Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanSTRONG MOTION RECORDS FROM THE 2011 OFFTHE PACIFIC COAST OF TOHOKU EARTHQUAKE
Saburoh MIDORIKAWA1, Hiroyuki MIURA2 and Tomohiro ATSUMI3
1Professor, Department of Built Environment, Tokyo Institute of Technology,
Yokohama, Japan, smidorik@enveng.titech.ac.jp
2
Assistant Professor, ditto, hmiura@enveng.titech.ac.jp
3
Graduate Student, ditto, atsumi.t.ab@m.titech.ac.jp

ABSTRACT: Owing to dense strong motion networks in Japan, many strong motion
records were obtained from the 2011 Off the Pacific Coast of Tohoku earthquake (Mw9.0). More than 2,000 records are available. This paper describes the outline of strong
motion networks in Japan and the observed records. Overall characteristics of groundmotion from the earthquake are also discussed.
Key Words: strong motion record, The 2011 Off the Pacific Coast of Tohoku earthquake

INTRODUCTION
The gigantic earthquake that hit the Pacific coast of the Tohoku region, northeastern Japan, on March
11, 2011, (the 2011 Off the Pacific Coast of Tohoku earthquake) registered a moment magnitude (Mw)of 9.0, the largest ever recorded in Japan. To understand the characteristics of strong ground motion
from such a gigantic earthquake is of great significance in preparing measures to reduce damage froma similar event in the future. No thorough examinations, however, have been done for thecharacteristics of ground motion from gigantic earthquakes. This is because that such a gigantic
earthquake rarely occurs, and their strong motion records have been only limited.
Many strong motion records were obtained from the March 11 earthquake owing to
implementation of dense strong motion observation in Japan. These records will provide valuable
information to reveal ground motion characteristics of gigantic earthquakes. This paper describes theoutline of strong motion networks in Japan and the observed records from the earthquake. Then,overall characteristics of ground motion from the earthquake are discussed.

STRONG-MOTION OBSERVATION NETWORKS IN JAPAN
Strong motion observation of Japan started in 1953. After that, the number of the strong-motion sites
was increasing. During the 1995 Kobe earthquake, however, few records were observed in thedisastrous belt zone where many buildings and infra-structures were totally collapsed. After theearthquake, importance of strong-motion observation has been strongly recognized. As a result,many nation-wide and local strong-motion observation networks were constructed. In total, more297

than 10,000 strong motion sites on ground are maintained by different institutions (Midorikawa,2005a). The main objective of the networks constructed is classified into two types; one is basic
research to obtain the time history data for analysis, and another is disaster management to obtain theseismic intensity data for quick and efficient emergency response decisions.
The nation-wide networks for research are such as K-NET (about 1,000 sites) and KiK-net (about700 sites) by National Research Institute for Earth Science and Disaster Prevention (NIED) andPARI-net (about 70 sites) by Port and Airport Research Institute. The other research institutes suchas Building Research Institute (BRI), National Institute for Land and Infrastructure Management,
National Institute for Rural Engineering, and Central Research Institute of Electric Power Industry,
have also their networks.
The networks for disaster management are such as JMA-net (about 600 sites) by Japan
Meteorological Agency, Prefectures-net (about 2,800 sites) by each prefectural office and MLIT-net(about 700 sites) by Ministry of Land, Infrastructure and Transport. The Prefecture-net wasestablished with initiative of Fire and Disaster Management Agency, and the instrument to measure theseismic intensity was installed at almost all the municipalities in Japan. Figure 1 shows locations ofthe sites for the nation-wide networks. In addition, lifeline companies such as Japan Highway Public
Corporation, Japan Railway Companies, and Nippon Telegraph and Telephone Corporation, have also
their nation-wide networks for disaster management. For example, the network by Japan Highway
Public Corporation consists of about 300 sites.
The local networks have been also constructed by universities, local governments and privatecompanies. In Sendai, Miyagi Prefecture, which is the largest city in the Tohoku region, two local
networks have been implemented by Tohoku University and Tohoku Institute of Technology,
respectively (Ohno et al., 2011; Kamiyama, 2011). In the Tokyo Metropolitan area, the high-density
seismic observation network of about 250 sites, called MeSO-net, has been installed at an interval

Fig. 1

Distribution of strong motion sites of nation-wide networks in Japan298

distance of about 5 km by Earthquake Research Institute (ERI), University of Tokyo (Sakai andHirata, 2009). Although the main objective of this network is not strong motion observation but tomonitor the seismic activity of Tokyo, the full-scale accelerations of the observation system are 1.5 g
and 0.5 g for horizontal and vertical component, respectively. ERI has also more than 60 strong
motion sites in the Tokai and Kanto regions (Kudo, 1999). The other universities such as Tokyo
Institute of Technology, Hokkaido Univ., Nagoya Univ. and Kyoto Univ., have also their localnetworks.
Local governments have also their network for disaster management. The city of Yokohama
developed the dense network which consists of 150 sites with spacing of about 2 km. Using theground motion data, the damage assessment system works immediately after the event (Midorikawa,2005b). The other major cities have the similar but smaller system. Lifeline companies such as
Tokyo Gas, Osaka Gas, and Toho Gas Companies, have also the network for the damage assessment
system.

OUTLINE OF OBSERVED STRONG MOTION RECORDS
Many strong motion records were obtained from the March 11 earthquake. About 1,200 K-NET andKiK-net records were made available soon after the earthquake (NIED, 2011). JMA released about
40 records as the sample data on the web site (JMA, 2011), and the additional 400 records are going tobe released. JMA is also compiling several hundreds of records from the Prefectures-network.
About 150 records from the MLIT network have been released (MLIT, 2011). BRI and PARI also
released their records (BRI, 2011; PARI, 2011). We tentatively collected the records from the K-NET,KiK-net (at surface), JMA, Prefectures, MLIT, PARI and BRI networks. The total number of thecollected records is about 2,400. Figure 2 shows the distribution of peak horizontal acceleration andvelocity. The peak horizontal accelerations higher than 500 cm/s2 and 1000 cm/s2 are observed at
210 and 34 sites, respectively. The peak horizontal velocities higher than 50 cm/s and 100 cm/s are
at 111 and 3 sites, respectively.

(a) Peak horizontal acceleration
Fig. 2(b) Peak horizontal velocity

Distributions of peak horizontal acceleration and velocity of observed strong motion records299

Among the records, the maximum peak acceleration observed is about 2.8 g at K-NET Tsukidate,Miyagi prefecture. The acceleration time history of the K-NET Tsukidate record is shown in Fig. 3.
The waveform is composed of two distinct phases producing long duration of strong shaking. In thesecond phase, pulse-like high accelerations appear in the north-south and vertical components. Suchhigh acceleration pulses are not observed at the surrounding sites, as shown in Fig. 4. Figure 5 shows
the orbit of the high-pass-filtered displacement in the vertical (NS-UD) plane, showing an arc-likeshape. This suggests that the foundation of the instrument caused combination of sway and rocking
motions. The high acceleration at K-NET Tsukidate may be due to partial uplifting of the foundationof the instrument, as has been discussed by Motosaka and Tsamba (2011), and may not necessarily
indicate actual ground acceleration.
Acc.(cm/s/s)

2800

NS
Max=2700.0(cm/s/s)

0Acc.(cm/s/s)

-2800
2800

EW
Max=1268.5(cm/s/s)

0Acc.(cm/s/s)

-2800
2800

UD
Max=1879.9(cm/s/s)

0-28000100

200300Time(s)Fig. 3NSAcceleration time history of record at K-NET Tsukidate
KiK-net陸前高田
K-NET大東

4KiK-net一関東

U

K-NET一関
KiK-net唐桑K-NET気仙沼
Kik-net藤沢KiK-net東和
K-NET東和
K-NET歌津K-NET Tsukidate

NS

K-NET築館-404KiK-net志津川
K-NET北上
K-NET豊里KiK-net田尻
K-NET大崎市古川
KiK-net小野田
K-NET石巻
K-NET大和
K-NET牡鹿-4K-NET塩釜

Dis.(cm)
DTime

Fig. 4Past-up of acceleration time histories atK-NET Tsukidate and its surrounding sites

Fig. 5300

Orbit of displacement of K-NETTsukidate record in vertical planeVel.(cm/s)

120

NS
Max=44.1(cm/s)

0Vel.(cm/s)-120120

EW
Max=109.7(cm/s)

0Vel.(cm/s)-120120UD

Max=15.7(cm/s)

0-1200100

200

300Time(s)Fig. 6Velocity time history of record at KiK-net Namie

The maximum peak velocity observed is about 110 cm/s at KiK-net Namie, Fukushima
prefecture. The velocity time history of the KiK-net Namie record is shown in Fig. 6. The durationof strong shaking is also long. Unlike the Tsukidate record, however, the waveform is composed of
not two distinct phases, but one indistinct phase with a high velocity pulse whose period is about 2 sec.
Such a large pulse is also observed at the nearby sites such as Fukushima No.1 nuclear power plantcomplex. This suggests that the area generating strong ground motion exists near the site.
From the local networks,
2011/ 0311/ 14: 46: 00
about 30 records were retrievedin Sendai (Kamiyama, 2011;Ohno et al., 2011).
Theobserved peak horizontal groundacceleration and JMA seismic
intensity range 215 to 1853 cm/s2
and 5.1 to 6.5, respectively. In
the Kanto region, more than 200records were obtained fromMeSO-net, and hundreds werefrom the other local networks,including about 90 records fromthe Yokohama city network.
Figure 7 shows the past-up of thevelocity time histories at linearlyaligned sites from northeast toTim e ( sec)
southwest in the Kanto region Fig. 7 Past-up of velocity time histories at linearly aligned sites(Tsuno et al., 2011).
from northeast to southwest in the Kanto region (Tsuno et al., 2011)
30 cm / sec
RMS

100

9080

7060

Dist ance ( km )

50403020

100100

SYO200300

400

GENERAL CHARACTERISTICS OF OBSERVED GROUND MOTION
Figure 8 shows attenuations of peak horizontal acceleration and velocity. In calculation of theshortest distance from the fault, the fault plane by Koketsu et al.(2011) shown in Fig. 1 is used. The
observed data are widely dispersed with distance, but the peak accelerations and velocities generally

301

Peak ground velocity(cm/s)

103

102

101

Tohoku Earthquake

Si and Midorikawa (1999)
Mw=8.0Mw=8.5
Mw=9.0

100 0
101

1010

210

3

102

101

100

Tohoku Earthquake
Si and Midorikawa (1999)(AVS30=300m/s)
Mw=8.0Mw=8.5Mw=9.0

10-1 010Fig. 8

101

102

Fault distance (km)

Fault distance (km)Attenuation of peak horizontal acceleration (left) and velocity (right)
102

PGA/PGV

Peak ground acceleration (cm/s/s)

are 200 to 1,000 cm/s2 and 20 to 80 cm/s for the distance of 50 kilometers, 100 to 500 cm/s2 and 10 to50 cm/s for 100 km, and 20 to 150 cm/s2 and 3 to 20 cm/s for 200 km, respectively. The figure also
shows attenuation curves obtained from attenuation relationships by Si and Midorikawa (1999) forearthquakes with a magnitude of 8.0, 8.5 and 9.0, respectively. Although the inclination ofattenuation of the observed data seems slightly steeper than the attenuation curves, on the average, itappears to be smaller than the curve for M9.0 and come between curves for M8.0 and M8.5.
As mentioned earlier, high accelerations over 1000 cm/s2 are observed at 34 sites, while peakvelocities over 100 cm/s are only at 3 sites. This may suggest that high frequency contents tend to bedominant in the earthquake. To check the frequency contents of the records, the ratio of peakhorizontal acceleration to peak horizontal velocity is calculated. Figure 9 shows the ratio with fault
distance. The ratio ranges 10 to 30 at shorter distance, and the values are larger in comparison withthe results in the previous study (Sawada et al., 1992), suggesting that the earthquake may generaterich high frequency motion. The ratio, however, becomes smaller with distance, and the averagevalues are about 5 and 2 at distances of 200 km and 500 km, respectively. The ratio shows strong
distance dependence, probably due to inelastic properties in the propagation path.

101100 110Fig. 9102Fault distance (km)103

Ratio of peak horizontal acceleration to peak horizontal velocity with fault distance

302

103

NSJMA Hachinohe

KiK-net Taro

KiK-net Kamaishi

KiK-net Karakuwa

KiK-net Tajiri

K-NET Haramachi

5000

KiK-net Hitachinaka

K-NET Choshi-500

Acc.(cm/s/s)

KiK-net Iwaki-higashi

0Fig. 10Distribution of duration

50100150Time(s)200250300

Fig. 11 Past-up of acceleration time histories

The records are also characterized by their long duration. The duration of ground motion iscalculated as the time interval between 5 percent and 95 percent of the total power of acceleration. In
the calculation, the records with length of longer than 300 sec. are used. The distribution of theduration is shown in Fig. 10. The observed duration is longer than 100 sec. at many sites, althoughspatial variation of the durations is large. In the area with peak acceleration higher than 200 cm/s2,
the duration ranges 40 to 120 sec. and seems shorter in the southern part of the area. Figure 11 shows
the past-up of the acceleration time histories at linearly aligned sites along the Pacific coast from northto south. At the northern sites, the waveform consists of two distinct phases, while it becomes asimple shape at the southern sites, resulting shorter duration in the south.
At the middle sites, thewaveform seems complex. This is probably due that the rupture mainly propagated to the south
while the rupture process is not simple (Furumura et al., 2011).

CONCLUSIONS
Many strong motion records were obtained from the 2011 Off the Pacific Coast of Tohoku earthquake(Mw 9.0), owing to implementation of dense strong motion observation in Japan. More than 2,000
records are available. The high acceleration records are observed at many sites. For example, therecords over 1000 cm/s are obtained at more than 30 sites. The attenuations of peak acceleration andvelocity are compared with the curves from the previous attenuation relationship. On the average,
they appear to be smaller than the curve for M9.0 and come between curves for M8.0 and M8.5. The
ratio of peak horizontal acceleration to peak horizontal velocity ranges 10 to 30 at shorter distance.
On the records, longer durations are observed. The duration ranges 40 to 120 sec. in the area withpeak acceleration higher than 200 cm/s2, and seems shorter in the southern part of the area, which isprobably due to the rupture process of the earthquake. Further investigation of the records will give
better understanding of the characteristics of ground motion from gigantic earthquakes.

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ACKNOWLEDGMENTS
The strong motion data used in this study are provided by JMA, NIED, MLIT, PARI and BRI. This
study is partially supported by the Global COE Program “International Urban Earthquake Engineering
Center for Mitigating Seismic Mega Risk” and the Grants-in-Aid for Scientific Research“Construction of Next Generation Ground Motion Prediction Equation (Project Number: 23241054,
Principal Investigator: K. Koketsu)”.

REFERENCES
BRI (2011). http://smo.kenken.go.jp/smdb
Furumura, T. et al. (2011). “Strong Ground Motions from the 2011 Off the Pacific Coast of Tohoku,
Japan (Mw=9.0) Earthquake Obtained from a Dense Nation-wide Seismic Network.” Landslides,
Vol. 8, No.3, pp.333-338.
JMA (2011). http://www.seisvol.kishou.go.jp/eq/kyoshin/jishin/ index.html
Kamiyama, M. (2011). “Strong Motion Records of the 2011 Off the Pacific Coast of Tohoku
Earthquake from Strong Motion Array Observation System by Tohoku Institute of Technology(Small-Titan).” Tohoku Branch of the Japanese Geotechnical Society, 35pp. (in Japanese).
Koketsu, K. et al. (2011). “A unified source model for the 2011 Tohoku earthquake.” Earth andPlanetary Science Letters, Vol. 310, No.3-4, pp.480-487.
Kudo, K.(1999). “Strong Motion Observation at Earthquake Research Institute, University of Tokyo.”
Seismological Society of Japan Newsletter, Vol.11, No.3, pp.16-18 (in Japanese).
Midorikawa, S. (2005a). “Strong Motion Networks in Japan – Progress after the 1995 Kobe
earthquake –.“ Proceedings of the International Symposium on Earthquake Engineering (ISEEKobe 2005), Vol. 1, pp.A-91-A-96.
Midorikawa, S. (2005b). “Dense Strong-Motion Array in Yokohama, Japan and Its Use forDisaster Management.” Directions in Strong Motion Instrumentation, Springer, pp.197-208.
MLIT (2011). http://www.nilim.go.jp/lab/rdg/index.htm
Motosaka, M. and Tsamba, T. (2011). “Investigation of High Acceleration Records at K-NETTsukidate Station During the 2011 Off the Pacific Coast of Tohoku Earthquake.” Proceedings of the
8th Annual Meeting of Japan Association for Earthquake Engineering, pp.24-25.
NIED (2011). http://www.kyoshin.bosai.go.jp/index_en.html
Ohno, S. et al. (2011). “Strong motion characteristics in Sendai during the 2011 Off the Pacific Coastof Tohoku earthquake.” Summaries of Technical Papers of Annual Meeting, Architectural Instituteof Japan, Vol. B2, pp.189-190 (in Japanese).
PARI (2011). http://www.mlit.go.jp/kowan/kyosin/eq.htm
Sakai, S. and Hirata, N. (2009). “Distribution of the Metropolitan Seismic Observation network.” Bull.
Earthq. Res. Inst., Univ. Tokyo, Vol. 84, pp.57-69 (in Japanese).
Sawada, T., Hirano, K. and Yamamoto, H. (1992). “Relation between maximum amplitude ration (a/v,ad/v2) and spectral parameters of earthquake motions.” Proceedings of the Tenth World Conferenceon Earthquake Engineering, Vol. 2, pp.617-622.
Si, H. and Midorikawa, S. (1999). “New Attenuation Relationships for Peak Ground Acceleration andVelocity Considering Effects of Fault Type and Site Condition.” Journal of Structural andConstruction Engineering, A.I.J., No. 523, pp.63-70 (in Japanese).
Tsuno, S. et al. (2001). “Distributions of Earthquake Ground Motions Observed in and around theTokyo Metropolitan Area during the 2011 Off the Pacific Coast of Tohoku Earthquake (Mw 9.0).”
Programme and Abstracts, Fall Annual Meeting of Seismological Society of Japan, P2-18 (inJapanese).

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