Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanHEALTH DISTURBANCE OF RESIDENTS
IN A HOUSE WITH LIQUEFACTION DAMAGE
IN MIHAMA WARD, CHIBA CITY
Chinami KEINO1 and Masayuki KOHIYAMA2
1

Undergraduate Student, Faculty of Science and Technology, Keio Univ.,
Yokohama, Japan, keinochinami@z7.keio.jp
2
Assoc. Professor, Faculty of Science and Technology, Keio Univ.,
Yokohama, Japan, kohiyama@sd.keio.ac.jp

ABSTRACT: The 2011 earthquake off the Pacific coast of Tohoku triggered liquefactionof soil in wide areas, particularly at the landfill in Kanto area. There were many residents
who complained about health disorders caused by a tilted house due to liquefaction. We
carried out a questionnaire survey to residents in Mihama Ward, Chiba City onearthquake damage to their house, health disturbance, etc., and constructed models of
health disturbance in terms of tilt angle. It is clarified that the number of residents who
suffer insomnia significantly increases when the tilt angle exceeds 1/100 rad.
Key Words: Great East Japan earthquake, Liquefaction, Floor tilt, Health disturbances,
Detached house

INTRODUCTION
Triggered by the Great Alaskan earthquake and Niigata earthquake in 1964, the liquefaction study
concerns many researchers so far. Particularly, there are several studies about health disturbances andthe tilt feeling of residents and users who live or work in a building tilted by liquefaction. Kitahara andUno (1965) carried out investigation concerning the residents and workers of buildings tilted by the
Niigata earthquake of June 16, 1964 by interviewing them in November 1964 and discussing about
causes of vertigo for example. Uno and Endo (1996) conducted investigation about 42 female
residents who lived at accommodation unit tilted by the Niigata earthquake, by interviewing them in1981 and performed experiments using tilt simulating equipment; i.e. they led examinees into a sloped
room and carried out an analysis about perception of examinees through the tilted window frame(Endo, Uno 1982). Similarly they made a study on examinee’s felling about their posture and the tilt
direction (Endo, Uno 1981). Fujii et al. (1998) surveyed about 100 liquefaction-damaged houses dueto the 1995 Hyogo-ken Nanbu Earthquake in Ashiya City, and as a consequence they established arelation between the tilt angle and the functional failure of a building. Yasuda and Hashimoto (2002)
and Yasuda (2004) also surveyed liquefaction-damaged housing estate in Abe-Hikona, Yonago City,
which was struck by the Western Tottori Prefecture earthquake in 2000. Accordingly they discussed
that 1/100 rad was the bearable limit of tilt angle of a house and, leveling repair was needed and madeon houses with lager slope because of health disturbances.

871

During the 2011 Great East Japan earthquake, soil was liquefied in wide areas. In particularly,
there were many liquefaction-damaged detached houses at reclaimed land in Kanto region. There were
numbers of residents who complained of health disturbances due to the large tilt of their houses. This
paper reports on survey results collected through questionnaire with interview during consultation
meetings aiming at repairing detached houses damaged by liquefaction, which were held at Mihama
Ward Office, Chiba City. Meeting participants were asked about characteristics of their residence,
seismic damage, health disturbances, disaster awareness, and their communications with housing
suppliers when purchasing house. A probability model of heath disturbance occurrence in terms of the
maximum tilt angle of a house due to liquefaction is presented based on the survey data.

OUTLINE AND RESULTS OF QUESTIONNAIRE SURVEY
Outline of questionnaire survey
This investigation was carried out through questionnaire survey interview in four sessions at
previously cited meeting place. At the dates of August 20, 21, 27 and 28, 2011, we interviewed 26, 12,
17 and 13 households, respectively. In total, 68 households responded to us, but one household did not
suffer liquefaction damage. Thus, the target of the analysis is 67 households composed of 80 persons(42 men and 38 women). Note that all the households were owner-occupiers.
Specification of houses
Fig. 1 shows the distribution of structural types of their houses; 41 (61%) houses were built of timber
framework and 8 (19%) houses light-gauge steel. Next, Fig. 2 shows the distribution of construction
year. There were not a small number of relatively newly built houses, which had been replaced oldhouses due to deterioration with age or change of an owner. Then, 22% of houses, which wereconstructed from 1971 to 1980, conformed to old standards of earthquake resistance; in 1981, theBuilding Standard Law of Japan had major amendment with respect to earthquake resistance. It should
be noted that 24 out of the 67 houses (36%) were made alteration or enlargement after construction by
their owner.
timber framework structure
RC structureothertimber 2×4 and woody panel structure
light‐gauge steel structure

41
0%

20%

8
40%

60%

3

13
80%

2
100%

Fig. 1 Distribution of structural types of houses (N = 67)
50%
40%
30%
45%

20%
10%

22%

19%

13%

0%
1971‐1980

1981‐1990

1991‐2000

2001‐2010

Fig. 2 Distribution of construction years (N = 67)872

In terms of a number of stories, 66 houses had two stories, and there was one three-storied house.
Regarding a type of use, 66 out of the 67 houses were exclusively residential dwelling houses, and theother one house was used as both a dwelling and an office.
Among the 67 houses, 36 (54%) were ready-built and 31 (46%) were custom-built. Fig. 3 shows
the distribution of foundation types. A large number, 47 (70%) of houses were built on footing
foundations, and 12 (18%) had mat foundations. Fig. 4 shows the distribution of existence of soil
reinforcement and subsurface exploration; three households (4%) conducted the soil reinforcementand 23 (34%) conducted subsurface exploration. Fig. 5 shows the number of households who
conducted subsurface exploration according to the construction years of their houses; the percentage
of conducting subsurface exploration is high for the houses built after 2001.
mat foundationtotal

footing foundation

pile foundation

12

custom‐built houseready‐built
house

unclear

47
8

0%

3 4 1

18

4

other

2

29
20%

40%

3 0
111

60%

80%

100%

Fig. 3 Distribution of constructional years (N = 67)
conducted
soil
3
reinforcement
subsurface
exploration
0%

23
20%

not conducted

unclear

37

27
12
40%

32
60%

80%

100%

Fig. 4 Distribution of existence of soil reinforcement and subsurface exploration (N = 67)8
conducted

7

not conductedhouseholds

6

unclear

5
4
3
2
1
0

1970 1975 1980 1985 1990 1995 2000 2005 2010

Fig.5 Number of households who conducted subsurface exploration according to the construction
years of their houses (N = 67)
Fig. 6 shows the number of households who received explanations about liquefaction and those about
earthquake resistance; 65 (97%) and 46 (69%) of households did not receive explanations aboutliquefaction and earthquake resistance, respectively. Fig. 7 shows the number of households who wereexplained about earthquake resistance according to the construction year of their houses; the873respondent households living in newly built houses tend to have received explanations about
earthquake resistance.
none
earthquake
protection

housing supplierarchitect

other

65

liquefaction

20

46
0%

20%

40%

60%

16

3 2

80%

100%

Fig.6 Distribution of existence of explanations about liquefaction and earthquake resistance (N = 67)
8
housing supplierarchitectnone
unclear7

households

6
5
4
3
2
1
0

1970 1975 1980 1985 1990 1995 2000 2005 2010

Fig.7 Number of households who were explained about earthquake resistance according to theconstruction years of their houses (N = 67)
Seismic damage
Here the situation of seismic damage to their detached houses is discussed. Fig. 8 shows the
distribution of damage certificates issued by the local government, Chiba City; 37 (55%) houses were
judged as partially destroyed, and there was no completely destroyed house. Fig. 9 shows the
distribution of damage ranks evaluated by insurance companies; 37 (55%) households weresubscribers of earthquake insurance, and 22 were judged as half loss and 10 as the complete loss.
no damagehalf collapse
not yet investigatedtotal 1

partially destroyed
partially destroyed with major damage37

10

footing foundation 1 4
mat foundation 0
0%

28

15

4

10

4
2

7

3
20%

40%

60%

80%

100%

Fig. 8 Distribution of damage certificates issued by the local government (N = 67)874

partial loss
total

half loss
4

footing
3
foundation
mat0
foundation
0%

complete loss

not yet investigated

22

10

15

8

4

1 0

20%

40%

1

non subscriber

30
1

20
7

60%

80%

100%

Fig. 9 Distribution of damage level according to earthquake insurance (N = 67)
Next the damage situation is described. Fig. 10 shows the situation of damage to the ground at the sitesof their house. Sand boiling occurred at 64% of the housing lots. Fig. 11 shows the distribution ofexistence of cracks in foundations and outer walls of their houses. There were comparatively morecracks in foundations than cracks in outer walls.
sand boilingcrack of the groundcollapse of fence
tilt of fence
no damage
0%

20%

40%

60%

80%

100%

Fig. 10 Damage to housing lots (N = 67)

foundations

nothing

cracks28

39

outer walls

40
0%

20%

27
40%

60%

80%

100%

Fig. 11 Existence of cracks in foundations or outer walls (N = 67)
Fig. 12 shows the relation between the maximum tilt angles of houses and construction years; these tilt
angles were surveyed by the local government, insurance companies, or home builders. The categoriesof damage certificates are indicated in the right side of the graph. Note that, considering thewide-spread liquefaction damage to houses in the Great East Japan Earthquake Disaster, the tilt of ahouse was additionally considered for the following two categories of damage certificates: Partially destroyed with major damage: equal to or more than 1/60 rad and less than 1/20 rad
 Partially destroyed: equal to or more than 1/100 rad and less than 1/60 rad
The criterion for ‘completely destroyed’ (tilt angle equal to or more than 1/20 rad) had been alreadyconsidered before the disaster. According to the figure, mat foundations were often employed in the
newly built houses; the houses with tilt angle exceeding 1/60 (≒0.017) rad tended to have footing
foundations, but there was no houses with the mat foundations of which tilt angle exceeded 1/60 rad.
Fig. 13 shows the distribution of damages to door fit; 85% of households claimed that they had
inconvenience that a door moved automatically due to tilt of their houses.

875maximum tilt angle [rad]mat foundations
footing foundations
pile foundations
unclearotherexistance of soil reinforcement and subsurface exploration
0.05

completely
destroyed
partially
destroyed
with
major
damage

0.04

0.03

0.02

partially
destroyed

0.01

0
1970

1980

1990
construction year

2000

2010

Fig. 12 Relation between the maximum tilt angles of houses and construction years (N = 64; thenumber of houses of which tilt angle is clarified)metal‐framed glass sliding window
shoji
fusumasliding door
door
no damage
0%

20%

40%

60%

80%

100%

Fig. 13 Distribution to damages of door fit (N = 67)
Health disturbances
In this section, health disturbances of the respondents are discussed. First, Fig. 14 shows the
distribution of age and gender of the respondents. It had a high percentage of senior people in age 60s
and especially women.
Fig. 15 shows the distribution of sensitivity to tilt; among the 80 respondents, 55 (men: 27,
women: 28) were clearly aware of the tilt of their houses. The ratio of the women who felt the tilt
strongly is larger than that of the men; possible explanations were that people who spent long time athouse and practice housework might feel tilt strongly.
Fig. 16 shows the relation between tilt adjustment time and the maximum tilt angle of a house.
The correlation between them is not clear, and the adjustment time seems to differ from one to another.
Fig. 17 shows certain symptoms of health disturbances caused by tilt, which the examinees
experienced between the occurrence of the Great East Japan earthquake and the present survey. There
were some examinees who complained about shoulder stiffness, foot pain, and other healthdisturbances, and some examinee stated that their sick became worse after the earthquake. It should be
noted that the causes of health disturbances could be not only related to the slope of the floor, but also
to the vibration of aftershocks.

876

性別

30s

40s

50s

total

2 6

17

woman

1 2

9

60s

70s

80s or more
3

18

34

1

4

21

gender

man 1
0%

13

8

4

20%

40%

60%

14

2

80%

100%

Fig.14 Distribution of age and gender of the respondents (N = 80)

年齢

not matter

adjusted to tilt

feel tilt

feel terrible tilt

total

25

34

60 or over

17

22

under 60

8

woman

10

10

11

6

10

性別

age

gender

man

12
16

15
0%

4
4

8

18

20%

40%

6

60%

1

80%

3
100%

Fig. 15 Sensitivity to tilt at the time of the survey (N = 80)
tilt adjustment time [day]

150
120
90
60
30
0
0

0.01

0.02
0.03
0.04
maximum tilt angle of a house [rad]0.05

Fig.16 Relation between tilt adjustment time and the maximum tilt angle of a house (N = 25; thenumber of examinees who answered both the maximum tilt angle and the time to adjust to tilt)
30
23

22

20

16
11

10
10

11
6

2

4

7
3

3

0

Fig.17 Health disturbance symptoms related to tilt between the occurrence of the earthquake and thepresent survey (N = 77; the number of examinees who answered the maximum tilt angle)877

As for the 55 examinees who were aware of the tilt, Fig. 18 shows the changes in health condition
between the earthquake occurrence and the present survey. Here also, it seems not possible to establish
a relation between those state changes and age or gender of the examinees.
Fig. 19 shows the existence of the examinees concerned with vertigo when going out of theirhouse; in particular, the women examinees who were in age 60 or over were concerned. There weresome examinees whose symptoms were worsened when they saw tilted power poles or tilted buildings.
Some examinees who got used to the tilt of their house felt that the outside world was leaning.

年齢

same as before

improved

total

20

60 or over12

adjustedworsened

14

18

9

3

14

3

age

性別

under 60

8

woman

5

9

8

4

0

9

2

gender

man

11
0%

6

20%

40%

60%

9

1

80%

100%

Fig. 18 Evolution of health state between the occurrence of the earthquake and the present survey (N =55; the number of examinees who were aware of the tilt)
nothing

vertigo性別

total

gender

37

woman

15

年齢

man

傾きに

13
22

60 or over

5
15

23

age

sensitivity
to tilt

18

under 60

143

felt badly tilt

65felt tilt

6

4adjusted to tilt

9

25
0%

20%

40%

60%

80%

100%

Fig. 19 Vertigo feeling when going out (N = 55; the number of examinees who were aware of the tilt)

HEALTH DISTURBANCE MODEL
The logarithmic probit models of health disturbances are constructed, in terms of the maximum tilt
angle of a house due to liquefaction. In the present survey, the data of the 77 examinees who replied
about the tilt angle are available. In order to complement this data, the data of past literature are also
considered. Figs. 20 and 21 show the survey results in Kitahara and Uno (1965) and Uno and Endo
(1996), respectively; Kitahara and Uno (1965) surveyed 66 persons and Uno and Endo (1996)
surveyed 42 persons.
Since the vertigo, headache, and insomnia symptoms were included in the data of all the above
three surveys, we focus on these three symptoms. The symptoms: feeling of rolling, feeling of waftage,878

wooziness, and vertigo in the data of the present survey and the survey in Uno and Endo (1996) are
categorized into “vertigo”, and they are aggregated with the survey data in Kitahara and Uno (1965).
To use the survey data of the past studies, the range of the tilt angles in degrees has been transformed
into median values of the intervals to obtain tilt angles in radians.
The maximum likelihood method is employed to construct the models, and models based only on
the present survey are compared with those based on all the three surveys. The parameters of theresulting models are presented in Table 1. Figs. 22-24 represent the models for vertigo, headache, andinsomnia, respectively. In the figures, points on 0% and 100% lines show data about respectively theabsence or the presence of the symptom in the above three survey data.
40
31

31

30

10

18

17

20

13

10

7

2

2

3

0

Fig. 20 Symptoms of health disturbances in Kitahara and Uno (1965) survey (N = 66)
40
38
30
21
20
10

11

9
3

3

3

2

3

0

Fig. 21 Symptoms of health disturbances in Uno and Endo (1996) survey (N = 42)
Table 1 Parameters of health disturbance models
Data
The present
surveyAll the threesurveysSymptoms

Logarithmic
meanMedian[rad]

VertigoHeadache
Insomnia
VertigoHeadache
Insomnia

–4.05
–3.26
–3.45
–3.23
–2.76
–1.58

0.01750.03850.03160.03950.06350.207

879

Logarithmic
standard
deviation
0.845
0.638
1.08
1.57
1.00
2.38

1
model based on this survey data

occurrence probability

0.9
0.8

model based on all surveys data

0.7
0.6

presence / absence in Kitahara
and Uno (1965) survey

0.5
0.4

presence / absence in Uno andEndo (1996) survey

0.3
0.2

presence / absence during in thissurvey

0.1
0
0

0.05
0.1
maximum tilt angle of a house [rad]0.15

Fig. 22 Occurrence probability model of vertigo in terms of the maximum tilt angle of a house1
model based on this survey data

occurrence probability

0.9
0.8

model based on all surveys data

0.7
0.6

presence / absence in Kitahara
and Uno (1965) survey

0.5
0.4

presence / absence in Uno andEndo (1996) survey

0.3
0.2

presence / absence during in thissurvey

0.1
0
0

0.05
0.1
maximum tilt angle of a house [rad]0.15

Fig. 23 Occurrence probability model of headache in terms of the maximum tilt angle of a house1
model based on this survey data

occurrence probability

0.9
0.8

model based on all surveys data

0.7
0.6

presence / absence in Kitahara
and Uno (1965) survey

0.5
0.4

presence / absence in Uno andEndo (1996) survey

0.3
0.2

presence / absence during in thissurvey

0.1
0
0

0.05
0.1
maximum tilt angle of a house [rad]0.15

Fig. 24 Occurrence probability model of insomnia in terms of the maximum tilt angle of a house880

It is observed that, in the models constructed from the data of the present survey, the number of people
who complain about health disturbances increases rapidly when the tilt angle exceeds 1/100 rad. The
curves based only on the resent survey are rather different from those constructed from the threesurvey data. The main reason of this difference is probably related to the span of age and gender of theexaminee as well as the span of the tilt angles; in the present survey, majority of the data areconcerning relatively small tilt angles compared with the survey of the past literatures.

CONCLUSIONSA questionnaire survey was conducted through a interview to liquefaction victims of the 2011 Great
East Japan earthquake, who lived in Mihama Ward, Chiba City. Based on the survey data, thelogarithmic probit models of health disturbances, i.e. vertigo, headache, and insomnia, wereconstructed, in terms of the maximum tilt angle of a house due to liquefaction. In the present survey,
the data of the 77 examinees who replied about the tilt angle were available.
In order to complement this data, the data of past literature, Kitahara and Uno (1965) and Uno andEndo (1996), were also considered; the data of 66 and 42 persons were available in these two surveys,
respectively. It is suggested that the tilt angle exceeding approximately 1/100 rad cause healthdisturbances. However, as the deviation of this tendency is not negligible, it is important even if the
maximum tilt angle is smaller than 1/100 rad to investigate conscientiously all the households toprevent health inconveniences.
The challenge for the future is to improve the reliability of the probability model to increase theconfidence of the final results. In addition, as the age of the respondents in Kitahara and Uno (1965)
are unclear, those in Uno and Endo (1996) are women between the age of 18 and 27, and those in thepresent survey are men and women of age 30 or over, a survey concerning a young adult segment, i.e.
less than 17 years and more particularly children, is expected.

ACKNOWLEDGMENTS
We thank residents in Mihama Ward, Chiba City for their kind cooperation to this research. We also
thank the Building Maintenance Division, Building Department, City Planning Bureau, the City of
Chiba, Japan Structural Consultants Association (JSCA) Chiba, and the counseling staff of theconsultation meeting for repairing houses damaged due to liquefaction, who cooperate with us,providing a valuable support.

REFERENCES
Endo, Y. and Uno, H. (1981). “A Study on the Sense of Equilibrium of Man: The Case of Sloping
Floor.” Summaries of Technical Papers of Annual Meeting Architectural Institute of Japan, Vol.
Architecture and Planning, 1237-1238. (in Japanese)Endo, Y. and Uno, H. (1982). “A Study on the Sense of Equilibrium of Man: The Case of Sloping
Window Frame.” Summaries of Technical Papers of Annual Meeting Architectural Institute ofJapan, Vol. Architecture and Planning, 1465-1466. (in Japanese)
Fujii, M., Ijuin, H., Tamura, M., and Ina, K. (1998). “Damage and Restoration of Foundation forHouses in Liquefied Areas by the Hyogo-ken Nanbu Earthquake: Concept for Restoration ofFoundation for Houses.” Soil Mechanics and Foundation Engineering, Vol. 46, No. 7, 9-12. (inJapanese)
Kitahara, M. and Uno, R. (1965). “Dizziness and Balance in the Sloping Room: Survey of Buildings
Tilted by the Niigata Earthquake.” (title translated by the authors) Practica oto-rhino-laryngologica,Vol. 58, No. 3, 145-151. (in Japanese)
Uno, H. and Endo, Y. (1996). “A Study on the Sense of Equilibrium of Man: The Threshold Value of881

the Sense of Equilibrium on Sloping Floors.” Journal of Architecture, Planning and Environmental
Engineering (Transactions of AIJ), No. 490, 119-125. (in Japanese)
Yasuda, S. and Hashimoto, T. (2002). “Liquefaction-Induced Settlements of Houses During theWestern Tottori Prefecture Earthquake.” (title translated by the authors) Proceedings of the 57th
Annual Conference of the Japan Society of Civil Engineers, 1029-1030. (in Japanese)
Yasuda, S. (2004). “Damage of Housing Estate Due to the Western Tottori Prefecture Earthquake.”(title translated by the authors) Sougou-Ronbun-Shi (New Frontiers in Architecture for Damage
Mitigation and Recovery from Disasters), Architectural Institute of Japan, Vol. 2, 45-46. (inJapanese)882