“Session A: Earthquake and Ground Motion” and “Workshop 1: Seismic Observation in Deep Boreholes and its Applications”

Further Advancement of Strong Motion Prediction-Expectation for deep boreholes seismic observation andgeophysical exploration from viewpoint of ground motion
evaluationK. Irikura (Univ. Aichi Inst. Tech.)

The 1995 Kobe Earthquake
urged to revise theRegulatory Guide forseismic safety of
Nuclear Power Plants

The 2007 Chuetsu-oki
Earthquake madefurther impacts andanxiety to people inJapan concerningseismic safety of
Nuclear Power Plants.

Today’s Topics
1. Developments of strong motion evaluation after the 1995 Kobe
erthquakes
2. Revised Regulatory Guide (2006) for Reviewing Seismic Designof Nuclear Power Reactor Facilities
3. Methodology of estimating ground motions from earthquakes
4. Seismic reevaluation (back-checks) of the existing
Nuclear Power Plants based on the Regulatory Guide
5. Expectation for deep boreholes seismic observationand geophysical exploration from viewpoint ofground motion evaluation
6. Summary and future direction

1. Developments of strong motion evaluation
after the 1995 Kobe earthquakes

Programs defining the Seismic Hazard in Japan
Long-term Evaluation:
Evaluate probabilities of the next occurrence of large earthquakes
for major active faults and subduction-zones along troughs.

Strong Ground Motion Evaluation
Construct seismic hazard maps, probabilistic and deterministic.
Probabilistic hazard map: predicted likelihood of ground motion
level occurring in a given area within a set period of time.
Shaking map for scenario earthquakes: strong ground motion
from hypothetical source models for specified active faults

Long-term Evaluationsof Active Faults and
Subduction-zone
Earthquakes(Predicted magnitude andprobability of occurrence
within 30 years)(Earthquake ResearchCommittee, 2004)

Long‐term Forecast (continued)
Next 30 years
Subduction earthquakes
Miyagi-oki 99 %Nankai Trough 50-60 %Inland Crustal earthquake
ISTL (inland fault) 14%
most active faults < 5%
Kobe eq. in 1995 0.02-8 %Subduction earthquake

Inland crustal
earthquakea/ (a+b)

Max probability for 30 yrs
1/100 yr event ~ 90 %1/1000 yr event ~ 20 %1/10000 yr event ~ 2 %Probabilistic Seismic Hazard Map
Long-term Forecast

×Surface Amplification

揺れの強さ←

Ground motion – Distance
Attenuation Relation

×＝ PSHM

Distance from Source Fault

HERP

Probabilistic Seismic Hazard Map (2005)
Probability ofground motions
equal to or larger thanseismic intensity (JMA)
6-lower within 30years.

Probabilistic Seismic Hazard Map (2005)- Where have recent disastrous earthquakes happened near Japan ? -Subduction earthquake
Inland-crust earthquakes

HERP

Framework of predicting strong ground motions
for crustal earthquake scenarios (Deterministic Approach)Framework of predicting strong ground motions-continuedSource ModelingGreen’s Functions

Deterministic Seismic Hazard Map

After Fujiwara, NIED, 2004

2. Revised Regulatory Guide (2006)
for Reviewing Seismic Safety of
Nuclear Power Reactor Facilities

Why did “Regulatory Guide” have to be revised ?
□Background
The previous “Regulatory Guide was made based on the most advanced knowledge(active fault survey, ground motion simulation based on response spectra, static
seismic-force, and so on) for that day in 1981.
A lot of new findings and knowledge on seismology and earthquake engineering wereaccumulated for 25 years since 1981.
Seismic design technology for “Nuclear Power Reactor Facilities” was also rapidly
developed for the last 25 years.
The impacts and lessons from the 1995 Kobe earthquake:
Studies about active faults, seismic source mechanisms, wave propagation ,earthquake-resistant structures have been remarkably proceeded.
In particular, methodology for predicting strong ground motions from specific sources
have been developed.
Introduction of “PSA (probabilistic safety assessment)” for seismic design of“Nuclear Power Reactor Facilities” in foreign countries, especially USA.

Basic Policy for Seismic Design -1
Important Facilities from the seismic design points shall be
designed to bear seismic force exerted from earthquake groundmotion and to maintain their safety function, which could be
postulated appropriately to occur very scarcely in the operational
period of Facilities from the seismological and earthquake
engineering standpoints in the vicinity of the proposed site.
Moreover, any Facilities shall be designed to bear the design
seismic force sufficiently which is assumed appropriately for everyclassification in the seismic design from the standpoint ofradiological effects to the environment which could be caused byearthquake.

16

Basic Policy for Seismic Design ‐2(Commentary)
The Design Basis Earthquake Ground Motion “Ss”
shall be estimated deterministically fromthe ground motions caused by sufficiently strong
earthquakes.
The existence of “Residual Risk” shall be realized andminimized as low as practically possible.
(Residual Risk is defined as a risk caused by the effects of theground motions that exceed the Design Basis Ground Motion.)17

Evaluation of Design Basis Ground Motion 1
1. Evaluate ground motions for the basis of seismic safety
design of facilities as following two types,(1) “Ground motions for specified sources” at the proposedsites, that is, site-specific ground motions whose source
to be identified with the proposed sites.
(2) “Ground motions for unspecified sources”, that is,ground motions whose source not to be identified.
2. Select plural number of earthquakes which are feared
making severe impact to the proposed site, active faults
and subduction earthquakes.
Active faults considered in the seismic design shall beidentified as the one of which activities since the late
Pleistocene epoch can not be denied.

Evaluation of Design Basis Ground Motion 1
3. Evaluate ground motion by both methods(1) empirical response spectra and (2) fault models.
(Commentary)
Evaluation using the fault model method should be
preferred in the case of earthquake whose source isnear the proposed site.
4. Consider uncertainty concerned with the evaluation processof ground motions.

Deterministic Method and Residual Risk -1
z Design basis ground motions are evaluated from specified
sources for given earthquake scenarios with source
models and propagation-path and local site effects andfrom unspecified sources with past earthquake data.
z Largest possible ground motions are estimatedconsidering physical limits with uncertainties. They are notalways worst-case ground motions.
Æ Therefore, some residual risk remains.
Æ Design basis ground motions are determined to lead tothe residual risk that is acceptably small.

Deterministic Method and Residual Risk -2
z Exceeding probabilities of the design basis ground motions
for the residual risk is estimated by probabilistic methods
considering all scenarios concerning earthquakes andground motions from earthquakes.
z Variability of the ground motions is estimated with standard
deviations of observed data.
z Epistemic and aleatory uncertainties need to be separately
estimated.
z The epistemic uncertainties are reduced by constraints on
propagation-path effects (velocity and Q structure) and local
site effects (rock and soil properties).
Deep boreholes seismic observation and geophysical exploration
contribute to reduction of the epistemic uncertainties.

Points of New Regulatory Guide -1
1. Deterministic approaches are emphasized in evaluating
design basis ground motions (DBGM) Ss’s withengineering decision.
2. On the other hand, the idea of probabilistic approaches istaken in the guide.
For example, they request consideration of “uncertainties”
of source parameters and propagation-path and site effectparameters and calculation of exceeding probability of theSs’s, to provide comprehensive information about theconservatism in evaluating the Ss’s.
3. The basic policy is to adhere the concept of “defense-indepth” and to ensure the necessary safety margin.

Points of New Regulatory Guide -2
4. PSA is not directly introduced in the guide.
Reasons: (1) No common understanding exists amongexperts concerning the maturity of the probabilistic safetyassessment approach for risk assessment. (2) A number
of issues still remain to be delivered because of lack ofbasic data and moreover the safety goal has not been
determined in the NSC at that time.
5. The risk that may cause serious damage to the nuclear
facilities due to the ground motions exceeding Ss isdefined as “residual risk”. The efforts to minimize the“residual risk” as low as possible should be made. The
safety review process refers to the exceeding probabilities
of Ss’s.
6. The next regulatory guide should be revised to introduce
probabilistic approaches in near future.

3. Estimation of ground motions
from earthquakes
based on the “Recipe”

Estimation of Strong Ground Motions
Predicted Strong
Ground Motion

Sedimentary Basin

Amplification due to
Sedimentary Layers

Crustal Structurein Propagation-Path
Seismic Source Fault

Attenuation and/or Excitation in
Propagation-Path(Propagation-Path Effects)

Source Effects(Predicted Ground Motions) = (Source Effects)*(Path Effects)* (Surface Geology Effects)

Recipe for Strong Motion Prediction
Outer Fault Parameters
Rupture area S is given.
Seismic moment Mo from the empirical relation of Mo-S.
Average static stress-drop Δσc from appropriate physical model(e.g., circular crack model, tectonic loading model, etc.)

Inner Fault Parameters
Combined area of asperities Sa from the empirical relations of S-Sa
or Mo-Ao.
Stress drop on asperities Δσa based on the multiple asperity model.
Number of asperities from fault segments.
Average slip of asperities Da from dynamic simulations.
Effective stress for asperities σa and background area σb are given.
Slip velocity time function given as Kostrov-like function.

Extra Fault Parameters
Rupture nucleation and termination are related to fault geometry.

θ1

Dip
a

StrikeSegment 2

ngle δ

W

Outer Fault Parameters

L
Sou
rc

θ2
StrikeSegment 1g
osmi
Se onnee
zzo

eA
re a

i
en

c

Source Characterization
Based onheterogeneous slip by
waveform inversion…

Outer Fault Parameters

S(=LW), Mo, Δσc

Inner Fault Parameters:

Sa, Δσa , etc

size and stress drop of asperities2008 Iwate-Miyagi Nairiku Earthquake (Mw 6.8)
Characterized Source Model

Comparison between Observed
and Synthetic Motions-200 syn-400

Vel. (cm/s)

Asp1

Dis. (cm)

Asp2

30

obs

0
-20

0
-10
-20

syn

20

30

-200

syn

30

40

Time(sec)

Black: Observed
Red : Synthetic

MYG011 EW
obs
syn

-400
20

30

40

30

40

30

40

20
obs

0
-20
-40

40

obs

20

0

40

20

-40
10

破壊開始点

Asp1

obs

20

余震1

Acc. (cm/s/s)

余震2

200

Vel. (cm/s)

Asp2

0

MYG011 NS

syn

20

10

Dis. (cm)Acc. (cm/s/s)

200

0
-10
-20

obs
syn

20

Time(sec)

2007 Noto-Hanto Earthquake (Mw 6.7)
Characterized Source Model

Comparison between Observed
and Synthetic Motions
Acc.(cm /s/s)

20

0 obs
syn

-50
0

Disp.(cm )

10

10

20

syn

-20
0

10

20

Time(sec)

Black: Observed
Red : Synthetic

30

10

20

30

10

20

30

10

20

30

obs

0

syn

-50

30

obs

0

ISK003 EW
obs

0-500 syn
-1000
30
0

0
Disp.(cm )Vel.(cm /s)

0-500 syn-1000
0Vel.(cm /s)

Acc.(cm /s/s)

ISK003 NS
obs

obs

0

syn

-20
0

Time(sec)

4. Seismic Reevaluation (Back-checks) of
the existing Nuclear Power Plants
based on the Regulatory GuideRe-evaluation of Seismic Safety Design of Nuclear
Facilities, so-called “Back-checks”• NSC(Nuclear Safety Commission of Japan) asked governmental intendances
to re-evaluate seismic safety design of all of existing nuclear power plants(NPP) for confirming their integrity on September, 2006, just after “the New
Guide” was in effect.
• NISA(Nuclear and Industrial Safety Agency, METI), promptly required
electric companies to re-evaluate seismic design of existing NPP’s
according to “the New Guide”• The electric companies started geological survey and reevaluation of design
ground motions for getting back-checks of the existing NPP’s.
• The Niigataken Chuetsu-oki earthquake on 16 July, 2007, occurred very close
to the Kashiwazaki-Kariwa Nuclear Power Plants at that time.

Flow of Seismic Reevaluation
According to New Seismic Regulatory Guide
A. Geological survey, evaluation of active faults
B. Evaluation of design basis ground motion Ss
Ground motion without
identifying earthquake source

Evaluate ground motions
Ground motions byfault model method

Define design basis ground motion

Refer

Exceedance prob.

Ground motions by
response spectra

C. Evaluation of seismic safety of facilities
Classification ofimportance33

Evaluation of seismic
safety of important
structures
Evaluation ofimportant comp‐onents and piping

Stability evaluation of basemat
Accompanying events(Stability of surrounding slope)
Accompanying events(Safety against Tsunami)

Items to bereflected toseismic safety
reevaluation
based on thefindings from
the
Chuuetsu‐oki
Earthquake
20
07

Site specific ground motion byidentifying earthquake sourceExample of Seismic Reevaluation-The Kashiwazaki-Kariwa Nuclear Power PlantSelected Active Faults and Folds Inland and Offshore
Faults

Fault
Length①Kakuta-Yahiko

54km

Inland②Kihinomiya

22km③ Katagai
断層名

16km
断層長さ

Nagaoka-Heiya Sei-en
Fault: Total length of
９１ｋｍ
考慮すべき断層長さ

Offshore

Nagaoka-Heiya Sei-en
Fault System

④Ｆ－Ｂ

36km

36km

①
Inland

Se
a

④

Ｆ Ｂ-

Offshore②

Evaluated Desin Basis Ground
Motions for the Nagaoka Heiya
Seien Danso評価

KKNPP

Fault

InlandLength ofSource Fault.

③

Design Basis G..M. Ss

Active Faults selected for D.B.S.M.

（Unit:gal)Maximum Acceleration

Old Regulatory Guide S2

Unit:１～４

Unit:５～７

2300

1209
450
34

Source Model of F-B Fault

Acceleration Time Histories from the F-B Fault Earthquake

Source Model of Naoka Heiya Sei-en Fault
Three Faults (Katagai, Kihinomiya, and Kakuta-Yahiko) are connected.

Acceleration Time Histories from the Nagaoka-Heiya Sei-enRim
Fault

 Response Spectra for the Design-basis Ground Motion

Unit 1

Acceleration (cm/s2)

Acceleration (cm/s2)（Free surface of base stratum ）Unit 52300Gal1209Gal450Gal450GalPeriod (s)― Ss-1H (F-B fault, response spectra)― Ss-2EW (F-B fault, fault model method)― Ss-3H (Nagaoka Plain Western Rim Fault Zone, response spectra)― Ss-4EW (Nagaoka Plain Western Rim Fault Zone, fault model method)― S2― Estimated ground motion on the free surface of base stratum at the time of the
Niigata-Chuetsu-Oki Earthquake

Period (s)5. Expectation for deep boreholes seismic
observation and geophysical explorationfrom viewpoint of ground motion evaluation

Expectation for deep boreholes seismic observationand geophysical exploration-1
z New technology has been developed for seismic observationin deep boreholes:
High-precision and broad-band velocity sensors with superhigh heat-resistance available for 3000 m deep.
Multiply-connected sensors in a deep borehole.
z Progress of advanced technology is expected for not only
measuring seismic signals but also sampling, monitoring,and recording other geophysical data.

Expectation for deep boreholes seismic observationand geophysical exploration-2
z Detailed 3-D velocity structure models with damping factorof each layer, combining vertical array and horizontal arrayobservationz Epistemic uncertainties are reduced in estimating
propagation-path and local-site effects based on
the detailed velocity models, and then ground motion
variability becomes smaller.
Examples from seismic reevaluation:
Influence of irregular structures on ground motions
near the Kashiwazaki-Kariwa Nuclear Power Plant
and near Hamaoka Nuclear Power Plant

Case of the Kasiwazaki-Kariwa Nuclear Power Plant -1

Case of the Kasiwazaki-Kariwa Nuclear Power Plant -2

Case of the Kasiwazaki-Kariwa Nuclear Power Plant -3

Case of the Kasiwazaki-Kariwa Nuclear Power Plant -4

Case of the Hamaoka Nuclear Power Plant -1
Accelerations at Base Mats from 2009 Suruga Bay Earthquake
PGA 109 gals
Unit 1

Unit 2

Unit 3109 gals

147 gals

163 gals
Unit 4426 gals
Unit 5

About 800 m

Case of the Hamaoka Nuclear Power Plant -2
Acceleration Response Spectra at Base Mats from 2009
Suruga Bay Earthquake (Mw 6.2)

Case of the Hamaoka Nuclear Power Plant -3
S wave Velocity Profiling using Offset
VSP
in the Hamaoka NPPNISA JW46‐1 (March 31, 2010)

Case of the Hamaoka Nuclear Power Plant -4
Map showing Location of Nuclear Power Reactor Units andS wave Velocity Profiling using Offset VSPNISA JW47‐2 (April 27, 2010)

Deep Boreholes Seismic Observation andGeophysical Exploration After NISA (2010)
Vertical-Array Observation
Strong Ground Motions
EL42m(surface)

EL-8m
EL-98mEL-298m

EL-900m●

seismometer~~

EL-1500m

S wave profileby S-wave logging

Separation of Up-going and Down-going Waves
in Boreholes Using Deconvolution Techniqueupgoing

upgoing
downgoing

downgoing

upgoing
downgoing

We can estimate the velocity and Q factor of seismic waves propagating inborehole separating upgoing and downgoing waves using vertical array data.

Laboratory Measurements of P- and SWave Velocities and Damping Factors
on Rock Core Samples
After NISA (2010)

Figures are quoted from Tanimoto (1995)

Evaluation of Heterogeneities of Velocity Structures

NSC ＷＧ２_６０－３ (2010)■Strength pf Random Velocity Fluctuation
Based on PS logging at Monju site
Depth
Range
（m）

AverageS
wave
Velocity（km/s）

Gradientof
Increment（1/s）

Correlation
Length a
（m）

Hurst
Index
ν

Standard
Deviation
ε

GL-38
～-238

2.56

0.43

8.6

0.24

0.165

もんじゅ(不均質）-500Normalized ACF

1Depth(m)

50

100

150

200

a = 8.6m
ε= 0.165

0.8
0.6
0.4
0.2
0

PS log.
fitting

-0.2
-0.4
0

250
-1500-1000 -5000500 1000 1500

ξξ
(m/s)
（m/s）
0（z）
0

Heterogeneities of S-Wave Velocities (left),ξ0（z）(middle)、ξ（z）（right）

10

20

30

40

50

Lag distance (m)Correlation Length and Standard Deviation
Of Velocity Heterogeneities

Expectation for deep boreholes seismic observationand geophysical exploration - 3
Improvement of detectability and hypocenter determination ofearthquakesÆUpgrading of active fault investigation and source modelstudies
Example:Ground motions from specified and unspecified sourcesAftershock Distribution of the 2007 Niigata-ken Chuetsu-oki
earthquake from the JMA Unified Catalogue

Aftershock hypocenters fromJMA Unified catalogue

Aftershock distribution
by on‐land and ocean‐bottom
seismometers

Bins with 2km wide

ERI, Univ. of Tokyo (2008)

Expectation for deep boreholes seismic observationand geophysical exploration - 4
Introduction of earthquake early warning to shut-downsystems of reactors
Æ Gain time of more than 2 seconds putting borehole sensorsof 3 km deep.
Example:For an earthquake with hypocentral distance of 10 km, P
wave travel time is about 1.4 seconds (10 km/6 km/s + 3 km/4km/s) and S wave arrival time is about 4.8 seconds (10km/3km/s + 3 km/2 km/s), then S-P time is about 1.4 seconds.

深層ボーリング江東（掘削深度3000m）のPS到達時間「震源深さ30km」
センサー位置7000mだと猶予時間：P波到達まで1.89秒、S波到達まで6.06秒(3.44+2.62)

地表
下総層群

200m

Vp=1.8 Vs=0.44

P=0.11 S=0.45

上総層群
三浦層群

1700m

Vp=2.2 Vs=1.3

P=0.68 S=1.15

2600m

Vp=3.0 Vs=1.8

P=0.3 S=0.5

3000m

Vp=5.0 Vs=3.0

P=0.08 S=0.13

江東の孔底

先新第三紀層Vp=5.5 Vs=3.3

センサー

P=0.72
S=1.217000m
P波検知時点でS波は－2.62秒
7000m以深

震源深さ 30km

0秒

23km÷6.1=3.77秒
Vp=6.1 Vs=3.623km÷3.6=6.39秒
リアルタイム地震情報利用協
議会

120

120
S波

P波

100
7000m観測（100億円）

80

80

60
製
造
ラ
イ

40

ン
停
止

耐震補強 ＋ EEWのEconomical
Gain
効果
Due to Damage
操業停止：2～3ヶ月
Mitigation
被害総額：30億円(US dollars)

60

40

3秒

20

ス
館
内
放
送

0

20

ガ

0.2秒

弁
遮

3000m観測（30億円）

断

1秒

地上観測

0 1 2 3 4 5 6 7 8 9 10 11 12
猶予時間、および最低限必要な制御・対処時間
Gain Time（秒）

猶予時間を作り出すための観測コスト （億円）

100

Construction cost of Drilling of Boreholes (million)(US Dollars)

Economical gain due to damage mitigation(million)(US Dollars)
減災効果 （億円）

Economical Gain due to Damage Mitigation versus Gain Time
半導体工場 事例１
by EEW System: Example
of Semiconductor Factory

0

REIC (2010)

6. Summary and Future Directions -1
1. National Seismic Hazard Maps in Japan have been made byprobabilistic and deterministic approaches, integrating
advanced knowledge about Earth sciences, engineering,and social sciences related to earthquakes and seismic
disasters since 1995 Kobe earthquake.
2. Ground motions from earthquakes caused to specified
source faults are evaluated using the “recipe” proposed by
the scaling relations of the outer and inner fault parameters.
3. Ground motions from the Niigata-ken Chuetsu-oki (NCO)
earthquake are well simulated with the characterized source
models as long as the source fault are specified by geomorphological and geological surveys.
4. Design basis ground motions for seismic safety of nuclear
facilities in Japan have been evaluated using deterministic
approaches as long as fault modeling is appropriately made.

6. Summary and Future Directions -2
5. Deep boreholes seismic observation and geophysicalexploration contribute upgrading of ground motion, reducing
epistemic uncertainties by more constrains on propagationpath and local site effects.
6. Upgrading of numerical simulation methods of groundmotions is inevitable to avoid the ergodic hypothesis and to
reduce standard deviation of ground motion variabilities, inorder to introduce probabilistic approaches in revision of thenext regulatory guide.

Acknowledgements• Strong motion data in Kik-net and K-NET was provided
by the National Research Institute for Earth Science andDisaster Prevention (NIED), Japan.
• Strong Motion Data at the Kashiwazaki-Kariwa Nuclear
Power Plant from the Niigataken-Chuetsu-Oki (NCO)
Earthquake of July 16, 2007, was provided by TEPCO.

63