seismic hazards · 1. korea institute of nuclear safety • seismic hazard vs. seismic risk –...

Joint IAEA-KINS: Workshop on Siting Evaluation for Nuclear Facilities on 16-20 April 2018 in Korea

Seismic Hazards

Hoseon [email protected]

Korea Institute of Nuclear Safety


CONTENTS

I. Earthquake Fundamentals

II. Earthquake Monitoring in KINS

III. Seismic Safety of NPP site in Korea

IV. IAEA Specific Safety Guide No. SSG-9

V. Remarks

1


• Seismic hazard vs. Seismic risk

– seismic hazard: a natural phenomenon such as ground shaking, fault

rupture, or soil liquefaction that is generated by an earthquake

– seismic risk: the probability that humans will incur loss or damage to

their built environment if they are exposed to a seismic hazard

• seismic risk = seismic hazard × vulnerability

2http://www.efehr.org


I. Earthquake Fundamentals

• From seismic source to ground motion

3

seismic source

path

site

ground motion

Modified Boore (1999)


• MW 7.8 Tangshan earthquake on July 28, 1976

– casualties: 242,769~700,000 dead

4

http://www.drgeorgepc.com

wikipedia


• MW 6.9 Great Hanshin (Kobe) earthquake on January 17, 1995


5

http://www.alamy.com

wikipedia


• MW 9.1 Indian Ocean earthquake on December 26, 2004

– casualties: 230,000~280,000 dead and more missing

6

http://highered.mheducation.comhttp://www.sheppardsoftware.com


• MW 7.9 Sichuan earthquake on May 12, 2008

– casualties: 87,587 dead and 18,392 missing

7

wikipedia

http://agnesngoy.blogspot.kr


• MW 7.0 Haiti earthquake on January 12, 2010


8

wikipedia

http://haitiearthquake.web.unc.edu


• MW 9.1 Tohoku earthquake on March 11, 2011

– casualties: 15,894 dead and 2,562 missing

9

wikipedia

http://agnesngoy.blogspot.kr

wikipedia


• MW 9.1 Tohoku earthquake on March 11, 2011

– Fukushima Daiichi nuclear disaster

10

http://www.dailymail.co.uk

http://www.dailymail.co.uk


• MW 7.8 Nepal earthquake on April 25, 2015

– casualties: 8,857 dead

11

wikipedia

http://www.abc.net.au


• World seismicity

12

http://www.sftext.com


• World seismicity

13

http://ds.iris.edu/seismon/


• The largest earthquakes: top 10

14

USGS


• Once upon a time in Japan …

15

http://www.madeinslant.com


• Earthquake

– definition: both sudden slip on a fault, and the resulting ground

shaking and radiated seismic energy caused by the slip, or by

volcanic or magmatic activity, or other sudden stress changes in the

earth

– aftershock: a small earthquake that follows the main earthquake

– foreshock: a small earthquake that often precedes a major

earthquake

16


• Elastic rebound theory

– the first theory to satisfactorily explain earthquakes

17

https://myprojectwiki.wikispaces.com


• Stress and earthquake

– stress changes and earthquake sequence

18

http://iopscience.iop.org


• Causes of earthquakes

– natural: tectonic, volcanic, meteorite, ice-quake

– artificial: explosion

– etc.: collapse

19

http://www.lanl.gov


• Earthquake and fault

– MS 8.0 Mino-Owari (Nobi) earthquake on October 28, 1891:

documented the comprehensive fault breaks visible on the surface

20

http://www.meijishowa.com

wikipedia



– MW 6.9 Great Hanshin (Kobe) earthquake on January 17, 1995

21

wikipedia http://home.hiroshima-u.ac.jp



– earthquake history of Southern California

22

http://www.drtoddfrench.com


• Fault

– a fracture along which the blocks of crust on

either side have moved relative to one another

parallel to the fracture

23

USGS

https://www.slideshare.net

https://www.geo.uu.nl


• Plate tectonics

– supported by a wide range of evidence that considers the earth's

crust and upper mantle to be composed of several large, thin,

relatively rigid plates that move relative to one another

24

http://geology.com

wikipedia


• Seismic belt

– circum-Pacific belt (Ring of Fire): 75% of the world’s seismic energy

– plate boundary: 95% of the world’s seismic energy

25

wikipedia


• Intraplate earthquake

– not occur near plate boundaries, but along faults in the normally

stable interior of plates

– present a weakness in the crust where it can easily slip to

accommodate regional tectonic strain

26wikipedia


• Earthquake size

– magnitude: a number that characterizes the relative size of an

earthquake based on measurement of the maximum motion

recorded by a seismograph

– intensity: a number (written as a Roman numeral) describing the

severity of an earthquake in terms of its effects on the earth's surface

and on humans and their structures

27

KMA https://www.flickr.com


• Magnitude

– measure of the energy released by an earthquake

• independent of distance

– measured by seismographs

• objective and quantitative

– different magnitudes for different seismic waves

• ML (local magnitude) is well-known (also known as the Richter magnitude)

• mb (body wave), MS (surface wave), MW (seismic moment) …

28http://geoadvanced.com


• Richter magnitude

– developed in 1935 by Charles F. Richter of

the California Institute of Technology as a

mathematical device to compare the size of

earthquakes

– defines magnitude as the logarithm of the

ratio of the amplitude of the seismic waves

to an arbitrary, minor amplitude, as

recorded on a standardized seismograph at

a standard distance

– ML = log10A – log10A0

– energy vs. magnitude: 101.5*ΔM

• ML 4.5 vs. ML 6.5 ☞ energy difference?

29

wikipedia

http://www.ux1.eiu.edu


• Moment magnitude

– seismic moment (M0): a measure of the size of

an earthquake based on the area of fault

rupture, the average amount of slip, and the

force that was required to overcome the

friction sticking the rocks together that were

offset by faulting

– MW = 2/3 log10(M0) – 10.7 (H. Kanamori)

30

USGS

http://www.gps.caltech.edu


• Fault size vs. Magnitude

– fault dimension (length, displacement, area) in a particular

earthquake correlates with the magnitude of the earthquake

31



• Magnitude vs. Frequency

– Gutenberg-Richter law: the relationship

between the magnitude and total number of

earthquakes in any given region and time

period of at least that magnitude

– log10N = a – b*M

• N: number of events ≥ M

• a: productivity

• b: b-value

32

USGSKHNP


• Intensity

– grades of the severity of earthquake impact

• natural phenomena, damage to man-made structures, human’s sensation

– basically a subjective and qualitative measure

– subject to site and structure conditions

• soil condition, groundwater level, slope of ground

• height, aging, material of structures

– various intensity scales have been developed

• JMAI (Japan), MMI (US), MSKI (Europe), etc.

– increasing as decreasing distance

• if the intensity is to be used as a measure of earthquake size, it should be

evaluated at a reference point, e.g., at the epicenter

33


• Modified Mercalli Intensity (MMI)

34

https://www.quora.com


• Magnitude vs. Acceleration vs. Intensity

– Gutenberg and Richter

• M = 2/3*Ie + 1.0

• log a = Ie/3 – 1/2

– USGS

• ShakeMap

35

KINShttp://crack.seismo.unr.edu


• Location

– hypocenter: point within the earth where an earthquake rupture starts

• latitude, longitude, depth

– epicenter: point on the earth's surface vertically above the

hypocenter

• latitude, longitude

36

http://www.seismo.ethz.ch


• Location

– use the fact that P and S waves travel at

different speeds to locate earthquakes (S-P

time)

– distance = S-P time * VP * VS / (VP – VS)

• S-P time = 8 sec; VP = 8 km/sec;

VS = 4 km/sec

• distance = ?

– need at least 3 seismic stations

• Origin time

– time at which an earthquake begins

– standardized time (UTC), local time (e.g. KST)

37

http://eqseis.geosc.psu.edu


• Focal depth

– shallow: 0 km~70 km

– intermediate: 70 km~300 km

– deep: 300 km~700 km

38

https://earthquakesandplates.wordpress.com


• Seismic wave

– an elastic wave generated by an impulse such as an earthquake or

an explosion

– travel either along or near the earth's surface (Rayleigh and Love

waves) or through the earth's interior (P and S waves)

39

http://web.ics.purdue.edu


• Seismic wave

– P wave (primary, compressional): seismic body wave that shakes the

ground back and forth in the same direction and the opposite

direction as the direction the wave is moving

– S wave (secondary, shear): seismic body wave that shakes the

ground right and left perpendicular to the direction the wave is

moving

40USGS

wikipedia


• Seismic wave

– Rayleigh wave: seismic surface wave causing the ground to shake in

an elliptical motion, with no transverse, or perpendicular, motion

– Love wave: surface wave having a horizontal motion that is

transverse (or perpendicular) to the direction the wave is traveling

41

USGS


• Components of seismic wave

– phase velocity (propagation)

– group velocity (modulation, envelope)

– amplitude

• measurement of particle motion in the medium

• half of the difference between max and min: ½ of peak-to-peak

• peak amplitude: absolute max amplitude

• conventional unit of peak acceleration: g (gravity)

42

wikipedia


• Components of seismic wave

– period, T: the time spent for one cycle (snap shot)

– wavelength, λ: the distance required for one cycle (seismogram)

– frequency, f: no. of cycles per second

– phase velocity: V = f × λ

43

http://bomeelectricity.blogspot.kr


• Seismic attenuation

– origins

• geometrical spreading: analogous to fading out of light

• inelastic attenuation: loss of energy due to medium defects

• scattering: due to medium heterogeneity, most significant at the near

surface

– typical form: ground motion prediction equation

• ln a = c1 + c2M + c3Mc4 + c5ln[r + c6exp(c7M)] + c8r + f(source) + f(site)

with δlna = c9

44https://www.slideshare.net


• Distance

– fault source

• rjb, rrup, rseis

– point source

• rcent, rhyp, repi

45

http://www.ce.memphis.edu


• Earthquake damage

– earthquake damage varies according to distance, region, etc. even if

earthquake sizes are same

– other causes?

• duration

• soil type

• seismic design

• liquefaction

• tsunami …

46

http://framework.latimes.com



– duration: a strong influence on earthquake damage

• even if the amplitude of the motion is high, short duration may not

produce enough load reversals for damaging response to build up in a

structure

• related to the time required for release of accumulated strain energy by

rupture along the fault

• bracketed duration is most commonly used

47

https://www.researchgate.net https://www.slideshare.net



– soil type: according to the soil type, the degree of site amplification is

different

• site effects by MW 8.0 Mexico City earthquake on September 19, 1985

48

http://www.wikiwand.com http://www.mexiconewsnetwork.com



– seismic design, seismic isolation, seismic control

49

http://hncblog.com



– liquefaction

• refers to the process by which water-saturated, unconsolidated

sediments are transformed into a substance that acts like a liquid, often

in an earthquake

50

wikipedia

http://civilarc.com



– tsunami

• a series of waves in a water body caused by the displacement of a large

volume of water, generally in an ocean or a large lake

• earthquakes, volcanic eruptions and other underwater explosions

(including detonations of underwater nuclear devices), landslides, glacier

calvings, meteorite impacts and other disturbances above or below water

all have the potential to generate a tsunami

51

wikipedia



– Spatial distribution of tsunami height by Tohoku earthquake on

March 11, 2011

52

http://www.coastal.jp


• Earthquake prediction

– concerned with the specification of the time, location, and magnitude

of future earthquakes within stated limits, particularly the

determination of parameters for the next strong earthquake to occur

in a region

– but, most scientists are pessimistic and some maintain that

earthquake prediction is inherently impossible

– MS 7.3 Haicheng earthquake on February 4, 1975

• observation of significant increase of micro-earthquakes → evacuation of

people → 2,041 killed (predicted casualty: more than 150,000) → the

most widely cited success of earthquake prediction

53http://www.thatsmags.com

wikipedia


• Seismograph

– instrument used to detect and record earthquakes

– generally refers to the seismometer and its recording device as a

single unit

• seismic sensor: accelerometer, velocity sensor

• seismic recorder

• charger, battery, UPS, network equipment …

54

http://www.kinemetrics.com

wikipedia

http://www.blessthisstuff.com


• Global seismographic network

55

http://www.hko.gov.hk


• Seismic stations in South Korea

– KMA, KIGAM, KHNP, KINS …

56

Choi et al. (2016)


• GSHAP

57

Malaysia

Indonesia

Philippines

Bahrain

Thailand

Tunisia

Vietnam

IraqJordan

Sudan

South Korea

Kazakhstan

Burkina Faso

Republic of the Congo

Ethiopia

Gabon

Ghana

Kenya

Madagascar

Mali

Nigeria

Senegal

Republic of South Africa

Uganda

France

Morocco

Republic of Cote d'Ivoire


• The Korean Peninsula is

– located at the far eastern part of Eurasian Plate

– within the intra-plate region several hundred km away from the

nearest plate boundary

58

Choi et al. (2012)


• Seismicity in the Korean Peninsula

– low seismicity, relatively smaller magnitude than that of inter-plate

earthquakes, spatially irregular epicenters

• however, on September 12, 2016, the largest instrumental event (ML 5.8)

was occurred nearby Gyeongju area and the second largest event (ML

5.4) in Pohang followed in 2017.

59

KMA


• ML 5.8 Gyeongju earthquake on September 12, 2016

– the largest event during the modern instrumental

recording period (since 1978)

– followed by numerous aftershocks (~600)

60

Kim et al. (2016) Lee and Song (2016)

wikipedia


• ML 5.4 Pohang earthquake on November 15, 2017

– the second largest event after 2016 Gyeongju earthquake

– cause significant infrastructure damage in Pohang

– followed by many aftershocks (~99)

61

KMA

https://blog.naver.com/pohangfood/

wikipedia


• Tsunami around the Korean Peninsula

62

Satake (2007) KMA


• Focal mechanism

– describes the deformation in the source region that generates the seismic

waves

– also known as a fault-plane solution

63USGS


• Damage caused by tsunami in the Korean Peninsula

64

KINS

http://blog.naver.com/


II. Earthquake Monitoring in KINS

• History

– government proclamation of earthquake preparedness measures (1997)

– deployment of seismic network (1998)

– opening of earthquake monitoring center (2001)

• Mission

– monitoring earthquake ground motions at nuclear facility sites

– analyzing characteristics of Korea earthquakes

– evaluating earthquake damages to nuclear structures

65

KINS


• Observation

– located at nuclear facility sites

– sensors and recorders

– ground motion recording & transmission

66

KINS


• Monitoring center

– located at KINS

– communication equipment

& computers

– data gathering & analysis

67

KINS


• Recordings of Gyeongju earthquake on September 12, 2016

– where is the closest station from the event? why?

68

KINS

49

148

26

254


• Recordings of Pohang earthquake on November 15, 2017

– where is the farthest station from the event? why?

69

KINS

88

107

46

278


III. Seismic Safety of NPP site in Korea

• World seismicity and nuclear power plants

70http://maptd.com


• Seismic preparedness step

71

Site Selection• Existence of capable fault

• Appropriateness of design earthquake

Construction• Appropriateness of seismic qualification on-site

• Inspection of seismic monitoring system (SMS)

Operation• Regular inspection

• Operation of earthquake monitoring network

Design• Appropriateness of seismic design

• Inspection of seismic qualification

• Regional and site investigation on geologic and

seismic characteristics

• Geology, seismology, geotechnical engineering

• Seismic design and qualification of the safety-

related SSCs* by dynamic analysis and test

• Seismic design engineering, structural engineering

• Inspection of seismic qualification (the safety-related

SSCs)

• Inspection of installation and capacity of SMS

• Regular inspection of SMS

• Check of the seismic safety of the safety-related

SSCs against earthquakes`

* SSCs: structures, systems and components


• Emergency response procedure

72

Earthquake

PGA ≥ 0.01 g

PGA ≥ 0.1 g

PGA ≥ design eq.

• Announcement of an alarm

• Shutdown of a nuclear reactor

• Announcement of facility

emergency

• Radiation emergency plan

• Restart of a nuclear reactor

• Check the safety-related

SSCs

• Restart of a nuclear reactor

• Shutdown of a nuclear reactor

• Announcement of site area

emergency


• Again

– from seismic source to ground motion

– if we can characterize seismic sources (e.g., faults), paths (e.g.,

crustal structures), and sites (e.g., subsurface) …

• it is possible to predict the maximum ground motion at the site

• design earthquake ground motion can be determined

73

seismic source

path

site

ground motion

Modified Boore (1999)


• Design Earthquake (ground motion)

– safe shutdown earthquake (ground motion) (SSE)

• seismic design for safety related SSCs

• at least 0.1g in peak ground acceleration

• SL-2 in IAEA terminology

– operating basis earthquake (ground motion) (OBE)

• seismic design for continuous operation

• SL-1 in IAEA terminology

– construction

• DE (ground motion) should be given in response spectra

74


• Response spectrum

– a plot of maximum responses of structures

of single-degree of freedom, in terms of

their natural frequencies

– representation of a structure by a simple

pendulum (single degree of freedom)

• pendulum mass (M) = sum of mass of

structure and attached facilities

• spring (k) = (shear) walls

• damping (c) = inelastic characteristics of

structure

– response spectra are provided for various

damping values of interest

– three types of response spectra

• (relative) displacement response spectra

• (relative) velocity response spectra

• (absolute) acceleration response spectra

75

https://www.linkedin.com


• Response spectrum

– tripartite chart

76

Moon et al. (2011)


• Related domestic regulations

– nuclear safety act

– regulations on technical standards for nuclear reactor facilities, etc.

• article 4 (geological features and earthquakes)

– notice of the Nuclear Safety and Security Commission No. 2014-10

(Technical standards for locations of nuclear reactor facilities)

• applicable foreign regulations: 10 CFR Part 100 Appendix A (Seismic and

Geologic Siting Criteria for Nuclear Power Plants)

– regulation criteria, regulation guide, safety review plan …

77


• Determination of DE in South Korea

– domestic regulation follows pre-revision version of US federal law

• deterministic method

• 10 CFR Part 100 Appendix A

– revision of US federal law on January 10, 1997

• probabilistic method

• 10 CFR Part 100 Subpart B 100.23

– current

• evaluation of DE by deterministic method

• appropriateness of DE by probabilistic method

78


• Procedures for determining DE

79

Collection and analysis of past earthquakes within a radius of 320 km from a site

- historical and instrumental earthquakes

- magnitude, depth, distance, recurrence interval

- seismic characteristics, focal mechanism, etc.

Analysis of relationships between past earthquakes and tectonic structures

- faults, folds, etc.

Establishment of seismotectonic provinces within a radius of 320 km from a site

Capable faults considered in design earthquake

Ground motions at a site from each seismotectonic province and capable fault

- ground motion prediction equations

- ground motion simulation

Site response analysis at a site

Controlling earthquake and design earthquake

Appropriateness of DE by probabilistic seismic hazard analysis

Determination of DE of a site


• Investigation of geosciences data

– geologic data

• identification of capable structures: faults, folds, etc.

– seismic data

• historical earthquakes: historical documents

• instrumental earthquakes: since 1900

• site-specific earthquakes: local seismic network

– check: reliability, accuracy, completeness

80


• Regional seismotectonic models

– general considerations

• seismic, geological, and geophysical data are combined to establish

regional seismotectonic models.

• it is not desirable to establish seismotectonic models that are more

sophisticated than the data support.

– seismic source

• capable tectonic structure

definition: a geological structure capable of generating earthquakes

characterization: location & geometry of geological structure, maximum

potential earthquake, earthquake recurrence rate, etc.

• seismotectonic province

definition: a region where earthquakes diffusely occur, but no specific geological

structure is identified to be responsible for those earthquakes.

characterization: similar to that of capable tectonic source

81


• Seismic source

– capable tectonic source (capable fault)

• movement at or near the ground surface at least

once within the past 35,000 years or movement of a

recurring nature within the past 500,000 years

• macro-seismicity instrumentally determined with

records of sufficient precision to demonstrate a direct

relationship with the fault

• a structural relationship to a capable fault according

to characteristics above mentioned items of this

paragraph such that movement on one could be

reasonably expected to be accompanied by

movement on the other

– seismogenic source (seismotectonic province)

• cover a wide range of seismotectonic conditions,

from a well-defined tectonic structure to simply a

large region of diffuse seismicity

82

KHNP


• Capable fault

– design against

• vibratory ground motions

• surface deformation

83

capable fault

vibratory ground motion surface deformation

seismic safety

(design earthquake)

integrity of foundation

(site suitability/layout)


• Capable fault

– for faults, any part of which is within 320 km of the site and which

may be of significance in establishing DE

– minimum length of fault to be considered versus distance from site

84

distance (km) minimum length (km)

0~32 1.6

32~80 8

80~160 16

160~240 32

240~320 64


• Capable fault

85

evaluating

earthquake potentialextending to plant?

yes

no

capable fault

unsuitable

site

determining

design earthquakes

eng. solution

exists?

suitable

site

yes

no


• DE considering of near fault

– in the case where a causative fault is near the site, the effect of

proximity of an earthquake on the spectral characteristics of DE shall

be taken into account

86

Noh and Choi (2007) Jo (2006)


• Ground motion prediction equation

– a prediction equation for seismic ground motion

attenuation from seismic source to a site

– basic parameter: magnitude and distance

• faulting type: thrust, normal, strike-slip, etc.

• seismic wave transmission: soil, rock, etc.

– consideration of scattering

– various types of ground motion

• maximum ground acceleration, velocity, displacement

• response spectral acceleration, velocity,

displacement

– domestic status

• past poor seismic stations

• absence of large sized earthquake (strong ground

motion)

87

Noh and Choi (2007)


• Seismic wave transmission

– ground motions at the site should be corrected for those effects of

• seismic properties of plant site different from those of recording sites

• layered structures of underground materials of the plant site

• significant topography around the plant site

– design earthquake

• the maximum site ground motions corrected for wave transmission

characteristics

– NPP site in South Korea

• located on the basis rock

• composed of competent material

88KHNP


• Seismic hazard/design earthquakes

– deterministic & probabilistic methods

– Korean regulation requires the deterministic method: mean annual exceeding

frequency of SSE should be less than 1.0E-3

• Deterministic approach

– step

• establish a seismotectonic model consisting of capable tectonic

structures and seismotectonic provinces (i.e., seismic sources)

• determine the max. potential earthquake (MPE) for each seismic source

• locate each MPE at the closest point to site

• calculate the site ground motion by each MPE by using proper ground

motion prediction equation

• take the largest ground motion among all MPEs (max. site ground motion)

89


• Deterministic approach (diagrammatic)

90

move

attenuation

move

move

attenuation

Choi et al. (2016)


• Probabilistic approach

– uncertainties are originally inherited in the seismic characteristics

since faulting and earthquakes are occurred at the deep part of the

Earth, but investigation and observation are generally performed at

the surface area

– step

• construct seismotectonic models in terms of seismic sources including

uncertainty in source boundary

• for each source, determine magnitude-frequency models and MPEs

including the associated uncertainties

• select proper attenuation equations including the uncertainties

• evaluate annual frequency of exceedance for various levels of ground

motions: mean, median, 15th-percentile, 85th-percentiles

91


• Probabilistic approach (diagrammatic)

92

Reactor

A1 A2

F2 F1

R

A3

Acc

eler

atio

n, a

a*

Distance, R

Increasingmagnitude mi


• Design earthquake by deterministic approach

– DE of NPPs in South Korea is determined to be

• 0.2g (in case of newly constructed NPPs is 0.3g) considering the MPE

ground motions and some safety margin

• ground motions and surface deformations caused by capable faults are

also considered in the seismic design of NPPs

• design earthquake are given in response spectra

93

KHNP


• Design earthquake by deterministic approach

– in the case where a capable fault is near the site, the maximum

ground motion from this fault does not affect the DE of the site

94

KHNP


• Check of the appropriateness of DE

– by probabilistic approach

• mean annual exceeding frequency of design earthquake of NPP sites in

South Korea is evaluated to be less than 1.0E-3, and it meets the criteria

of the related regulatory guides

95

KHNP


• Design earthquake by probabilistic approach

– current global tendency to determine design earthquake by

probabilistic approach

• regulatory researches on the assessment of design earthquake by

probabilistic approach are in progress, the reflection to NPP sites in

Korea or not will be judged after reviewing their applicability

• regulatory guide 1.208 (U.S.NRC): a performance-based approach to

define the site-specific earthquake ground motion

– before applying design earthquake by probabilistic approach, related

domestic regulations should be revised

96

U.S.NRC


• Seismic safety of NPP site in Korea

– Through data analysis on geological and seismological

characteristics of the region within a radius of 320 km from the site

and the detailed geological survey of the area within a radius of 8 km

from the site

• NPPs in Korea are believed to be safe enough against the maximum

potential earthquake ground motion

– However, September 12, 2016 event with magnitude 5.8 (ML) nearby

Gyeongju area, which is the largest instrumental one in South Korea

• no significant damage to NPPs, but utility shutdowned 4 units located

nearby the epicenter within 4 hours

– The second largest event (ML 5.4) in Pohang followed in 2017

• cause significant infrastructure damage in Pohang

– Establishment of short and long term plans for reinvestigation

earthquake causative faults nearby NPP sites and reassessment of

design earthquake are in progress.

97


• Research on seismic source characterization of the September

2016 earthquake for reevaluating seismic safety of nuclear power

plant sites (from April 2017 to December 2021)

– Identification of the active fault for the Gyeongju earthquake and its

seismic source characterization

– Estimation of the maximum ground motion for the adjacent nuclear

power plants (NPP)

– Establishment of the long-term monitoring/preparedness system for

seismic hazard

– Interpretation of 3-D fault structure at and around the focal area of

the Gyeongju earthquake

– Development of evaluation technique for seismic safety of NPP sites

considering the Gyeongju earthquake

98


• Research on seismic source characterization of the September

2016 earthquake for reevaluating seismic safety of nuclear power

plant sites

– Establishment of microearthquake monitoring system and

development of its management technique

99Ree (2017)


IV. IAEA Specific Safety Guide No. SSG-9

100IAEA


• Background

– seismic hazard curves and ground motion spectra for the

probabilistic safety assessment of external events

– feedback of information from IAEA reviews of seismic safety studies

for nuclear installations performed over the previous decade

– collective knowledge gained from recent significant earthquakes

– new approaches in methods of analysis, particularly in the areas of

PSHA and strong motion simulation

• Objective

– vibratory ground motion hazards, in order to establish the design

basis ground motions and other relevant parameters

– potential for fault displacement and the rate of fault displacement that

could affect the feasibility of the site or the safe operation of the

installation at that site

101


• Necessary information and investigations

– need a comprehensive and integrated database of geological,

geophysical and seismological information

– investigation of 4 spatial scales

• regional investigations (typically 300 km): maps at a scale of 1:500,000 or

larger

• near regional investigations (typically not less than 25 km): maps at a

scale of 1:50,000

• site vicinity investigations (typically not less than 5 km): maps at a scale

of 1:5,000

• site area investigations (typically one square kilometer): maps at a scale

of 1:500

102

greater details towards the site


• Seismological database

– prehistoric and historical earthquake data

• date, time and duration of the event

• location of the macroseismic epicenter

• estimated focal depth

• estimated magnitude, the type of magnitude and documentation of the

methods used to estimate magnitude

• maximum intensity

• isoseismal contours

• intensity of the earthquake at the site

• estimates of uncertainty for all of the parameters

• an assessment of the quality and quantity of data

• information on felt foreshocks and aftershocks

• information on the causative fault

103



– instrumental earthquake data

• date, duration and time of origin

• coordinates of the epicenter

• focal depth

• all magnitude determinations

• observed foreshocks and aftershocks (dimensions and geometry)

• information that may be helpful in understanding the seismotectonic

regime

• macroseismic details

• asperity location and size

• estimates of uncertainty for each of the parameters

• information on the causative fault, directivity and duration of rupture

• records from both broadband seismometers and strong motion

accelerographs

104



– project specific instrumental data

• a network of sensitive seismographs having a recording capability for

micro-earthquakes be installed and operated

• earthquake analysis in connection with seismotectonic studies of the near

region within and near such a network

• strong motion accelerographs within the site area

• appropriately and periodically upgraded and calibrated instrumentation

105


• Seismotectonic model

– two types of seismic source

• seismogenic structures that can be identified by using the available

database

• diffuse seismicity (consisting usually, but not always, of small to moderate

earthquakes) that is not attributable to specific structures identified by

using the available database

– earthquake catalogue

• selection of a consistent magnitude scale for use in the seismic hazard

analysis

• determination of the uniform magnitude of each event in the catalogue on

the selected magnitude scale

• identification of main shocks (i.e. declustering of aftershocks)

• estimation of completeness of the catalogue as a function of magnitude,

regional location and time period

• quality assessment of the derived data, with uncertainty estimates of all

parameters

106


• Seismotectonic model

– magnitude-frequency relationship

• including the maximum potential magnitude

– maximum potential magnitude

• upper limit of integration in a probabilistic seismic hazard calculation and

in the derivation of the magnitude–frequency relationship

• scenario magnitude in a deterministic seismic hazard evaluation

– paleoseismic study

• identification of seismogenic structures on the basis of the recognition of

effects of past earthquakes in the region

• improvement of the completeness of earthquake catalogues for large

events, using identification and age dating of fossil earthquakes

• estimation of the maximum potential magnitude of a given seismogenic

structure

• calibration of probabilistic seismic hazard analyses, using the recurrence

intervals of large earthquakes

107


• Evaluation of the ground motion hazard

– ground motion hazard

• should preferably be evaluated by using both probabilistic and

deterministic methods of seismic hazard analysis

• when both deterministic and probabilistic results are obtained,

deterministic assessments can be used as a check against probabilistic

assessments in terms of the reasonableness of the results

– uncertainty

• both aleatory and epistemic uncertainties should be taken into account

– ground motion prediction models: attenuation relationships

• be current and well established at the time of the study

• be consistent with the types of earthquake and the attenuation

characteristics of the region of interest

• match as closely as possible the tectonic environment of the region of

interest

• make use of local ground motion data where available

108


• Uncertainty

109

aleatory epistemic

natural variability modeling or knowledge uncertainty

not reducible reducible with more information

addressed through integration over

parameter distributionaddressed through use of a logic tree



• Evaluation of the ground motion hazard

– ground motion prediction models: seismic source simulation

• fault geometry parameters (location, length, width, depth, dip, strike)

• macroparameters (seismic moment, average dislocation, rupture velocity,

average stress drop)

• microparameters (rise time, dislocation, stress parameters for finite fault

elements)

• crustal structure parameters, such as shear wave velocity, density and

damping of wave propagation (i.e. the wave attenuation Q value).

110


• Probabilistic seismic hazard analysis (PSHA)

– step

• evaluation of the seismotectonic model for the site region in terms of the

defined seismic sources, including uncertainty in their boundaries and

dimensions.

• for each seismic source, evaluation of the maximum potential magnitude,

the rate of earthquake occurrence and the type of magnitude–frequency

relationship, together with the uncertainty associated with each

evaluation

• selection of the attenuation relationships for the site region, and

assessment of the uncertainty in both the mean and the variability of the

ground motion as a function of earthquake magnitude and seismic source

to site distance

• performance of the hazard calculation

• taking account of the site response

– evaluation of the annual frequency of exceedance of a specified level

of ground motion at a site due to one or more seismic sources by

integrating over all relevant contributions

111


• Deterministic seismic hazard analysis (DSHA)

– step

• seismogenic structure

the maximum potential magnitude (MPM) should be assumed to occur at the

point of the structure closest to the site area of the nuclear power plant (NPP)

when the site is within the boundaries of a seismogenic structure, the MPM

should be assumed to occur beneath the site

• diffuse seismicity

the MPM in a zone that includes the site of the NPP should be assumed to

occur at some identified specific horizontal distance from the site

the MPM associated with zones in each adjoining seismotectonic province

should be assumed to occur at the point of the province boundary closest to the

site

• ground motion prediction equations (attenuation relationships or, in some

cases, seismic source simulations): should be used to determine the

ground motion that each of these earthquakes would cause at the site

• taking account appropriately of both aleatory and epistemic uncertainties,

and incorporating the site response

112


• Potential for fault displacement at the site

– a fault is considered capable

• it shows evidence of past movement or movements (such as significant

deformations and/or dislocations) of a recurring nature within such a

period that it is reasonable to conclude that further movements at or near

the surface may occur

• a structural relationship with a known capable fault has been

demonstrated such that movement of the one fault may cause movement

of the other at or near the surface

• the maximum potential magnitude associated with a seismogenic

structure is sufficiently large and at such a depth that it is reasonable to

conclude that, in the current tectonic setting of the plant, movement at or

near the surface may occur

– site vicinity scale investigation

• very detailed geological and geomorphological mapping, topographical

analyses, geophysical surveys (including geodesy, if necessary),

trenching, boreholes, age dating of sediments or faulted rock, local

seismological investigations and any other appropriate techniques to

ascertain the amount and age of previous displacements

113


• Potential for fault displacement at the site

– probabilistic fault displacement hazard analysis (PFDHA)

• same procedures as are used to perform a probabilistic seismic hazard

analysis

• λ (D > d|t): the derived rate at which the surface or near surface fault

displacement D exceeds the value d in time t at the site

• P (D > d|m,r): the probability that the surface or near surface fault

displacement D exceeds the value d given an earthquake of magnitude m

on seismic source i located at a distance r from the site

• Levels of ground motion hazard

– SL-1

• corresponds to a less severe, more probable earthquake level that

normally has different implications for safety

– SL-2

• associated with the most stringent safety requirements

114


• Design basis response spectra

– site response analysis

• take into account the geological and geotechnical conditions at a site as

part of the estimation of ground motion

– uniform hazard response spectra

• selecting the values of the response spectral ordinates that correspond to

the annual frequencies of exceedance of interest from the seismic hazard

curves

– standardized response spectra

• having a smooth shape is used for engineering design purposes and to

account for the contribution of multiple seismic sources represented by

an envelope incorporating adequate low frequency and high frequency

ground motion input

115


V. Remarks

• Earthquake fundamentals

– provided basic knowledge about earthquake concept, principle,

phenomenon, etc. so as to enhance understanding of seismic

hazards

• Earthquake monitoring in KINS

– monitoring earthquake ground motions at nuclear facility sites

independently by regulatory institute


– current global tendency to determine design earthquake by

probabilistic approach

• regulatory researches are in progress

• related domestic regulations will be revised

116



– NPPs in Korea are believed to be safe enough against the maximum

potential earthquake ground motion

• however, short and long term plans for reinvestigation earthquake

causative faults nearby NPP sites and reassessment of design

earthquake are in progress after Gyeongju earthquake

• IAEA specific safety guide No. SSG-9

– vibratory ground motion hazards, in order to establish the design

basis ground motions and other relevant parameters

– potential for fault displacement and the rate of fault displacement that

could affect the feasibility of the site

117

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