Does the Denjozan Fault intersect the Sabae Fault?
~Fault route tracing by using bicarbonate ions as tracers~
Fukui Prefectural Takefu High School
Rikuta Kayatani Hiroaki Sakashita Atsuya Serikawa Taichi Hashimoto[Abstract] We investigated the relationship between the Denjozan Fault and the Sabae Fault located in the
Reihoku region of Fukui Prefecture, by using bicarbonate ions as tracers. As a result, we found out that the
Denjozan Fault extends move westward from the route shown on the active fault map by the Geospatial
Information Authority of Japan. We also found the Denjozan Fault reaches just before the Sabae Fault, butdoes not intersect it. This means the Sabae Fault is more dominant than Denjozan Fault. We could not clarify
the position of the Denjozan Fault in this research, so we will try to elucidate it in the future.
Introduction
There are many active faults in the Reihoku area,
Fukui Prefecture. The Sabae Fault is one of them, areverse fault and extending in a direction fromsouthern Fukui City to Echizen City. The latest
activity of this fault is thought that it may be slide at
500-3000 years ago, and this area has attracted
attention as less seismic area. (Okamoto et al.,2010) (Fig.1). Further, there is another active fault
named Denjozan Fault which extends fromsoutheastern Fukui City to eastern Sabae City. It isa reverse fault with a lateral displacement
component. Okamoto et al.(2008) pointed out thatthe Denjozan Fault may be a boundary of seismic
activity because of the difference strike for the Fukui
Plain East Margin Fault Zone and the Neotani Fault
system at the Denjozan Fault (Fig. 2). Actually, in the
Fukui Earthquake (1948, M7.1) and the Nobi
Earthquake (1891, M8.0), faults’ rupture did not
progress beyond the Denjozan Fault that boundary(Okamoto et al., 2008). We elcidated the Denjozan
Fault will reach to the seismic blank area near the
Sabae Fault or not. Okamoto speculate that the
Denjozan Fault intersects the Sabae Fault near
Chudoin (Fig.3) in Sabae City. Water of the pond at
Chudoin began to gush at a crack (Fig.4) from theNovember 2, 2018 earthquake (Kii Channel).
The fault crossing is one of the important
problems in topography but hasn’t been studied indetail. The relationship between the Denjozan Fault
and the Sabae Fault is unknown. However, therelationship between active faults is extremely
important information when considering disasterprevention at seismic blank. Therefore, weinvestigated the relationship between the Denjozan
Fault and the Sabae Fault, and confirm whether theyintersect or not.
1

2 Method
Tracers are sometimes used to pick up the route ofa streams. In a previous study, we researched bytracing the route of the Sabae Fault by using thetracers. The method is observing fluoride ions inspring water and groundwater (Ishizuka et al., 2020;
Otomo et al., 2021; Adachi et al., 2022). Therefore,
we first investigated substances that we could be
used as tracers for the Denjozan Fault. But, we
could not find out fruoride ion such water. We
focused on bicarbonate springs. Carbonate springs
are called "natural ramune", because the carbon
dioxide produced by underground magma isdissolved into groundwater on high concentrations.
There are some carbonate springs in Sabae Cityand the eastern part of Echizen City (Fig.5). This
carbonate spring is thought to gush out along the
Denjozan Fault. We compared the ions containing inthat carbonate spring with water in Chudoin Pond.
The concentration of bicarbonate ions wasdetermined by using bromocresol green/methyl red
ethanol solution as reagent. And, bicarbonate ion
concentrations were analyzed by neutralization
titration using aforesaid substance as a reagent(Ministry of the Environment, 2014). Other ion
concentrations
were
analyzedbyionchromatography (Educational Research Center).
The results are shown in Table 1. The groundwaterat Takefu High School was used as a basement data.
The spring water at Chudoin, located on the Sabae
Fault, contains more fluoride ions than the
carbonate springs. On the other hand, the carbonate
spring associated with the Denjozan Fault contains
little fluoride ions and a large bicarbonate ion. Thismeans that the water quality for Denjozan Fault
System is clearly different from the spring water at
Chudoin. Therefore, we thought that bicarbonate
ions could be used as a tracer of the Denjozan Fault
System. The reason is as follows. When a fault
exists underground with underground pressure
increasing at deep underground, water rise up
through the fault zone. If the deep groundwatercontains high levels of bicarbonate ions, shallow
ground water for rich bicarbonate ion. It is also
thought that ground water spread laterally throughthe fault zone (Fig.6). As a result, the concentrationof bicarbonate ion in spring water and groundwater
near a fault zone is considered to be higher than that

in the surrounding area. This theory has been
confirmed by our previous research on fluoride ionsat the Sabae Fault(Adachi et al., 2022). Furthermore,
by applying Okada (1979), it has been confirmedthat this concept can be applied to areas with thickalluvium zone on the fault. Therefore, we traced theroute of the Denjozan Fault and investigated its
relationship with the Sabae Fault by measuring andcomparing the concentrations of bicarbonate andfluoride ions in spring water and groundwater.
3 Result
In this study, shown in the red box in Fig.7, thesurvey area extends from in Sabae City to northern
Echizen City. The route of the Denjozan Fault shownin the active fault map by the Geographical Survey
Institute to the Hino- River area in the E-W direction.
Table 2 shows the fluoride and bicarbonate ion
concentrations in spring water and groundwater at
110 sites those we have been surveyed (Fig.8).
However, there were some sites for no sample
information (left blank).
Of the results, the bicarbonate ions are shown on
the topographic map with color-coded (Fig.9). The
locations where carbonate springs do not exist today
but where there is evidence of the existence ofcarbonate springs in the past are indicated on the
topographic map by the symbols shown in Fig.9.
Fig.10 shows the distribution on bicarbonate ionsconcentration at 110 sites. By examining the
distribution of bicarbonate ions, we were able to infer
the line shown by the blue arrows in Fig.10.
4 Consideration(1) Can bicarbonate ions be used as a tracer for the
Denjozan fault?
The fluoride ions that could be used in the Sabae
Fault are not so common in the carbonate springs,
gushing at pound in association with the Denjozan
Fault, as seen in Table 1. Therefore, it cannot be
used as a tracer for the Denjozan Fault. In addition,in the area of the Denjozan Fault (the distribution offluoride ions is discontinuous), so we cannot
examine the route.
On the other hand, bicarbonate ions are rich incarbonated springs. But in the area of the Sabae
Fault with the exception of the 45 sites in Fig.8, there
were no sites where the concentration ofbicarbonate ions exceeded 100 mg/L. Therefore,high concentrations of bicarbonate ions are effective
tracers of the Denjozan Fault.
(2) Does the Denjozan Fault intersect the Sabae
Fault?
The survey revealed that the Denjozan Fault
reaches to point 45 in Fig.8 just before the Sabae
Fault. This location (point 45 in Fig.8) is on thenorthwest side of the Sun Dome in Funatsu-cho in
Sabae City where an underground passage passes
under the JR Hokuriku Line (Fig.11). The Sabae
Fault passes through this point. As shown Table 3,
the collected groundwater contains bicarbonate ionsequivalent to those of a carbonate spring. It also
contains fluoride ions rarely found in carbonatedspring water, as much as the spring water from
Chudoin. Therefore, it contains both properties ofspring water from the Denjozan Fault and the Sabae
Fault.
However, no points with high bicarbonate ion
concentrations have been found western point(Fig.12). We concluded that the Denjozan Fault
does not extend west of this point. If the Denjozan
Fault is in contact with the Sabae Fault, thengroundwater with high concentrations of bicarbonate
ions migrating from the east through the fault zone
would be spread around the Sabae Fault. However,there were no areas where the bicarbonate ion
concentration exceeded 100 mg/L other than in the
groundwater in the area surrounding the Sabae
Fault. This meaned that the Denjozan Fault is notconsidered to intersect the Sabae Fault. Therefore,
the Sabae Fault is more dominant than the
Denjozan Fault.
5 Future
In this study, we measured the concentration ofbicarbonate ions of groundwater to investigate theroute of the Denjozan Fault. We were able to clarify
the following.
・ Bicarbonate ion can be used as a tracer of the
Denjozan Fault.
・ The Denjozan Fault extends westward from theroute shown on the active fault map by the
Geospatial Information Authority of Japan.
・The Denjozan Fault does not intersect the Sabae
Fault, and the Sabae Fault has influence on the
Denjozan Fault.
We concluded that one line extends further west
than the route in the GSI's active fault map, asshown in Fig.10. However, from a different
perspective, there could be two lines as shown in
Fig.13. In fig.14, Okamoto (2014) shows theepicenters of earthquakes in the studying area
during the period from April 2006 to March 2009 andthe routes of the Denjozan Fault and the
Shirotsubakiyama Fault shown by the active fault
map by the GSI. This figure seems to indicate theexistence of the two lines in Fig.13. But sinceearthquakes tend to occur near estimated faults, theactual faults are thought to pass through the area
where the epicenters of earthquakes areconcentrated (the area circled in red in Fig.14). This
area is about 2,000 to 3,000 m south of the route of
the two faults shown on the active fault map by theGSI, so further investigation is required and will be
the subject of a future study.
Thanks
We would like to thank Professor Takuo Okamotoof the Fukui National College of Technology foradvices on earthquakes and faults, Mr. Yasuhide
Imazawa, Director of the Science Education Divisionof the Fukui Prefectural Institute of Education, for his
help with the ion analysis of spring water, Mr. Osamu
Kimizuri of Shimo-Shinjo Town in Sabae City for histeachings on the carbonic acid springs at Mt.Sanri,
And many residents for their help in collecting
groundwater.
References
Adachi, M. et al., 2022. Groundwater analysis iseffective for exploring the route of faults ~The
analysis of groundwater is effective to elucidate
the route of a fault.In: Takefu High School Project
Research Papers:28-37.
Ishizuka, C. et al., 2020. The Sabae Fault - Exploring
the route of the fault using spring water. In: Takefu
High School Project Research Papers:26-35.

Nature Conservation Bureau, Ministry of theEnvironment, 2014.Revised:163pp.
Okada, A.,1979.Geology,Geotechnical of Aichi
Prefecture (Part4) (Active fault).Earthquake
Subcommittee, Aichi
Prefecture
DisasterPrevention Council.
Okamoto, T. et al., 2008. M4.5 earthquake that
occurred in the eastern part of Sabae City on
December 21, 2007. Earth Monthly,30 (10):431438.
Okamoto, T. et al., 2010. Tectonics’ of low seismicity
area recognized at Sabae City in Fukui Prefecture.
Bulletin of Fukui National College of Technology(44):35-40.
Okamoto, T. et al., 2014. Fault structure separating
the seismically active zone in the eastern part ofSabae City, Japan. Journal of Fukui National
College of Technology Bulletin of Fukui National
College of Technology (48):51-54.
Otomo, N. et al.,2021.The Sabae Fault passes
through Mt. Murakuni, Echizen City, Japan-Using
soda spring to clarify the route of it. In: Takefu HighSchool Project Research Papers:28-31.
https://www.gsi.go.jp/top.html (GSI home page)

Figure and Table

Fig.1 Less Seismic Blank Zone around the Sabae Fault. (Okamoto et al., 2010)

Fig.2 Active Faults in the Reihoku Area, Fukui Prefecture. (Okamoto et al., 2008)

Fig.3 Chudoin Temple.

Fig.4 Water gushing from a crack in the pond.

Fig.5 Carbonate springs in Sabae City and the eastern part of Echizen City.

Table1 Ionic Concentration for Carbonate Spring and Chudoin spring water. (unit : mg/L)

Fig.6 Rising and Movement of Groundwater through Fault zone.

Fig.7 Area of surveying. (inside red frame)

Fig.8 Sampling site.

Phase

Mark

M o r e t h an 1 0 0 0
500 ～ 999
100 ～ 499
50 ～ 99le ss t h an 5 0
Past c ar bo n at e
spr in g r e c o r ds
(unit : mg/L)
Fig.9 Mark of bicarbonate ions. (ranking)Table2 Ion concentrations at each survey site. (numbers correspond to Fig.８)
No

ion concentrations(mg/L)
Location
1 2-chome,Asahi-machi,Sabae-Shi

Ｆ0.0232 4-chome,Asahi-machi,Sabae-Shi

ＨＣＯ3-

No

ion concentrations(mg/L)
Location

14

5 6 Funaeda-cho,Sabae-Shi

9.8

5 7 Besshi-cho,Sabae-Shi

Ｆ0.051

ＨＣＯ3109.8
31.7

3 4-chome,Asahi-machi,Sabae-Shi

－

15.3

5 8 Besshi-cho,Sabae-Shi

0.040

58

4 Azouda-cho,Sabae-Shi

0.024

101.3

5 9 Matsunari-cho,Sabae-Shi

0.074

440.6

5 Kamikobata-cho,Sabae-Shi

34.8

6 0 4-chome,Mizuochi-cho,Sabae-Shi

6 Kamikobata-cho,Sabae-Shi

34.2

6 1 2-chome,Miyamae-cho,Sabae-Shi

19.5
42.1

7 Ochii-cho,Sabae-Shi(Benzaiten-yama)

0.043

45.8

6 2 2-chome,Miyamae-cho,Sabae-Shi

8 Ochii-cho,Sabae-Shi

0.127

168.4

6 3 Yokogoshi-cho,Sabae-Shi

37.8

9 Obana-cho,Sabae-Shi

0.033

112.9

6 4 Tsubae,Nishibukuro-cho,Sabae-Shi

68.3

79.3

6 5 Hinode-cho,Sabae-Shi

2977.86 6 Ainoki-cho,Echizen-Shi

0.026

89.1

0.024

58.6

1 0 Kanadani-cho,Sabae-Shi

0.030

36.6

37.2

1 1 Kamikochi-cho,Sabae-Shi(Kamikochi-kosen)－

1 2 Kamikochi-cho,Sabae-Shi(Sanbazaka-syozu)

0.039

70.8

6 7 Akasaka-cho,Echizen-Shi

1 3 Kamikochi-cho,Sabae-Shi(Togen-syozu)

0.008

65.9

6 8 Akadani-cho,Echizen-Shi(Uriwari-syozu)

0.023

50

1 4 1-chome,Kaminaka-cho,Sabae-Shi

50

6 9 Awatabe-cho,Echizen-Shi

0.001

47.6

1 5 2-chome,Kaminaka-cho,Sabae-Shi

35.4

7 0 Awatabe-cho,Echizen-Shi

0.015

59.2

1 6 Kawashima-cho,Sabae-Shi－

4.3

7 1 Iehisa-cho,Echizen-Shi

0.027

70.8

1 7 Kawada-cho,Sabae-Shi

0.066

133

7 2 Inayose-cho,Echizen-Shi

0.023

48.8

1 8 Kawada-cho,Sabae-Shi

0.065

85.4

7 3 Uriu-cho,Echizen-Shi

0.059

30.5

1 9 Kawada-cho,Sabae-Shi

0.079

89.7

7 4 Uriu-cho,Echizen-Shi

0.022

22.4

2 0 Kitanaka-cho,Sabae-Shi

0.047

90.9

7 5 Uriu-cho,Echizen-Shi

0.025

16.3

2 1 Kitanaka-cho,Sabae-Shi

0.032

90.3

7 6 Uriu-cho,Echizen-Shi

0.032

38.6

37.8

7 7 Uriu-cho,Echizen-Shi

0.024

42.7

35.4

7 8 Uriu-cho,Echizen-Shi

0.036

38.6

34.2

7 9 Kiyone-cho,Echizen-Shi

0.020

1587.740.3

8 0 1-chome,Kunitaka,Echizen-Shi

0.032

48.3

96.4

8 1 2-chome,Kunitaka,Echizen-Shi

0.076

93.7

2 7 Shimokobata-cho,Sabae-Shi

37.8

8 2 3-chome,Kunitaka,Echizen-Shi

0.032

51.6

2 8 Shimokobata-cho,Sabae-Shi

34.2

8 3 3-chome,Kunitaka,Echizen-Shi

0.051

30.5

2 9 Shimokobata-cho,Sabae-Shi

50.7

8 4 Kuninaka-cho,Echizen-shi

－

502.8

3 0 Shimokobata-cho,Sabae-Shi

26.9

8 5 Kudashi-cho,Echizen-Shi

0.014

67.7

3 1 Shimokobata-cho,Sabae-Shi

54.9

8 6 Takaoka-cho,Echizen-Shi

0.043

137.9

58.6

8 7 Takagi-cho,Echizen-Shi

0.031

46.3

299

8 8 Teraji-cho,Etizen-Shi

0.076

107.4

3 4 2-chome,Shinyokoe-cho,Sabae-Shi

42.7

8 9 Nakashinjo-cho,Echizen-Shi

3 5 2-chome,Shinyokoe-cho,Sabae-Shi

31.7

9 0 Nakatsuyama-cho,Echizen-Shi

－

292.3

2 2 Goromaru-cho,Sabae-Shi
2 3 Goromaru-cho,Sabae-Shi(Kosarae-syozu)

0.034

2 4 Sadatugu-cho,Sabae-Shi
2 5 Sadatugu-cho,Sabae-Shi
2 6 Shimokobata-cho,Sabae-Shi

0.061

3 2 Shimosinjo-cho,Sabae-Shi
3 3 Shimosinjo-cho,Sabae-Shi

0.112

12.2

3 6 1-chome,Chosenji-cho,Sabae-Shi(osyozu)

0.194

62.2

9 1 Namigaki-cho,Echizen-Shi

3 7 2-chome,Chosenji-cho,Sabae-Shi(Chudoin)

0.510

81.2

9 2 Nishikochi-cho,Echizen-Shi

0.010

67.1

3 8 Jichu-cho,Sabae-Shi－

1751.39 3 Nishisyozakai-cho.Echizen-Shi

0.111

268.5

3 9 Nakano-cho,Sabae-Shi

25.6

9 4 Nishisyozakai-cho.Echizen-Shi

0.043

113.5

4 0 Nakano-cho,Sabae-Shi

28.1

9 5 Bajyome-cho,Echizen-Shi

0.062

57

109.2

9 6 1-chome,Hachiman(Takefu High School)

0.028

33.6

0.068

36.6

53.7

4 1 Nishibukuro-cho,Sabae-Shi

0.036

4 2 Hashitate-cho,Sabae-Shi

0.082

96.4

9 7 2-chome,Hachiman,Echizen-Shi

4 3 Higashishimizu-cho,Sabae-Shi

0.051

175.7

9 8 Haruyama-cho,Echizen-Shi

83

4 4 1-chome,Fumatsu-cho,Sabae-Shi

0.028

21.4

9 9 Haruyama-cho,Echizen-Shi

65.3

4 5 4-chome,Fumatsu-cho,Sabae-Shi

0.208

648

1 0 0 Higashikashio-cho,Echizen

0.031

91.5

4 6 4-chome,Fumatsu-cho,Sabae-Shi

0.034

41.4

1 0 1 Higashisyozakai,Echizen

0.042

107.4

4 7 4-chome,Fumatsu-cho,Sabae-Shi

0.025

58.7

1 0 2 1-chome,Murakuni,Echizen-Shi

0.041

34.6

4 8 4-chome,Fumatsu-cho,Sabae-Shi

0.023

24.4

1 0 3 2-chome,Murakuni,Echizen-Shi

0.038

25.4

4 9 4-chome,Fumatsu-cho,Sabae-Shi

0.031

10.9

1 0 4 3-chome,Murakuni,Echizen-Shi

0.039

41.4

5 0 4-chome,Fumatsu-cho,Sabae-Shi

0.052

21.1

1 0 5 3-chome,Murakuni,Echizen-Shi

0.045

41.4

5 1 4-chome,Fumatsu-cho,Sabae-Shi

0.029

39.2

1 0 6 3-chome,Murakuni,Echizen-Shi

0.038

38.6

5 2 4-chome,Fumatsu-cho,Sabae-Shi

0.036

24.4

1 0 7 3-chome,Murakuni,Echizen-Shi

0.042

19.6

5 3 4-chome,Fumatsu-cho,Sabae-Shi

0.025

43.6

1 0 8 4-chome,Murakuni,Echizen-Shi

0.037

56.3

5 4 4-chome,Fumatsu-cho,Sabae-Shi

0.052

48.8

1 0 9 Yamamuro-cho,Echizen-Shi

0.020

79.9

5 5 4-chome,Fumatsu-cho,Sabae-Shi

0.022

32.7

1 1 0 Yokozumi-cho,Echizen-Shi(Enoki-syozu)

0.032

78.7

Fig.10 Distribution of bicarbonate ion concentrations in spring water and groundwater.

Fig.11 JR Hokuriku Line underpass.(4-chome,Funatsu-cho,Sabae-Shi)

Table3 Analyzing results of spring water at JR Hokuriku Line underpass.

Fig.12 Distribution of bicarbonate ion concentration rank in groundwater around
JR Hokuriku Line underground passage. (the red plot is underpass’s)

Fig.13 Two lines seen in the analyzing results.

Fig.14 Distribution of two faults and epicenters (The red circle is the Concentrated zoneof the epicenter). (Okamoto et al., 2014)