JOINT CONFERENCE PROCEEDINGS
9th International Conference on Urban Earthquake Engineering/ 4th Asia Conference on Earthquake Engineering
March 6-8, 2012, Tokyo Institute of Technology, Tokyo, Japan

EARTHQUAKE MOTION OF THE 2011 OFF THE PACIFIC COAST OF TOHOKU
EARTHQUAKE AND THE SITUATION OF ISSUING VARIOUS EARTHQUAKE ALARMS
Yutaka Nakamura1,2)
1) President, System and Data Research, Tokyo, Japan2) Visiting Professor, Department of Built Environment, Tokyo Institute of Technology, Japan
yutaka@sdr.co.jp

Abstract: The 2011 off the Pacific coast of Tohoku Earthquake emerged various phenomena. This paper describes thedistribution and the propagation of the real-time seismic intensity and the situation of issuing various earthquake alarms.
Real-time Intensity, RI, is a physical value defined from the power per unit mass of the earthquake motion, so it ischaracterized to be possible to grasp a physical value in realtime, unlike JMA intensity calculated as artificial value with60 second-length earthquake motion after the event. Although Earthquake Early Warnings (EEW) by JMA was issued for
public at 14:46:49 on March 11, 2011 (JST), the area issued the alarm was restricted and a lot of damaged areas ofintensity 5+ were not included. Earthquake alarm system for JR Shinkansen-line also failed to issue the P-wave alarm,and a conventional alarm system as a backup system just worked by exceeding the trigger level of 120 Gal, issuing thealarm later than initial status (40 Gal of trigger level) at 1985. In contrast, a simulation result of FREQL using thewaveform of K-NET Kitakami station shows that FREQL detected the event at 14:46:40 and issued the P-wave alarm at
14:46:46. An actual working FREQL at a base of the Oshika Peninsula issued the P-wave alarm at 14:46:54 and estimatedexact earthquake parameters without magnitude as same as that obtained by simulation.

1. INTRODUCTION
The 2011 off the Pacific coast of Tohoku Earthquake(hereafter the 3.11 earthquake) emerged various phenomena.
This paper describes the distribution and the propagation of
the real-time seismic intensity and the situation of issuing
various earthquake alarms. And what is necessary forearthquake disaster prevention using the experiences fromthe 3.11 earthquake is discussed and propose for nationalorganization like JMA, Japan Meteorological Agency.

2.

REAL-TIME INTENSITY RI

From a viewpoint of the vulnerability of variousstructures, a damage index DI was proposed, that is anearthquake motion index relating to the earthquake early
warning (Nakamura, 1998). Then, in consideration of theclose relationship between DI value and the instrumental
seismic intensity of JMA, Ijma, DI is redefined as real-time
intensity RI (Nakamura, 2003). DI and RI are defined fromthe power per unit mass of the earthquake motion, so it ischaracterized to be possible to grasp a physical value
momentarily, unlike Ijma calculated as artificial value with60 second-length earthquake motion after the event. DI and
RI are defined as follows.

DI = log(|a·v|)
RI = DI + 6.4

(1)
(2)

Here a is an acceleration vector (m/sec/sec) and v isa velocity vector (m/sec). An operator “·” of Equation (1)indicates an inner product. And the frequency range islimited to 0.5 to 5 Hz. Because RI can be calculatedsequentially in realtime and can detect P wave, it is possible
to utilize not only for the early warning for big earthquake
but also assist proper countermeasures after an event byoffering the power of seismic strong motion accurately.
The relationship between RI and MMI, Modified
Mercalli Intensity, is shown as follows.
MMI = (11/7)*RI + 0.5(3)

3. EARTHQUAKE MOTION VIEWED FROM RI
Figure 1 shows the change of RI more than zero ofK-NET stations at Aomori, Miyagi, Fukushima, Ibaraki andChiba prefectures corresponding to the difference of theepicentral distance between the epicentral distance of eachstation and the shortest epicentral distance (127km),
separated to the north and south part for the rupture point ofthe 3.11 earthquake. This figure shows the situation properlyof the earthquake motion propagation from some sourcesDifference between Epicentral Distance in km and 127km fromTime in second from 2011/03/11, 14:46:26JST(a) Distribution of Maximum Realtime Intensity RI(2) Change of RI on Time Domain at Various Sites

Figure 1 Distribution of Maximum Realtime Intensity and Change of Realtime
Intensity on Time Domain at Various Sites

with time difference. In southern side, RI grew gradually andreached its maximum value more than intensity 5 taking alot time, while RI in case of northern side reached its
maximum value relatively early.
Taking advantage of the features of RI to be able toshows the intensity of the earthquake motion in real-time, it
is possible to draw a propagation of the earthquake motion
with distribution of RI of each station instantly. The motion
picture is opened on our website (http://www.sdr.co.jp). The
motion picture shows the situation that the earthquake
motion reached wide area between far off Sendai andSanriku area and spread at once, and then RI grew gradually.
Because an area with large intensity spread increasingly
toward to south side, the intensity slowly grew larger andreached its maximum value quite later than the epicentral
area.
4.
OPERATING CONDITIONWARNING SYSTEMOFVARIOUS

Figure 2 shows the variation of real-time intensity
around the nation using strong motion records of K-NET
and other organization with alarm situation. Horizontal axis
is a difference of the epicentral distance adding + or –corresponding north and south to the epicenter and verticalaxis is elapsed time from 14:46:26 on March 11, 2011, thestart time of the waveform recording of K-NET Oshikastation, the fastest detection station. Colored circles indicate

the value of RI, peak and the time of maximum value aslegend. Also circled number corresponds to the sequencenumber of the early earthquake information by JMA for theinformation based on the estimated intensity more than 3 or
4. From variation on time, an onset time of each intensity
grade and maximum intensity delays roughly according to
the difference of the epicentral distance in northern Tohoku
area. On the other hand, although P wave arrived in advancein Kanto region, a time reaching each intensity grade
increasingly slow and a time reaching maximum intensity isquite late.
While the earthquake early information by JMA wasissued for public at 14:46:49 (23 seconds from start) on
Figure 2, the issued area was restricted all part of Miyagi and
Iwate prefecture, and restricted part of Fukushima, Akita andYamagata prefecture. And it was not issued for the otherdamaged area with maximum intensity more than 5, so itmust be said that the alarm is issued unreasonable.
Meanwhile, because hypocentral distance is more than 120
km even in close area to epicentral region, a duration time of
the initial motion estimated more than 15 seconds. So people
in the area had enough time margins before suffering large
earthquake motion after noticing the earthquake occurrence.
However it seems to be possible for the earthquake early
information by JMA to be valuable for earthquake disasterprevention, there is no report to help something specifically.
Earthquake alarm system for JR Shinkansen-line, thebullet train, also failed to issue the P-wave alarm, and aconventional alarm system just worked by exceeding the300
14:51:00

100

240

MisawaMorioka

Tsukidate
0200

Aomori

Yamabiko #144 Max

300

400

229s: Emergency Warning via NHK
226s: Tsunami Warning by JMA via NHK

14:50:00

180
14:49:00

120

137s: End of EEW via NHK…

Time in seconds from 2011/03/11,14:46:26 JST

14:52:00-100

Hayate #27-200

Yamabiko #61-300

Fukushima
Sendai3.0
360-400

Tsukuba
Mito

4.0

Shinjuku

5.0

Warning Area
①Miyagi, Iwate,
Fukushima butAizu, south inlandof Akita andYamagata but
Shounai andOkitama; JMA#4②Add. Aizu,Shonai,Okitama, Ibaraki,
coast of Akita,
Sampachi-Kamikitaof Aomori, Kaetsu ofNiigata, north-eastof Chiba and southof Saitama; JMA#7③Add. Tochigi andeast of Kanagawa;JMA#10④Add. the rest ofAomori, Chuuetsu,
south of Gumma,
north of Saitama,
the rest of Akita,
north-west of Chiba
and the 23 wards ofTokyo; JMA#12

6.0
Yokohama

Realtime Intensity
RImaxRimax©SDR: 2011.4.7., modified at 5.19 and 7.3

7.0

14:48:00④79s

6037s:
EEW of
JR②36s
Shinkansen①2 3 s: EEW o f JMA③44s

14:47:00

2 8 s: EEW via NHK

0-400

20s: First EEW of FREQL-300

south side

-200

-100

0100

200

Epicentral
Distance
in km
minus
127km
Difference
betweenEpicentral
Distanceand127 kmDifference
betweenEpic.Dis.
and
127km

300

RI MMIPeakMax
6.5 10.7
6.0 9.9
5.5 9.1
5.0 8.4
4.5 7.6
4.0 6.8
3.5 6.0
2.5 4.4
2.0 3.6
1.5 2.9
0.5 1.3
0.0 0.5
P-arrival

400

north side

Figure 2 Variation of Realtime Intensity around the Nation using Strong Motion
Records of K-NET and other Organization with Alarm Situation.

trigger level, 120 Gal (=cm/s/s) in 14:47:03. This time islater at least five seconds than initial system in 1985 withtrigger level of 40 Gal. And if the system installed samesystem which issued P wave alarm successively at the timeof the 2004 Niigataken-Chuetsu earthquake, the additional
leading time is estimated 15 seconds or more. The current
earthquake early alarm system that failed to issue the alarmin this time is similar system to that of JMA.

Figure 2 also shows the result of simulation ofFREQL installed close to epicenter. Here, FREQL is anonsite earthquake alarm system practical used for private
railway companies and other factories. A simulation result ofFREQL using the waveform K-NET Kitakami station showsthat FREQL detected the event at 14:46:40 and issued theP-wave alarm at 14:46:46.
An actual working FREQL at a base of peninsulaissued the P-wave alarm at 14:46:54 and estimated exact
earthquake parameters, location and depth, without
magnitude. The simulation results for this case agree withthe actual situation. It shows the validity of the FREQL
simulation.
Tsunami warning was issued about three minutes after
earthquake detection. It was enough early but that wasunderestimated and modified information was not accuratelytransferred for local people. Because organizations without
JMA is restricted to issue these kinds of warnings as tsunami
warning by low, local government could not start
independently activity for evacuation although feeling large
and long abnormal earthquake motion.
5. DISCUSSION
The 3.11 earthquake is abnormal earthquake withextremely long duration even for Japanese people used tofeel earthquake motion commonly. Most of Japanese people
including a people on vehicles noticed the earthquake
motion by themselves before enlarged motion without anywarnings. This situation can be understood easily by Figure
2. Relatively large motion started some tens seconds before
the large motion. Since many people felt this abnormal
earthquake motion as natural tsunami alert, there was only afew people started activity for evacuation immediately.
Especially staffs of local government did not start any
activities immediately and waited tsunami warning fromJMA, although a few minutes. This inactive approach seems
to enlarge tsunami damage of this earthquake. People inTohoku area, commonly hit by tsunami, have a legend to
escape before anything else in case of large earthquake. In
spite of this legend, there are many losses in this time. It isnecessary to review in detail of the matter of this situation,
but there are no signs to start review by third party. At leastconsidering objectively, it must be thought that there weresome problem on tsunami warning and countermeasures. Itis possible to estimate that the people could not escapeindependently judging the dangerousness by choice, becauseof tsunami warning only issued by JMA and excessive senseof safety for huge coastal levee. Moreover frequent excess
tsunami warning for foreshocks might cause crying wolf
effect. Although the activity for evacuation must reflect local
characteristics, the activity is triggered by the warning fromJMA, central bureaucracy. This situation seems to beabnormal. After the Kobe earthquake disaster, sixteen years
ago, why JMA amended a law to restrict issuing tsunami
warning by judgment of local government? It may cause
dependency for central bureaucracy and luck of decision on
activity for disaster prevention, if local government could
not judge by themselves. So although the author demands a
correction at every opportunity, the situation continues today
without granted the request. Not only tsunami warning but
also EEW, early earthquake warning, is also under same
situation. Even EEW by JMA could not be issued before alarge motion in case of M7-class earthquake in damage area(within 30 to 50 km), public information continues saying

useful. Although the 3.11 earthquake was a rare chance that
EEW by JMA can be useful, the system failed to issue theproper warning. As a result, EEW by JMA is protected by
low but can not protect local people. The author thinks thatJMA with nation wide observation network must focus toinform immediately exact earthquake parameters of main
shock and aftershocks by parallel way and it must be
possible for various organizations to issue earthquake
warnings. This will enable to determine the severe damaged
area quickly and help the rescue activity. As said before,
earthquake warning must be realized by local organizationsin their domain and the warning issued by central
bureaucracy is meaningless. What is required for JMA is not
warning, and they must provide the exact earthquake
information for quick response. It is expected to realize
rational correspondence just after the earthquake.
6. CONCLUSION
This paper shows that real-time intensity RI cancomprehensibly express the distribution of the seismicintensity and the propagation of the earthquake motion of the2011 off the Pacific coast of Tohoku Earthquake. Earthquake
early warning by JMA can gain only comparable or a little
long time margin comparing with on-site FREQL or
ordinary alarm seismometer, so the merit cannot berecognized. It has been also cleared that Earthquake early
warning by JMA is not applicable for the near-field
earthquakes. Earthquake early warning by JMA is not a kindof a system operated under a low because it is feared adverse
result from excessive expectation. It seems to be necessaryto amend Meteorological Service Act as abolish theunnecessary restrict on earthquake early warning or tsunami
warning, base on a view that such a kind of restrict causes
the serious damage of the 3.11 earthquake. Finely-tuned
responses are required for a disaster like epicentral
earthquake or tsunami because of the strong reflection of thelocal conditions. It is desirable to change the centralized wayof JMA and handle in close coordination and cooperation
with local authorities specified familiar with local
circumstances. A system to directly link the necessary
information to the area must be established and the author
expects JMA to support the system.
Acknowledgements:
In this paper, the waveform data was mainly provided by
K-KET and KIK-net of NIED, National Research Institute for Earth
Science and Disaster Prevention. The author would like to sincerely
express his highest appreciation and gratitude to people and theorganizations.
References:
Nakamura, Y. (2003), “Examination of a Rational Strong Motion
Index – Relationship between the DI value and the other strong
motion indices –”, the 27th JSCE Earthquake Engineering
Symposium.
Nakamura, Y. (1998), “A New Concept for the Earthquake
Vulnerability Estimation and its Application to the Early
Warning System”, Early Warning Conference ’98.