The 2011 off the Pacific coast of Tohoku Earthquake:
Outline and some topics
Yutaka Nakamura 1, Tsutomu Sato 1, Jun Saita 1

Abstract
The 2011 off the Pacific coast of Tohoku Earthquake emerged various phenomena. This paper describes the distribution 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 thealarm was restricted and a lot of damaged areas were not included.
EEW for Shinkansen-line consisting of JMA type instrument, also
failed to issue the P-wave alarm, and only a conventional alarm system worked by exceeding the trigger level of 120 Gal (=cm/sec2).
One FREQL, a single-station-system, nearby base of Oshika peninsula succeeded to detect the earthquake, to issue P wave alarm and to
determine the earthquake parameters reasonably but magnitude. However even the site was on hard ground, it needed 15 seconds to issue P
wave alarm. Proposed technique estimates the origin time and locationfrom the P-wave detection time of at least 5 sites. In case of the 2011
off the Pacific coast of Tohoku Earthquake. The location estimated 3.7
seconds after the first P-wave detection. Growing up the magnitude,
P-wave alarm can be issued around 6 seconds after P-wave detection.
Also this earthquake caused severe damage in a wide sphere. Evenin Tokyo metropolitan area liquefaction was observed. From a viewpoint of earthquake disaster prevention, it is important to grasp thevulnerability from the inventory survey before the expected event.
This paper explains the vulnerability index Kg value and compares theliquefaction caused by this earthquake with the results of the microtremor measurement in 1990. For example, at Maihama area we had 4
measurement points. In this area, Kg value was 9.8 to 34.9 (micro
strain/Gal) and this agrees with the field investigation.
_______________________________
1 System and Data Research Co., Ltd., Japan.
11

12

Yutaka Nakamura, Tsutomu Sato, Jun Saita

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 isnecessary for earthquake disaster prevention learning from the experiences of the 3.11 earthquake is discussed and the author proposes fornational organization like JMA, Japan Meteorological Agency.
On the other hand, the 3.11 earthquake caused severe damage inwide sphere focusing mainly around eastern Japan area. And even inTokyo metropolitan area, more than 200 to 300 km far from the focal
region, liquefaction was occurred in many places. By the way, the ultimate and proper countermeasure against earthquake disaster is tomake all the structure earthquake resistance. For this, it is important tograsp the vulnerability from the inventory survey before the expected
event.
This paper explains the vulnerability index Kg value derived fromthe result of microtremor measurement and adopts Kg value for the
microtremor measurement in 1990 to estimate the possibility of liquefaction. Then Kg value compares the liquefaction situation caused by
the 3.11 earthquake.
2. Outline of the 3.11 earthquake
2.1. Realtime 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 [1]. Then, in consideration of theclosely relationship between DI value and the instrumental seismic intensity of JMA, Ijma, DI is redefined as real-time intensity RI [2]. DI
and RI are defined from the power per unit mass of the earthquake
motion as Equations. (2.1) and (2.2), so it is characterized to be possible to grasp a physical value momentarily, unlike Ijma calculated as
artificial value with 60 second-length earthquake motion after the
event.
12

The 2011 off the Pacific coast of Tohoku Earthquake: Outline and some topics

DI  log( |a•v| )RI  DI  6.4

13

(2.1)
(2.2)

Here a is an acceleration vector (m/sec/sec), v is a velocity vector(m/sec), and then the product of these vectors is known as a power
density in unit of W/kg. An operator “•” of Equation (2.1) indicates aninner 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 for the early warning for
big earthquake but also assist proper countermeasures after an event
by offering the power of seismic strong motion accurately.
By the way, the power density of a mankind is roughly 1.0 W/kg,
and this amount of power density corresponds to 6.4 of the seismic intensity in Japan. The relationship between RI and MMI, Modified
Mercalli Intensity, is shown as follows.
MMI  (11 / 7)  RI  0.5(2.3)

2.2. Earthquake motion viewed from RI
Figure 2.1 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(127 km), separated to the north and south part for the rupture point of
the 3.11 earthquake. This figure shows the situation properly of theearthquake 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 in real-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 the13

Yutaka Nakamura, Tsutomu Sato, Jun Saita

14earthquake motion reached wide 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.
2.3. Discussion

2011/03/11, 14:46:26JST

Difference between Epicentral Distance in km and 127km fromThe 3.11 earthquake is abnormal earthquake with extremely long
duration even for Japanese people used to feel earthquake motioncommonly. Most of Japanese people noticed the earthquake motion bythemselves before reaching enlarged motion without any warnings.
Although this abnormal motion started some tens seconds before thelarge motion, there was only a few people started activity for evacuation immediately. Especially staffs of local government did not startTime 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

Figure1 Distributionof Maximum
Realtime Intensity
andIntensity
Change ofand
Realtime
Figure2.1. Distributionof Maximum
Realtime
Change ofIntensity on Time Domain at Various Sites

Realtime Intensity on Time Domain at Various Sites

14

The 2011 off the Pacific coast of Tohoku Earthquake: Outline and some topics

15

any activities immediately and waited tsunami warning from JMA,
although it was only a few minutes. This inactive approach seems toenlarge tsunami damage of this earthquake. It is necessary to review indetail of the matter of this situation, but there are no signs to start review by third party. People may not judge to escape by themselvesbecause of independency on the tsunami warning of JMA limited bylow or on the huge coastal levee higher than estimated tsunami heightby JMA. Moreover frequent excessive tsunami warning by overestimation might cause crying wolf effect.
Although the activity for evacuation must reflect local conditions,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? Deprivation
the judgment from local government causes dependency for central
bureaucracy and lack of decision on activity for disaster prevention
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 indamage area (within 30 to 50 km), public information continues saying the EEW by JMA is useful. The 3.11 earthquake was a rare chancethat EEW by JMA can be useful, but no specific example that EEW of
JMA was useful was reported. Therefore it is clear that the systemfailed to issue the proper 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 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 make enable to determine the severe damaged area quickly and help the rescue activity. As mentioned
before, both earthquake and tsunami warning must be realized by local organizations in their domain and the warning issued by central
bureaucracy is meaningless. If the offshore observatory of sea-wave
height were distributed for coastal municipalities in realtime, the losses by tsunami will decrease drastically.
3. Earthquake Early Warnings
15

Yutaka Nakamura, Tsutomu Sato, Jun Saita

16©SDR: 2011.4.7., modified at 5.19 and 7.3

7.0

Yamabiko #144 Max

300
14:51:00

100

240

MisawaMorioka

Tsukidate

0

200

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-100

Aomori-200

Hayate #27-300

14:52:00

Yamabiko #61

3.0
360-400

Fukushima
Sendai4.0

Tsukuba
Mito

Yokohama

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-Kamikita
of Aomori, Kaetsu of
Niigata, north-eastof Chiba and southof Saitama; JMA#7③Add. Tochigi andeast of Kanagawa;JMA#10④Add. the rest of
Aomori, Chuuetsu,
south of Gumma,
north of Saitama,
the rest of Akita,
north-west of Chiba
and the 23 wards ofTokyo; JMA#12

6.0
Shinjuku

Realtime Intensity
RImaxRimax

3.1. Working condition of various warning systems

14:48:00

④79s

60

37s:
EEW ofJR
Shinkansen①2 3 s: EEW o f JMA③44s

14:47:00

0
-400

②36s

2 8 s: EEW via NHK

20s: First EEW of FREQL-300

south side

-200

-100

0

100

200

Difference
betweenEpicentraland127 kmEpicentral
Distancein kmDistance
minus
127km
Difference
betweenEpic.Dis.
and
127km

300

RI MMI
PeakMax
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

Figure3.1.2 Variation
RealtimeIntensity
Intensityaroundaroundthe
theNation
EasternJapan
using
StrongFigureVariation of Realtime
using
StrongMotionRecordsof Records
K-NET andother Organization
with Alarm Situation.
Motionof K-NETand other Organization
with Alarm Situation

16

The 2011 off the Pacific coast of Tohoku Earthquake: Outline and some topics

17

Figure 3.1 shows the variation of real-time intensity at eastern Japan 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 to north and south to the epicenter and vertical axis is elapsed time from 14:46:26 on March 11, 2011
(JST), the start time of the waveform recording at MYG011 Oshika,
the fastest detection station. Colored circles indicate the value of RI,
peak and the time of maximum value as legend. Also circled number
corresponds to the sequence number of the EEW by JMA based on theestimated intensity more than 3 or 4. An onset time of each intensity
grade and maximum intensity delay 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 timereaching each intensity grade increasingly slow and a time reaching
maximum intensity is quite late. While the earthquake early in formation by JMA was issued for public at 14:46:49 (23 seconds fromstart) on Figure 3.1, 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 other damaged area with maximum intensity more than 5, so it must be said that thealarm was issued unreasonable. Meanwhile, because hypocentral distance is more than 120 km even in limited area to epicentral region, aduration time of the initial motion is estimated more than 15 seconds.
So people in the area had enough time margins before suffering large
earth quake motion after noticing the earthquake 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 tohelp something specifically. Earthquake alarm system for JR Shinkansen-line, the bullet train, failed to issue the P-wave alarm, and a conventional alarm system just worked by exceeding the trigger level,
120 Gal (=cm/s2) in 14:47:03. This time is later at least five seconds
than initial system installed in 1985 with trigger level of 40 Gal. And
if there were same system which issued P wave alarm successively at
the time of 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 alarm in this time is similarsystem to that of JMA.
17

18

Yutaka Nakamura, Tsutomu Sato, Jun Saita

Figure 3.1 also shows the result of simulation of FREQL which isassumed to be installed at K-NET or KiK-net sites. Here, FREQL isan earthquake early warning system essentially differs from that of
JMA. FREQL is unique system characterized by its functions to distinguish P wave from ground motion, to determine the earthquake 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 aspractical system for a disaster prevention system of railway companies
or other organization. Please see the detail of FREQL in the paper [3].
FREQL detected the event at 14:46:40 and issued the P-wave alarm at
14:46:46 as a simulation result with waveform of MYG008 Kitakami.
An actual working FREQL at a base of Oshika peninsula issued Pwave alarm at 14:46:54 and estimated exact earthquake parameters,
location and depth, exception of magnitude. The simulation results forthis case agree with the actual situation. FREQL took some to issue P
wave alarm after earthquake detection, because the site is extremely
hard rock site and the earthquake motion grew very slow to large motion, FREQL required rather long time to judge the earthquake motion
danger. The P wave alarm was issued exceeding 2.1 of PI, RI value
during initial motion, and the earthquake motion reached finally 5.5 of
RI at that site. This earthquake motion seems not to cause serious
damage around the site. It shows the validity of the FREQL simulation.
3.2. Proposal of the new estimation technique of earthquake parameters from multi station information
One FREQL station nearby base of Oshika peninsula succeeded todetect the 3.11 earthquake, to issue P wave alarm and to determine theearthquake parameters reasonably exception of magnitude. Howevereven the site was on hard ground, it needed 15 seconds to issue P
wave alarm. So this paper compares the early P wave alarm between
ordinal FREQL single-site-estimation and the other multi-detection
method using FREQL technique, and then considers a possibility ofearlier earthquake warning.
(1) Estimation of origin time and location of a source
18

The 2011 off the Pacific coast of Tohoku Earthquake: Outline and some topics

19

Origin time and location of a source (latitude, longitude and depth)
are estimated from P wave detection time information of more than
five stations using least squares method, assuming a P wave propagation velocity as 6 km/sec. Consideration below uses strong motion
records of K-NET and KiK-net and assumes that the station has an instrument corresponds to FREQL and sends a time of P wave detection
in real time, and monitors a detection, an alarm, growth of magnitude
and so on. That is, initial estimation is done with P wave detection information from first five stations, and the estimation is updated as often as receiving the information from the other station and the result iscompared with the result before. If the scatter of the results is in predefined range (5 km in this paper), the result is fixed. If a density ofstrong motion observatories is less than 20 km, it will be expected thatthe location is fixed within 4 seconds after first P wave detection. In
case of simulation for the 2004 Niigata-ken Chuetsu earthquake and2010 Taiwan Kaohsiung earthquake, the source locations can be determined in 1.04 seconds and 1.69 seconds after first P wave detection,
respectively. In contrast, the JMA method with multi observation required about 5 seconds in average and 5.4 seconds the 3.11 earthquake.
(2) Estimation of magnitude
Magnitude is estimated by a formula below [4], based on the amplitude of P wave and its frequency by Gutenberg-Richter.
M  1.59(log Vp  log R)  1.53

(3.1)

Here, Vp is P wave amplitude of vertical motion in mkine (= 0.001
cm/sec) and R is epicentral distance in km.
Although Equation (3.1) supposes that the value of Vp is observed
on a hard ground, K-NET station is not always installed on a hardground. So the earthquake motion amplification factor A for each station is estimated as Table 3.1 based on the estimate formula for seismic intensity [5], and Equation (3.1) is modified as follows.
M  1.59(log Vp  log R)  1.53 1.59 log A

19

(3.2)

Yutaka Nakamura, Tsutomu Sato, Jun Saita

20

Table 3.1 the amplification characteristics at station of k-net and kik-net
Site
MYG011
MYG008MYG002
MYGH03
MYGH12
MYG010
IWTH25
IWTH26
IWT010
AKT023
IWTH24
MYGH02
FKSH03

OshikaKitakami
UtatsuKarakuwa(kik)Shizugawa(kik)Ishinomaki
Ichinoseki-W(kik)Ichinoseki-E(kik)Ichinoseki
Tsubakidai
Kanegasaki(kik)Naruko(kik)Takasato(kik)Sum of
data
9
11
14
13
13
12
10
11
9
8
10
6
12

Averaege of RI
amplification
1.504
0.749
1.203
0.375
0.350
1.683
0.854
1.203
0.805
0.500
1.133
0.136
1.128

Dispersion of
2logA
0.885
0.602
0.570
0.589
0.629
0.864
0.740
0.858
0.888
0.706
0.771
0.712
0.319

Constant termEq.(3.2)of Fig.(2)
0.33
0.93
0.57
1.23
1.25
0.19
0.85
0.57
0.89
1.13
0.63
1.42
0.63

Although epicentral distance is calculated based on a rupture startpoint estimated in first few seconds, epicentral distance will bechanged by the progress of fault rupture. And also main shock will arrive after the initial motion. So Equation (3.2) can be adopted for atime window R/4Cr after P-wave detection. Here, Cr is rupture velocity of the fault. And a rupture time for 1/4 of the epicentral distancefrom the start point of the rupture. In this time, the scatter of the estimated magnitude will be less than ± 0.2 during the applying time.
After fixing the epicenter, magnitude is estimated from Equation(3.2) and then the P wave alarm can be issued based on the M- relation if a station seems to be danger. Because this method can grasp thelocation of the earthquake relatively accurately, it is possible to determine an area needed alarm with tremendous precision. Finally averaged magnitude will be the magnitude of whole system.
3.3. Discussion
In case of the 2008 Iwate and Miyagi earthquake (M7.2), information from five stations is observed 3.46 seconds after first detection
at IWTH25 Ichinoseki-Nishi station, and the location of the epicenteris determined latitude 39.008˚N, longitude 140.875˚E and depth of 4.6 km. Then after 0.55 seconds, information from MYGH02 Naruko
station was added and the location of the epicenter moved to latitude
39.027˚N, longitude 140.867˚E and depth of -2.1 km. Because the difference was within 5 km, the estimation was fixed. The depth was mi20

The 2011 off the Pacific coast of Tohoku Earthquake: Outline and some topics

21

nus value but less than 5 km so the depth fixed as 0 km. The epicenter
by JMA was latitude 39.028˚N, longitude 140.880˚E and 8 km depth.
In case of the 3.11 earthquake, information from five stations is observed 2.54 seconds after first detection at MYG001 Oshika station,and the location of the epicenter is determined latitude 36.376˚N, longitude 146.094˚E and depth of 381.6 km. Then after 1.13 seconds, information from MYG010 Ishinomaki station was added and the loca10

Tsubakidai Ｍ fixed
Ichinoseki-E Ｍ fixed Naruko Ｍ fixed
Ichinoseki-W Ｍ fixed99
Magnitude M

88

Tsubakidai
Kanegasaki Ichinoseki-E

M7.2 by JMA

77

S
wave arrival.
Ｓ波到着時刻高郷を除くTakasato) Ichinoseki-W(exclude

Ichinoseki

系列1
系列2
系列3
系列4
系列5
系列6
系列7

Takasato
at Takasato,66

S wave arrival is later.
Ichinoseki Ｍ fixed
Takago Ｍ almost fixed

Naruko55

Kanegasaki Ｍ fixed

44
33
2

-2

-1

-2

-1

11
0
22
33
Time from earthquake detection (sec)

44

0

55

Figure 3.2 The growth of magnitude of the 2008 Iwate and Miyagi Earthquake10

karakuwa Ｍ fixed Kitakami Ｍ fixed
Shizugawa Ｍ fixed
Utatsu Ｍ fixed
Shizugawa
Kitakami
Alarm level Ｍ7.7
karakuwa

Ishinomaki

33
2
-5
-5

0

0

Takasato
TakasatoＭ

SＳ波到着時刻
wave arrival.
高郷
fixedfor Takasato) Takasato(except(exclude
Takago)
高郷を除く

P wave alarm at Oshika

55

P wave alarm at Utatsu

66

P wave alarm at Ishinomaki

77
P wave alarm at Karakuwa
P wave alarm at Shizugawa
P wave alarm at Kitakami

Magnitude M

88

44

Utatsu Oshika

M9.0 by JMA

99Ishinomaki Ｍ fixedOshika Ｍ fixed

10
55
10
1515
2020
2525
Time from earthquake detection (sec)3030

Figure 3.3 The growth of magnitude of the 2011 off the Pacific coastof Tohoku Earthquake

21

3535

22

Yutaka Nakamura, Tsutomu Sato, Jun Saitation of the epicenter moved to latitude 38.023˚N, longitude 143.331˚E
and depth of 10.8 km. The difference of estimation was quite large.
After 0.89 seconds, information from MYG030 Towa station was additionally arrived and the location of the epicenter moved to latitude
38.003˚N, longitude 143.356˚E and depth of 81.1 km. Because the difference of the location is within 5 km but the depth was quite differ
for each other but the reliability of the depth estimation at this region
was low, the fixed estimation became the second one with 4.56 seconds. Also, the epicenter by JMA was latitude of 38.103˚N, longitude
142.860˚E and depth of 24 km.
Figures 3.2 and 3.3 show the progress of the magnitude based onequation 3.3 with the information of first six stations for each earthquake. Information of FKSH03 Takasato station was added as an example of little far station as a reference for both figures.
In case of the 2008 earthquake, applicable time is only 1-2 seconds
for the first six stations and the magnitude grew drastically andreached and was fixed 7.2 around one second after detection. In caseof FKSH03 Takasato station about 170 km away, the magnitude grew
relatively slow and stopped within about three seconds. Finally themagnitude was fixed about 7.
In case of the 3.11 earthquake, applicable time was about 13-15
seconds during the growth of the magnitude and the magnitude was
fixed. In case of FKSH03 Takasato station about 300 km away, themagnitude grew yet slower and stopped after the applicable time. The
magnitude reached or was estimated to reach further finally more than
8 for each station. Magnitude 7.7 seems to be the alarm level for eachstation based on the M- relation and the alarm could be issued mainly about six seconds and 15 seconds at least after detection.
Thus it shows that it is possible to issue the alarm six seconds at theearliest after detection. This is almost same time for the earliest Pwave alarm of single detection method for over all sites. For example
Karakuwa station detected P wave at 14:46:40 and issued 14:46:46.
Because in case of the single-station detection system seen in Figure
3.4, the alarm seemed to be issued at 14:46:54, this multi-detection
method can be expected to gain time 8 seconds. Figure 3.4 shows thealarm time of the multi-detection method on the time-line of real timeintensity RI [2] with RI = 1.5 as P wave alarm level.
22

The 2011 off the Pacific coast of Tohoku Earthquake: Outline and some topics

PI alarm at Ishinomaki
Ishinomaki RI=0.0

PI alarm at Shizugawa

PI alarm at Karakuwa
Shizugawa RI=0.0
Karakuwa RI=0.0
Utatsu RI=0.0

PI alarm at Utatsu

Kitakami RI=0.0

PI alarm at Kitakami(The fastest alarm by FREQL)

The time of source fixed.

6th time of P wave detection

35
35

Scale of real-time seismic intensity RI : 5

1st time of P wave detection

Corresponding to Hypocentral distance

42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8

23

PI alarm at Oshika
Oshika RI=0.0

40
45
50
40
45
50
Standard time in Japan: 2011/3/11 14:46:**

55
55

Figure 3.4 P wave alarm time of first 6 sites of the 2011
off the Pacific coast of Tohoku Earthquake

4. Liquefaction
4.1. Vulnerability index Kg value for ground
Vulnerability index K values is proposed as an index to estimate
the strain of ground or the focused part of the structure against esti23

Yutaka Nakamura, Tsutomu Sato, Jun Saita

24

mated earthquake motion, derived from the predominant frequency F
and its amplification factor A of microtremor, and the dimensions of
the structure. The common estimating equation of the strain  or  is asfollows.

 or   K  a(4.1)

Here, K and a are K value and the acceleration value at the baseground, respectively.
In case of ground, Kg value, K value for ground, is defined as follows;  eAd / h eAa /  2 / h eAa /( 2F ) 2 (4 F / Vs )
 eAa /( 2F ) 2 (4 FA / Vb )(4.2)

 eA 2 / F /( 2Vb ) A 2 / Fe /( 2Vb )a

Here, e is input efficiency and Vb and Vs are the velocity of the baseground and surface layer, respectively, in unit of m/s. Also d is displacement at base ground and h is depth of the surface ground.
Hence,

 e    Kg  a(4.3)

Here, Kg  A2 / F and   e /( 2Vb) . In a discussion below, a dimension of Kg sets in /Gal to make clear the relationship that the productof Kg and a indicates strain. Vb can be assumed 600m/s in Japan.
It seems that the input efficiency e may be fluctuated by the waveform of input earthquake motion. In case of the single pulse wave,
large acceleration is required to cause large strain so the input efficiency e must be small. However in case of common event causing
24

The 2011 off the Pacific coast of Tohoku Earthquake: Outline and some topics

25

liquefaction including the 3.11 earthquake has enough long duration,
so input efficiency e can be set 0.6 and then  becomes 1.0. Thus, e  Kg  a(4.4)

The trial on the determination of liquefaction occurrence using Kgvalue will be described below.
4.2. Result of microtremor measurement and liquefaction occurrenceThis paper uses the result of microtremor measurement conducted
in 1990 [6]. The instrument for this measurement was PIC, Portable
Intelligent Collector, a microtremor measuring tool with a threecomponent sensor and data logger units. The microtremor was repeatedly recorded for 40.96 seconds (4,096 data in 100 Hz sampling) at
every measurement site, and a 10.24 seconds length data was chosefrom a viewpoint of less artificial noise. Then the selected data was
Fourier transformed. After that, the horizontal to vertical spectrum ratio was calculated for each component of every measurement and finally H/V spectrum ratio was derived as an averaged spectrum ratio[7]. Predominant frequency F and its amplification factor A are readfrom the H/V spectral ratio. Procedures above had been done in 1990.
This paper calculates Kg value from this result in 1990 to eliminate
any artificial processing and estimates the strain in the surface groundlayer with the acceleration value at the time of the 3.11 earthquake observed nearby sites. Then the proposed index and method are verified
their validity with comparing the estimated strain with the actual liquefaction situation.
(1) Maihama area
Maihama is a reclaimed area filled in 1970s and locates at easternside of Tokyo metropolitan area. Tokyo Disney Land built on it. In
1990, microtremor measurement was conducted at four corners of areclaimed land as MH01 to MH04 shown in Figure 4.1. Kg value
ranges 9.8 to 34.9 /Gal (=micro strain/(cm/sec2)) for MH01 to MH04
as shown in Figure 4.2. A nearby strong motion station, K-NET
25

Yutaka Nakamura, Tsutomu Sato, Jun Saita

26

Urayasu, recorded 164 Gal (= cm/sec2) as maximum acceleration.
Here this maximum acceleration value is 5HzPGA, 5Hz low passed
peak ground acceleration, to restrict the acceleration value to explainAfter Prof. Yasuda of TDU.

This air-photo was shoot at 1990.
MH101

MH102

MH104
MH103

Figure 4.1 Measurement Point and Liquefaction Situation
at Maihama Area

Amplification Factor A,
Predominant Frequency F,
Kg Value
固有振動数Ｆ／増幅倍率Ａ／Kg値

Distribution 舞浜地区のＦ、ＡおよびKg値の分布
of F, A and Kg value at Maihama
100
MH04
MH01

Kg Value

MH02

Kg値

MH03

34.9

10

Aplification
増幅倍率ＡFactor A
PrediminantFrequency F
固有振動数Ｆ

1

0.1
-10

10
30
50
70
90
110
TDL駐車場入口付近測点MH01から道路沿いに測った距離：任意スケール
Distance in units of 30m

Figure 4.2 Distribution of Kg value, Predominant Frequency
F and Amplification Factor A at Maihama Area

26

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27

ing the damage situation properly. And because the amplification factor is assumed about 4 for the ground in this area, maximum acceleration at base ground can be assumed 41 Gal.
From the boring investigation in Urayasu, close to this reclaimed
area, Vb can be estimated about 300m/sec, so the  in equation (4.3)
becomes 2.0. In this case estimated strain will be double. So the strain
in the surface ground is estimated roughly 1240, 1290, 820 and 2710 
for MH01 to MH04, respectively. If strain more than 1000  causesliquefaction as it is often expressed, it seems that liquefaction occurs
at MH01 and MH02, does not occur at MH03 and severely occurs at
MH04. Figure 4.1 also shows the result of the field survey of the liquefaction situation after Yasuda [8]. We can see that the Kg value distribution agrees with the liquefaction situation.
(2) Omori and Oi area
Omori and Oi area in northwest part of Tokyo bay and the mainpart of Oi had been filled up in before 1940s. Measurement points
were set along EW line between a park west side of JR Omori train
station and Oi container wharf, and along NS line in the center of Oi
pier (see Figure 4.3). Figure 4.4 shows the Kg value distribution. This★
★

Figure 4.3. Distribution of Measurement Point and Reported Damage
at Omori an d Oi Area ( : Reported Damage)27

Yutaka Nakamura, Tsutomu Sato, Jun Saita

28

大森・大井埠頭地区と舞浜地区のKg値分布
50
OF13

45

Kg
Value
計測されたKg値

40

MH04

35
30

OF16 OF14

25
20

MH01

MH02

OF107

OF108

15

OF12
OF15

10
MH03

5
0
0

50
100
東西測線に沿った距離：任意スケール

150

Distance

Figure 4.4. Distribution of Kg Value at Omori and Oi Area

Figure 4 Distribution of Kg Value at Omori andfigure shows that Kg value exceeds 15 around the wharf and a park in
the west side of the reclaimed Oi
land. Liquefaction occurs around thepier [9], and also a park in the center of reclaimed land temporaryclosed a baseball ground because of liquefaction and informed damage as crack at artificial shore. There is no more information of damage for this area. In any case the liquefaction situation is less severe
than that of Urayasu or other area.
Kg values corresponding to this damage information are small value around 10 except more than 23 at the pier and more than 15 aroundthe park. Considering that the strain of 1000  is required for liquefaction, it shows that liquefaction must be caused more than 100, 43 and
67 Gal of the acceleration at the base ground, respectively. Because
here is old reclaimed land, Vb must be less than 600 m/sec, but greaterthan 300 m/sec at Urayasu area. It seems that the acceleration between
50 and 100 Gal were required for causing liquefaction in the nondamaged area, although between 22 (=43/2) and 67 Gal were requiredfor damaged area. So Kg value distribution gives proper result for the
possibility investigation of liquefaction.
(3) JR Keiyo-line

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29

JR Keiyo-Line is running along northeast coastal line of Tokyo bay.
Nishi-Funabashi

Minami-Funabashi
Shin-Narashino
Kaihin-Makuhari
Kemigawahama
Inagekaigan
Chibaminato

Soga

Figure 5Distribution of Measurement Points

Keiyo-LinePoints for JR Keiyo-line
Figure 4.5. Distributionfor
of JR
Measurement
Kg>12 corresponds to about 1000
30
30

30

10
10

1.0
1.0

2.0
2.0

3.0
3.0

4.0
4.0

Nishi-Funabashi

5.0

6.0

0
0.0

7.0
1.0

2.0
2.0

3.0
8.0 4.0
3.08.0
4.0

5.0
6.0
9.0
5.0 9.0
6.0

Minami-Funabashi Shin-Narashino

7.0
7.0

Kaihin-Makuhari

蘇我

蘇我

千葉みなと
千葉みなと

千葉みなと
千葉みなと
稲毛海岸
稲毛海岸

検見川浜
検見川浜

稲毛海岸
稲毛海岸

検見川浜
検見川浜

千葉みなと
千葉みなと
稲毛海岸
稲毛海岸

10.0
13.0
15.0
8.0
11.0
13.0
18.0
10.0 9.0
11.0
12.0
13.016.0
14.0
15
8.0
9.0 10.0
10.011.0
11.0 12.0
12.0 12.0
13.0 14.0
14.0 15.0
15.0
16.0 17.0
17.014.0
18.0 19.0
19.0 20.0
20.0

り
海浜幕張
海浜幕張

検見川浜
検見川浜

5

00
0.0
0.0

新習志野

稲毛海岸
稲毛海岸

10

55

10.0 9.0
8.0
10.0
8.0
9.0

検見川浜
検見川浜

海浜幕張
海浜幕張
海浜幕張
海浜幕張

新習志野
新習志野

15

新習志野

20

西船橋

Kg値
Kg=10
=10

南船橋

15
15

25
西船橋
西船橋

20
20

南船橋
南船橋

25
25

←ここからは震災後のgoogle衛星写真あり←ここからは震災後のgoogle衛星写真あり
Here and after, it is possible to confirm with Google Map

Kg=10

13.0
15.0
10.0
11.0
13.0
18.0
11.0
12.0
13.016.0
14.0
15.0
10.011.0
11.0 12.0
12.0 12.0
13.0 14.0
14.0 15.0
15.0
16.0 17.0
17.014.0
18.0 19.0
19.0 20.0
20.0

Kemigawahama

16.0
16.0

17.0
17.0

Inagekaigan

18.0
18.0

19.019.0

Chibaminato

20.020.0

21.021.0

22.022.0

Soga

23.0 23.0

24.0 24.0

6 Distribution of Possible Damage and Kg Value for JR Keiyo-Line
Liquefaction：Figure By
Yasuda(2011) Chiba Envi. Research Center Google Earth

No Liquefaction： By Yasuda(2011)
Figure 4.6. Distribution of Possible Damage and Kg Value for
JR Keiyo-line

29

30

Yutaka Nakamura, Tsutomu Sato, Jun Saita

Microtremor measurement in 1990 was conducted every 100m for
22.5km between Nishi-Funabashi train station and Soga train station(see Figure 4.5). Figure 4.6 shows distribution of Kg value for the distance from Nishi-Funabashi station, the western end of the measured
area. An area marked dark pink and light blue indicates a portion ofliquefaction and not liquefaction, respectively, after Yasuda [8]. Also
light pink indicates liquefaction after Chiba Prefectural Environmental
Research Center [10]. After 7 km, purple part indicates a possible areawith liquefaction from comparing Google Earth photos before and after the earthquake.
It seems that distribution of Kg value in Figure 4.6 agrees with theresult of reconnaissance survey. And at the area of liquefaction occurrence, Kg value is mostly more than 10. Maximum acceleration
around this area can be estimated about 50 Gal because observed acceleration was around 200 Gal and amplification factor is assumed 4.
With considering the low Vb as 300 m/sec, the strain is estimatedabout 1000  when Kg>10. It is able to be thought that the liquefaction judgment is almost proper.
(4) JR Kashima-line
JR Kashima-Line is running through marsh land in northern greater
Tokyo area. Microtremor measurement in 1990 was conducted every
100m from south to north between JR Katori station and JR Kashima
Soccer Stadium station. In this area, we have no public information ofliquefaction occurrence. So we have compared aerial photos opened
by Google Earth to find out differences between before and after theearthquake. Figure 4.7 shows distribution of Kg value for the distancefrom Katori station, the southern end of the measured area. An area
marked pink and brown indicates a possible area with liquefaction anddamage for embankment, respectively. Although this is not a result ofreconnaissance survey, it seems that the damage relates to the changeof Kg value and threshold level for damage occurrence is little morethan 10 of Kg. Because this area is rather close to the epicentral area,
observed earthquake motion was larger than that of Tokyo bay area.

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31

Figure 4.7. Distribution of Measurement Point, Possible Damage andKg Value for JR Kashima-line

5. Conclusion
This 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 3.11 earthquake.
And this paper compares between the early P wave alarm using
multi-detection method with FREQL P wave detection and that of single-station detection. As a result, a tendency is seemed that the slower
magnitude grew, the farther the station locates. Although P wave
alarm is relative earlier for the distant earthquake, it is confirmed thatsome station can issue earlier alarm with the multi-detection method
and more exact magnitude and location of the epicenter can be determined promptly. A single site detection system is commonly early detection system for earthquake alarm system, however it sometimes requires rather long process time for P wave alarm in case of an earth31

32

Yutaka Nakamura, Tsutomu Sato, Jun Saita

quake growing the motion gradually. On the other hand, because a
multi-detection system uses only information of P wave detection time,
the system provides exact earthquake parameters as source locationand magnitude promptly, and could be possible to advance issuing the
P wave alarm. Currently, JMA issues the earthquake early warning as
an activity required by law. However national institutions with nation
wide observation network must concentrate into prompt announcement of the accurate source location and magnitude from their network. This is the primary role of the national institutions and will contribute to the action immediately and accurately after earthquake.
On the other hand, from a viewpoint of earthquake disaster prevention especially against liquefaction, this paper adopted the proposed
index Kg value for liquefaction occurrence based on the result of microtremor measurement conducted in 1990, and then compared between the result of determination of the liquefaction possibility andthe actual liquefaction situation at the time of 3.11 earthquake. As aresult, it confirmed that liquefaction occurred at the site with Kg value
more than 12. And also the possible damaged area only from thechange of the aerial photographs before and after the earthquake on
Google Earth agrees with the result of the microtremor measurement
along the railway in 1990. The validated technique here is a simple
technique to measure microtremor and it can realize an inventory survey. So it will be possible to take a proper countermeasure based on
the ordinary investigation technique in detail for an area fell out by
this proposed technique. And also it is possible to confirm an effectthe countermeasure work with a change of microtremor characteristics
before and after the work.
EEW 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 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 from excessive 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 kind of restrict causes the serious damageof the 3.11 earthquake. Finely-tuned responses are required for a dis32

The 2011 off the Pacific coast of Tohoku Earthquake: Outline and some topics

33

aster like epicentral earthquake or tsunami because of the strong reflection of the local conditions as geography, local culture, or regional
industry. It is desirable to change the centralized way of JMA andhandle 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.

Acknowledgement
In this paper, the waveform data was mainly provided by K-KETand KIK-net of NIED, National Research Institute for Earth Scienceand Disaster Prevention. The authors would like to sincerely express
our highest appreciation and gratitude to people and the organizations.

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[3] Nakamura, Y. (2007): FREQL and AcCo for a Quick Response
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Yutaka Nakamura, Tsutomu Sato, Jun Saita[6] Nakamura, Y. and Takizawa, T. (1990): Ground Motion Characteristics around the Ooi Reclaimed Land in the Tokyo Bay Area Estimated by Microtremor Measurements, Proceedings of the Eighth Japan Earthquake Engineering Symposium, 679-684.
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[8] Yasuda Laboratory Web Site on Tokyo Denki University(2011), http://yasuda.g.dendai.ac.jp/[9] Tokimatsu, K. et al (2011): Damage for Ground caused by the2011 off the Pacific coast of Tohoku Earthquake, Research Reporton
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