2.224
Fault breccia 130 102.524 212.932 167.412 26.167 2.195 3.756 3.155 0.470 5.141 16.023 11.944 0.126
Fault gouge 6 134.697 150.205 144.521 6.420 2.873 3.226 3.039 0.480 10.129 12.509 11.330 0.969
U(ppm) Pe(b/e)
Rock type N Min Max Mean Std. Dev. Min Max Mean Std. Dev.
Argillaceous sandstone 3419 1.050 15.511 7.5056 2.279 2.749 8.773 3.900 0.500
Carbonaceous slate 1559 1.496 12.946 7.983 2.562 4.386 8.292 6.284 0.673
Carbonaceous sandstone 142 4.435 11.722 7.387 2.092 4.146 7.072 5.576 0.833
Sandstone 9204 1.143 13.538 5.288 2.181 2.270 7.093 3.812 0.752
Sandy mudstone 56 2.533 5.713 4.1459 0.905 3.012 4.225 3.534 0.314
Slate 14,692 0.886 17.58 6.370 2.575 0.091 7.570 4.207 0.904
Fault breccia 130 4.914 11.376 8.321 1.545 3.668 7.677 5.860 0.813
Fault gouge 6 4.875 6.224 5.529 0.560 4.341 5.190 4.870 0.411

Fig. 4a–c, correspond to an increase in the clay content. This can ad- (Hirono et al., 2015). This might indicate that the carbonaceous ma-
ditionally be seen in Fig. 5, where a continuous increase in (GR) and terial is vulnerable in earthquakes. Fig. 11 shows the crossplot of (GR)
photoelectric absorption (Pe) is observed. The cross-plots of (K) versus vs Neutron porosity (CNL). As mentioned by, the crossplot of (GR) vs
(Th) (Fig. 6) show a trend of increasing (K) with increasing (Th) for all (CNL) shows several relationships. From Fig. 11, there are two straight
rock types. This trend observed in log data was approximated using line relationships between the log parameters. For the straight line Clay
regression analysis: (Th)= 2.337× (K) +3.386 and the linear model content area, change in porosity (CNL) usually involves change in clay
gives a satisfactory fit to the data. The trend shown in Fig. 6 possibly content (GR) (probably related to grain size changes). The straight line
explained a strong relationship between (Th) and aluminosilicates. porosity region, on the other hand, shows that the increase in porosity
Aluminosilicates are a major constituent of clay minerals. However (U) and (GR) is partly dependent on the porosity of the measured rocks
shows no apparent relationship with (K) and (Th) (Figs. 7–8). This in- (decrease in GR). The above effects can additionally be viewed from the
dicates that (U) must be influenced by other factors in addition to crossplot of (GR) vs Acoustic transit time (Fig. 12). Fig. 13 shows a
aluminosilicate abundance (Ehrenbergand and Svana, 2001). From crossplot of (GR) vs Density. From this figure, it can be observe of that
Figs. 4–8, the data of lithological units overlap significantly, which there is a continuous slight increase in (DEN) with increase in (GR).
indicates the similarity of their mineral composition. This similarity This is based on the change in porosity which involves a change in clay
causes ambiguities of interpretation. Consequently, additional diag- content (possibly related to grain size changes). It should be noted that
nostic information from other logs was useful, within WSFD-4. Fig. 9 the log signature to clay is influenced by its composition and porosity.
shows crossplot of (GR) vs. Resistivity (RD). From closer examination of The geological meaning of radioactivity lies in the distribution of
Fig. 9, a constant relationship is seen in low resistivity values and (GR) (K), (Th) and (U). Most rocks are radioactive to some degree, meta-
values range from 44.78 API to 228.71 API. From Serra (1972, 1979), morphic and igneous rocks more so than sedimentary. Many studies
Dresser Atlas (1983) and Gearhart (1983) clay resistivity values are exist on how to identify individual clay minerals using SGR data (e.g.
between 0.5 Ω m and 1000 Ω m while the (GR) ranges from 24 API- Hurst, 1990; Adams and Richardson, 1960; Hassan and Hossin, 1975;
1000 API. Based on these values, the crossplot of (GR) vs. Resistivity Myers, 1987; Myers and Wignall, 1987; Parkinson, 1996; Serra, 1979).
(RD) may additionally conclude that the WSFD-4 lithologies are clay From these studies, most of the findings have only local significance.
content. Thus, it is the permeability of the clay which contributed to Therefore there is no well bounded method for clay mineralogy iden-
low resistivity readings. Again, from Fig. 9, an opposite inflection is tification using SGR log data. It has been proposed that (Th/K) ratios
seen with the increase in resistivity values (decrease in permeability) in may be utilized to show clay minerals (e.g. Edmundson and Raymer,
slates and sandstones lithologies which may indicate the abundance of 1979; Hassan and Hossin, 1975; Quirein et al., 1982; Fertl, 1983; Da-
quartz. In this area, slates and sandstones lithologies consequently show vies and Elliott, 1996; Myers and Wignall, 1987). However, Hurst
low (GR) values. Fig. 10 shows the crossplot of (GR) vs Spontaneous (1990) rejected this method mentioning that the precision for the
potential (SP). From this figure, the entire data set shows no apparent identification of a specific clay mineral is not justified. Additionally,
correlation between (GR) vs (SP) (correlation coefficient = 0.22). Luthi (2001) did not support the reliability of the proposed method. On
However, carbonaceous slate lithology can be distinguished from the the other hand, Hassan et al. (1976) studied the chemical composition
other lithologies and it is characterized by the highest mean value of and mineralogy of 500 samples of several lithologies from different
(SP) and (GR) (as well as (K), (Th), (U), Table 1), and lowest resistivity environments and in their samples, the (Th) content correlated with the
(Fig. 9). This may indicate the smallest grain size and highest clay content of clay minerals and the (Th) content in illite ranges from 6 to
content of carbonaceous slate as compared to other lithologies. Clays 22 ppm while the smectile is in between 10 and 24 ppm (Rider, 2002).
are fairly weak mechanically (Wu et al., 1975). Carbonaceous slate is So, from Table 1, and Hassan et al. (1976) as well as Dresser Atlas
the principal lithology of the Northern segment of YBF zone (Fig. 2). (1983) cited in Rider (2002), this study may concluded that argillac-
Carbonaceous material has also been viewed at the surface and/or in eous sandstone (mean values of Th = 9.675 ppm), sandstones (mean
drill core of the Southern segment of YBF zone (WFSD-1) (Yang et al., values of Th = 7.688 ppm), sandy mudstones (mean values of Th =
2013; Liu et al., 2016) and of the GAF zone (WFSD-3)(Li et al., 2015) 9.321 ppm), and slates (mean values of Th = 9.123 ppm) lithologies
respectively. Moreover, it has also been viewed in drill core of TCDP probably contain illite. However, carbonaceous slates (mean values of

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A. Amara Konaté et al. Applied Radiation and Isotopes 128 (2017) 75–85

(a)

(b) Fig. 5. Crossplot of Total Gamma Ray vs. Photoelectric index.

6
.38
)+3
7 *(K
.33
=2
Th

(c) Fig. 6. Crossplot of Potassium vs. Thorium.

Fig. 4. a. Crossplot of Total Gamma Ray vs. Potassium. b. Crossplot of Total Gamma Ray
vs. Thorium c. Crossplot of Total Gamma Ray vs. Uranium.

Fig. 7. Crossplot of Potassium vs. Uranium.

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A. Amara Konaté et al. Applied Radiation and Isotopes 128 (2017) 75–85

Po
r
os
ity
nt
conte
Clay

Fig. 8. Crossplot of Thorium vs. Uranium.

Fig. 11. Crossplot of Total Gamma Ray vs Neutron porosity.

Po
ro
si
ty
u
Quartz

nt
conte
Clay

Fig. 9. Crossplot of Total Gamma Ray vs. Resistivity.

Fig. 12. Crossplot of Total Gamma Ray vs Acoustic transit time.

Fig. 10. Crossplot of Total Gamma Ray vs Spontaneous potential.

Fig. 13. Crossplot of Total Gamma Ray vs Density.

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A. Amara Konaté et al. Applied Radiation and Isotopes 128 (2017) 75–85

Fig. 14. The crossplot of between the log parameters; GR, Pe, K, Th, U, CNL, DEN, and RD. The insitu physical property display variations in fault rock within WFSD-4.

Th = 12.045 ppm) and carbonaceous sandstones (mean values of Th = lithologies possibly contain illite. While carbonaceous slates and car-
11.483 ppm) possibly contain mixed-layer illite-smectite. This study bonaceous sandstones probably contain mixed-layer illite-smectite and
also attempts to discover the clay mineralogy of the lithologies using chlorite. However, the petrologic and mineralogic cores and outcrops
the photoelectric absorption (Pe) of gamma rays since it is an out- investigation should be made to support understanding the relationship
standing indicator of mineralogy (Doveton, 1994). Based on the Pe log between SGR log patterns and the various clay minerals.
generalized analysis guide as set in Doveton (1994) and Table 1, the
result suggests that argillaceous sandstone (mean values ofPe = 3.90 b/
3.2. Fault rock
e), sandstones (mean values ofPe = 3.812 b/e), sandy mudstones
(mean values ofPe = 3.534 b/e) and slates (mean values ofPe = 4.207
The Northern segment of YBF (2012–2265 m) located in Fig. 3 is
b/e) lithologies possibly contain illite. In contrast, carbonaceous slates
characterized by the lowest resistivity log values and the highest (GR),
(mean values ofPe = 6.284 b/e) and carbonaceous sandstones (mean
(K), (Th), (U), (SP), and (Pe) as compared to other sections in the well.
values ofPe = 5.576 b/e) probably contain chlorite.
Additionally, the Northern segment of YBF has significant high (CNL)
On account of the overall analyses, this study may conclude that
and (AC) while it has low (DEN) values. The above conventional logs
argillaceous sandstone, sandstones, sandy mudstones and slates
have been utilized by Li et al., (2013, 2015) in the localization of YBF

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A. Amara Konaté et al. Applied Radiation and Isotopes 128 (2017) 75–85

correlation coefficient values, (K) shows the highest correlation value

with (GR), hence it is the largest contributor followed by (Th) and (U)
to the (GR) in fault rock from WFSD-4. Therefore, a continuous increase
in (GR) as (K), (Th), (U), and (Pe) increase seen from Fig. 14a-d possibly
reflect the increase in clay content. Fault breccia shows the highest
percentage of clay content because it has the highest concentrations of
radioactive material. The presence of clays in a fault zone increases the
probability of slip (Li et al., 2013, 2014). Close inspection of Fig. 14e–g
show that (RD) tends to decrease as (AC) and (GR) increase and
probably represents clay in fault rocks. The (CNL)-(DEN) crossplot
(Fig. 14g) displays a trend toward high density (low porosity) with
increase in (CNL). This could probably represent clay content in fault
rocks. The (DEN)-(CNL)-(GR) crossplot can differentiate fault breccia
from fault gouge (Fig. 15). From the visual inspection of Fig. 14a–g, we
can observed that fault breccia tend to have the highest (GR), (AC) and
(CNL), while showing the lowest (RD) and (DEN). This may suggest that
the Principal Slip Zone (PSZ) in the YBF-Northern segment may occur in
fault breccia. Fig. 16. present photographs showing fault breccia and
carbonaceous slates (host rock).
The comparison of the log studies of the Northern segment of YBF
Fig. 15. Crossplot of Total Gamma Ray vs Neutron porosity vs Density. (this study) to those obtained from the Southern segment of YBF (Li
et al., 2014) and the Guanxian-Anxian (GAF) fault (Li et al., 2015),
show that the (PSZ) in the Southern segment of YBF (Li et al., 2014) and
in the (GAF) fault possibly occur in a fault gouge. While in the YBF-
Northern segment, the PSZ may occur in fault breccia. What causes
these differences is an open question, and the possible explanation
could be that the style of fault formation is governed by some elements
such as the stress state during slip, and the rock type and physical
properties of the host rock (Davis and Reynolds, 1996).
Based on Table 1, and Hassan et al. (1976) and Dresser Atlas (1983)
cited in Rider (2002), and Doveton (1994), we may conclude that fault
breccia might contain illite/smectite and chlorite while fault gouge
possibly contains illite/smectite and illite. Nonetheless, the mineralogic
analysis of core samples from WFSD-4 hole is not available to support
these hypotheses.
However, Si et al. (2014) has revealed the presence of clay minerals
such as smectite, illite, and chlorite from WFSD-1 drilling core within
the Principal Slip Zone on the YBF-southern segment. Additionally,
from the San Andreas fault which is perhaps the most intensively in-
vestigated fault zone in the world (Schleicher et al., 2009), an in-
vestigation on rock cuttings from the several segments of the fault zone
wells (pilot and main hole) have discovered a diverse assemblage of
clay minerals: chlorite, illite, smectile, illite–smectite, chlorite, chlor-
ite–smectite, and talc and serpentine fragments (Solum and van der
Fig. 16. (a) Core photography of Fault breccia in WFSD-4 (depth 2187–2190 m). (b) Core Pluijm, 2005; Solum et al., 2006; Schleicher et al., 2006; Moore and
photography characteristics of carbonaceous slate in WFSD-4 (depth 2059–2062 m). The Rymer, 2007; Bradbury et al., 2007). The occurrence of these clay
particle seize of fault breccia is significantly larger than the carbonaceous slate. Some of minerals is usually connected with brittle deformation under low-
the gravel retains the lamina before crushing while there are also some show flaser temperature conditions and fluid–rock interaction (Wu et al., 1974;
bedding and bedding distribution. Carbonaceous slate bedding surface along the bedding
Evans and Chester, 1995; Moore and Rymer, 2007). Therefore, the
plane is vague; Because of the carbonaceous, lithology is more brittle, fragile, small pieces
of broken rock can be seen in the image, and it is of low resistivity from the view of
presence of clay minerals, illite–smectite and chlorite from WFSD-4 drill
conventional logging data. hole is a possible cause of fault weakness in the Yingxiu–Beichuan fault.
In this study, fault and the host rocks show comparable clay mi-
Southern segment and GAF segment respectively. Besides, as mentioned nerals. Additionally, they show comparable log responses (Table 1).
earlier, from the examination of the WFSD-4 cores (Fig. 2), the depth Similarly, the core analysis of TCDP indicated that the major mineral
interval 2012–2265 m consists of a continuous fault zone with fault compositions are comparable in both fault and host rocks (Isaacs et al.,
breccia of different scale and very few fault gouges. For these reasons, 2007). These are indicating that fluids circulated through the fault zone
we agree that the depth interval 2012–2265 m represent a large scale and led to an accumulation of clay minerals (Duan et al., 2015) and the
fault zone. physical properties of the fault rock are related not only to the fault
To investigate details of the rock physical properties in the fault rock itself but also to the protolith (Li et al., 2014).
rocks of WFSD-4 hole, a crossplot was performed between the logging
parameters; (GR), (Pe), (K),(Th), (U), (AC), (CNL), (DEN) and (RD). 4. Conclusion
Fig. 14a-g show the crossplot of the aforementioned log parameters
from 2012 m to 2265 m. As can be seen in Fig. 14a-d, a linear corre- The WFSD drill hole provided us with a chance to characterize in
lation exists between (GR) against (K), (Th), (U) and (Pe) respectively situ rock physical properties in an active fault. Statistical multi log
(correlation coefficient =0.80; 0.76; 0.71 and 0.62). From the analysis and crossplot analysis of SGR log together with others logs
allowed us to better characterize variations in lithology and fault rock

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physical properties, and to find the relationship between log parameters Ocean. Sci. 18, 183–221.
Keys, W.S., 1979. Borehole geophysics in igneous and metamorphic rocks, in Society of
involved in this study. Fault breccia exhibited the highest (GR), (AC) Professional Well Log AnalystsAnnual Logging Symposium, 20th, Tulsa,Okla., 1979,
and (CNL), while showing the lowest (RD) and (DEN). This may suggest Transactions: Houston, Society of Professional.
Parkinson, D.N., 1996. Gamma-ray spectrometry as a tool for stratigraphical interpreta-
that the Principal Slip Zone in the YBF-Northern segment may occur in tion: examples from the western European Lower Jurassic. In: Hesselbo, S.P.,
fault breccia. However, petrologic and mineralogic cores and outcrops Parkinson, D.N. (Eds.), Sequence Stratigraphy in British. Geology Special Publication,
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Kinoshita, M., Kimura, G., Saito, S., 2014. Seismogenic processes revealed Through the
lationship between SGR logs patterns and the various clay minerals. Nankai Trough Seismogenic zone experiments: core, log, Geophysics, and
The extrapolation of the clay mineralogy of the WFSD-4 drill hole show Observatory measurements. Dev. Mar. Geol. 7, 641–670.
Li, H., Wang, H., Xu, Z., Si, J., Pei, J., 2013. Characteristics of the fault-related rocks, fault
that argillaceous sandstone, sandstones, sandy mudstones and slates
zones and the principal slip zone in the Wenchuan Earthquake Fault Scientific
lithologies possibly contains illite. While carbonaceous slates and car- Drilling Project Hole-1 (WFSD-1) Tectonophysics 584, pp. 23–42.
bonaceous sandstones possibly contain mixed-layer illite-smectite and Li, H., Xu, Z., Niu, Y., Kong, G., Yao, H., 2014. Structural and physical property char-
acterization in the Wenchuan earthquake Fault Scientific Drilling project — hole 1
chlorite. Fault breccia may contain illite-smectite and chlorite while (WFSD-1). Tectonophysics 619–620, 86–100.
fault gouge possibly contains illite-smectite and illite. The work carried Li, H., Wang, H., Xu, Z., Li, T., Si, J., Sun, Z., 2015. Lithological and structural char-
out on the WFSD-4 represents progress of understanding fault rocks (as acterization of the Longmen Shanfault belt from the 3rd hole of the Wenchuan
Earthquake Fault Scientific Drilling project (WFSD-3). Int. J. Earth Sci. 1–20. http://
well as lithology) in the Wenchuan earthquake. However, this study dx.doi.org/10.1007/s00531-015-1285-9.
still needs more information about chemical, physical, and mechanical Liu, J., Li, H., Zhang, J., Zhang, B., 2016. Origin and formation of carbonaceous material
veins in the 2008Wenchuan earthquake fault zone. Earth Planets Space 68, 19.
properties from surface and laboratory studies of the fault cores to http://dx.doi.org/10.1186/s40623-016-0399-z.
understand fully the mechanical and slip-weakening effects in the Luthi, S.M., 2001. Nuclear Spectroscopy Logging, Geological Well Logs pp 183–215.DOI
Yingxiu–Beichuan fault. http://dx.doi.org/10.1007/978-3-662-04627-2_10 PrintISBN 978-3-662-04629-6.
Springer Berlin Heidelberg.
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Acknowledgments Sedimentological Studies. Univ. of London.
Myers, K.J., Wignall, P.B., 1987. Understanding Jurassic organic-rich mudrocks: new
concepts using gamma-ray spectrometry and palaeoecology: examples from the
We thank Wenchuan Earthquake Fault Scientific Drilling Project of Kimmeridge Clay of Dorset and the Jet Rock of Yorkshire. In: Leggett, J.K., Zuffa,
China (WFSD) for providing data. The receiving editor (Dr. Jeffrey S. G.G. (Eds.), Marine Clastic Sedimentology: Concepts and Case Studies.
Graham & Trotman, London, pp. 172–189.
Schweitzer) and anonymous reviewers are also thanked for the im- Moore, D.E., Rymer, M.J., 2007. Talc bearing serpentinite and the creeping section of the
provement of this manuscript. San Andreas fault. Nature 448 (16), 795–797. http://dx.doi.org/10.1038/
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