TechnicalPhotographs
Note of the Nationalof NIED Research
Nojima Fault
Institute
Drilling
for Earth
CoresScienceat Hirabayashi
and Disaster
Borehole
Prevention,- K.OMURA
No.229et;al.
April, 2002

Photographs of NIED Nojima Fault Drilling Cores
at Hirabayashi Borehole
Kentaro OMURA ＊ 1, Ryuji IKEDA ＊ 2, Tatsuo MATSUDA ＊ 1, Takashi ARAI ＊ 3,
Kenta KOBAYASHI ＊ 4, Koji SHIMADA ＊ 5, Hidemi TANAKA ＊ 6,
Tomoaki TOMITA ＊ 7, and Satoshi HIRANO ＊ 8
National Research Institute for Earth Science and Disaster Prevention (NIED),
omura@bosai.go.jp, mtatsuo@bosai.go.jp＊2
National Research Institute for Earth Science and Disaster Prevention (NIED);
current affiliation:Hokkaido University, ikeryu@ep.sci.hokudai.ac.jp＊3
University of Tokyo;
current affiliation: National Institute of Advanced Industrial Science and Technology (AIST), t.arai@aist.go.jp＊4
Niigata University, kenkoba@gs.niigata-u.ac.jp＊5
Waseda University; current affiliation: University of Tokyo, shimada@eps.s.u-tokyo.ac.jp＊6
University of Tokyo, tanaka@eps.s.u-tokyo.ac.jp＊7
University of Tsukuba＊8Japan Marine Science and Technology Center (JAMSTEC), hiranos@jamstec.go.jp＊1

Abstract
We collected fault zone cores from the Nojima Fault, which was activated by the 1995 Hyogoken Nanbu Earthquake,
continuously from depths between 1,000 m and 1,838 m by drilling through the fault plane about one year after theearthquake. The cores were all granitic rocks, including porphyritic intrusive rocks in spots and remarkably fractured
zones consisting of cataclastic rocks at three depths: around 1,140, 1,300, and 1,800 m. Core samples in fracture zones
were polished for precisely observing fault related rock structures. In total, about 2,210 polished pieces were made andphotographed. In addition, we took photographs of all the cores placed in core boxes. Those photographs were converted
into digitized images (JPEG format) and stored on two volumes of CD-ROM. These digitized images of fracture zone cores
are suitable for mesoscopic observation and quantitative image processing.
Key words: Fracture zone, Fault rocks, Digital image, Nojima Fault, 1995 Hyogoken Nanbu Earthquake

1. Introduction
Analysis of fault rocks provides important informationon the slip behavior of fault planes. In particular, precise
observation of the structure of fault rocks is indispensable
for illustrating their distribution across a fault plane. We
succeeded in collecting fault rocks continuously from
depths between 1,000 and 1,838 m by drilling through theNojima Fault plane about one year after the 1995 Hyogoken
Nanbu Earthquake, which activated the fault (Ikeda, 2001;
Ikeda et al., 2001).
Cores were all granitic rocks, including porphyritic
intrusive rocks in spots and remarkably fractured zones
consisting of cataclastic rocks at three approximate depths:
1,140, 1,300, and 1,800 m (Ikeda et al., 2001; Omura et al.,2001a). Core samples in fracture zones were so damaged
that we fixed the surface of each core piece with an epoxy
resin and cut it vertically into two halves. The cut surface
of one of the two halves was fixed again by epoxy resin andwas polished into a plane surface (polished piece). The
other half of the core was used for chemical analysis or

making a thin section, etc. (Matsuda et al. 2001a, 2001b). A
total of about 2,210 polished pieces were made from thecores from three fracture zone intervals: 1,054.00 - 1,189.55
m, 1,276.70 - 1,336.70 m, and 1,774.90 - 1,828.40 m. By meansof macroscopic observations with the naked eyes, weinvestigated the precise distribution of fault related rocks inthe fracture zones and its mechanical significance for thefracture zone activity (Tanaka et al., 2001; Kobayashi et al.,2001a, 2001b; Omura et al., 2001b). We took photographs of
all the cores placed in core boxes and the all polished pieces.
Those photographs were converted into digitized images(JPEG format) and stored on two volumes of CD-ROM.
We introduce in this technical note the CD-ROM volumes
containing the digital images. Those images of fracture zone
cores are suitable for mesoscopic observation andquantitative image processing. The images will provide
important records of the fault that have just slipped by theearthquake.

― 1 ―Technical Note of the National Research Institute for Earth Science and Disaster Prevention, No.229 ; April, 2002
Table 1

Outline of drilling and core recovery of the NIED Hirabayashi borehole.

Drilling site
(Fig. 1, Fig.2)

About 302 m SE from the surface trace of the Nojima fault.
Lat.: N 34∞ 34" 42.9'
Long.: E 134∞ 58" 23.6'
Alt.: 65m

Drilling Depth

1838.8 m (drilling length, strictly speaking)

Drilling Radius

193.7 mm (10 - 250 m)
149.2 mm (250 ñ 1,000 m)
97.5 mm (1,000 m ñ 1,838 m)

Inclination

Increase from 0∞ to 7∞ 20' (0 - 994 m)
Decrease from 7∞ 20' to 1∞ (994 ñ 1,450 m)
Less than 1∞ (1,450 ñ 1,838 m)

CoringSpot coring at 5 points (0 ñ 1,000 m)
All coring (1,001 ñ 1,838 m)
64 mm radius

Lithology(Fig. 3)

Granodiorite and Tonalite.
Porphyritic intrusive rocks in spots.
Cataclastic rocks in three fracture zones around 1,140, 1,300 and 1,800 m.

Fig. 2

Photograph of the drilling rig at the NIED
Hirabayashi borehole beside the surface traceof the Nojima Fault.

2. Core collection
Drilling of the NIED Hirabayashi borehole and core
recovery is described in Table 1. The coring recovery rate
was almost 100 % below a depth of 1,101.5 m. Collectedcores were placed in a total of 188 core boxes (5 lines ◊ 1 m= 5 m length in a box).
3. Core handling
About 2,210 polished pieces were made from cores in 25
Fig. 1

Location of the NIED Hirabayashi boreholeand geological map around the borehole.

boxes from depths between 1,054.00 and 1,189.55 m, 12 boxes
from depths between 1,276.70 and 1,336.70 m, and 11 boxes
from depths between 1,774.90 and 1,828.40 m. We madepolished pieces according to the following procedure and― 2 ―Photographs of NIED Nojima Fault Drilling Cores at Hirabayashi Borehole - K.OMURA et al.

Fig.3

Vertical projection of the NIED Hirabayashi borehole and the Nojima Fault with lithological columns as
determined by core observations, and with profiles of physical properties in the borehole as determinedby borehole loggings. Three fracture zones were found around the depths of 1,140, 1,300 and 1,800 m.
GSJ (Geological Survey of Japan) also drilled into the Nojima Fault next to the NIED borehole and founda fracture zone around a depth of 700 m. One of the three fracture zones found in the NIED borehole mayconnect with the fracture zone found in the GSJ borehole. We made polished core pieces from cores inthree depth intervals shown by hatched area in the figure, corresponding to the three fracture zones.

― 3 ―Technical Note of the National Research Institute for Earth Science and Disaster Prevention, No.229 ; April, 2002

Fig. 4. (Tanaka et al., 1999; Matsuda et al., 2001b).
(1) Fix the core pieces in a core box with epoxy resin.
(2) Number the fixed core pieces.
(3) Cut the fixed core pieces vertically into two halves: onefor a polished piece (archival half), and the other for
analysis (working half).
(4) Fix with epoxy resin again if necessary and polish the
cut surface of the archival half.
(5) Take photographs of polished surfaces with 35 mm color
film.
(6) Make Photo-CD from the 35 mm negatives.
(7) Convert from the highest resolution image on the
Photo-CD to JPEG format image for each polished piece.
(8) Copy JPEG format images onto CD-R.
4. Contents of CD-ROM
We copied all digital images (JPEG format) of the coreboxes and polished pieces onto two volumes of CD-ROM.;
The first CD-ROM consists of images of core boxes Nos. 1
to 100 and images of polished pieces from around theFig.4 Core handlings to make polished pieces
from fracture zone core samples.

fracture zone at 1,140 m made from cores in core box Nos. 31
to 55., The second CD-ROM consists of images of coreboxes Nos. 101 to 188 and images of polished pieces fromfracture zones at around 1,300 and 1,800 m made from core

5. Summary

box Nos. 74 to 85 and Nos. 175 to 185. Each CD-ROM has

Fracture zone cores retrieved by drilling through thetwo folders, each consisting of photographs of the core

Nojima Fault, which was activated by the 1995 Hyogoken

box and polished pieces. The former consists of core box

Nanbu Earthquake, were cut into polished core pieces.

photographs in numbered order, and the latter consists ofDigital images of the polished surfaces as well as all cores

folders corresponding to the core boxes, from which polishedplaced in core boxes were stored on CD-ROM in twopieces were made (Fig. 5).

volumes. These digitized images are suitable for mesoscopic

In addition, each volume contains a file describing theobservation and quantitative image processing.

depths and lengths corresponding to the core piece numbers.
The file also contains data on degrees of deformation, or
pulverization and alteration of the core pieces estimated by
the method proposed by Tanaka et al. (1999). According tomesoscopic observations, the degrees of deformation, or
pulverization and alteration were classified into four
categories based on the relative density of the
microfractures and on the decreasing percentage of mafic
minerals: 0 (weak), 1, 2, 3 (strong). Figure 6 shows the relative
distribution frequency of cores corresponding to each of
the 4 (deformation) ◊ 4 (alteration) categories in the analyzed
depth intervals. This diagram has information on the historyof fracture and alteration processes to form the present-day
distribution of fault rocks in the fracture zones.

― 4 ―Photographs of NIED Nojima Fault Drilling Cores at Hirabayashi Borehole - K.OMURA et al.

Fig. 5

Schematic diagram of the contents of the two CD-ROM volumes. Each CD-ROM has two folders: one(ìCoreBoxPhotoóî) consists of core box photographs and the other (ìCorePiecePhotoóî) consistsof photographs of the polished pieces. The width of a core box equals about 1 m. Black and white scalebar in a core piece photo equals 2.5 cm.

― 5 ―Technical Note of the National Research Institute for Earth Science and Disaster Prevention, No.229 ; April, 2002

Fig. 6

Relative distribution frequency of cores corresponding to deformation and alteration categories. The
summation of the length of the core pieces corresponding to each category is divided by total length of
the analyzed interval: (a) 1,054.00 ñ 1,189.55 m, (b) 1,276.70 ñ 1,336.70 m, and (c) 1,774.90 ñ 1,828.40
m. Flakes are smashed fragments that could not be fixed to make polished pieces.

Acknowledgments

K., Sano, H., Sawaguchi, T., Tanaka, H., Tomita, T.,We would like to A. Yamasaki, T. Sawaguchi and N.

Tomida, N., Hirano, S., and Yamazaki, A. (2001a):

Tomida for their help preparing a large number of core pieces.

Examination of mineral assemblage and chemical

We also thank to staff of Sumiko Consultants Co., Ltd forcomposition in the fracture zone of the Nojima Fault attheir efforts in drilling through the fault fracture zone and1,140 m depth: Analyses of Hirabayashi NIED drill core.

recovering cores.

The Island arc, 10-3/4, 422-429.
7) Matsuda, T., Arai, T., Ikeda, R., Omura, K., Kobayashi,

References

K., Shimada, K., Tanaka, H., Tomita, T., and Hirano, S.

1) Ikeda, R. (2001): Outline of the fault zone drilling project(2001b): Chemical Analysis along Fracture Zones (1,140

by NIED in the vicinity of the 1995 Hyogo-ken Nanbu

m, 1,300 m, 1,800 m Depth) of the Hirabayashi NIED

earthquake, Japan. The Island arc, 10-3/4, 199-205.

Drilling Core of the Nojima Fault. Rep. NIED, 61, 183-

2) Ikeda, R., Iio, Y., and Omura, K. (2001a): In situ stressmeasurements in NIED boreholes in and around the fault

193.
8) Omura, K., Ikeda, R., Iio, Y., Arai, T., Kobayashi, K.,

zone near the 1995 Hyogo-ken Nanbu earthquake, Japn.

Shimada, K., Tanaka, H., Tomita,T., Hirano, S., and

The Island arc, 10-3/4, 252-260.

Matsuda, T (2001a): Characteristics of Logging Data for3) Ikeda, R., Omura, K., Iio, Y., Arai, T., Kobayashi, K.,

Fracture Zones in Hirabayashi NIED Borehole Drilling

Matsuda, T., Shimada, K., Tanaka, H., Tomita, T., andthrough Nojima Fault. Rep. NIED, 61, 155-171.

Hirano, S. (2001b): Drilling Investigation through the9) Omura, K., Ikeda, R., Arai, T., Kobayashi, K., Shimada, K.,

Nojima Fault of the 1995 Hyogo-ken Nanbu Earthquake,

Tanaka, H., Tomita, T., Hirano, S., and Matsuda, T (2001b):

Japan. Rep. NIED, 61, 141-153.

Fault Rock Distribution in a Fracture Zone at a 1,800 m

4) Kobayashi, K., Hirano, S., Arai, T., Ikeda, R., Omura, K.,

Depth of the Hirabayashi NIED Core Collected by Nojima

Sano, H., Sawaguchi, T., Tanaka, H., Tomita, T., Tomida,

Fault Drilling. Rep. NIED, 61, 173-182.

N., Matsuda, T., and Yamazaki, A. (2001a): Distribution10) Tanaka, H., Higuchi, T., Tomida, N., Fujimoto, K., Ohtani,of fault rocks in the fracture zone of the Nojima Fault atT., and Ito, H. (1999): Distribution, deformation anda depth of 1,140 m: Observation from the Hirabayashi

alteration of fault rocks along the GSJ core penetrating

NIED core. The Island arc, 10-3/4, 411-421.

the Nojima Fault, Awaji Island, Southwest Japan. Jour.

5) Kobayashi, K., Arai, T., Ikeda, R., Omura, K., Shimada, K.,

Geol. Soc. Japan, 105-1, 72-85.

Tanaka, H., Tomita, T., Hirano, S., and Matsuda, T.

11) Tanaka, H., Matsuda, T., Omura, K., Ikeda, R., Kobayashi,(2001b): Textures of Fault Rocks in the Fracture Zone ofK., Shimada, K., Arai, T., Tomita, T., and Hirano, S.

the Nojima Fault at a Depth of 1,300 m: Observations(2001b): Complete Fault Rock Distribution Analysis alongfrom the Hirabayashi NIED Drilling Core. Rep. NIED, 61,

the Hirabayashi NIED Core Penetrating the Nojima Fault

223-229.

at 1,140 m Depth, Awaji Island, Southwest Japan. Rep.

6) Matsuda, T., Arai, T., Ikeda, R., Omura, K., Kobayashi,― 6 ―NIED, 61, 195-221.

(Accepted : March 28, 2002)

Photographs of NIED Nojima Fault Drilling Cores at Hirabayashi Borehole - K.OMURA et al.

野島断層 NIED 平林ボーリングコア写真小村健太朗 *1・池田隆司 *2・松田達生 *1・新井崇史 *3
小林健太 *4・島田耕史 *5・田中秀実 *6
富田倫明 *7・平野 聡 *8
防災科学技術研究所
防災科学技術研究所 (現在;北海道大学)*3東京大学 (現在;産業技術総合研究所)
*4
新潟大学
*5
早稲田大学 (現在;東京大学)
*6
東京大学
*7
筑波大学
*8
海洋科学技術センター
*1
*2

要

旨

1995 年兵庫県南部地震で活動した野島断層を貫く掘削により，地震の約 1 年後に 1,000m から 1,838m の深さまで連続的に断層帯コア試料が採取された．コア試料は，ほとんどが花崗質岩で，所々に porphyritic な貫入岩を含み , また
1,140m，1,300m と 1,800m 周辺の 3 箇所で破砕および変質の著しい断層岩からなる破砕帯が見いだされた．破砕帯のコ
ア試料は,断層活動に関連した構造の詳細観察のため，全体でおよそ2,210個の研磨片に整形され，研磨面の写真が撮られた．写真画像は JPEG 形式のデジタル画像データに変換され，2 枚の CD‑ROM に収録された．破砕帯コア試料のデジタル化されたイメージは，メソスコピックな観察と定量的な画像解析に有効である．
キーワード：破砕帯，断層岩，デジタル画像，野島断層，1995 年兵庫県南部地震― 7 ―