KR9700364

Overview of the Tectonic Environment

in Korea with Reference to HLW Disposal

Chun-Soo Kim

KAERI

1. Introduction

It is worldwidely accepted by most of the countries with nuclear energy

programs that deep geological disposal in a stable geological environment is a

feasible means of isolating HLW for very long time. The geological condition

of the Korean peninsula, a major link between the Pacific active margin and the

Asian mainland, should be reviewed in terms of the stability over geological

time scales for a deep geological repository. Comprehensive understanding of

the tectonic evolution of the peninsula will be great help to develop the technical

feasibility and performance assessment methodology for HLW disposal in

geologic formation.

A significant research is recently carried out as an integrated geoscience

approach on the tectonics and geodynarnics of the Eastern Asian continent.

However, many hypotheses on tectonic evolution should be proved by further

studies. This short paper is summarized on the long stability of the Korean

peninsula from data available at present. Most of the information are based on

Geology of Korea(1987), Geology of Korea(1996), and Tectonic Evolution of

Eastern Asian continent(1997).

2. Tectonic Setting

2.1 Tectonic Evolution

The Korea peninsula is located in the area where the Eurasian continent is

contacted with the west Pacific mobile belt. Whereas the Japan archipelago is

characterized by active mobile belt, the Korean peninsula has a close affinity

with the Asian continent in geology and tectonic setting(Fig. 1). In a broad

category, the peninsula occupying the eastern margin of the Korea-China

platform belongs to a part of the shield area regarded as stable land of cratonic

nature, but has some differences from the stable platform. In platforms, deep

rifts are usually absent and major uplifts/troughs do not have linear structures,

and igneous activity is usually slight without granitic intrusions. On the other

hand, deep rifts in the peninsula cut the basement and troughs formed in the

Paleozoic period are usually linear, and Mesozoic and Cenozoic troughs are filled

with thick continental clastic sediments. Moreover, the orogenies occurred were

accompanied by volcanic and granitic intrusion, and neotectonic movements are

relatively intensive. These tectonic characteristics are considered as the

marginal geosyncline phenomena of platform with superimposed tectonic

elements during the Meso-Cenozoic era.

The Korea-China platform was converted into a stable massif after the

crustal movement in the late Lower Proterozoic era(1.8 Ga ago)which is known

as a great transitional age in crust development. Unlike other platforms in the

world, The Korea-China platform was under a strongly mobilized state after

having been converted into a platform. There were the rift type mobile belts

such as Imjingang and Okchon Fold belts during the middle Paleozoic age,

foreland basin in the margin of the platform during the late Meso-Cenozoic age,

and the tectonic sturctures of the Meso-Cenozoic age were superimposed on the

peninsula. The tectonic evolution of the Korean peninsula can be divided into

three stages as follows :

• Ancient geosyncline stage : Archean(2.6 Ga) - Proterozoic(1.8 Ga)

• Stable platform stage '• Middle Proterozoic(1.7 Ga) - Late Paleozoic(260 Ma)

• Stage influenced by the movement of west Pacific plate : Mesozoic(230

Ma) - Holocene(present)

For the geotectonic units of the peninsula, the Mesozoic orogeny is most

important. In the wide area of East Asia, magmatism, volcanism, and the

deformation/metamorphism of the sedimentary covers of platform occurred

intensively during the Mesozoic era. The tectonic movement in this era is

explained as a transitional development of platform into geosyncline stage. The

Mesozoic tectonic activity started in the Middle Triassic period is the most

vigorous crustal movement in the entire Korean peninsula, accompanied by

folding, fault bock movement and igneous intrusion. These phenomena are

special tectonic movements which are not found in the platform or geosyncline

zone in general. It is considered that more intensive orogeny and fault blocks

followed by magmatism within the continent occurred due mainly to the

influence of the subduction of the west Pacific plate. Such tectonic movements

intensified gradually from the north to the south and from the west to the east,

resulted from the eastward subduction zone of the Pacific plate.

The tectonic movements in the peninsula are considered to be divided into

three correlated stages, one after the other from the beginning of the Mesozoic

era as follows :

• Middle-Upper Triassic(210-180 Ma) :

- Songnim disturbance in Korea,

- Indosinian movement in China

- Akiyoshi movement in Japan

• Middle-Upper Juras sic (180-136 Ma)

- Daebo orogeny in Korea

- Early phase of the Yenshan movement in China

- Mid-phase of the Sakawa movement in Japan

- Nevadan orogeny in North America

• Upper Cretaceous-Paleocene( 120-40 Ma)

- Bulguksa disturbance in Korea

- Last stage of the Yenshan movement in China

- Alpine orogeny in Europe

- Laramide orogeny in North America

After the Mesozoic tectonic movements, the whole of Korea had been

uplifted. The Cenozoic tectonic activity was not intensive as the previous

tectonic movements and is generally represented by mafic to intermediate

volcanic activities in limited areas. Pleistocene alkali volcanic eruption took

places in NNE trending rift zones as well as the Mt. Paektu, UUung and Cheju

islands.

2.2 Tectonic Provinces

The tectonic framework of the Korean peninsula is considered to consist of

the eastern extension of the Korea-China platform in the northern part of the

peninsula and the northeastern extension of the Yangtze platform in the

southern part. However, some differences exist in geologic settings and

structural events between the peninsula and the continent, and thus the further

study is necessary to reach the conclusive correlation.

Since the tectonic province was first described in 1933, many revision made

on the basis of the geological time unit rather than structural distinction(Fig. 2).

More recently the division of tectonic units was proposed by the stabilization

time of the original crust. Among the tectonic units proposed, massif and fold

belts which are more relating to radioactive waste disposal are as follows ;

• Archean - Early Proterozoic massif

- Rangnim massif (North Korea)

- Kwanmo massif (North Korea)

- Kyonggi massif (South Korea)

- Ryongnam massif(South Korea)

• Upper Proterozoic-Upper Paleozoic fold belt

- Okchon fold belt(Upper Proterozoic; South Korea)

- Imjingang fold belt(Middle Paleozoic; North Korea)

- Tumangang fold belt(Upper Paleozoic! North Korea)

The Kyonggi massif is located in the central part of the Korean peninsula

and bounded by Imjingang fold belt and Okchon fold belt in the north and

south, respectively. In the oldest folded basement of Kyonggi massif,

metasomatic granites are widely developed and highly metamorphosed schists

and migmatites in the metasomatic outliers exhibit mostly amphibolite to

granulite facies. Also, the metasedimentary rocks consisting of quartzite, quartz

schist are extensively exposed in the southwestern part of the Kyonggi massif.

The fault structure has largely two directions. One is parallel to the tectonic

direction of NE distributed in the south of the massif, the other has a NNE

direction in the north of the massif.

The Ryongnam massif, located in the southern part of the peninsula, is

bounded by the Okchon fold belt on the north. On the southeast, it contacts to

the basement of Cretaceous sedimentary basin(Kyongsang basin). The massif

consists of gneiss and schist in early Proterozoic metamorphic group and is

characterized by a ploymetarnorphic region due to orogenies in many times.

The crystalline basement is exposed mainly on the northeastern part and various

kinds of gneiss, migmatite and crystalline schist are developed in the

southwestern part.

Fault systems developed are in NE-NNE, NWW and EW-NEE directions.

Faults with a NE direction proedominate on the southwestern part of the

peninsula and faults with a NNE direction increase gradually towards the

southeast. Faults with a EW-NNE direction are characterized as thrusts

inclined to the south.

The Okchon fold belt is extended over 450km in length and 50 ~ 80km in

width, between the Kyonggi and Ryongnam massifs. The fold belt is divided

into two regions on the basis of metamorphic fades, metamorphic zone in the

southwestern region and nonmetamorphic zone in the northeastern region.

3. Igneous Activity

The intrusive and effusive rocks in the Korean peninsula were formed from

the Archean to the Quaternary and the plutonic rocks are occupied by nearly

one-half of the peninsula(Fig. 3). The majority of igneous rocks in Korea are

granites and their varieties. Intermediate plutonic rocks of mainly diorite are

exposed as small stocks in the southern part of the inland and along the east

coast of the northern part. The distribution of mafic and ultramafic plutonics is

almost limited to the tectonic regions. Among these plutonic rocks, the rock

mass suitable for a host rock of repository based on the areal extent and

tectonic environment is summarized in Table 1 .

4. Volcanism

Volcanism in the peninsula has occurred thoughout most of the geological

ages from Archean to Holocene with igneous activity. But the most prominent

volcanism was taken place in the period of the Upper Jurassic- Lower

Cretacepus(160~100Ma ago). Volcanic activities in these periods took place

along large fault zones and were vigorous during sedimentation in the Mesozoic

basin. Volcanic activities in the basin play an important role in establishing the

stratigraphy sequences of the Mesozoic basins.

The Cretaceous volcanism continued up to the early Tertiary(50Ma ago). But

it was relatively inactive throughout the Paleogene and intermittently in the

Neogene. The volcanism was continued to the Quaternary in several areas, i.e.

Mt. Paektu, Chugaryong fault zone and Cheju island. According to historical

records, several volcanic activities in Korea were dated between 1000 and 1600

AD.

5. Seismicity

In terms of plate tectonics, the Korean peninsula is located within the

Eurasian plate. The Pacific plate subducts under the Eurasian plate in Japan

and under the Indo-Australian plate in New Guinea, while the Indo-Australian

plate collides with the Eurasian plate in the Himalayas. Also the Philippine

plate subducts under the Eurasian plate along the Philippine trench. Therefore,

earthquakes in Korea are ascribed to the intraplate seismicity (Fig. 4).

In Korea, historical earthquake records date back to 2 AD and the

instrumental data were collected from 1905. Based on historical seismicity, the

southeastern part and the southwestern part of the peninsula turned out to be

seismic zones, whereas the seismicity of the Rangnim Massif and Paektu

volcanic zone in the northern part is remarkable weaker than the other tectonic

provinces(Fig. 5). The distribution of earthquakes associated with the

instrumental data shows that the seismicity is stronger in the southern and

western parts of the peninsula than in the other regions(Fig. 6). However, deep

sources of earthquakes are distributed in the northeastern part and in the East

sea. In general, the close correlation between seismicity and Quaternary

tectonics in the Korean peninsula can not be found. Quaternary tectonics are

rather limited to volcanic eruptions in certain regions. Most of the earthquakes

might occur in zone of weakness, mainly along faults. Particularly, earthquakes

having MM intensity more than 4 are related with fault structures. It appears

that many of the faults created during the Mesozoic orogenies have generated

earthquakes afterwards. Therefore a number of major faults and tectonic

boundaries of the peninsula may be active even though they were formed before

the Cenozoic.

The intraplate seismicity is characterized by a high degree of irregularity

both in space and time. The depths of earthquake sources are estimated to 10—

12km below ground in general. The most destructive earthquakes since 1905

were Ssanggyesa earthquake on July 4, 1936 and Hongsung earthquake on

October 7, 1978. The MM intensity of these earthquakes is VII and the

magnitude of the Hongsung earthquake turned out to be about 5.2. According

to the historical earthquake records, the strengthening period in Korea is for

about 500 years and the weakening period for about 200 years. This tendency

have alternated each other from 2 AD to the present.

6. Conclusion

Korea is located in a stable platform which was subjected to major periods

of significant tectonic movement between about 180 and 100 million years ago.

And then subsequent tectonic activities have been diminished and limited to in

local areas. In the present stage, the distruptive natural phenomena are

characterized as sudden activities, i.e. volcanisim and seismicity, in the localized

particular areas, which can be avoided by excluding certain areas in the early

stage of siting.

The plutonic intrusion in Korea occurred from the Proterozoic-Cretaceous era,

resulting in a large areal extent. The wide distribution of plutonic rock is

important consideration as the potential host rock, allowing flexibility of siting.

The fracture zones developed in the peninsula are more or less systematic and

most of the fracture zones in large scale has been reactivated subsequently

along pre-existing fractures. Thus the competent host rock mass for a

repository will be available in the distributed area of plutonic rocks.

REFERENCES

[1] Geology of Korea(1987) (ed. Lee, D.S.), Geological Society of Korea,

Kyohaksa Co., Seoul, 514p.

[2] Geology of Korea(1996) (chief ed. Paek, R.J.), Institute of Geology, State

Academy of Sciences DPR of Korea, Foreign Languages Books

Publishing House, Pyongyang, 631p.

[3] Tectonic Evolution of Eastern Asian Continent(1997) (ed. Lee, Y.I. and Kim,

J.H.), International Symposium on the Occasion of the 50th

Anniversary of the Geological Society of Korea, Sept. 24-25, 1997,

Seoul, Korea, 273p.

[4] Cluzel, D,. Lee, B.Y. and Cadet, J.P., 1991 Indosinian dextral ductile fault

system and synkinematic plutonism in the southwest of the

Ogcheon belUSouth Korea). Tectonophysics, 194:131-151.

[5] Chwae U. and Jun, M.S.Q996) The seismotectonic interpretation of Korean

Peninsula, in 1996 Symposium on seismology in East Asia,

KIGAM, Oct. 15-18, 1996 Daejon, Korea.

[6] Lee, K.(1996) Earthquakes of Korea, in 1996 Symposium on seismology in

East Asia, KIGAM, Oct. 15-18, 1996 Daejon, Korea.

Table 1. Characteristics of plutonic rocks as potential host rock of HLW repository

Archean toEarly Proterozoic

Lower-MiddleProterozoic

Jurassic

Cretaceous

«impkx

Jirisan complex,Kyonggi complex

Bunchon granite(2100+50 Ma)Hongjesagranite gneiss(1800-1750 Ma)Sosan granite gneiss(1420±70 Ma)

Deabo granites(180-140 Ma)

Buiguksa granite(-135 Ma)

t4 («£ru&*ve active?

Granite bodies bygranitization, metasomatism infolding stage, partly dykes ofmagmatic origin

Batholith, stock of contemporaneousor post stages of geosyncUne fold

Batholith, stock along fracture inplatform

Intrusion in forms of stock or platealong fracture in platfrom

- Garnet-biotite gneissicgranite

- Pophyroblastic granite- Leuco granite- Pegmatitic granite

- Biotite granite- Leuco granite- Granodiorite- Quartzdiorite

- Gabbro diorite- Biotite granite- Fine granied two micagranite

- Quartz diorite- Graphic granite- Granoporphyry- Alkali granite

In graduation withArchean Early-Proterozoic,penetrated by dykes

Injector intrude Archean& Lower Proterozoic,overlain bymetasediinentary group

Penetrate Upper Paleozoic,overlain by Upper Jurassic

Penetrate Upper Jurassicand Certaceous, overlainby Upper Cretaceous-Paleocenc

118°E

MONGOLIA

X4AEANPlATfttRJA

- 40° N

I18«E

Fig. 1. General tectonics setting of the Korean Peninsula[4]

1. Tuman Basin

2- Kwanmobong Massif

3. Tanchon Folded Ben

3-1. Amnok Folded Belt

4. Nangnim Massif

5. Pyongnam Basin

6. Kyonggi Massif

6-L Ongjin Basin

6-2 Ctiungnam Depression Zone

6-3. Ktngju Depression Zone

7. Okch'on Foided Belt

7-L Okchon Neogeosyndinal Zone

7-2 Okch'on Paleosyndinal Z«.;e

8. Ryongnam Massif

8-1. Taebaeksan Zo«

8-2. Chinsan Zone

9. Kyongsang Basin

9-1. Yongdong-Kwangju

Depression Zone

10. Yonrl Basin

11 Cheju Volcanic Island

A. KilchuMyongction Graoen

B. Ch'ugaryong Fault Zone

Fig. 2. Detailed tectonic provinces in Korea[l]

TT

UGENO

I Quattrnary iitrusv«i

I 1 T«ti«ry t i t n n v n

i Uin &<iralai>t«M «•«»'

9 m Lm Colanoia mUi

| I tallK utru»«

9 ^ H | Trimc muu9v«

banu

! •«•

K«wi»iil«rojc«-H««(ni(iiMoie wtmsuss

Fig. 3. Distribution of granitic rock mass in KoreaQ]

1904 1 / 1 0: 0 - - 1992 12 / II 24: 0 M: 4 . 5 - ».8

7 ••

e ':

60ka

60

Fig. 4. Seismicity map of shallow earthquakes (focal depth<60 km and

magnitute>4.0) in E. Asia(1964~1992)[5]

H* 27410

42

40

38-

36-

34.

126 128 130

-42

-40

0 60 100 200KM

-38

-36

-34

124 126 128 130

Fig 5. Epicenters of Korean historical earthquakes having MMI equal

to or greater than V during A.D. 2-1905[6]

42

40

38

36

34

124r

Magnitude

126 128 130

42

• o

40

0 50 100 200KM

124 126 128

38

36

34

130

Fig. 6. Epicenters of Korean instrumental earthquakes having magnutude

equal to or greater than 4.0 during A.D. 1905-1993[6]

Overview of the Tectonic Environmentin Korea with Reference to HLW Disposal

October, 1997

Chun Soo Kim

KAERI, Korea

XISAICHGEOLOGIC TIME ( M a Ago )

Dec. 31

A| AH LH

n-NQZOIC

Dec. 25

MESOZOIC

Dec.

:nPALLOZOIC

TVou. 13

PROTEROZOIC

July 17_

ARCHEAN

Jan. 1CALENDARYEAR

VOI LANK H(X>:' PUITONK H.tXT-

-egend of geological map of Korea(l : 1,000,000).

c3

VDa>vo

Ht rrt>i-i

50O

ot rs(urt

oo

nMp)o

re

Os

rt O

o ••da M

o^> op) n>D. Wft) M

•O (Brt Wrt)O.gl-h Q-i-lOS

5 Archean Craton

Rift

Accreted Crust

Island Arc; Accreting

Subduction Zone

Ocean Island Chain

Oceanic Lithosphere

Mid-ocean Ridge

Rift; Passive Margin

Archean Craton

i—i Paleoproterozoic igneous— rocksfr\ Paleoproterozoic igneous

rocksNeoproterozoic groups

Mesoproterozoic groups

3 Paleoproterozoic groups

• Archean groups

Precambrian groups in Korea, northeastern China and Japan.

SokchoEAST SEAOF KOREA

WEST SEAOF KOREA

25 50kmI I

Tectonic schema of Kyonggi Massif.

(T) Kimpho-Kansong Fault Zone, (2) Kongju Fault, (3) Wonsan-Seoul Fault Zone.

The legend is the same as Fig.7.3. Only 1 means the Kyonggi and Sosan Groups and 2 points to the Chunchon Group.

hhk

<Si

SOUTH SEA OF KOREA

Tectonic Schema of Ryongnam Massif, Okchon Fold Belt, Raktonggang Basin, Yong-il Basin and SamchokBasin.

The legend is basically the same as Fig.7.3. Besides, the following ones are added.

(A) Okchon Fold Belt, (B) Ryongnam Massif, (C) Raktonggang Basin, (D) Yong-il Basin, ( | ) Samchok Basin.

Tertiary Tertiary strata

Cretaceous— Tertiary I I I H Granitic rocks & Porphyries[ 1

intrusion

Cretaceous

Yuch'on Group

I I Hayang Group

Shindong Group

Pre-Cretaceous [I Basement roc

( > _ _ Zfi j o k

SimpUfied geologic map of the Kyongsang Basin.

Distribution of the Cretaceous sedimentary and volcanic rocks. Several selectedsedimentary basins described in text are: Kyongsang Basin(l), Yongdong Basin(2),Chinan Basin (3), Umsong Basin(4), P'ungam Basin (5), Basin along Chaeryong River(A), Basin near Pydnyang (B), and Basin near Onsong (C).

F.AST SEA OF KOHEA

RUSSIA

YOSOUTH SEA Of KOREA

CDJ t j u 1 (1

Deep fracture diagram deciphered on space photo (1:4,000,000).A. Clear fracture, B. Unclear Fracture, C. Circular structures.

EAST/CHINA SEA s

Schematic development model of the Yellow Sea Basin(Cretaceous-Tertiary)(after Jun et al., 1994)

129 130

Correlationship between geological map and distribution of local eventsduring 1988-1996.

RUSSIA

C H f

EAST SEA OF KOREAWKnsan

WEST SEA OF KOREA00

Ullung I s .o I

Tok Is.

66km

SOUTH SEA OF KOREA

Jeju Is.

Fracture diagram of Korea.

1. First class fractures, 2. Second class fractures, 3. Third class fractures, 4. Fractures determined by space photograph and geo-physical data, 5. Normal fault, 6. Reverse fault, 7. Thrust, 8. Wrench fault, 9. Active fault.Names of fault zones: 1. Susongchon, 2. Kyongsong-Kilju, 3. Musan-Kimchaek, 4. Sodusu, 5. Puktaechon, 6. Jasong-Myong-chon, 7. Jangpari, 8. Kosochon, 9. Phungso, 10. Pujongang, 11. Amnokgang, 12. Wiswn-Huchang, 13. Kanggye, 14. Chong-chongang, 15. Kumjingang, 16. Changsong-Unsan, 17. Taeryonggang, 18. Tongnim-Unjon, 19. Jangnim, 20. Namgang, 21.Hwangju-Koksao, 22. Jaeryonggang, 23. Unpba-Haeju, 24. Kujang-Kumya, 25. Taedonggang-Ryesonggang, 26. Rimjingang,27. Sinwon-Osan, 28. Kanghwa-Kosong, 29. Wonsan-Scoul, 30. Hongchon, 31. Kongju, 32. Jangsong-Mungyong, 33. Okchon,34. Samchok, 35. Tanyang, 36. Yongyang, 37. Hwasangdong, 38. Ryangsan. 39. Milyanggang, 40. Samchong-Sangju, 41.Posong-Sachon.

• Curriculum Vita© of Chun-Soo Kim

0 Education

• Bachelor of Science in Geology, Seoul National University,Korea, 1972

• Master of Science in Geological Engineering, University of

Missouri-Rolla, USA, 1977

• Doctor of Philosophy in Engineering Geology, McGil! University,

Canada, 1984

t> Experience

Or, C.S.Kim has joined in KAERI since 1988. Major research

areas and experiences include fracture hydrogeology, synthesis of

geologic/hydrogeologie/liydrochemical data, evaluation of

hydrogeological properties of earth materials. He also has

experiences in slurry pond reclamation, and characterization of

groundwater system for urban development and land use. *

|> Other

• Board member of the Korean Society of Groundwater

Environment :

1993 - Present

• Editorial member of the Geological Society of Korea : 1992 -

Present

•Editorial member ai Korean Society of Engineering Geology :

1991- 1997

•Member of Interniuionai Association of Engineering Geology •

1988 - Present