Fifth International Conference on Urban Earthquake Engineering
March 4-5, 2008, Tokyo Institute of Technology, Tokyo, Japan

ON-SITE ALARM – THE EFFECTIVE EARTHQUAKE EARLY WARNING
Yutaka Nakamura1), 2)
1) President, System and Data Research Co., Ltd., Japan2) Visiting Professor, Dept. of Built Environment, Tokyo Institute of Technology, Japan
yutaka@sdr.co.jp

Abstract: The most important countermeasure against earthquake risk is to have all structures strong enough for the
possible earthquake load. In this regard, an early warning system should be installed to reduce the possibility ofearthquake disaster. An early warning system is required mainly to issue an alarm to have a time margin for evacuatingor shutting down key facilities, and not to determine exact earthquake parameters. Thus the early warning system must
be realized independently with On-Site alarm and the government and other public authorities must release accurate
earthquake information immediately after the earthquake.

1. INTRODUCTION
There are two kinds of the earthquake alarm as in Fig.1.
One is “On-Site Alarm” which is the alarm based on theobservation at the side of the objects to be warned. The
other is “Front Alarm” which is the alarm based on theobservation near the epicentral area for the warning topossible damaged area. “Front Alarm” is transmitted byusing communication networks, so the alarm is also called as“Network Alarm”.
For each, there are two more kinds of alarm. One isthe alarm exceeding the preset level, so-called “S-wave
Alarm” or “Triggered Alarm”. And the other one is thealarm during the preliminary motion, so-called “P-wave
Alarm”.
As the first stage of the earthquake alarm, the simple
triggered alarm had been realized. This is the alarm
seismometer observing the strong motion just near theobjective for the alarm, and when the earthquake motion
exceeds the preset level, the alarm seismometer issues thealarm. Although because of the anxiety of false alarm, it isFig.1 Comcept of Earthquake Early Warning- 45 -

not able to set the alarm level low and the alarm is issued
almost same time to the severe strong motion, it is useful tostop the gas supply or other systems automatically.
Next, to extend the margin time before the strong
motion arrival, it was considered the way to observe theearthquake near the focal area, so-called “Front Alarm”.
This idea originally had been offered in 1868 by Dr. Cooper.
He proposed to utilize the propagation time of theearthquake motion from the epicenter to alarmed area andsupport the activities for escape. More than 100 years after
this original idea, the first system realizing the “Front
Alarm” was developed as the coast line detection system for
Tohoku Shinkansen line in 1982. After this, SAS, Sistema
de Alerta Sísmica, for Mexico City started operation in 1991.
Then the next system was considered to detect theinitial part of the earthquake motion and issue the alarm
based on the risk of the earthquake. The first P wave
detection system for practical use, UrEDAS, Urgent
Earthquake Detection and Alarm System, was realized as thefront alarm system for Tokaido Shinkansen line in 1992, andthen almost same system was installed for Sanyo
Shinkansen line in 1996.
The 1995 Great Hanshin Disaster triggered to develop
earlier P wave alarm system because of the impression ofnecessity to make on-site P wave alarm. This is Compact
UrEDAS and it was installed for Tohoku, Joetsu and Nagano
Shinkansen lines and Tokyo metro subway network.
And then Wakayama prefecture decided to install
UrEDAS for their own tsunami disaster prevention systemand started test operation in 2000.
As the new generation of UrEDAS and Compact
UrEDAS, the new small-sized instrument FREQL, Fast
Response Equipment against Quake Load, is developed toshorten the processing time for alarm and to combine thefunctions of UrEDAS and Compact UrEDAS. After P
wave detection, FREQL can issue the alarm within one

Damages for Bridge

100

al
20G

10

l
Ga
40

1

3

120
Gal

2.1 UrEDAS
Main UrEDAS functions are estimation of magnitude
and location, vulnerability assessment and warning within a
few seconds of initial P wave motion at a single station.
Unlike the existing automatic seismic observation systems,
UrEDAS does not have to transmit the observed waveformin real time to a remote processing or centralized system andthus the system can be considerably simplified.

No Damage
Damages for Embankments

80G
al

2. Principal EEW: UrEDAS, Compact UrEDAS andFREQL

UrEDAS calculates parameters such as back azimuth,
predominant frequency for magnitude evaluation andvertical to horizontal ratio for discrimination between P and
S waves, using amplitude level for each sampling in realtime. These calculations are basically processed in realtime without storing waveform data. UrEDAS processes
these calculation continuously regardless of whether or not
an earthquake occurs, and calculates just like filtering, so thenumber of procedures is not increased in the event of anearthquake. UrEDAS can detect earthquakes in P-wave
triggering with the amplitude level, and then estimates
earthquake parameters such as magnitude, epicentral andhypocentral distance, depth and back azimuth from the resultof real-time calculation in a fixed period. UrEDAS canissue an alarm based on the M-Δ diagram as in Fig.3
immediately after earthquake detection. This new way ofalarm is referred to as the M-Δ Alarm. Moreover UrEDAS
can support restarting operation based on the detailed
earthquake parameters.

Epicentral Distance in km

second (minimum in 0.2 seconds) and estimate theearthquake parameters at one second. Since 2005, FREQL
has been adopted for the hyper rescue team of Tokyo fire
department to save the staffs from the large after shocks
during their activity. The hyper rescue teams are famous of
the salvage of the child from the land slide after the 2004
Niigataken Chuetsu Earthquake, and they were afraid of thehazard caused by the aftershocks at that time.
On the other hand, it is necessary for local facilities tograsp immediately their “own” strong motion index for thequick response. For this purpose, a simple seismometer“AcCo”, Acceleration Collector, was developed. This
unique palmtop seismometer has a bright indicator, memory
and alarm buzzer and relay connecter.
On-Site alarm is more important than network alarm,because network alarm is sometime missed during data
communication. From the view of this, it is not enough toreceive the Earthquake Early Information from JMA, Japan
Meteorological Agency, EEI. Contrary with this, FREQL
has both functions of UrEDAS and Compact UrEDAS for
On-Site Alarm and Network Alarm. And also AcCo has
simple alarm functions for On-Site Alarm.
Fig.2 shows systems of EEW: UrEDAS, Compact
UrEDAS, FREQL and AcCo.

4

5

6

7

8

Magnitude M

Fig.3 M-D DiagramVideo Photos at
the 1995 Kobe Earthquake

P wave arrival

Principal motion arrival

Time(1) UrEDAS(2) Compact U.

(3) AcCo
P wave arrival

Fig.4 Video Photos examples at focal region(4) FREQL

The 1995 Hyogoken-Nanbu Earthquake also provided
the motivation for Compact-UrEDAS development. Fig.4
shows several pictures from the VTR shoot in the focal
region, initial P-wave motion was detected as something
happening, and then severe motion started. In an interview
with victims, although there were only a few seconds
between detection of something happening to earthquake(5) FREQL of Portable Type

Fig.2 UrEDAS, Compact UrEDAS, FREQL and AcCo

- 46 -

recognition, there was anxiety and fear because they could
not understand what was happening during this period andfelt relieved after recognition of earthquake occurrence. To
counter this kind of feeling, earlier earthquake alarm was
required: Compact UrEDAS was developed to issue thealarm within one second of P-wave arrival.
2.2 Compact UrEDAS
Compact
UrEDAS
estimates
theexpected
destructiveness of the earthquake immediately from theearthquake motion directly, not from the earthquake
parameters as UrEDAS, and then issues the alarm if needed.
To estimate earthquake dangerousness, the power of theearthquake motion is calculated from the inner product ofacceleration vector and velocity vector, but this value will belarge. Hence Destructive Intensity (DI) is defined as thelogarithm of absolute value of this inner product as in Fig. 5.
・ Seismic Inertia Force F = ma, “a” is seismic acceleration
・ Seismic Motion Energy E = mv2/2, “v” is seismic velocity
・ Destructiveness of Motion relates power PW = Fv = mav

Destructive Intensity DI,

E = mv2/2
F = maDI = log|av|, DI-value = max(DI)PW = mav

Fv（（（

Fig.5 Definition of DI

efficiently and damage can be estimated precisely.
2.3 FREQLFREQL is integrated the functions of UrEDAS,
Compact UrEDAS and AcCo. Which is to say that
FREQL can estimate the earthquake parameters one second
after the P wave detection faster than UrEDAS, can judge
the dangerousness of the earthquake motion within one
second, minimum in 0.2 seconds, after P wave detection
faster than Compact UrEDAS, and can output the
information and alarm based on both acceleration and RI,
Realtime Intensity, in real time same as AcCo.
And the all components of seismometer, sensors, A/D
converter, amplifier, CPU and so on, are put together insmall aluminum die-cast vessel of almost 5 inches cube, andthe system is electrical isolated. So the FREQL is easy toinstall and the structure of FREQL is noise proof.
FREQL also has functions to omit the influence ofelectrical thunder noise and to detect the P wave after rather
small pre-shock. Thus it is able to say that FREQL solved
the known problems of the ordinary earthquake early
warning systems. It is known that there was a pre-shock at
the time of the 1994 Northridge earthquake attacked Los
Angels and the 1995 Hyogoken-Nanbu Earthquake attacked
great Hanshin area. It seems to be failing for the early
warning system except FREQL that it is not possible to issue
the alarm for large earthquake motion if the pre-shock exists
just before the destructive earthquake because the pre-shockis recognized as small event. And also it seems to bedifficult for the huge system to keep running perfectly under
the destructive earthquake motion. It is uncertain only withsuch remote systems because of information lack. It must
be considered on installing the onsite warning system for theimportant facility.
FREQL is toward to the new field for the early warning
system, as for the hyper rescue teams of Tokyo fire
department under the severe situation with the risk ofaftershocks (see Fig. 7).

Fig.6 Change of DI
Fig. 6 shows the change of DI as a function of time.
When the P wave arrives, DI increases drastically. PI value
is defined as maximum DI within t seconds after P-wave
detection. This value is suggested to be used for P-wave
alarm. Subsequently, DI continues to increase slowly until
the S-wave arrival, after which it reaches its maximum value
which is called the DI value. This value relates toearthquake damage and is similar to the Instrumental
Intensity scale of JMA or MMI, Modified Mercalli Intensity.
Instrumental JMA seismic intensity can be determined only
after the earthquake has terminated. On the other hand, DI
has a very important practical advantage, because it can becalculated in real time soon after the P-wave arrival withphysical meaning. In other words, with the continuous
observations of DI, an earthquake alarm can be issued- 47 -

Fig.7 New Field for EEWHyper rescue teams made a miraculous activity but theactivity was always in a risk of large after shocks. After theactivity at the damaged area of the 2004 Niigataken-Chuetsu
Earthquake, the Tokyo fire department approached us toadopt FREQL as a support system for the rescue activity,

Fig.8 An example of alarm timings by simple triggers
in case of the 2000 Tottoriken-Seibu Earthquake
E E L:I o Frf J onM
A: t 1
0
Fr
on km
t
10
30 k m50 k mkm

2.4 AcCo
Because usual seismometers were expensive andrequired an expert of installation and maintenance, so they
were installed for limited facilities. After the Kobe
earthquake, the number of seismometer was increased but at
most thousands sets for whole Japan. It is not so muchbecause it means one set per several tens km2 or per several
ten thousands person.
Even so there are many
seismometers in Japan, but many hazardous countries have
only a few seismometers. So it is difficult to take exact
countermeasure against earthquake disasters because it is
impossible to grasp and analysis the damage based on thestrong motion records and to draw a plan of the city withcertain strategy.
AcCo was developed to realize a simple seismometer toissue alarm and record the strong motion in low cost. Since
AcCo is just a palmtop size instrument, it can indicate not
only acceleration but also the world's first real time intensity.
So AcCo can issue alarm with the trigger of both
acceleration and intensity.
AcCo indicates acceleration and intensity if the
5HzPGA (5 Hz low passed peak ground acceleration)exceeds 5 Gals as in Fig.2(3). Intensity can be chose from
RI, MMI or PEIS, Philippine Earthquake Intensity Scale.
AcCo can output the digitized waveform via serial port andalso record the waveform for the two largest events withdelay memory. AcCo can work with AC power supply andbackup battery for seven hours.
Because AcCo indicates acceleration as inertial force
and RI as the power of the earthquake motion, it is useful tolearn the sense for the meaning of acceleration and intensityfrom the experience. This sense is required for the exact
image against the earthquake motion.
AcCo is applied for many fields as warning system,
education, kindergarden, factory, train operation and so on.
And also AcCo is used not only in Japan but also in out sideof Japan for a instance, Taiwan, Philippine and etc..

2.5. Alarm timing and margin time gained by EEW
In case of the system requiring the earlier warning withno error or accidental warning, it is necessary to install asystem with high reliability and sophisticated as FREQL.
But in general, it seems to be useful even the simple warning
system in general. This kind of system seems to be usefulenough in many cases under the situation of several alarms
per year even in higher seismic activity area of Japan.
AcCo 10 Gals alarm or RI 2.0 alarm can play the role of thissimple early warning.
Fig.8 shows the relationshipexample between the alarm timings. Since the AcCo 10
Gals alarm or RI 2.0 alarm is a little later than the P wave
alarm of FREQL, it is enough earlier than the ordinary
triggered S wave alarm.

FR
EQ

taking notice of the portability, rapidness and accuracy of thewarning. FREQL for Tokyo fire department was consistsof FREQL main body, power unit with backup battery forthree hours, central monitoring system and the portable
alarm instrument with more than 105dB loud alarm androtary light.
Tokyo fire department has equipped the FREQL unit
form spring of 2005, and since 2007, three hyper rescue
teams is operating. At the time of their rescue activity after
the 2005 Pakistan earthquake, they reported that FREQL
works in right manner. Now, there are many FREQL of
portable type equipped at local fire stations in Japan.
And the FREQL of permanent type are used in many
field such as subway, nuclear power plant, high-rise building,semiconductor facilities, and etc., in Japan.
Now, in Berkeley and in Pasadena, FREQL has started
test observation. These projects are doing under the
support by UC Berkeley and Caltech. I hope this FREQL
network growth to Pan-Pacific Tsunami Warning System.

it
n-S
O
L:
EQ
FR

e

30km, 50km from Epicenter
Invalid
Area forEEI of
JMA

5+2

On-SiteEpicenter
Front Site
10km
30km
50km

Hypocenter

Fig.9 Margin time by EEW- 48 -

Depth=15km

Fig.9 shows gained margin time by EEW. Basic
condition for calculating margin time is assumed as follows:
focal depth is15km, velocity of P-wave and S-wave are vp =6 km/s and vs = 3.5 km/s, respectively, front detection site at
10 km, 30 km and 50 km from the epicenter.
Based on the calculation for 10km, EEI of JMA comes
after S wave arrival within a 30 km radius as confession by
JMA. On-Site alarm by FREQL can keep at least morethan one second even just above the epicenter; and moremargin time than front alarm by JMA within about 55 km
radius from the epicenter. This distance corresponds forout line of the damage area for over M7. It means that the
EEI of JMA is not available the estimated damaged area up
to M7, so it seems that it is not useful for the recent Japanese
earthquake in this 20 years. Contrary to this, the on-site
FREQL alarm is available even around the focal area; ofcourse the margin time is just a few seconds. So we shouldtake a hard look at the on-site alarm and put it into practicaluse. It is also useful for popularization of earthquake
disaster mitigation. It seems that there are many fields not
so effected by false alarm if reset easily. Official
information as correct location and magnitude must be
informed within few minutes for the exact clear of the alarm.
And this kind of information must keep suitable redundancy
so there must be informed from several organizations.

Processing Time for Warning

Processing Time for Alarm in seconds

10

cf.: JMA System
EEI of JMA

SDR Products

5
3
2
1

Average 5.4s

UrEDAS ３sec.

UrEDAS
start of test

JR Tokaido shinkansen
Wakayama prefecture
Tsunami Warning S ystem,and etc.

Min. in 2s

Compact UrEDAS １sec.
JR Tohoku Shinkansen,Tokyo Metro, and etc.

0.5
0.2
0.1
1980

FREQL min. in 0.2sec.
Tokyo, Osaka and etc. Fire Departments

1985

1990

1995

2000

2005

2010

year

Fig.11 Overview of the 2004 Niigataken-Chuetsu Earthquake
section damaged was between Muikamachi and Nagaoka.
Trains traveling on this section received the alarm
immediately, proving that the alarm system settings wereappropriate.
The UD component of earthquake motion predominate
the high frequency more than 10 Hz. The Shinkansen line
runs from north to south and the EW component seems toeffect derailment. In the case of the EW component, there
is a peak at 1.5 Hz and the range of 1 to 2.5 Hz predominates.
The natural frequency of the Shinkansen vehicle is included
this frequency range.
The Kawaguchi observatory detected the P wave 2.6
seconds after the earthquake occurred, and one second after
that, or 3.6 seconds after the event, issued a P-wave alarm.
When the derailed train, Toki #325, encountered theearthquake motion when traveling at 75 m from the Takiyatunnel exit of 206km000m, it was three seconds after
earthquake occurrence. 3.6 seconds after the earthquake, thetrain received the alarm from the Compact UrEDAS and thepower supply was interrupted. The Shinkansen train
situated automatically to apply the break immediately at theinterruption of power supply. The driver put on theemergency brake after recognizing the Compact UrEDAS
alarm. The S-wave hit the train 2.5 seconds after the alarm,and more one second later, a strong motion with fiveseconds duration hit the train. Fig.12 shows the schematic

Fig.10 Change of processing time for EEW
Shin-Nagaoka SSP

Toki#406

3. Practical Operation Example of Compact UrEDAS
At the time of the 2004 Niigataken Chuetsu Earthquake,
Mjma 6.8, there were four trains running in the focal area.
There are four observatories called Oshikiri SP, Nagaoka
SSP, Kawaguchi SS and Muikamachi SP, from north tosouth. Of these stations, Kawaguchi and Nagaoka issued
both the P-wave and the S-wave alarms, and the others
issued only the S-wave alarm. Every station issued thealarm for the section to the next station (see Fig.11). At
first Kawaguchi and then Nagaoka issued the P-wave alarm.
Subsequently, Oshikiri and Muikamachi issued the 40 Gals
alarm. As the result, trains Toki #325 and #332 received
the alarm 3.6 seconds after the earthquake occurred, Toki
#406 4.5 seconds after and Toki #361 11.2 seconds. The- 49 -

Takiya Tunnel

Uonuma Tunnel

434Gal Toki#325 Myouken Tunnel

Nagaoka St.

P-wave: 3.5s
P-Alarm: 4.5s
S-wave: 6.7s

P-waveP-wave: 3.3s
P-Alarm: 3.9s
S-wave: 6.4s

Shin-Kawaguchi SS

846GalP-wave: 2.9s
P-Alarm: 3.9s
S-wave: 5.9s

S-waveDepth 13km

Source : Rupture Begins
0

2

4

6

8

10 km

2004/10/23, 17:56:00.30
Time is the absolute timein seconds from17:56:00.

Fig.12 Schematic diagram for this earthquake

diagram for this earthquake.
As the result of simulation using the strong-motion
records at Kawaguchi and Nagaoka, real-time intensity (RI)
rose sharply with the earthquake motion arrival and
immediately reached the P-wave alarm level. This RI is areal-time value and the maximum value fits the instrumental
intensity of JMA. Because FREQL, the new generation ofCompact UrEDAS, improves the reliability of P-wave
distinction, FREQL can issue the alarm immediately after
the P-wave alarm threshold is exceeded. If FREQL had
been installed instead of Compact UrEDAS, both
Kawaguchi and Nagaoka observatory would issued theP-wave alarm 0.2 and 0.6 seconds after P-wave detection,
respectively. Table 1 summarizes the simulation results. In
this case, the P-wave alarm reached the derailed section
before P-wave arrival. Accordingly, FREQL minimizes
Table 1 Summarize the上越新幹線沿線地震検知点（一部simulation results
検知点
新六日町
Alarm andAccident
Site 新川口
Kawaguchi 滝谷Ｔ出口新長岡
Tunnel Exit Nagaoka
5HzPGA(Gal) (Gal) 270
5HzPGA
846846434434
RImax
6.6
5.8
RImax
(MMI) 4.9 6.6 (10.9)
5.8 (9.6)
17時56分 17:56:00.3
17時56分 17:56:00.3
17時56分 17:56:00.3
17時56分
検知時間
Origin Time
Recorded
Detecting Time
地震10Gal
8秒
秒
3 3秒
s
4 s4秒
P-wavearrival Time 4.4
2.92.6推定P波
3.33.03.53.5推定P警報
3.6Time of RI >2
4.14.53.13.6
RI2超過
P-waveAlarm Time6.4
3.92.83.92.84.54.1
3.43.3
10Gal超6.6Time ofMax. Acc >10Gal
4.74.740Gal超9.4
Time ofMax. Acc >40Gal
4.24.2
5.96.0TimeAmaxof 5HzPGA11.4
7.77.7
9.49.5
RImax
10.6
9.5
Time
of RImax 13.4
8.17.8the process time for alarm.
Fig.13 shows the details of the derailment. The
derailed train, Toki #325, consisted of 10 cars, from car #10
to car #1 along the traveling direction. The number ofderailed axles is 22 out of a total of 40 axles. The last car,#1, fell down the drain besides the track and tilted by about
30 degrees. The open circle indicates the location of
broken window glass. The quantity of broken grassappears greater on the left due to the something bounce fromthe sound barrier, and tends to break one or two cars after thederailed car. The amount of broken glass from car #1 isexceeded by that of car #2.
If it is assumed that the glass broken of car #2 wascaused by the derailment of cars #4 and #3, the paucity ofbroken glasses from car #1 suggests that car #2 did not derail
during the earthquake motion. It is estimated that thefrictional heat between the vehicle and the rails caused
elongation and slightly rift up at the joints of 206km700m,
and car #1 derailed, making car #2 derail.
Deformation performance of viaducts is specified
within one cm under the loading of the seismic design force.
Although the designed natural frequency corresponding to
the deformation performance is 2.5 Hz, in practice it is 3.5
Hz. The viaduct may thus be considered to behave
statically against the earthquake motion less than around 1.5
Hz. Fig.14 shows the relative deformation derived fromthe dimension of the viaduct columns. The meshed line
shows the averaged deformation for each viaduct block, and
it is estimated that the relative large occurred at the area

- 50 -

Fig.13 Detail of the derailment
farther from the tunnel exit. Taking into account the timingof earthquake occurrence, this is the point of derailment.
Fig.15 outlines the circumstances of the derailment. It
seems that the derailed cars were on the large displacement
section accidentally. The later the alarm reached, the more
the number of derailed car, because of the risk of running theAKIHA
BARA

SHIN
JUKU
TOKYO

Fig.16 Subway network of Tokyo Metro Company

Fig.14 Performance of the deformation
large displacement section. As a result, if the friction heatrelease value were higher, the derailment situations weremore severe. On the other hand, the early warning slows
the train down, which means that the main shock hits thetrain before the large displacement section and decreases
while the train travels the section. The number of the

5 seconds

Fig.17 The 2005 Chiba North-West Earthquake

Final Derailment Situation

Fig.15 Estimated situation of the derailment
derailed cars is thus expected to decrease and the derailment
damage must be minor. In this regard, the P-wave alarm of
the Compact UrEDAS demonstrates its effectiveness atmaking the derailment non-catastrophic.
4. An Example of Integrated Systems for EEW andQuick Response against Strong Motion- 51 -

Tokyo Metro, Subway Company, built the newearthquake early warning/quick response system based on
the experience of the 2005 Chiba north-west earthquake,
Mjma 6.0. Tokyo Metro network is the core of the railway
transportation system for the entire Tokyo metropolitan area
as in Fig.16.
In July 2005, the earthquake attacked the Tokyo
metropolitan area as in Fig.17. This earthquake occurred at
35.5N and 140.2E with about 73km in depth, and the
maximum JMA intensity was 5+ corresponding to MMI
VIII approximately.
This earthquake occurred at
north-west of Chiba prefecture and caused a traffic
disturbance widely in Tokyo metropolitan area. All thetrain operation had been stopped for a long time after theearthquake, although a severe damage was not caused evenin the area of high intensity. The longest down time for the
train operation was more than seven hours. That of Tokyo
Metro was four hours.
Tokyo Metro had to check all track on foot, because
the control reference value for train operation exceeded.

The value of Tokyo Metro is 100Gal of 5HzPGA. Thisvalue varies by Train Company. To check the track on footis the reason why had all train operation been stopped for along time.
After the earthquake, we proposed a new system forearly warning and quick response with basic idea as follows.
It is necessary for the control against the earthquake to equip
the system not only to issue the early warning but also to
support the quick and rational recovery work after theearthquake. Tokyo Metro Company accepted our proposal,
and replaced and built the new early warning/quick response

FREQL network: 6 sites
AcCo network: 33 sites(1) Networks of FREQL and AcCo
<FREQL System>
6 seismometers

FREQL

Communication unit

Simulation of the System

Tokyo Metro
Operating Center

Terminal
block

system as followed.
The system consists of two seismometer networks asshown in Fig.18. One is the early warning system network
consisting six sets of FREQL to control or stop the train
operation immediately after the earthquake occurrence.
And the other is the network of the portable digitalseismometer consisting of 33 sets of AcCo in every about
three kilometers mesh to grasp more detailed seismic motion
on their service area.
The information from both FREQL network and
AcCo network are gathered to the operation center anddisplayed on the individual monitoring system. The
monitoring system for AcCo can indicate the integrated
information from AcCo and FREQL on the subway network
image. The AcCo monitoring system is also installed on
the control table for each subway line.
At the time of the earthquake, the early warning
system detects at first the earthquake immediately and thenthe 33 local seismometers inform the actual earthquake
motion of each site independently and rapidly as in Fig.19.
This system realized quick response and restart of the train
operation because the early warning became faster andchecking zone after earthquake was optimized. Thisupdated system is expected to realize quicker response
during and after.

<AcCo System>
Train control(stop the train)

Monitoring system
for FREQL<AcCo System>
33 seismometers

Monitoring system
for AcCo

Train control(restart the train
operation)

AcCoCommunication unit

Monitoring system
for AcCo

Display the collected seismic motion.

(2) Outline of Systems

Fig.19 Display example when earthquake occurred
For the large system as the train operation, it isnecessary for the control against the earthquake to equip thesystem not only to issue the early warning but also to
support the quick and rational recovery work after theearthquake.
5. Discussion
It seems that the difference between real time
seismology (RTS) and real time earthquake engineering(RTEE) is the way of contribution indirectly or directly forpractical use, as same as the difference between science andengineering. RTS makes the countermeasure soon after theearthquake rational and prompt by sending information
universally to be useful for public. And RTEE sends the(3) Monitoring System for AcCo
Fig.18 New Earthquake Early Warning System- 52 -

information for certain customers as a trigger of thecountermeasures against the earthquake disaster. From theview of time domain, RTS is required by the rational action
after the earthquake terminated and RTEE is necessary forthe immediate response just after the earthquake occurrenceor earthquake motion arrival.
RTS needs high accuracy on the information but not
immediate, so it is possible to utilize effectively theknowledge and experience on seismology andinfrastructures as observation networks. The task are to be
more accurate the information on the earthquake observationand to deliver rapidly to all people.
On the other hand, the most important aim of RTEE is
to decrease the degree of the disaster or the possibility of thedisaster occurrence so it is necessary to issue alarm rapidly
and certainly. For this purpose, at first it must be concerned
to install own observation system for the alarm, without
relying the information from the other authorities. And
then, it is possible to use the other information if it can bereceived. It is necessary to customize the way of issuingand utilizing the alarm depends on the situation for eachcustomer and fields. Again, it is risky to rely to theinformation only from the other authorities using the datatransmission network under the situation of earthquake.
In Japan, JMA has started delivering the EEI,
Earthquake Early Information, on 1st October 2007. It isclear that EEI is belonging to RTS. So it is only a result ofearthquake observation and must be delivered widely for
public with no restriction for receiving. Since for somecase, it may be possible to use it as alarm, but generally tosay, EEI is mainly for the rational countermeasures after
earthquake termination. It must be used for release of the- 53 -

EEW by the people quickly if the alarm is not needed.
From the view of this, the most important is accuracy andthe delay of few seconds is not a problem, because the errorof this kind of information may cause a serious confusion.
It is enough that the accurate information is delivered within
one or two minutes after the event. Alarm must be released
rationally and EEI may play an important role as one of theuseful tools for this.
It is necessary to grasp the distribution of earthquake
motion at the early stage. It is recommended to progress
the earthquake disaster prevention with the combination of
the public information such as EEI by JMA rather late andlocal dense and quick information by the people.
Acknowledgements:
Many thanks are due to those people and organizations
involved in the our developing project for Earthquake Early
Warning
References:
Nakamura Y., Earthquake Warning System of Japanese National
Railways (in Japanese), Railway Technology, Vol.42, No.10,
pp.371-376, 1985.
Cooper, J.D.: Earthquake Indicator, San Francisco Daily Evening
Bulletin, 3rd November 1868.
Nakamura, Y.: Earthquake Early Warning and Derailment of
Shinkansen at the 2004 Niigataken-Chuetsu Earthquake (inJapanese), Jishin Journal, No.41, pp25-37, Association for theDevelopment of Earthquake Prediction, June 2006.
Nakamura Y., UrEDAS, Urgent Earthquake Detection and Alarm
System, Now and Future, 13th WCEE, paper #908, 2004.
Nakamura Y., On a Rational Strong Motion Index Compared with
Other Various Indices, 13th WCEE, paper #910, 2004.