10th International Workshop on Seismic Microzoning and Risk Reduction
September 25, 2013,Tokyo, Japan
National Graduate Institute for Policy Studies (GRIPS), Roppongi, Tokyo

Some features of strong ground motions and structural damage
during the 2011 Mw 9.0 Off the Pacific Coast of Tohoku
Earthquake

Kojiro Irikura and Susumu Kurahashi
Ai hi IInstituteAichi
tit t off TTechnology,
h lJJapan

Today’sy Topicsp
1. Some features of structural damage during the 11 March2011 Mw 9.0 Tohoku earthquake
2 Short-period
2.
Short period source model estimated from strong motiondata
3. Period-dependence of rupture processes
4. Recipe of predicting strong ground motions for
subduction megathrust earthquakes
5 Estimation
5.
E ti ti off strong
tgroundd motionsti
att ddamagedd sites
itduring 2013 Tohoku earthquake for fragility curves ofb ildibuildings

Outline of the 2011 Tohoku Earthquake
2011/03/11, 14:46. Depth=24km, Interplate• Mw=9.0 ( the largest
g earthquakeqrecorded in Japan)

Tsukidate stationin Kurihara cityy Largestg• JMA seismic intensity=7.
PGA approached 2933 gal(Tsukidate, Kurihara city of MiyagiPrefecture )•Focal region was very large (450km X200km)•Damage area was wide (20 prefectures,Tokyo, Osaka)• Over 1200 strong ground motion
records were observed all overJapan.
JapanPeak Ground Acceleration

3

Buildings damage data (FDMA, 2012)
Total collapse

Partial collapse

Partial damage
March 11, 2012

Geospacial Information Authority

4

Period characteristics of ground motions
Kobe Earthquake, 1995

JR Takatori
JR-Takatori

Teq=2πPGV/PGAq5

Relationship between Total-Collapse Ratio and Seismic Intensity
Dependence on construction year during 1995 Kobe earthquake
Red：before 1961
Green：1961-1981
Blue：after 1981

Before 1961

1961 1961
1961-1961

After 1981

5.0

5.5

6.0

6.5

After investigation in Nishinomiya during 1995 Kobe earthquake (CDMC,2004)

2 Short-period2.
Sh
i d source modeld l estimatedid ffrom strong
motion data

 Five distinctive wavapackets were detected on strong motion
sesimograms at stations near the source fault.
 The arrival azimuths of those wavepackets were estimated using
the semblance analysis in several small arrays
arrays.
gareas (SMGAs)() are
The locations of strongg motion generation
coincident with the origins of those wavepackets.

Re-estimation of Locations of SMGAs from Semblance Analysis of WavePackets seen in Short-Period Seismograms
Wave pachet 2

Wave packet 3
Wave packet 4
Wave packet 1

Wave packet 5

After Irikura and Kurahashi (2011)

Simulation of Strong Ground Motions during the 2011 Tohoku
Earthquake Using the Empirical Green’s Function Method

 Strong Motion Generation Areas are relocated using the semblance analysis ofthe wave-packets in small arrays.
 The observed data from medium-sized earthquakes occurring near each strong
motion generation area are adopted as the empirical Green’s functions.
 Strong motion records of the 2005 Miyagi-Oki earthquake (Mw 7.2) are used
pGreen’s functions for SMGA1 ((WP1)) and SPGA3 ((WP2).
)
as the empirical

Mini-arrays (A, B, C, D, E, F, and G)
for estimating arrival azimuths of wave-packets

Semblance Analysis for Wave Packets
using Local Arrays
R1/Vs
R2/Vs

STN1

STN2
STN3

Revised Model

SMGA2
SMGA1

SMGA4

SMGA5

SMGA3

L,W,MoStress drop

SMGA1

34×34

2.68E+20

16

SMGA223.1×23.1

1.41E+2020SMGA3

42.5×42.5

6.54E+2020SMGA4

25.5×25.5

1.24E+20

25.2

SMGA5

38.5×38.5

5.75E+2025.2

Comparison of Observed and Synthsized （SMGA1,2,3のみ）

MiyagiOnagawasite

Acceleration Records with remarkable distictive pulses
Horizontal NS

Horizontal EW

黒：Obs.
赤：Syn.

Heterogeneity of stress parameters inside SMGA
Heterogeneous stress parametersinside SMGA⊿⊿σYXMatsushima and Kawase (2006)

Uniform slip velocity model

Heterogeneous slip velocity model 1 (x2)

Heterogeneous slip velocity model 2 (x4)Distinctivepulse

Period range
g of gground motions g
generated from the SMGAs

 Longer-period motions from the Strong Motion GenerationAreas (SMGAs) are estimated using numerical Green’s
functions: the Discrete Wavenumber method (Bouchon,(Bouchon1981) and the Reflection/Transmission coefficient matrix
method (Kennet, 1983) using a stratified medium.
 Effective period range of ground motions generated fromthe SMGAs are confirmed by comparing simulated motions
with observed motions.
 Verification of the fault parameters are made, mainly inner fault
parameters of Strongg Motion Generation Areas ((SMGAs))pestimated using the empirical Green’s function method

Velocity Structure Models (Vs）
1-D velocity structures from stations to source are modeled comparing synthetic motions with observed
ones from small events.

MYGH06Vs
S波速度(km/s)

MYGH04Vs
S波速度(km/s)
0234

50

3

4

50

100

100

100

200

200

200

300

300

300

400

400

400

500
600

700

700

800

800

修正モデルVs
Identified

900

初期モデルVs
Initial1000

0

S波速度(km/s)
24深さ(m))0600

0615151520202025304045
50

修正モデルVs
初期モデルVs

深さ(km)

510深さ(km)5404550

S波速度(km/s)
24010355修正モデルVs
初期モデルVs

0535

41000
速度(km/s)
2410303600

9000252500

800

修正モデルVs
修デ初期モデルVs

1000

61700

900

0

深さ(km)

20500

Deep
Structure10深さ(m)

深さ(mm)

Shallow
Shll
Structure

1MYGH08
S波速度(km/s)
Vs

253035

修正モデルVs
初期モデルVs

404550修正モデルVs
初期モデルVs

6

Comparison between Observed and Synthetic Motionsin Miyagi Prefecture
Observed
Synthetic

Frequency Range
0.05 – 1.0 Hz

Comparison between Observed and Synthetic Motionsin Kanto Region
Observed
Frequency Range
0.05 - 1Hz

CalculatedComparison between Observed and Synthetic Motionsin Miyagi Prefecture
Frequency Range
0.01 - 0.1Hz

Observed
C l l t d
Calculated

Comparison between Observed and Synthetic Motionsin Miyagi
y g Prefecture
Frequency Range
0.01-1Hz

Observed
Synthetic3. Period-dependence
3
P i dddoff rupture processes– Comparison of short-period source model and long-period
source models
d l iinverted
d llong-periodi d strong motion
i ddata,tsunami waveforms, geodetic data  Short-period
psource models usingg backprojection
p jof teleseismic
short-period P-waves (e.g. Ishii, 2011; Honda et al., 2011) Long-period source models
l inverted ffrom tsunami data ((Fujii etal., 2012) , geodetic data (Iinuma et al., 2012) and joint data(Yokota et alal.))Comparison between slip distribution using long-period
motions ((Suzuki et al,, 2011)) and SMGAs in this studyy

Slip distribution inverted fromllong-period
i d motions
tifiltfilteredd0.01-125Hz (100 – 8 s)

SMGAs estimated from short-period
short period
motions filtered 0.15-10Hz (6.6 – 0.1 s)Comparison of Short-Period Source Model in This Study with Short-Period Released
Energy by the back-projevtion method
US Array Data by Ishii (2011)

Kanto Array Data by Hoda et al, (2011)

Slip Distribution of the 2011 Tohoku Earthquake
DPS data including inland andoff-shore observation

Geographical Institute (2011)

Tsunami Waveform Data

Fujii and Satake (2011)

4 Recipe
4.
R i off predicting
di i strong groundd motions
iffor
subduction-zone megathrust earthquakes
 Rupture process of subduction
subduction-zone
zone megathrust earthquakes show
period-dependence.
 New source image for period-dependent source process isexpressed as multi-step heterogeneous-source-model.
 Strong ground motions of engineering interest in the period-range
from 0.1 to 10 sec are estimated using the basic characteristic source
model with outer-fault parameters and inner fault parameters,that is, just one step heterogeneity source model.

Multi-Step Heterogeneous
Source Model - 1
Second step: Heterogeneity model
for very short-periods
0 05 – 0.2
0.05
02s

First step: Heterogeneity model
for short periods 0.1 – 20 s

Comparison between SMGAs in this study and source locations of pastq
off the Pacific coast of Tohoku
earthquakes

Heterogeneous Model for Broad-band Motions from 0.1 to 10 s
The SMGAs are locatedaalongo g oute
outer edge ofo thet elarge slip delineated basedon the seismicity rate
(Kato and Igarashi,Igarashi 2012)
Brue solid line is the outeredge of the large-slip zoneof the mainshock, ~35 km.

Stress parameter (σa) on
strong motion generation
areas is given as ~ 26 MPa
from the empirical relations
for mega-thrust earthquakes.

5. Estimation of strong ground motions at damaged sites
d i 2013 TTohoku
duringh k earthquakehk
 Velocity structures beneath strong motion stations are identified byuse of earthquake H/V spectral ratios (Kawase et al., 2011).
 Empirical Green’s
Green s functions at bedrock beneath the strong motion
station are calculated with observed ground motions on the surface
from small events and transfer functions between surface andbedrock.
 The transfer functions at damaged sites are calculated fromvelocity structures beneath the sites using microtremor H/V (Arai andTokimatsu 2000; Sanchez
Tokimatsu,
Sanchez-Sesma,
Sesma et al,al 2011)2011).
g sites duringg the mainshock are Ground motions at damaged
calculated the transfer functions, the empirical Green’s functions andthe short-period source model of the mainshock.

3.1 Methodology of estimating ground motions atddamaged
d sites dduring theh mainshockh k
Kyoshin NET
Kyoshin-NET
Small earthquake
station
OGK(ω)
Eo Fo=Eo

Damagedg siteM i h kMainshock

EGD(ω)= BDM(ω)xTFD(ω)

Observed wave・・・

TFK(ω) =2 EoETFD(ω)

BK(ω)=OGK(ω)/TFK(ω)
E

Incidence wave
FMainshock BKM (ω)

BDM (ω)Short-period source model

By Kurahashi and Irikura, 2013 32

Microtremor measurement
Microtremor H/V in Osaki and Kurihara, Miyagi

33

4.3 Fragility curves in subdistricts
CR C
CR:
Collapsellratioi
R2=0.0001

R2=0. 462

Peak Ground Acceleration

Peak Ground Velocity

R2=0.332

R2=0.446

JMA Seismic Intensity

Spectral Intensity

34Summary
1. The 2011Tohoku earthquake (Mw 9.0) produced devastating tsunamiwaves, causing
i 16
16,500500 ffatalities
t liti (i(includingl di missing)i i ) andd serious
iddamageto nearby Fukushima nuclear power plants. Extremely strong and longduration ground motions were also generated, but damage due to strong
ground motions were relatively less.
2.

psource model of the 2011 Tohoku earthquake
q((Mw 9.0)) have
Short-period
five distinctive strong –motion-generation areas (SMGAs) fitting observed
acceleration and velocity records to synthetic motions. The SMGAs arelocated west of the hypocenter and along the down-dip
down dip edge of the source
fault. Synthetic motions from the SMGAs match well with observed motionsin the period-range from 0.1 to 10 sec.

3.

Period-dependence of rupture process was found, that is large slips inshallow zones of the source fault near the trench west of the hypocenterand short-period
short period generation in deeper zones west of the hypocenter
hypocenter.

4.

Strong ground motions of engineering interest in the period-range from 0.1
to 10 sec are estimatedid using
i theh characteristichi i source modeld l withi h outerfault parameters and inner fault parameters as the recipe of predicting
strong ground motions for subduction earthquakes.

Basic Characterized Source Model
Step 1: Heterogeneous Model for Broad-band Motions from 0.1
to 10 sec-Comparison between observed and synthetic waveforms
in the region near the source fault (Miyagi and Onagawa)Comparison of Seismic Intensity
between Observed and Synthetics
Iwate
岩手Pref.

6

Miyagi Pref.
宮城

7

Synthetics
計算震度

Synthetics
計算震度75432654321

10001234560

71456767Ibaragi Pref.
茨城

76Synnthetics
計算
算震度

Syntheetics
計算
算震度

63

観測震度

Fukushima
福島P fPref.

72

Observed

Observed

観測震度

54
32

54
32
1

1000

1

2

3

4

観測震度

5

Observed

6

70

12

3

4

観測震度

5

Observed