Journal of Natural Disaster Science, Volume 28, Number 1, 2006, pp15-24

Investigation of Human Injuries during the July 26, 2003 Northern Miyagi Earthquakewith Focus on Furniture Overturning
Takeshi SATO1, Masato MOTOSAKA1 and Akira MANO1
Disaster Control Research Center, Tohoku University, Japan

1(Received for, 12, May, 2006 and in revised from 22, Aug., 2006)

ABSTRACTIn the morning of 26 July 2003, a powerful shallow inland earthquake of Magnitude 6.4 on the JMA scaleoccurred in northern Miyagi Prefecture, Japan. Severe damage was concentrated in several towns around the epicenter because of the medium-sized earthquake, shallow focus and high frequency predominance. The
Architectural Institute of Japan (AIJ), dispatched members of the technical working group to investigate the earthquake damage and learn lessons from the disaster.
We analyzed the results of the investigation regarding (1) human injuries, the causes and distribution; (2) estimation of furniture overturning; (3) relationship between structural damage and overturning damage of furniturein buildings; (4) relationship between the furniture overturning ratio and the following preparedness ratio basedon a follow-up survey in the focal area.
The potential for human injury in earthquakes is increasing due to urbanization, high rise buildings and theaging of society.

1. INTRODUCTION
A powerful shallow inland earthquake of magnitude
Mj=6.4(JMA scale) occurred at 7:13 JST on 26 July, 2003 innorthern Miyagi Prefecture, Japan (2003 Northern Miyagi
Earthquake). The epicenter was located at a depth of 12 km at
38.40˚ N, 141.17˚ E. On the same day, a foreshock and the largest
aftershock of Mj=5.6 and Mj=5.5 hit the same area at 00:13 JST
and 16:56 JST with epicenters approximately 3 km and 11 km
north of the mainshock respectively. The strongest groundmotions in seismogram history were recorded and very high seismic intensity reaching upper 6 on the JMA scale, which corresponds to about 10 on the MMI scale, were observed at many
earthquake sites.
These earthquakes caused a total of 675 injuries; of which 51
persons were seriously injured. Of the 16,060 houses that weredamaged, 1,276 houses collapsed. Fortunately, no fatalities or
missing persons were reported. According to the Fire and Disaster
Management Agency of the Ministry of Internal Affairs andCommunications, the economic loss was over 32 billion yen. As
the earthquake was medium-sized, with shallow focus and highfrequency predominance serious damage was concentrated in several towns around the epicenter. The disaster relief law wasapplied to five towns: Naruse, Yamoto, Kanan, Nango andKashimadai Town.
Over the last one hundred years, the area has suffered damage
from both inland and oceanic earthquakes. Kagami (2005) reported on the seismological and geological environment in the area

affected by the 2003 Northern Miyagi Earthquake. Inland earthquakes such as the 2003 Northern Miyagi Earthquake occurred in
1962 with Mj=6.5 and in 1900 with Mj=7.0. Plate boundary earthquakes also periodically occurred at an average interval of 37
years. Earthquakes of 7.5 magnitude occurred off Miyagi
Prefecture in 1978, 1936, 1897 etc. The most well-known seismic
disaster is the Off Miyagi Earthquake that occurred in 1978.
Reoccurrence is expected in the near future with extremely highprobability.
The total population of the five towns is approximately
80,000, of which 675 were injured. Most of the injuries occurredin Yamoto Town, which accounts for approximately 70% of thetotal injuries. The ratio of injured people to the population in
Yamoto Town is approximately 1.3%. The high level of injury
was mainly due to the high population concentration and strong
seismic ground motion in this town. Human injury was investigated by NHK: Japan Broadcasting Corporation, IFD: IshinomakiFire Department and the AIJ Investigation Committee. As there
was little information on injuries reported to the Disaster
Countermeasures Headquarters in Miyagi Prefectural Government,
an immediate hearing survey was conducted in hospitals in the
focal area to identify the causes of the injuries. The investigation
showed that more than half of all injuries were caused by overturning furniture and falling objects.
In this study, the earthquake is outlined and human injury due
to overturning furniture is described. Finally, the lessons of theearthquake disaster are highlighted.

KEY WORDS: 2003 Northern Miyagi Earthquake, human injury, furniture overturning, fragility curve, earthquake preparedness

T. SATO, M MOTOSAKA AND A. MANO

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Table 1. Municipal area and population of the five towns*1 The population is estimated based on the resident registers as of the end of June 2003 just before the 2003 Northern Miyagi Earthquake.
*2 The ratio of farmhouses to households is based on the values of the agriculture and forestry industry census in 2000.
*3 The population is based on the final values of the national census in 1975.
*4 Data of the Densely Inhabited District; DID in Sendai City is based on the final values of the national census in 2000.

areas in the five towns are farmland.
The five towns were incorporated with each other by 2006.
Kanan Town was incorporated into Ishinomaki City in April 2005.
Yamoto Town and Naruse Town were combined as the new
Higashi-Matsushima City in April, 2005. Nango Town and theneighboring Kogota Town were combined as the new Misato
Town in January, 2006. Finally, Kashimadai Town was incorporated into Furukawa City and renamed Osaki City in March, 2006.
In this paper, evaluation units before the incorporation are used.
3. STRONG GROUND MOTIONS

Fig. 1

Location map of the area of damage in Miyagi Prefecture(★: epicenter of mainshock)2. REGIONAL CHARACTERISTICS
The five towns affected by the earthquake are located innorthern Miyagi Prefecture (Fig. 1). With numerous clear water
rivers such as the Kitakami River, many marshes and a rich landscape, the region has a beautiful natural environment and the mainindustry is agriculture. The region is affected by earthquakes andflooding.
Social data on the five towns are shown in Table 1 in comparison with Sendai City. Except Yamoto Town, the population density for the municipal area is approximately 200 people per square
kilometer. In Nango and Kanan Town, the occupation of half thehouseholds is farming. Excluding Yamoto Town, the populationof the five towns has been almost unchanged since 1978 at thetime of the Off Miyagi Earthquake. These data show that mostA strong shallow earthquake caused severe damage in theregion near the epicenter affecting Naruse, Yamoto, Kanan, Nango
and Kashimadai Town, where JMA intensity of lower 6 to upper 6
occurred as shown Table 2. The distributions of several strong
ground motions are shown in Fig. 2 (Motosaka and Ohno, 2004).
The strong ground motion was mainly distributed in the region
near the epicenter as shown in Fig. 2 because of the shallow focus
and middle class magnitude. Some large peak ground accelerations were recorded by JMA and local office stations. For example, during the foreshock, Naruse Station at a distance of 3.5 kilometers from the epicenter recorded 2,005 gal as PGA.
Unfortunately, most of the strong ground motion records were lost
because of overwriting by many aftershock data.
We investigated the tombstones, the turnover monuments andthe questionnaire seismic intensity to clarify the earthquake groundmotion characteristics as the AIJ Investigation Committee. The
results of the questionnaire survey on the seismic intensity in the
focal area show that there was an extremely narrow zone reachingan estimated seismic intensity of 7 during the mainshock. The
good relationship between measured and estimated seismic intensities in the focal area was clarified (Ochiai, 2004). The questionnaire survey is effective for evaluating the distribution of not only
ground motion but also damage. The results were used for analyzing furniture overturning and human injury.

INVESTIGATION OF HUMAN INJURIES DURING THE JULY 26, 2003 NORTHERN MIYAGI EARTHQUAKE WITH FOCUS ON FURNITURE OVERTURNING

Table 2.

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List of large amplitude records of five towns(a) Seismic intensity(b) PGA(c) PGV

Fig. 2 Distributions of JMA measured seismic intensity, PGA and PGV during the mainshock

4. STRUCTURAL DAMAGE OF BUILDINGS
4.1 Regional characteristics of building structure
We investigated the building damage in the region as the AIJ
Investigation Committee. The purpose of the investigation was toclarify the relationship between the earthquake ground motion andthe building damage in a statistical way not in individual detail.
Shibayama et al. (2005) reported the results of the damage investigation of buildings by earthquake as the AIJ Investigation
Committee. In the paper, 93% of the investigated buildings wereconstructed of wood. The majority of houses were made of wood
whereas the majority of public facilities were of non-wooden construction. Figure 3 shows the classification by the construction
age of wooden buildings based on the forecast investigation ofearthquake damage by Miyagi Prefecture in 2004. The boundariesof the construction age are set at the time when the seismic designcode of buildings was revised. Buildings before 1981 are an objectof diagnosis for seismic performance in Japan. In the case of thefive towns, wooden structures designed according to the old seismic design code account for approximately 70% in total. Thisvalue is slightly higher than those of Miyagi Prefecture and Sendai
City.
4.2 Outline of statistical analysis
Most of the houses in the area were made of wood. The number of damaged wooden houses of the five towns as investigatedby Miyagi Prefecture is shown in Table 3. Here, we define theFig. 3

Classification by construction age for woodenbuildings

damage ratio of wooden houses as the sum of damaged houses,
including the severely damaged and collapsed houses as one andthe moderately damaged houses as half in the total wooden houses.
The damage ratio was highest in Naruse Town at 16%. The average in the five towns is approximately 8% with considerable deviations. The damage distribution of wooden houses was limited to anarrow area of the five towns in Miyagi Prefecture.
4.3 Typical examples of building damage
Typical examples of building damage are shown in pho-T. SATO, M MOTOSAKA AND A. MANO

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Table 3.

Counts of damaged wooden houses in Miyagi Prefecture (12 March, 2004)*1 Forecast investigation of earthquake damage by Miyagi Prefecture in 2004

Photo. 1 Severely damaged wooden house

Photo. 2

Photo. 3

Photo. 4

Damage of pilotis structure

Non-damaged wooden house

Photo. 5

Fallen concrete block

Collapsed wooden house

Photo. 6

Damage in kitchen

INVESTIGATION OF HUMAN INJURIES DURING THE JULY 26, 2003 NORTHERN MIYAGI EARTHQUAKE WITH FOCUS ON FURNITURE OVERTURNING

Table 4.

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Number of injured persons determined by Miyagi Prefecture (2 March, 2004)*1 Population based on the basic resident register at the end of June 2003.

tographs taken by the authors. A severely damaged old wooden
house is shown in Photo. 1. A wooden house that had been
designed in line with the new seismic code as shown in Photo. 2
incurred no damage even though it was near the house in Photo. 1.
This suggests that the seismic performance differs according to age
and design. Photograph 3 shows a collapsed wooden house constructed in 1920. The light roof of this house had been replacedwith heavy Japanese tiles ‘kawara’ without a seismic retrofit of thestructural frame. The roof fell whilst maintaining the shape.
Structural damage to a wooden house with a soft first story used asa store is shown in Photo. 4.
In the focal area, many concrete and stone walls were damaged. Similar damage occurred as a result of the Off Miyagi
Earthquake in 1978 causing human casualties. A fallen concrete
block wall in a school zone is shown in Photo. 5. At the time thatthe mainshock occurred, most people were assumed to be at home.
The ratio of people usually at home based on a life investigation by
NHK (2000) is approximately 85%. In the focal area, there were
few injuries caused by collapsed block walls. Vulnerable structures should be immediately improved in anticipation of a new off
Miyagi Earthquake.
Photograph 6 taken by NHK shows indoor damage to a
kitchen in Yamoto Town. The mainshock occurred at breakfast
time on Saturday morning, which shows that kitchens as well as
bedrooms and living rooms require earthquake preparedness.
Public buildings are generally constructed as reinforced concrete structures of three or four stories. There was only minor
damage to the reinforced concrete buildings in the region designed
in line with the new seismic code after 1981. Few reinforced concrete buildings designed in line with the old seismic code in thesurrounding regions sustained structural damage. Three reinforced
concrete buildings of particular interest were Hukaya Hospital,
Kitamura Elementary School located in Kanan Town andKashimadai Hospital in Kashimadai Town.
5. HUMAN INJURIES
5.1 Outline of human injuries
The number of persons injured in Miyagi Prefecture is shownin Table 4. As with the concentration of building damage, approximately 90% of injuries were sustained by persons in the fivetowns. The maximum value in the region exceeded 1% in YamotoFig. 4

Relationship between the damaged house
ratio and the human injury ratio

Town. Even in the five towns, the human injury ratio was widelydifferent between Yamoto Town and Kashimadai Town. The seriously injured ratio is defined as the ratio of the seriously injured tothe total number injured. The average of the five towns wasapproximately 7%. Because the value is often taken in the range
from 5% to 10% for earthquake disasters in Japan, a general result
was shown.
The relationship between the damaged house ratio and thehuman injury ratio is shown in Fig. 4 with the empirical line basedon the Hanshin-Awaji Earthquake Disaster in 1995. The present
results correspond closely with those of past earthquake disasters
except for those of Naruse Town. The figure shows the human
injury ratio when the damaged house ratio is used as an indirectindex. The causes of human injury should be noted not only by thedamage to houses.
5.2 Causes of human injury
Immediately after the mainshock, the causes of human injury
were investigated by NHK and IFD. They obtained data by conducting a hearing survey at hospitals in the region. Each area of
the investigation is shown in Fig.5. NHK covered a wide area
including Sendai City, while the survey of IFD was limited to the
management area of Ishinomaki City and nine peripheral towns.
There were no injured persons in Onagawa, Ogatsu, Kitakami and20

T. SATO, M MOTOSAKA AND A. MANO

Fig. 5

Area covered by NHK and IFD

Oshika Town. IFD data was almost perfectly collected in theinvestigation area. However, Nango and Kashimadai Town in thefive towns were not included in the area of IFD. NHK data wascollected from some hospitals in the investigation area.
By using common items in the hearing survey, the distributionof the major causes were plotted as shown in Fig. 6. In the IFD
data, furniture overturning has the largest percentage of 35%.
NHK data shows objects falling to be the highest cause rather thanfurniture overturning because the investigation area of the IFD waslimited to near the focal area. Furniture overturning and objects
falling amount to approximately 50% of the total.
Figure 7 shows injury by age. The young age group is lessthan 15 years old. The middle age group is from 15 to 64 years
old. The old age group is 65 years old or more. In the old age
group, the cause by furniture overturning is dominant with thelargest percentage of 40%. This indicates that improvement of
indoor space by taking measures against falling objects and overturning furniture is the most effective mitigation for human injury
especially for vulnerable people such as the young and the elderly.
The injury ratio by age is shown in Fig. 8. The IFD data on
Yamoto Town was used. The injury ratio increases for older people, reaching 2% for the old age group. This figure also shows theinjury ratio by sex. Females have approximately double the injury
ratio for all age groups. This tendency occurred in other recent
earthquake disasters such as the 2000 Western Tottori Prefecture
Earthquake and the 2001 Geiyo Earthquake (Murakami, 2001).
The ratio of injured humans by age is shown in Fig. 9.
Injuries in the old age group accounts for approximately 40% of
the total. This finding indicates that the aging of society will
increase the vulnerability to human injury.
Most buildings in the focal area have a one or two story
wooden structure because the area is farmland. The seismic
motion of the furniture is almost equal to that of the ground surface. But, in an urban area many people would be exposed to highhazard because of the high story buildings and high risk of furniture overturning.
Figure 10 shows injury causes by sex in the old age group.
Half the number of causes of injury occurred due to furniture overturning and injuring females in the old age group.

Fig. 6

Fig. 7Main causes of injury

Contents of injury causes by age

6. DAMAGE INVESTIGATION OF FURNITURE
OVERTURNING
6.1 Outline of questionnaire survey
Three months after the event, we conducted a questionnaire
survey to determine the seismic intensity and the damage distribu-

INVESTIGATION OF HUMAN INJURIES DURING THE JULY 26, 2003 NORTHERN MIYAGI EARTHQUAKE WITH FOCUS ON FURNITURE OVERTURNING

Fig. 8

Ratio of injury by age

Fig. 9Fig. 1021

Fig. 11

Distribution of furniture overturning ratio

Fig. 12

Fragility curve of furniture overturning

Injury by age

Contents of injury causes by sex in old age

tion with high spatial resolution in the five towns. The survey
method revised by Ota et al. was used (Ohta et al., 1998). The
questionnaire sheets were distributed to 4,000 households having apupil at elementary school. The statistics of the questionnaire survey are shown in Table 5. The effective collection ratio of the survey was approximately 60% in most towns. The sampling ratio,
which is defined as the ratio of the number of effective answers tothat of the total households accounts for approximately 10%. The

evaluation was conducted for each district of the elementary
school.
The distribution of the furniture overturning ratio for each district is shown in Fig. 11. The value is defined as the ratio of thetotal number of house in which furniture overturned to the numberof households in which furniture did not overturn. High numbers
were recorded in Hirobuchi and Nango districts. The maximum
ratio reached 95% in Hirobuchi district. On the other hand, theminimum was 19% in the second Kashimadai district. The ratio
sharply decreases by distance from the epicenter.
6.2 Fragility curve for furniture overturning ratio
The fragility curve for the furniture overturning is shown in
Fig. 12. The seismic intensity evaluated by the questionnaire survey is used as a strong ground motion index. In this figure, theOkada and Kagami’s relationship (1991) is also plotted. The present results agree with the relationship. The range of the estimatedT. SATO, M MOTOSAKA AND A. MANO

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Table 5. Statistics of questionnaire survey*1 Households based on the basic resident register at the end of June 2003.

(a) Structural damage ratio(b) Indoor damage ratio

Fig. 13 Damage ratio distribution of structures and indoors by the age of construction of wooden houses

seismic intensity of 6.5 from 5.5 corresponds with seismic intensity 6 of the JMA scale. In this range, the furniture overturning ratiochanges rapidly.
6.3 Relationship between structural and indoor damage
The relationship between structural and indoor damage wasanalyzed by using the results of the questionnaire survey. The
structural damage classified by the house construction age isshown in Fig. 13 (a). In this figure, “cracked walls” and “fallen
walls” are defined as damage to the nonstructural elements inwooden houses. The “structural damage” shows damage such aslarge movement of the structural frame. Structural damage tended
to be less for houses of newer construction. Indoor damage classified by the house construction age is shown in Fig. 13 (b). The
results of (a) and (b) in Fig. 13 show quite a different tendency.
The indoor damage occurred almost uniformly independent of thehouse construction age. These data together with the previous
observations indicate that in order to mitigate human injury, earthquake preparedness against furniture overturning is necessary evenfor new houses.

ability to earthquake disasters in the focal area. The state of
improvement of building structures, and exterior and indoor spaces
was investigated by a hearing survey of the households in theregion in addition to the questionnaire survey. The results of furniture overturning are shown in Table 6 and Fig. 14. The ratio ofearthquake preparedness to prevent furniture overturning reached
25% at maximum before the event. The average in the region wasapproximately 18% with considerable derivation. In Fig. 14, theearthquake preparedness ratio summed up before and after the
event is proportional to the furniture overturning ratio. The earthquake preparedness of the region where the furniture overturning
ratio was lower had not improved even in the five towns.
This finding suggests that the influence of the disaster lesson
decreases according to the distance from the focal area.
Administrators and mass communication frequently reminded citizens of the necessity of earthquake preparedness to mitigate human
injury caused by furniture overturning, but the effects are insufficient. Interactive risk communication with the residents may be
more effective.
7. DISCUSSION

6.4 Investigation for improvement of vulnerability
One year after the event, we investigated the change in vulner-

The epicenter was approximately 40 km distant from Sendai

INVESTIGATION OF HUMAN INJURIES DURING THE JULY 26, 2003 NORTHERN MIYAGI EARTHQUAKE WITH FOCUS ON FURNITURE OVERTURNING

Table 6.

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Statistics of hearing survey of earthquake preparedness ratio

ing tends to decrease, because the building structures have beenstrengthened through revision of the building code. The potential
for human injury is increasing in urban areas such as Sendai City.
8. CONCLUSIONS

Fig. 14 Relationship between furniture overturning ratio and preparedness one
year after the event

City. Sendai City is the biggest city in Tohoku district with a population of one million. The damage to Sendai City was negligible
during the 2003 Northern Miyagi Earthquake, because the maximum seismic intensity in Sendai City was lower than 5 on the
JMA scale.
In the case of a densely inhabited districts in Sendai City, thepopulation has increased more than 50% since the previous Off
Miyagi Earthquake in 1978. But the lessons of the 2003 Northern
Miyagi earthquake are extremely valuable when determining disaster measures for the next off Miyagi earthquake in Sendai City.
Even if the next of Miyagi earthquake is similar to the previous
earthquake in 1978, the situation of earthquake damage due tochanges in the social environment between periodically repeatedtimes is very different. For example, the number of households in
Sendai City doubled since the previous earthquake, which occurred
28 years ago. There were only about 50 apartment buildings ofmore than 10 stories in Sendai City in 1978. Now there are tentimes as many of such buildings. The number of people exposed
to high hazard such as the strong floor response in an indoor space
has increased. Human injury due to structural damage to the build-

The main conclusions obtained are as follows.
(1) The 2003 Northern Miyagi Earthquake was outlined and sometypical examples were shown.
(2) The causes of human injury and the age and sex ratios wereanalyzed based on data from five towns as the focal area. The
results show that furniture overturning is the main cause of
injury.
(3) The furniture overturning ratio based on the questionnaire survey was evaluated. The present results agree with past relationships.
(4) Indoor damage occurred almost uniformly independent of theconstruction age. These data together with the previous datasuggest that for the mitigation of human injury, earthquake
preparedness against furniture overturning is necessary evenfor new houses.
(5) One year after the event, the results of the hearing survey
show that the earthquake preparedness of regions where thefurniture overturning ratio was lower has not improved evenin the five towns.
(6) The potential for human injury caused by furniture overturning is increasing because the population exposed to high hazard such as the strong floor response in indoor spaces has
increased.
ACKNOWLEDGMENTS
We thank the members of the technical working group of the
Earthquake Disaster Investigation Committee, the chairman ofwhich is Prof. S. Otani, Chiba University, of the Architectural
Institution of Japan for the helpful discussions. We were supported during this work by Prof. S. Masuda and Lecturer Y. Murayama
of Tohoku University and Mr. A. Shibayama of Kogakuin
University. The assistance of the students of the Graduate Schoolof Science, Engineering and Economics of Tohoku University andT. SATO, M MOTOSAKA AND A. MANO

24

Kogakuin University in the fieldwork is also appreciated. This
work was supported by a Grant-in Aid for Scientific Research,
No.15800009, from the Japanese Ministry of Education, Science,Sports and Culture.
We are grateful to NHK Sendai Station and Ishinomaki Fire
Department for providing the statistical data used in this study.
Finally, we thank the following organizations for their supportin executing the questionnaire survey. The board of education of
Miyagi Prefectural Government and the five towns, 20 elementary
schools in the five towns and all residents who cooperated with ourinvestigation.
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