DAMAGE PROPAGATION CAUSED BY
INTERDEPENDENCY AMONG CRITICALINFRASTRUCTURES
Yozo GOTO1, Takeyasu SUZUKI2, Iwao SUETOMI3, Yasuhiro SHOJI4,
Mai TSURUTA4, Shojiro KATAOKA4 and Hikari SUZUKI5
1

Environment and Disaster Research Institute, Fuji Tokoha University a.p.
National Research Institute for Earth Science and Disaster Prevention
2
Graduate Schools of Medicine and Engineering, Yamanashi University
3
Department of Research Engineering, Japan Engineering Consultants Co., Ltd
4
Earthquake Disaster Prevention Division, National Institute for Land andInfrastructure Management, Ministry of Land, Infrastructure and Transport
5
Environment and Disaster Division, Tokyo Office, Mikuniya Corporation

ABSTRACTInterdependency among critical infrastructures such as electric power, water, gas, transportation,
telecommunication, finance, medical services, administrative services, etc. is investigated from pastdisasters, sorted out as matrices and analyzed by FTAs and influence diagrams. Next, a propagation
model is developed using interdependency structure matrices. Then, the influence of theinterdependency is surveyed quantitatively through a case study of an anticipated earthquake disaster in
the Tokyo metropolitan area. The results show that almost all the infrastructures are interdependent,
and electric power, telecommunications, and highway systems have a greater influence on otherinfrastructures. Furthermore, active utilization of cellular-phone mail, car-navigation systems, marinetransportation, air transportation and pre-agreement with related organizations are found to be effective
for quick restoration.
KEYWORDS
interdependency, infrastructure, disaster, mitigation, earthquake, flood, FTA, influence diagram

INTRODUCTION
Our everyday lives and industrial activity are supported by various infrastructures such as roads,

railroads, electric power, gas, water, sewerage, and telecommunications. Various infrastructures,
especially in urban areas, are highly complex. If a large-scale disaster such as an earthquake occurs insuch areas, each infrastructure is damaged not only by the disaster itself, but also by damage tointerdependent infrastructures. These kinds of damage propagate to one another and affect society andeconomic activities that support urban functions, possibly leading to enormous social loss.
For example, in the Kobe Earthquake in 1995, traffic congestion caused by paralysis of signals, etc. andbreakage of lifelines caused by bridge collapses seriously hampered the emergency functions of
hospitals, administrative services, etc. This showed the need for a well prepared recovery strategy thattakes into account the damage propagation structure among interdependent infrastructures in a massive
urban disaster.
Existing researches on the damage propagation structure and its effects in Japan include fundamental
research by Nojima (1988), et al.; and Kameda (1992), et al.; research on the propagation structure by
Katayama (1989), Sato, et al.; research on the influence of a massive blackout accompanying a typhoonby Katayama (1992), Yamasaki, et al; research on the earthquake disaster propagation structure in urban
areas by Kawashima (1993), et al.; Otsuka (1996), et al.; and investigation reports on the interaction
among cases of lifeline damage during the Great Hanshin Earthquake by Nojima (1996), et al.; andKameda (1997), et al.;. However, there has been insufficient research on practical countermeasures todamage propagation resulting from the deepening interdependency among today's urban infrastructures,and on the effect of the rapid development of information-and-telecommunications.
Goto (2007), et al. of the Kawasaki Laboratory of the National Research Institute for Earth Science andDisaster Prevention (this laboratory was closed in March 31, 2007) and the Earthquake Disaster
Prevention Division of the National Institute for Land and Infrastructure Management cooperated ininvestigating the details of damage propagation among infrastructures during recent disasters. They
analyzed the damage propagation structure of today’ urban infrastructures, estimated the effect of theinterdependency quantitatively through a case study, and investigated mitigation measures. This paper
reports these results.
Here, the authors would like to express their appreciation for the advice of the Investigative
Commission, which consisted of Professor Fumio Yamazaki of Chiba University, Professor Tadanobu
Sato of Kobe Gakuin University, Professor Nobuoto Nojima of Gifu University, professionals of
lifeline companies, etc.

SURVEY OF DAMAGE PROPAGATION DURING RECENT DISASTERS
Actual examples of damage propagation among critical infrastructures during recent earthquake andheavy rain disasters were investigated. Overseas examples of disasters that may happen in Japan werealso checked. Here, the critical infrastructures comprise "electric power", "gas", "waterworks", "sewer","information-and-telecommunications", "road", "railroad", "port", "airport" and "social functions" suchas "transportation and physical distribution", "passenger services", "finance", "medical treatment", and"administration (including police and fire-fighting )."Damage Propagation Examples in Earthquake Disaster
Examples of damage propagation during the Kobe Earthquake (January, 1995) and the Niigata Chuetsu
Earthquake (October, 2004) were investigated. Information was obtained from literature on both
earthquakes and from hearing investigations on the Niigata Chuetsu Earthquake. 10 business units ofcritical infrastructures in Niigata prefecture were visited in the end of November, 2006.
The investigation items were as shown below.

(1) Influence from other infrastructures that suffered a great deal of damage(2) Action taken to prevent damage propagation to other infrastructures(3) Prior measures whose effectiveness was verified(4) Measures that other infrastructures need to take(5) Foreseeable damage propagation in mega cities
The results of the investigation are outlined as follows.
The effects of damage propagation were identified. However, emergency response and restoration
activities by each infrastructure organization generally functioned effectively. For example, althoughalmost all business places were equipped with a backup power supply, there were problems withtransportation for refueling operations. Moreover, cooperation among infrastructure organizations
through regional liaison council did not function effectively during the restoration activities.
There were 127 actual examples of damage propagation extracted from the literature on the Kobe
Earthquake. There were 89 such examples for the Niigata Chuetsu Earthquake, including hearing
investigation results. The collected examples were classified into damage propagation from otherinfrastructures (terminal) and damage propagation to other infrastructures (origin), as shown in Table 1.
TABLE 1
Number of Actual Examples of Disaster Propagation

Electric power
Gas
Waterworks
Sewer
Information-andtelecommunications
Road
RailroadPort
AirportTransportation and Physicaldistribution, Passenger service
Finance
Medical treatment
Administration including
Police and Fire-fighting

Great Kobe
Earthquake

Niigata Chuetsu
Earthquake

Heavy Rain &SnowfallFrom others To others(Terminal) (Origin)

From others To others(Terminal)(Origin)

From others To others(Terminal) (Origin)

6
13
8
16

21
2
16
1

8
6
6
12

29
1
7
4

1
1
4
2

14
0
0
2

15

18

12

16

5

7

7
8
4
0

38
22
4
0

14
9
0
0

24
6
0
0

2
2
0
0

13
0
0
0

13

1

9

0

7

0

11
15

0
0

0
8

0
0

1
3

0
0

11

4

5

2

9

1

In the Kobe Earthquake, there were many examples of propagation from electric power, road, andrailroad to other infrastructures. Conversely, there were many examples of propagation to gas andsewer from other infrastructures.
In the Niigata Chuetsu Earthquake, there were many examples of propagation from electric power androad to other infrastructures, and many examples of propagation to gas and sewer from otherinfrastructures, as in the case of the Kobe Earthquake. However, there were very few examples ofdamage propagation from railroad to other infrastructures. This clearly showed the dependence on roadtraffic in the mountainous area of Niigata Chuetsu.
In
bothearthquakes,
there
were
many
examplesoftheinfluenceof
information-and-telecommunications on other infrastructures. However, in the Niigata Chuetsu

Earthquake, there were many examples involving cellular phones, thus reflecting the rapid change in
the information-and-telecommunications environment since the Kobe Earthquake.
Damage Propagation Examples in Heavy Rain and Heavy Snowfall Disaster
Damage propagation was also investigated in the disasters of the Fukuoka flood (June, 1999), Tokai
heavy rain (September, 2000), Fukushima and Niigata heavy rain (July, 2004), typhoon No.16 (August,2004), typhoon No.23 (October 2004), and the 2004 heavy snowfall. The information was obtained
from the literature. As the result, 37 examples of damage propagation were acquired. These examples
are also shown in Table 1.
As for the earthquakes, there were many cases of propagation of electric power and road to otherinfrastructures. However, there were many stoppages of electric equipment and apparatuses due tosubmersion in water, which does not generally occur in seismic hazards.
Overseas Damage Propagation Example
A massive power blackout occurred in northeastern North America, including parts of the United States
and Canada, in August, 2003, and Hurricane Katrina struck the southern United States in August, 2005.
These events were investigated to study actual examples of damage propagation among criticalinfrastructures and to examine the possibility of similar events occurring in Japan.
The investigation comprised a study of the literature, and news stories were also investigated fromwebsites as a supplement. 21 examples were acquired from the northeastern North America power
failure, and 12 were acquired from Hurricane Katrina. The "origin infrastructure" and the "terminal
infrastructure" were obtained for each example. They were then classified according to their occurrence
probability in Japan under three categories: "unlikely to occur in Japan", "similar examples occurred inJapan" and "could occur in Japan, but no examples seen up to now".
The following six examples fell into the "could occur in Japan" class.
[Electric power to Road] Street tunnel closed due to stop of ventilator caused by power failure[Electric power to Aviation] Airport closed due to power failure[Electric power to Administration] Impossible to use cameras and various electronic bulletin boards,
thus hampering information gathering and dissemination.
[Waterworks to Medical treatment] Dialysis treatment difficult due to low water pressure.
[Waterworks to Administration] Fire-fighting hampered by low water pressure.
[Information-and-telecommunications to Administration] Trouble extends to communication withoutside.

ANALYSIS OF DAMAGE PROPAGATION STRUCTURE
Arrangement of Damage Interdependency Matrix
The collected damage propagation examples were arranged in matrix form. The infrastructure thatcauses damage to others (origin), and the infrastructure that suffers damage from others (terminal) wereallotted to a sequence and, respectively. This matrix is called “damage interdependency matrix”. It was
divided into three phases: "damage propagation immediately after disaster", "damage propagation in
emergency response activity", and "damage interdependency influence in restoration work".
Addition to and reexamination of the initial damage interdependency matrix were performed throughbrainstorming by the Investigative Commission imagining a disaster caused by a Tokyo metropolitan

near-field earthquake. Furthermore, experts of the relevant infrastructure organizations checked andadded items through weighting evaluation work, discussed below. Thus, the final damage
interdependency matrix was created, as shown in Table 2 – Table 4. These tables omit description ofeach element due to space limitation, and existence of interdependence is shown by hatching.
The "damage propagation immediately after disaster" matrix shows that the origin infrastructures in theorder of electric power, road, information-and-telecommunications and gas influence many otherinfrastructures. Some actual examples of damage propagation in a mega-city are "damage to telegraphpoles and electric wires due to building-collapse", "communication obstacle by two or more place
cutting of a multiplex circuit", "stop of stock market due to damage to network infrastructure", etc.
The "damage propagation in emergency response activity" matrix shows that roads have the greatest
influence on other infrastructures, and that information-and-telecommunications has thesecond-greatest influence The "damage interdependency influence in restoration work" matrix also
shows that roads and information-and-telecommunications influence other infrastructures in many
ways.
Among the collected examples arranged into these matrices, "road block by collapse of buildings","shortage of space for restoration work base because of school grounds being occupied by temporary
houses", etc. are noted as examples in which confined space affects restoration works, and the scarcity
of unused lands in the mega cities in Japan is a problem.

Table 2
Damage Propagation Immediately after Disaster
OriginTerminal
Electric power
Gas
Waterworks
Sewer
Information &Telecom.
Road
RailroadPort
AirportTransportation
Finance
Medicaltreatment
Administration

Electric
power

Gas

Water

Sewer

I.& T.

Road Railroad

Port

AirportTransMedical Adminporta- Finance treatistration
Ment
tion

Table 3
Damage Propagation in Emergency Response Activity
OriginTerminal
Electric power

Electric
power

Gas

Water

Sewer

I.& T.

Road Railroad

Port

AirportTransMedical Adminporta- Finance treatistration
Ment
tion

Gas
Waterworks
Sewer
Information &Telecom.
Road
RailroadPort
AirportTransportation
Finance
Medicaltreatment
Administration

Table 4
Damage Interdependency Influence in Restoration Work
OriginTerminal
Electric power

Electric
power

Gas

Water

Sewer

I.& T.

Road Railroad

Port

AirportTransMedical Adminporta- Finance treatistration
ment
tion

Gas
Waterworks
Sewer
Information &Telecom.
Road
RailroadPort
AirportTransportation
Finance
Medicaltreatment
Administration

Analysis by FTAs
The micro propagation structure was analyzed by using FTAs (Fault Tree Analysis). Typical FTAs areshown in Figure 1 and Figure 2. It is shown out that gas influences the water examination andinformation-and-telecommunications influences system control of the sewer function. It is also shownthat waterworks influences many hospital functions. If the patient-conveyance function is included,road and telecommunication also influence hospital functions.

下 水of
道 sewage
機 能 の 支 disposal
障TroubleDamage of sewer
functionTransportationof
汚 泥 の 輸 送 delay
遅 延
sludgePump stop

下 水 道 管 路 の 損 傷

ポ ン プ の 停 止

制 御 シ ステ ム のstop
停 止ControlsystemStop of water
examination

用 水 の of不 足
Shortagewater

水 質 検 査 の 停 止

電 力Electric
Power

都 市 ガ スGas

上 水 道
Waterworks

情 報 通 信Informationand telecommunication

道 路
Road

鉄 道
Railroad

Figure 1: FTA for sewage disposal

病 院 decline
機 能 の 低 of
下 hospital
Functional

医 薬 品 ofの 不足Shortage
medicalTroubleof hemodialysis,
人 工 透 析 ・輸 血 治 療
等 の支 障transfusion
treatment,etc..

医 療 用 水不 足
Shortageofのmedical

病 院of
給food
食 の supply
停 止
Stop

エ レ ベ ー ター の 停 止

Stop of elevator

電 力Electric
Power

都 市 ガ スGas

上 水 道
Waterworks

道 路
Road

Figure 2: FTA for hospital function

ボ イ ラー の 停 止

Stop of boiler

Analysis by Influence Diagram
The mechanism of damage propagation currently written in the damage interdependency matrix can be
typified as physical damage propagation, functional damage propagation and restoration trouble.
Functional damage propagation has the feature of having time and spatial spread of influence andphysical damage propagation generates physical functional damage immediately after a disaster.
Restoration trouble affects the time during which restoration takes. These three damage connection
relations were analyzed by influence diagrams (influence charts), which show the many infrastructuresas origin points or terminal points of influence.
In the influence diagram, the influence relations between infrastructures are connected by arrows. An
infrastructure is expressed as a node, and influence relations are expressed as effective arcs. The resultof the analysis on the Kobe Earthquake is shown with nine infrastructures other than social functions inFigure 3 to Figure 5.
In physical damage propagation, road and railroad act as an origin point and affect other infrastructures.
However, electric power is an origin point of many arcs in functional damage propagation. Moreover,for restoration trouble, road and information-and-telecommunications are the origins of many arcs.

Road

Road
Rail R.

Power

Rail R.

Power

Port

Port

Air P.

Gas

Air P.

Gas

Water

Water

Telecom.

Telecom.
Sewer

Sewer

Figure 4: Influence diagram of
Functional Damage Propagation

Figure 3: Influence diagram of
Physical Damage Propagation
Road

Rail R.

Power

Port

Air P.

Gas

Water
Telecom.
Sewer

Figure 5: Influence diagram of
Restoration TroubleIt is characteristic that roads are not origin points in functional damage propagation. However, forphysical damage propagation and restoration trouble, roads are origins of interdependence of many
infrastructures. They are connected with almost all infrastructures, especially for restoration trouble.
So,it is suggested that the functional recovery of roads will greatly affect the progress of restoration ofother infrastructures. Meanwhile, there is little that makes roads terminal points, i.e., roads rarely
receive damage propagation from other infrastructures.
Speaking about road more, as it is mainly the origins in the physical damage propagation and therestoration trouble, a prior measure not generating physical damage propagation and recovering its ownfunction promptly after damage would lead to early restoration of other infrastructures in considerable
extents.
QUANTITATIVE EVALUATION OF DAMAGE PROPAGATION
Based on the damage propagation structure analyzed above, a quantitative method for evaluating
damage propagation between infrastructures was developed. A case study assuming a disaster caused
by a Tokyo metropolitan near-field earthquake was then performed, and the influence of infrastructureinterdependency was discussed basing on this evaluation.
Fundamental Consideration
Damage expansion due to damage propagation between infrastructures starts from the moment of adisaster occurrence and continues for several days to several weeks, depending on the size of thedisaster. Moreover, restoration problems resulting from damage to other infrastructures may occur
during restoration work. Damage expansion and restoration problems also result from infrastructureinterdependency, and accumulate with time. A model containing a time concept, like a system
dynamics model, is needed to estimate this cumulative increase. In this study, however, the total
damage caused by the interdependency was estimated simply, in snapshot form one day, one week andone month after a disaster occurrence.
The socio-economical damage increased by damage propagation between infrastructures can be
expressed conceptually by the following formula.
TSI:
Socio-economical damage due to damage
propagation among infrastructures

X

FD:
Functional deficiency degree
when damage occurs to
infrastructure

=

X

SI:
Socio-economical
damage factor

RD:
Rate of damage occurrence
when damage to otherinfrastructures influences theinfrastructure concerned

X

X:
Initial damage ofeach infrastructureThis study, taking into account the interdependency influence, we evaluated the functional damage toeach infrastructure, namely, FD x RD x X, when the origin infrastructure suffered a great deal ofphysical damage due to the earthquake. However, the TSI and the SI were not investigated. They arereserved as a future research tasks.
In the case study, the damage propagation modeling (the formula (1)) expressed in matrix form wasused. Here, the input vector X is the initial damage to each infrastructure, and the interdependency

structure matrix C (FDij x RDij) denotes the greatness of the influence of damage propagation among
infrastructures.
Output (damage due to firstcycle damage propagation) Y

Interdependency
structure matrix C

Input (initial damage) X

c11
c21

c12
c22

x1
x2

.
.

...
...

cm1

cm2

?

∑ xjcj1
j?

∑ xjcj2
j

.
.

=

?

∑ xjcjm

...
...
...
...
...

c1n
c2n

--- (1)... . .
...
.
xn
c mn

j

In addition, if there is no change in interdependency structure, the damage due to multi-cycle damage
propagation can be obtained from formula (2).
Yk: Damage due to k-th cycle damage propagation?

yk = ∑ CkX--- (2)?

Evaluation of Input Vector X
The input vector X was evaluated assuming a Tokyo metropolitan near-field earthquake. Each elementof the input vector was set into "outage rate" (1- "supply rate") of the main function of each
infrastructure. The outage rate within the Tokyo metropolitan area was considered and was evaluatedusing the damage assessment result of the Central Disaster Prevention Council of the Japanese
Government. The set result of the outage rate is shown in Table 5
Table 5
Assumed Outage Rate of Infrastructure Function due to Tokyo Metropolitan Near-field Earthquake

Electric power
Gas
Waterworks
Sewer
Information & Telecom.
Road
RailroadPort
Airport

1 day
0.129
0.190
0.333
0.011
0.093
0.400
0.500
0.448
0.000

1 week
0.000
0.175
0.064
0.006
0.052
0.250
0.300
0.445
0.000

1 month
0.000
0.104
0.012
0.001
0.000
0.100
0.100
0.411
0.000

Evaluation of Interdependence Structure Matrix C
In quantifying interdependence structure matrix C, which describes the damage propagation influenceamong each infrastructure, weighting for functional damage propagation was evaluated throughquestionnaire surveys of specialists contributing to the Investigative Commission and of experts in each
infrastructure organization. The respondents evaluated FD and RD from the standpoint of theinfluenced infrastructure (terminal) in the Tokyo metropolitan area.

The functional deficiency degree FD was evaluated in five steps of 4-0 (4: fatal influence - 0: with noinfluence) considering the functional damage propagation phenomena indicated in Table 3. The rate ofdamage occurrence RD was evaluated in five steps of 5-1 (5: serious influence spreads to the whole - 1:
hardly influences the whole system) considering the vulnerability of the infrastructure system in theTokyo metropolitan area and the system forms (facility density, multiplicity, redundancy, etc.) that
become effective in the mitigating the damage propagation influence. The elements of interdependency
structure matrix C were evaluated in twenty-one steps according to FDij x RDij.
In addition, weightings concerning physical damage propagation and restoration problems (considering
Table 2 and Table 4) were also evaluated in a similar way, but they are not shown in this paper becauseof space limitation.
The evaluated elements of the interdependency structure matrix are shown in Table 6. The influencesfrom origins such as "electric power", "information-and-telecommunications", and "road" are great.
However, for convergence of the high cycle propagation calculation, it is necessary to normalize thevalue of each coefficient of an interdependency structure matrix. By trying some normalizing numbers,
1.5 times (=30) the maximum of the weighting values was found to be optimal.
Table 6
Interdependence Structure Matrix C
OriginTerminal(Socialfunction)

Terminal (Infrastructure)

Terminal
Electric power
Gas
Water
Sewer
Telecom.
Road
RailroadPort
AirportTransportation
Finance
Medical treatment
Administration

Origin (Infrastructure)
Power

Gas

Water

Sewer

Telecom.

Road

RailroadPort

Airport

--1
3
8
4
9
16
12
8
12
8
12
16

1
---1
2
1
0
4
1
3
1
1
6
2

2
1
---4
0
0
4
3
3
4
1
16
8

0
0
1
---0
0
4
1
3
1
1
4
1

0
8
2
1
---4
16
4
8
12
20
6
20

0
4
2
0
12
---1
8
4
16
6
12
2

0
1
0
0
0
6
---3
4
4
2
0
2

0
3
0
0
0
0
0
---0
1
0
0
12

0
0
0
0
0
0
0
0
---1
0
0
0

Calculation Result of Case Study
Damage expansions for each infrastructure under the interdependency influence at timings of one day,one week and one month after disaster occurrence were calculated up to the 3rd propagation cycle. The
result one day after disaster occurrence is shown in Figure 6. Functional damage beyond the initialdamage appeared in all the infrastructures under the propagation influence among infrastructures.
Functional damage of "aviation" was influenced by damage to other infrastructures, although no initialdamage to itself was assumed.
Figure 7 shows the terminal infrastructures according to each origin infrastructure. The influence of"electric power", whose weight of functional damage propagation was great, turned out to be small incomparison with "road", "information-and-telecommunications" and "railroad". This is considered toresult from the rather small setup of damage rate in comparison with "road", "railroad", etc. in theinitial damage set of a Tokyo metropolitan near-field earthquake.
The weighting value might vary with different conditions assumed by different evaluators. It istherefore necessary to achieve homogeneity of weighting by clarifying the standard and by including
two or more respondents from different positions etc.

Damage rate
100%

Normalize value = 30
80%

3rd order influence60%

2nd order influence
1st order influence

40%

Initial damage
20%

Airport

Port

Railroad

Road

Information &Telecom.

Sewer

Waterworks

Gas

Electric Power

航空

港湾

鉄道

道路

情報通信

下水道

上水道

ガス

電力

0%

Figure 6: One day after disaster outbreakTerminal

Damage rate increment
80%
80%

Airport
Port

60%
60%

Railroad
Road

40%
40%

Telecom.
Sewer

20%
20%

Water
Gas
港
湾

航
空

Airport

鉄
道

Port

道
路

Railroad

情
報
通
信

Road

下
水
道

Information &Telecom.

上
水
道

Sewer

ガ
ス

Waterworks

電
力

Gas

Origin0%Electric Power0%

Figure 7: Terminal infrastructure according to origin infrastructure

Electric power

INVESTIGATION OF DAMAGE MITIGATION MEASURES
Measures for mitigating damage propagation implemented by each infrastructure organization were
investigated from the literature and hearing examination. Results were divided into commonly usedmeasures and measures peculiar to particular infrastructures.
Typical common measures were "formation of many routes and networks of supply route", "placing
backup functions in a distant area", "disposition of satellite cellular phones", "equipping business-use
vehicles with car-navigation systems", "practical use of cellular phone e-mail ", "practical use ofmarine transportation and air transportation", "temporary restoration by temporary piping","pre-agreement with related organizations", etc.
Typical peculiar measures were "disposition of dynamo car (electric power)", "blocking of pipe andaqueduct (gas and waterworks)", "practical use of a restoration support system (gas)", "water supply totall building by pressuring-type pump car (waterworks)", "power backup to relay stations by portable
dynamo (information-and-telecommunications)", "relief of congestion by message service at disaster(information-and-telecommunications)", "practical use of well water, adjustment reservoir anddesalination plant of sea water (medical treatment)", "conveyance of medical supply by motorcycledelivery service (medical treatment)", "change to distributed type network from put-together typenetwork (finance)" and "allocating habitation of emergency response personnel to neighborhood tobusiness place (finance)".

CONCLUSION AND FUTURE SUBJECT
The results of this research are as follows:(1) Damage propagation among infrastructures occurred in almost all infrastructures immediately aftera disaster. Electric power, gas, information-and-telecommunications and road had high probabilities ofaffecting other infrastructures.
(2) In the case study assuming a Tokyo metropolitan near-field earthquake, functional problems beyond
initial physical damage appeared in all infrastructures due to damage propagation among infrastructures.
In particular, large effects of damage propagation originated from "road", "information-andtelecommunications" and "railroad".
(3) In addition, a setup of initial damage (rate of problems) had a big influence on the result.
(4) "Installation of back up generator against power failure", "formation of many routes and networks
against stoppage of lifeline", "habitation of initial response staff to neighborhood of business place" etc.
have been commonly implemented in infrastructure organizations. These measures are thought to beeffective for disaster mitigation in a mega-city. "Deliberations and adjustments over road burial at timeof restoration", "advance base for restoration team" etc, are the measures that can be implemented
commonly in the future.
The following are future extensions and subjects.
(1) The damage interdependency matrix created by this research is utilizable for prediction of damage
propagation phenomena in each infrastructure at the time of the disaster mitigation response.
(2) It is also applicable to carrying out emergency drills for a scenario assuming damage propagation
among infrastructures. It is expected that new subjects and new measures corresponding to a disasterwill be identified by implementation of such training.
(3) Further investigations of phenomena not generated in previous disasters are required, especiallyconsidering the maintenance situation of today's infrastructure.
(4) Damage propagation influence in case of a Tokyo metropolitan near-field earthquake was evaluatedby weighting the damage propagation based on the damage interdependency matrix. For more reliable
quantitative evaluation, further development is required of calculation techniques, etc. In particular,
since many infrastructures have network structures, evaluation considering damage spreading through a
network is needed.
(5) Construction of a simulation model that can quantitatively evaluate socioeconomic propagationinfluence is needed for evaluation of the overall damage effect on our lives and economic activities,
and for developing mitigation measures,.

ACKNOWLEDGEMENT
This study was carried out by the Cabinet Office Countermeasures-against-Disasters Coordination
Expense in fiscal year 2006. The authors are grateful for many useful discussions with "theInvestigative Commission for the damage propagation mitigation between critical infrastructures(chairman: Professor Fumio Yamazaki)", and for the idea of modeling damage propagation from Dr.
Zenji Shyumuta of the Central Research Institute of Electric Power Industry. Moreover, they were
provided the valuable data of the Niigata Chuetsu Earthquake by the infrastructure organizations
concerned. They express their sincere gratitude to all.

References
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