accepted paper, 15WCEE

Earthquake Motion ofthe 2011 off the Pacific Coast of Tohoku Earthquake andthe Situation of Issuing Various Earthquake Alarms
Yutaka Nakamura
System and Data Research Co., Ltd., JapanSUMMARY:
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. Although Earthquake Early Warnings (EEW)
by Japan Meteorological Agency (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 were not included. EEW for Shinkansen-line also
failed to issue the P-wave alarm, and only a conventional alarm system worked by exceeding the trigger level of120 Gal. In contrast, a simulation result of FREQL using the waveform 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 abase of the Oshika Peninsula issued the P-wave alarm at 14:46:54 and estimated exact earthquake parameters
without magnitude.
Keywords: Earthquake Early Warning, Realtime Intensity RI, FREQL

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 RI and the situation of issuing various earthquake alarms. And what is necessary forearthquake disaster prevention learning from the experiences of the 3.11 earthquake is discussed andthe author proposes for national organization like JMA, Japan Meteorological Agency.

2. REAL-TIME INTENSITY RI
From a viewpoint of the vulnerability of various structures, a damage index DI was proposed, that is
an earthquake motion index relating to the earthquake early warning (Nakamura, 1998). Then, inconsideration of the close 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 from thepower per unit mass of the earthquake motion, so it is characterized to be possible to grasp a physicalvalue momentarily, unlike Ijma calculated as artificial value with 60 second-length earthquake motion
after the event. DI and RI are defined as follows.
DI = log(|a·v|)
RI = DI + 6.4

(2.1)
(2.2)

Here a is an acceleration vector (m/sec/sec) and v is a velocity vector (m/sec). An operator “·” ofEquation 2.1 indicates an inner product. And the frequency range is limited to 0.5 to 5 Hz. Because RI
can be calculated sequentially in realtime and can detect P wave, it is possible to utilize not only forthe early warning for big earthquake but also assist proper countermeasures after an event by offering

accepted paper, 15WCEE
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(2.3)

3. EARTHQUAKE MOTION VIEWED FROM RI

Difference between Epicentral Distance in km and 127km fromFigure 3.1 shows the change of RI more than zero of K-NET stations at Aomori, Miyagi, Fukushima,
Ibaraki and Chiba prefectures corresponding to the difference of the epicentral distance between theepicentral distance of each station and the shortest epicentral distance (127km), separated to the northand south part for the rupture point of the 3.11 earthquake. This figure shows the situation properly ofthe earthquake motion propagation from some sources with time difference. In southern side, RI grew
gradually and reached its maximum value more than intensity 5 taking a lot time, while RI in case ofnorthern side reached its maximum value relatively early.
Taking advantage of the features of RI to be able to shows the intensity of the earthquake motion inreal-time, it is possible to draw a propagation of the earthquake motion with distribution of RI of eachstation 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 and reached its maximum
value quite later than the epicentral area.

Time in second from 2011/03/11, 14:46:26JST(a)
1 Distribution of Maximum Realtime Intensity RI(2) Change of RI on Time Domain at Various Sites

Figure 1andChange
ChangeofofRealtime
RealtimeIntensity onFigure
3.1 Distribution
DistributionofofMaximum
MaximumRealtime
Realtime Intensity
Intensity andIntensity on Time Domain at Various Sites
Time Domain at Various Sites

4. OPERATING CONDITION OF VARIOUS WARNING SYSTEM
Figure 4.1 shows the variation of real-time intensity at eastern Japan using strong motion records ofK-NET and other organization with alarm situation. Horizontal axis is a difference of the epicentral

accepted paper, 15WCEE©SDR: 2011.4.7., modified at 5.19 and 7.3

7.0300
14:51:00

100240MisawaMorioka

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 but
Aizu, 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

distance adding + or – corresponding to north and south to the epicentre and vertical axis is elapsed
time from 14:46:26 on March 11, 2011, the start time of the waveform recording at K-NET Oshikastation, the fastest detection station. Colored circles indicate the value of RI, peak and the time ofmaximum value as legend. Also circled number corresponds to the sequence number of the early
earthquake information by JMA for the information 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 advance in Kanto region, a time reaching each intensity grade increasingly

14:48:00④79s

6037s:
EEW ofJR②36s
Shinkansen①2 3 s: EEW o f JMA③44s

14:47:00

2 8 s: EEW via NHK0-400

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 4.42.0 3.6
1.5 2.9
0.5 1.3
0.0 0.5
P-arrival

400

north side

Figure4.1 Variationof Realtime
Intensity
aroundaroundthe Eastern
using
StrongMotionRecordsFigure
2 Variationof Realtime
Intensity
the Japan
Nationusing
StrongMotionRecordsof
K-NET
andother
Organization
withAlarm
Situation.
of K-NET and other Organization with Alarm Situation

accepted paper, 15WCEE
slow and a time reaching maximum intensity is quite late.
While the earthquake early information by JMA was issued for public at 14:46:49 (23 seconds fromstart) on Figure 4.1, the issued area was restricted all part of Miyagi and Iwate prefecture, andrestricted part of Fukushima, Akita and Yamagata prefecture. And it was not issued for the otherdamaged area with maximum intensity more than 5, so it must be said that the alarm is issued
unreasonable. Meanwhile, because hypocentral distance is more than 120 km even in close area toepicentral 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 theearthquake occurrence. However it seems to be possible for the earthquake early information by JMA
to be valuable for earthquake disaster prevention, there is no report to help something specifically.
Earthquake alarm system for JR Shinkansen-line, the bullet train, also failed to issue the P-wave alarm,and a conventional alarm system just worked by exceeding the trigger level, 120 Gal (=cm/s/s) in
14:47:03. This time is later at least five seconds than initial system in 1985 with trigger level of 40 Gal.
And if the system installed same system which issued P wave alarm successively at the time of the2004 Niigataken-Chuetsu earthquake, the additional leading time is estimated 15 seconds or more. The
current earthquake early alarm system that failed to issue the alarm in this time is similar system tothat of JMA.
Figure 4.1 also shows the result of simulation of FREQL assuming installation close to epicenter. Here,
FREQL is an earthquake early warning system essentially differs from that of JMA. FREQL is uniquesystem characterized by its functions to distinguish P wave from ground motion, to determine theearthquake parameters independently at installed site. Also FREQL can issue P wave alarm based on
the dangerousness of the detected earthquake motion with realtime data processing. FREQL has been
operated as practical system for a disaster prevention system of railway companies or otherorganization. Please see the detail of FREQL in the paper (Nakamura, 2007). In this paper FREQL
simulation is the realtime processing of the waveform data to judge its dangerousness for P wavealarm.
A simulation result of FREQL using the waveform 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 peninsula issued the P-wave alarm at 14:46:54 and estimatedexact earthquake parameters, location and depth, without magnitude. The simulation results for thiscase agree with the actual situation. It shows the validity of the FREQL simulation.
On the other hand, tsunami warning was issued about three minutes after earthquake detection. It wasenough early but that was underestimated and modified information was not accurately transferred for
local people. Because organizations without JMA is restricted to issue these kinds of warnings astsunami 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 with extremely long duration even for Japanese people
used to feel earthquake motion commonly. Most of Japanese people including a people on vehicles
noticed the earthquake motion by themselves before enlarged motion without any warnings. Thissituation can be understood easily by Figure 4.1. This abnormal motion started some tens secondsbefore the large motion. Since many people felt this abnormal earthquake motion as natural tsunami
alert, there was only a few people started activity for evacuation immediately. Especially staffs oflocal government did not start any activities immediately and waited tsunami warning from JMA,
although it is only a few minutes. This inactive approach seems to enlarge tsunami damage of thisearthquake. However, people in Tohoku area, commonly hit by tsunami, had a legend to escape before
anything else in case of large earthquake, there are many losses in this time. It is necessary 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 were some problem on tsunami warning andcountermeasures. It is possible to estimate that the people could not escape independently judging thedangerousness by choice, because of tsunami warning only issued by JMA under low and excessive
sense of safety for huge coastal levee higher than estimated tsunami height by JMA. Moreoveraccepted paper, 15WCEE
frequent excess tsunami warning based on over-estimation for foreshocks might cause crying wolf
effect. Although the activity for evacuation must reflect local conditions, for instance, landform andvegetation, the activity is triggered by the warning from JMA of central bureaucracy. This situation
seems to be abnormal. After the Kobe earthquake disaster, sixteen years ago, why does JMA amend 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, thesituation continues still today without granted the request. Not only tsunami warning but also EEW,
early earthquake warning, is also under same situation. Although EEW by JMA could not be issued
before a large motion even in case of M7-class earthquake in damage area (within 30 to 50 km), public
information continues saying the EEW by JMA is useful. Although the 3.11 earthquake was a rare
chance that EEW by JMA can be useful, the system failed to issue the proper warning. As a result,
EEW by JMA is protected by low but can not protect local people. The author thinks that JMA withnation wide observation network must focus to inform 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 therescue activity. As said before, both earthquake and tsunami warning must be realized by localorganizations in their domain and the warning issued by central bureaucracy is meaningless. What isrequired 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. Many observed
data by JMA must be issued in realtime. If the offshore observatory of sea-wave height were
distributed for coastal municipalities in realtime, the losses by tsunami will decrease drastically.

6. CONCLUSIONThis paper shows that real-time intensity RI can comprehensibly express the distribution of the seismic
intensity and the propagation of the earthquake motion of the 2011 off the Pacific coast of Tohoku
Earthquake. EEW by JMA can gain only comparable or a little long time margin comparing withon-site FREQL or ordinary alarm seismometer, so the merit cannot be recognized. It has been also
cleared that EEW by JMA is not applicable for the near-field earthquakes. Earthquake early warning
by JMA is not a kind of a system operated under a low because it is feared adverse result fromexcessive expectation. It seems to be necessary to amend Meteorological Service Act as abolish theunnecessary restrict on earthquake early warning or tsunami warning, base on a view that such a kindof restrict causes the serious damage of the 3.11 earthquake. Finely-tuned responses are required for adisaster like epicentral earthquake or tsunami because of the strong reflection of the local conditions. It
is desirable to change the centralized way of JMA and handle in close coordination and cooperation
with local authorities specified familiar with local circumstances. A system to directly link thenecessary information to the area must be established and the author expects JMA to support thesystem.

AKCNOWLEDGEMENT
In this paper, the waveform data was mainly provided by K-KET and KIK-net of NIED, National ResearchInstitute for Earth Science and Disaster Prevention. The author would like to sincerely express his highest
appreciation and gratitude to people and the organizations.

REFERENCES
Nakamura, Y. (2007), FREQL and AcCo for a Quick Responce to Earthquakes, Earthquake Early WarningSystems, Springer-Verlag, 2007/08, pp.307-324.
Nakamura, Y. (2003). Examination of a Rational Strong Motion Index – Relationship between the DI value andthe other strong motion indices –, the 27th JSCE Earthquake Engineering Symposium, 54.
Nakamura, Y. (1998). A New Concept for the Earthquake Vulnerability Estimation and its Application to the
Early Warning System, Early Warning Conference ’98.