Proceedings of the International Symposium on Engineering Lessons Learned fromthe 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, JapanSTRONG MOTION RECORDS OF THE GREAT EAST
JAPAN EARTHQUAKE OBSERVED AT FUKUSHIMADAI-ICHI NUCLEAR POWER PLANT AND
FUKUSIHIMA DAI-NI NUCLEAR POWER PLANT
Hiroyuki MIZUTANI1, Isao NISHIMURA2 and Katsuichiro HIJIKATA31Deputy Manager, Seismic Engineering Group, Nuclear Seismic Engineering Center,
Nuclear Asset Management Department, Tokyo Electric Power Company,Tokyo, Japan
2Manager, Seismic Engineering Group, Nuclear Seismic Engineering Center,Nuclear Asset Management Department, Tokyo Electric Power Company,Tokyo, Japan
3General Manager, Nuclear Seismic Engineering Center, Nuclear Asset Management Department,
Tokyo Electric Power Company, Tokyo, Japan

ABSTRACT: Strong motion simulations for Fukushima Dai-ichi and Dai-ni are carriedout applying two models as a source fault model of the main shock. The result of thesesimulations well reproduce response spectra of the observation records at each site, andsuggest that the asperity, or strong motion generation area, near the sites for each model
have the largest impact in the higher frequency range of strong motion.
Key Words: Great East Japan earthquake, downhole array strong motion records, rockoutcrop strong motion, empirical Green’s function method, strong motion
generation area

INTRODUCTIONOn March 11th, strong motions caused by the Great East Japan earthquake were observed atFukushima Dai-ichi Nuclear Power Plant and Fukushima Dai-ni Nuclear Power Plant. There were 53
seismometers installed at Fukushima Dai-ichi NPP and 43 at Fukushima Dai-ni NPP, both in thebuildings and free field borehole arrays. At Fukushima Dai-ichi NPP, peak acceleration of 550Gal wasobserved on the foundation slab of the reactor building of Unit 2, and 305Gal at Fukushima Dai-ni
Unit 1. Observation records in the Fukushima Dai-ichi reactor buildings are almost the same level as
the response simulation result using the design basis ground motion Ss although some of the peakacceleration values slightly exceeded those of the simulation results.
Here strong motion simulations for Fukushima Dai-ichi and Dai-ni are carried out applying twomodels as a source fault model of the main shock. Also rock outcrop motions are estimated for eachsite using strong motion records at the downhole arrays, in order to evaluate the ground motion during
the main shock at these NPP sites’ compound.

314

STRONG MOTION OBSERVED AT FUKUSHIMA DAI-ICHI AND DAI-NI NPP
At Fukushima Dai-ichi Nuclear Power Plant and Fukushima Dai-ni Nuclear Power Plant, seismic
observations have been made by seismometers installed in the site foundation, reactor building of each
unit, and seismic observation house. At Fukushima Dai-ichi Nuclear Power Plant, total of 53
seismometers are installed for seismic observation. As for the Fukushima Dai-ni Nuclear PowerStation, 43 seismometers are installed. Figure 1 - 4 show the overview of seismic observation points at
Fukushima Dai-ichi Nuclear Power Plant and Fukushima Dai-ni Nuclear Power Plant, and observed
strong motion records during the earthquake in the downhole arrays at each NPP site.
True North  Plant North (PN)

Seismic observation housefor free field borehole array (north)

MagneticNorth

(6-G1)

0500m

Unit 6 Reactor building

Unit 6 Turbine building

Unit 5 Reactor building

Unit 5 Turbine building

Unit 1 Reactor building

Unit 1 Turbine building

Unit 2 Reactor building

Unit 2 Turbine building

Unit 3 Reactor building

Unit 3 Turbine building

Unit 4 Reactor building

Unit 4 Turbine building

Seismic observation housefor free field borehole array (south)(4-G1)
Seismic obervation point

Fig. 1 Schematic location of the downhole seismic arrays installed at Fukushima Dai-ichi NPP

True North  Plant North (PN)
MagneticNorth

Unit 4 Reactor building

Unit 4 Turbine building

Unit 3 Reactor building

Unit 3 Turbine building

Unit 2 Reactor building

Unit 2 Turbine building

Unit 1 Reactor building

Unit 1 Turbine building

Seismic observation housefor free field borehole array(1-G1)00
Seismic obervation point

500m

Fig. 2 Schematci location of the downhole seismic array installed at Fukushima Dai-ichi NPP

315

01000

500
44
28

GS1

1500

2000

800
1200

460
-5.0m

-39.9m

GS2(G.L.)
0.0m
-8.0m
-14.0m
-16.0m

(O.P.)+34.9m+26.9m+20.9m+18.9m-34.0m-38.0m

+0.9m
-3.1m

Acceleration (gal)(G.L.)
0.0m
-2.0m

700
350
0-350-700

Acceleration (gal)(O.P.)+34.9m+32.9m

700
350
0-350
-700

GS1

0

600

50

100

1730

-108.0m-73.1m590-234.9m

200

250

0

150

200

250

200

250

150

200

250

150

200

250

345

50

100

Time (sec)650-200m

GS2

GS3-109.1m-157.0m-122.1m

1810

GS3

700
350
0-350
-700
0

321

50

100

150

Time (sec)-230.0m-230.9m

Free surface ofthe base stratum

GS4-144.0m

Acceleration (gal)-134.9m-195.1m-196.0m

Acceleration (gal)

-100m

150

Time (sec)

52

GS4

700
350
0-350
-700
0355

50

100

-264.0m

730-229.1m

2000

Acceleration (gal)Time (sec)

GS5700350
0-350-7000360

50

100

Time (sec)-300m-334.9m

S-wavevelocity

GS5Acceleration Time histories (EW direction)

P-wavevelocity

Fig. 3 Soil profile with seismometer locations and observed acceleration time history
in the south free field bore hole array at Fukushima Dai-ichi NPP(G.L.)
0.0m-2.0m

FF1-5.5m-17.7m

FF20500

1000

350

890

1500

2000

(G.L.)
0.0m
-4.0m

1620

470

-51.0m-62.2m-38.8m

FF3FF1700
3500-350-700
0382

50

100

150

200

250

150

200

250

150

200

250

200

250

Time (sec)
Acceleration (gal)-5 0.0m(O.P.)+12.2m+8.2m

Acceleration (gal)(O.P.)+1 2.2m+1 0.2m

1800-105.0m

FF2700350
0-350-7000274

50

100-92.8m

Time (sec)
Acceleration (gal)

530

1880

FF3

700
350
0-350
-700
0211

50

100

Free surface ofthe base stratum
810-200m-212.2m

FF4S-wave
velocity-170.0m-157.8m-180.2m-168.0m

Acceleration (gal)Time (sec)

FF4

700
350
0-350-700
0180

50

100

150

Time (sec)

Acceleration Time histories (EW direction)

1950

P-wavevelocity

Fig. 4 Soil profile with seismometer locations and observed acceleration time history
in the free field bore hole array at Fukushima Dai-ni NPP

316

GROUND MOTION SIMULATION AT FUKUSHIMA DAI-ICHI AND DAI-NI NPP SITESAs for the Great East Japan Earthquake, several source models are proposed using GPS data,tsunami records, strong motion records or teleseismic records. Source models proposed by Kamae andKawabe (2011) and Irikura and Kurahashi (2011) are ones which can be used for the estimation ofstrong motion including high frequency range, crucial for the seismic safety evaluation of nuclearfacilities. Here ground motion simulations at Fukushima Dai-ichi and Dai-ni NPP site are conductedusing source models by Kamae and Kawabe (2011) and Irikura and Kurahashi (2011), in order toevaluate source characteristics of the main shock and effect on the sites.
Ground motion simulation using the source model by Kamae and Kawabe (2011)
First, ground motion simulation using the source model by Kamae and Kawabe (2011) is carriedout. Fig. 5 shows the characterized source model consisting of five asperities proposed for the mainshock, its source parameters and the source parameters of the two small events observation records ofwhich are used as Empirical Green’s Functions (EGFs) in order to synthesize ground motion of themain shock.
Fig. 6 shows the computed acceleration time histories and response spectra at a depth of 200m
(GS4 and FF4), compared with the observation records at the same location. Not only the waveforms
but also response spectra are consistent with the observed ones.
Fig. 6 also shows calculated response spectra for the ground motion produced by each asperity
compared with the one produced by the whole source area. These comparisons suggest that strong
motions in the high frequency range at each NPP site are mainly generated by the asperities near thesites (Asp 3 – 5).

Source parameters for the main shock
S (km2)M0 (N･m)Δσ(MPa)rise time (s)rupture startingtime (s)EGF

Source parameters for the small events used as EGF*JMA, **F-net

Fig. 5 The source modlel and source parameters (quoted from Kamae and Kawabe (2011))

317

500

0Acc(Gal)

1000

Observed

50100

150

500
250
0-250-500

200

250

Synthetic

050

100

150200100

速00
2000
10(h=0.05)
05002001010050

150

20

度(cm/s)101
Obs-EW
Syn-EW0.1

11050.1

Whole area
ASP1
ASP2
ASP3
ASP4
ASP5

2
10.1

250

2

10200

Pseudo Response Velocity (cm/s)

500
250
0-250-500

Response Spectrum(cm/s)

Acc(Gal)

GS4-EW (Fukushima Dai-ichi, O.P.-200m))/s(cm(cm)

0.0
1
0.5
0.1

100.2

Period(sec)Time(s)0.5

12510Period(sec)
周 期(秒)

500(cm)/(cm10FF4-EW (Fukushima Dai-ni, O.P.-200m)

2000s)
210(h=0.05)00

500200Observed

Acc(Gal)

050

100

150

500
2500-250-500

200

250

Synthetic

Pseudo Response Velocity (cm/s)

1000

500
2500-250-500

Response Spectrum(cm/s)

Acc(Gal)

200

100

速50

100

150

200

250

100
50

1

50

20

度

10(cm/s)1
Obs-EW
Syn-EW0.1

00
101050.1Whole area
ASP1
ASP2
ASP3
ASP4
ASP5

2
10.1

1
Period(sec)Time(s)100. 0
1
0.5
0.1

0.2

0.5

12

5Period(sec)
周 期(秒)

Fig. 6 Calculated acceleration time histories and response spectra using the source modelby Kamae and Kawabe (2011)

Ground motion simulation using the source model by Irikura and Kurahashi (2011)
Secondly, ground motion simulation using the source model by Irikura and Kurahashi (2011) iscarried out. Fig. 7 shows the characterized source model consisting of five strong motion generation
areas (SMGAs) with large slip velocity or high stress drop like asperities defined by Kamae andKawabe (2011), with its source parameters and the source parameters of the three small events which
are used as Empirical Green’s Functions (EGFs) for the ground motion simulation of the main shock.
Fig. 8 shows the computed acceleration time histories and response spectra at a depth of 200m
(GS4 and FF4), compared with the observation records at the same location. Both synthesized
waveforms and response spectra are consistent with the observed ones.
Calculated response spectra for the ground motion produced by each SMGA are also shown in
Fig.8, compared with the spectra produced by the whole source area. In the high frequency range
ground motions generated by SMGA4 and SMGA5 mainly control the level of the strong motion, andthe other SMGAs have influences on the ground motion level in relatively lower frequency range ateach NPP site.

318

10

Source parameters for the main shock

Source parameters for the small events used as EGF

1F
2F

Event AEvent B

Event C

Origin time※１

2011/03/10 06:24

2007/11/26 22:51

2009/02/01 06:51
SMGA 5EGF

SMGA 1-3

SMGA 4

Latitude（deg）※１

38.17237.30436.717

Longitude（deg）※１

143.045141.757

141.279

Depth（km）※１

9.3

44.1

47.0

MJMA※１

6.8

6.0

5.8

M0※２

5.51×1018

7.66×1017

4.65×1017*1JMA, *2F-net

Fig. 7 The source modlel and source parameters (quoted from Irikura and Kurahashi (2011))(cm500Observed

Acc(Gal)

050

100

150500250
0-250-500

200

250

Synthetic

1000
Obs-EW
Syn-EW

100

速50

100

150

200

100

1011500250
0-250-500

200

250

Synthetic

50

100

150200

250

020

0

10050

50. 1

20.2

Obs-EW
Syn-EW100

122/s(cm(cm)10

Whole area 00
0SMGA1 2
SMGA2
SMGA3
SMGA4SMGA5200

Period(sec)

1000

0.5510周 期(秒)Period(sec)

速1001)010(h=0.05)050

0200010505020

度10(cm/s)

10.1

050

100.0
10.50.1

10Pseudo Response Velocity (cm/s)

150

Response Spectrum(cm/s)

Acc(Gal)Acc(Gal)

10000

20FF4-EW (Fukushima Dai-ni, O.P.-200m)

50(h=0.05)

1050

500

02

1Period(sec)Observeds)

10.1

250Time(s)500250
0-250-500/(cm度(cm/s)

0.1

0Whole area
SMGA1 2000
SMGA2
SMGA3
SMGA4
SMGA5

10200

Pseudo Response Velocity (cm/s)

500
250
0-250-500

Response Spectrum(cm/s)

Acc(Gal)

GS4-EW (Fukushima Dai-ichi, O.P.-200m))

1050.121

0.1

1Period(sec)Time(s)100. 01
0.5
0.1

0.2

0.5

12Period(sec)
周 期(秒)

Fig. 8 Calculated acceleration time histories and response spectra using the source modelby Irikura and Kurahashi (2011)

319

510

ROCK OUTCROP MOTION ESTIMATED FROM INVERSE ANALYSIS
AT FUKUSHIMA DAI-ICHI AND DAI-NI SITE
Now rock outcrop motions are back-calculated using strong motion downhole array records during
the main shock at each NPP sites, based on the inversion analysis using the genetic algorithm
combined with one dimensional linear response analysis. Fig. 9 shows back-calculated soil layer
model that minimizes the misfit of observed and computed transfer functions between any of the two
depth in the south downhole array at Fukushima Dai-ichi NPP site, and Fig. 10 shows estimated rockoutcrop motions at each NPP site, compared with design basis ground motion Ss which are also
defined as rock outcrop motions at every NPP sites.
Estimated value

Initial value

O.P.

ThicknessDensity

S-wavevelocity

S-wavevelocity

Dumpingh(f)=h0×f-α

（m）

（m）

(g/cm3)

(m/s)

(m/s)

h0

α

GS1 (O.P.+32.9m)

A

振幅
Amplitude

10

Fixed parameters

10

-3.1
-5.0
-49.1
-73.1
-97.1
-100.0-109.1-155.1-195.1-196.0-200.0-210.1-300.0

6.0

2.10

8.0
22.0

285

2.00

280

252

1.73

460

400

520

486

1.9

1.73

44.1

1.73

24.0

1.80

24.0

1.80

2.9

1.77

9.1

1.77

46.0

1.77

40.0

1.76

0.9

1.76

4.0

1.76

10.1

1.76

89.9

1.81

－1.81

1510520Frequency(Hz)
440

0.291

0.25

0.274

1.00

GS2 (O.P.-5.0m)

10Amplitude
振幅

+18.9

2.10

B

1

B: O.P.-5.0m/O.P.-100m

0.1

GS3 (O.P.-100m)

0510

1520

Frequency(Hz)
0.107
590

0.67

10C592

GS4 (O.P.-200m)
650

659

振幅
Amplitude

+26.9

2.0

1

C: O.P.-100m/O.P.-200m

0.1
00.063730

5101520Frequency(Hz)

D

10

1.00

740

Amplitude
振幅

+32.9

A: O.P.+32.9m/O.P.-5.0m

0.1+34.9

GS5 (O.P.-300m)

1

D: O.P.-200m/O.P.-300m0.1

Seismometers*Fixed parameters are determined by PS logging.

05101520Frequency(Hz)Fig. 9 Back-calculated soil model and transfer functions of the south downhole array at Dai-ichi NPP site

100150200

250

DBGM Ss-1H
DBGM Ss-2H
DBGM Ss-3Hrock outcrop（NS）
rock outcrop（EW）

2.11
0.01

0.02

0.05

0.1

0.2

0.5

12

5200

250

10(h=0.05)

200101

1000

200
100
50

0.
150

Pseudo Response Velocity (cm/s)

205150Time(s)500200100100
0.
1100(cm)
12000.
050

500

50

Pseudo Response Velocity (cm/s)

500

500(h=0.05)

1020

100

1000

(cm(cm)

1000-500/s 2)Time(s)/s 2)

501000500-800

0-250(cm0-400

427

250

1000

400

Estimated rock outcrop ground motion (NS)
500

2000

675

Acceleration (gal)Acceleration (gal)

Estimated rock outcrop ground motion (EW)
800

2010)
5

DBGM Ss-1H
DBGM Ss-2H
DBGM Ss-3Hrock outcrop（NS）
rock outcrop（EW）

0.
01

2
1
0.01

100.02

0.05

0.1

0.2

0.5

1

Period (sec)Period (sec)

Fukushima Dai-ichi

Fukushima Dai-ni

2510Fig. 10 Estimated acceleration time histories and response spectra of the rock outcrop motions

320

CONCLUSIONS
Strong motion simulations at Fukushima Dai-ichi and Dai-ni NPP sites are carried out applying
two models as a source fault model of the Great East Japan earthquake. Also rock outcrop strong
motions are calculated for each site using downhole strong motion records, in order to evaluate theground motion at these NPP sites’ compound. The followings conclusions are made tentatively.
1) The source models proposed by Kamae and Kawabe (2011) and Irikura and Kurahashi (2011) well
reproduce the strong motion observed at Fukushima Dai-ichi NPP and Fukushima Dai-ni NPP site.
Ground motions generated by asperities (or SMGAs) near site mainly control the level of the strong
motion in the high frequency range, and the other asperities (or SMGAs) have influences on theground motion level in relatively lower frequency range at each NPP site.
2) The peak accelerations of the back-calculated rock outcrop motion at a depth of 200m are 675 Gal
and 427 Gal at Fukushima Dai-ichi and Dai-ni NPP site respectively. Estimated rock outcrop motions
are almost the same level as the design basis ground motion Ss at Fukushima Dai-ichi NPP site
although peak acceleration value slightly exceeded that of Ss. At Fukushima Dai-ni NPP, estimatedrock outcrop motions are below the level of Ss.

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