THE CHI-CHI EARTHQUAKE AND THE SEISMIC GEOTECHNICAL …hkieged.org/HKIE/download/Paper - Prof Lin-a final.pdf · 2018-03-21 · The state-of-the-practice of geotechnical engineering

The state-of-the-practice of geotechnical engineering in Taiwan and Hong Kong 52

THE CHI-CHI EARTHQUAKE AND THE SEISMIC GEOTECHNICAL

ENGINEERING PRACTICE IN TAIWAN

Meei-Ling Lin

Department of Civil Engineering

National Taiwan University, Taipei Taiwan

Abstract: The Chi-Chi earthquake struck central region of Taiwan on September 21, 1999,

with a magnitude of 7.3, caused severe ground failures and damages to lives and properties.

In this paper, the geotechnical hazard caused by the Chi-Chi earthquake is summarized.

Based on the reconnaissance of the hazard, the significances of types of failures are identified

and the effects on the seismic geotechnical engineering practice are discussed.

INTRODUCTION

Taiwan is situated at the juncture zone of the Euro-asia Continental Plate and the Philippine

Sea Plate with a northwest tectonic movement of the Philippine Sea Plate. As the

consequences of the tectonic actions, the Philippine Sea Plate subducts underneath the

Euro-asia Plate in the northward direction, while the Euro-asia Plate subducts underneath the

eastward direction as illustrated in Fig.1. Due to this active tectonic activity, the Central

Mountain Range as well as the Coastal Mountain Ranges are produced, and the prevailing

geological formations and structural patterns align approximately parallel to the longitudinal

Figure.1 Geotectonic actions in the vicinity of Taiwan (After Angelier, 2001).


Figure. 2 The distribution of active faults with estimated magnitude larger than 6 and

geological formations of Taiwan (the Central Geological Survey, 2000)

axis of the island. The distribution of active faults with estimated magnitude larger than 6 and

geological formations of Taiwan are shown in Fig.2. In Fig. 2, only the faults with length

longer than 5 km which correspond to earthquake magnitude of 6, and being active in the last

10000 years are considered. The topography and geological conditions are highly related to

the tectonic activity, where the mountain area composes about 77% of the whole area and the

geological formations are highly fractured and fragile. As the results of the tectonic activity,

Taiwan is among the most active seismic districts in the world. With the earthquake records

since early 1900, it was found that the earthquakes have been triggered by the subduction of

the plates and faulting action inland, and earthquakes with magnitude larger than 6 were most

likely to be hazardous. In Fig.3, the epicenters of the historical earthquakes with magnitude

greater than 6 in the period from 1900-1999 are plotted (Shin, 1999). As shown in Fig.3,

although most of the earthquakes with magnitude larger than 6 have been triggered by the

subduction action, the earthquakes triggered by faulting action inland were usually more

hazardous and caused more catastrophic damages because of the shallow focal depth and

being close to the heavily populated areas.


119 120 121 122 123

Longitude(E)

21

22

23

24

25

26

Latitude(N)

6.0-6.5

6.5-7.0

> 7.0

:

:

:

Figure 3. The historical earthquakes with magnitude greater than 6 from 1900 to 1999. The

asteroids represent the earthquakes occurred after the Chi-Chi earthquake. (Shin, 1999)

THE CHI-CHI EARTHQUAKE AND ITS EFFECTS

The Chi-Chi earthquake struck central region of Taiwan on September 21, 1999, with a local

magnitude of 7.3, had caused severe ground failures and loss of lives and properties. The total

casualties were 2505, and 11305 people were injured. The number of houses collapsed were

51392, and 55455 houses were damaged. The direct loss caused by the earthquake summed

up to 11.4 billions US dollars, and the indirect loss was 22.8 billions US dollars. The total loss

added up to 34.2 billions US dollars. The earthquake was triggered by the faulting action of

the Chelungpu fault, with a fault rupture length of 105 km. The Chelungpu fault is a shallow

thrust east-dipping fault which moved westward. The focal depth of the earthquake was only

8 km, which meant a tremendous amount of energy was released near the ground surface. The

maximum peak horizontal ground acceleration recorded was about 1 g, and the maximum

peak vertical ground acceleration recorded was 0.7 g. The distribution of the measured ground

motion along with the seismic intensity was as shown in Fig. 4 (Shin, 1999). Noted that three


Figure. 4 The isoseismal map of the Chi-Chi earthquake (the Central Weather Bureau)

triggered events were also recorded, and the effects could be observed as some areas far away

from the Chelungpu fault were displaying higher seismic intensity in Fig 4. The final ground

displacements caused by the thrusting of the fault were surveyed using GPS (Huang, et. al.,

1999), and the distribution of the displacements was as shown in Fig. 5. The maximum

horizontal displacement was about 9 m, and the maximum vertical displacements was about 6

m. With such strong ground motion and large displacements, the damages were tremendous. A

reconnaissance effort was called by the National Center for Research on Earthquake

Engineering, National Science Council. Based on the reconnaissance report of the

geotechnical hazard investigation group called upon by NCREE (2000), the geotechnical

hazard caused by the earthquakes includes: landslide, foundation failure, liquefaction and

subsidence, retaining wall failure, and damages to tunnels, etc. Due to the significant extents

of the damages caused by the earthquake, only the failures associated with liquefaction,

foundation failures, and landslides and the subsequent effects on the practicing geotechnical

engineering will be discussed in this paper.


120.1 120.5 120.9

Longitude (E)

23.5

24.0

24.5

Latitude (N)

Chelungpu Fault

Mainshock (M 7.3)

Final Displacement Distribution

TCU068

TCU052

TCU102

TCU053

TCU082

TCU054

TCU067

TCU065

TCU072

TCU071

TCU074

TCU089

TCU078

TCU075TCU120

TCU076

TCU129

TCU122

CHY024

CHY025

CHY101

21 Sep. 1999 Chi-Chi Earthquake

LEGEND

Horizontal Disp.

Fault Line

Strong-motion Station

1 meter

up

down

Vertical Disp.

20 kilometers

(Value in meter;Direction in degreefrom North counter-clockwise)

(9.2; 58¢X)

(6.5; 32¢X)

(1.1;212¢X)

(1.0;227¢X)(0.9;233¢X)

(1.1;213¢X)

(1.1;241¢X)

(1.5;254¢X)

(1.3;256¢X)

(4.0; 38¢X)

(3.0; 40¢X)

(2.3; 55¢X)

(2.2; 53¢X)

(1.3; 59¢X)

(1.2;263¢X)

(0.9;241¢X)

(1.2;245¢X)

(0.8;257¢X)

(0.5;258¢X)

(0.3;255¢X)

(0.5;140¢X)

(0.7;254¢X)

(1.0;195¢X)

0.5;243¢X)

Rebound

Figure 5. The distribution of final ground displacements caused by Chi-Chi earthquake. The

arrows indicate displacement quantity and its direction whereas values appeared in

parenthesis. (Huang, et. al.,1999; the Central Weather Bureau)

Soil Liquefaction and Associated Ground Subsidence

Field investigation of soil liquefaction was conducted at designated areas reporting signs of

soil liquefaction and ground subsidence. A total number of 176 items were reported and

documented for the investigated area. The distribution of the items and the surface rupture of

the Chelungpu fault are as shown in Fig. 6. Because soil liquefaction would only occur at

specific ground condition, therefore there is no clear relationship between distribution of

reported items and the fault. However, the distribution of liquefaction cases appeared to

correspond well to the seismic intensity distribution.

Severe condition of soil liquefaction was reported at wharf 1 to 4, Tai-Chung Harbor where

sink holes with diameters as large as 5 m were observed. The area with most widely spread

soil liquefaction condition was in the town of Yuan-Lin, while Nan-Tou city and Wu-Fong

also reported fairly large number of liquefaction items. The largest single area suffering soil


liquefaction was 4 hectare. Soil liquefaction could cause damages to all kinds of buildings and

infrastructures. Based on the data collected, statistical analyses were performed, and

distribution of damages to different types of structure was as shown in Fig.7.

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Miao-Li

Tai-Chung

Nan-Tou

Chung-Hua

Yun-Lin

Jai-Yi

0 30 60Kilometers

N

EW

S Figure 6. The distribution of the soil liquefaction cases. (Lin, Liao, and Ueng, 1999)

道路(43件)

4%

橋樑(11件)

1%

堤防(25件)

2%

房屋(998件)

93%

Figure 7. The distribution of types of structures damaged by soil liquefaction

Embankment(25 cases) Road(43 cases)

Bridge(11 cases)

Building(998 cases)


In Fig. 7, the damages to buildings out number other types of structures, because buildings are

the most encountered structures in the areas. The damages to buildings could be divided into

three different types, i.e. subsidence, tilting and collapse. Typically soil liquefaction causes

the ground to loose bearing capacity, which induces subsidence and unequal settlement of the

building. Therefore, subsidence is the most encountered type of damage, while tilting due to

unequal settlement is the second most reported damage. Soil liquefaction seldom induces

collapse of building. In the areas surveyed, more than 200 buildings have undergone

subsidence of more than 0.5 m, and about 50 buildings have undergone lateral displacement

of more than 1 m.

Foundation Failures

Field investigation of foundation failure was conducted in 19 towns and cities where

population densities were higher. The reconnaissance subgroup for foundation failure has

reported and documented a total number of 457 items, the locations of the failure and the

surface rupture of the Chelungpu fault are as shown in Fig. 8. The items of foundation failure

concentrated in cities and towns located within a short distance from the epicenter, such as

Wu-Fong, Ming-Chien, and Chi-Chi. In addition, the towns and cities where the fault rupture

passed through also reported a significant amount of foundation failures, such as Juo-Lang,

Tong-Shi, and Tang-Ji. A close relationship between the locations of foundation failure and

fault rupture could be found. The foundation failures in the area close to the epicenter were

likely caused by the excessive ground motion, while foundation failures along the fault were

likely caused directly by surface rupture. Some items of foundation failure were also reported

where soil liquefaction occurred. However, in these areas, the major effect of liquefaction was

subsidence; foundation failure caused by liquefaction was not so significant.

Accordingly, the characteristics of foundation failures could be classified into three different

types:

(1) foundation failures caused by fault rupture,

(2) foundation failures caused by soil liquefaction,

(3) failures at the interface of foundation and super-structure.

Statistical analysis was performed on the collected data, and the distribution of different types

of failure mechanism reported is as shown in Fig.9. In Fig. 9, the failure at the interface of

foundation and super structure is the most encountered failure type, which accounts for 60 %

of the failure cases, while foundation failure caused by faulting is the second one with 26 %.

Foundation failure caused directly by soil liquefaction only takes up 14% of all the foundation

failure items. The results indicated that proper connection at the interface of foundation and

super-structure was essential.

Slope Failures

The subgroup for slope failure has reported a total number of 436 items of slope failure, and

the distribution of slope failure along with the surface rupture of Chelungpu fault are as

shown in Fig.10. Following the initial reconnaissance, the Council of Agriculture took actions

in surveying of landslides based on the aero-photo and SPOT satellite images taken a few

days after the earthquake. There were more than 21,900 landslides with total area of more

than 8,600 hectare identified as shown in Fig. 11. The slope failures distributed from Miao-Li

to Jai-Yi counties as shown in the figure, and almost all items located to the right or hanging

wall of the thrust fault, where the mountain terrain located. The slope failures in Tai-Chung

county, and Nan-Tou county were most widely spread. In Tai-Chung county, the most severe

slope failure was along the Central Trans-island Highway; and in Nan-Tou county, a large


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Miao-Li

Tai-Chung

Nan-Tou

Chung-Hua

Yun-Lin

Jai-Yi

0 30 60Kilometers

N

EW

S Figure 8. The distribution of foundation failure cases

26%

14%

60%

斷層引致基礎隆起破壞

土壤液化引致基礎破壞

非斷層區之基礎與上部結構界面破壞

（277件）（67件）

（123件）

Figure 9. The distribution of types of foundation failure

Foundation failure caused by faulting,

Foundation failure caused by soil liquefaction,

Failure at the interface of foundation and super-structure.

(123 cases)

(67 cases) (277 cases)


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Miao-Li

Tai-Chung

Nan-Tou

Chung-Hua

Yun-Lin

Jai-Yi

0 30 60Kilometers

N

EW

S

Figure 10. The distribution of the slope failure cases

Figure 11. Distribution of landslide caused by Chi-Chi earthquake based on SPOT

images.(Council of Agriculture, 2000)


scale slope failure of Juo-Juo peaks covered an area as large as 950 hectare, which was major

shallow sliding and spalling of gravelly material. In Juo-Feng-Err mountain area, a dip slope

sliding occurred with an area of 200 hectare, 29 people were buried. In Yun-Lin county, a

massive dip slope failure occurred in the Tsao-Ling area which covered an area of 400 hectare

and with an amount of 120 million cubic meter of deposit material. The large amount of

material deposited in the valley of Ching-Sui river, and a dammed-up lake was formed.

63%

22%

11%

4%

岩石滑移、岩屑崩滑

落石、翻轉型破壞

平面破壞、弧形破壞、楔型破壞

路基流失、潛移、重力拱曲、其他

Figure 12. The distribution of type of slope failure cases

2% 8%

24%

36%

30%

<30°

30-44°

45-59°

60-75°

>75°

Figure 13. The distribution of slope angle of slope failure cases

Preliminary statistical analyses were performed on the data to identify the characteristics of

the slope failure. Types of failure mechanism, and the slope angle of the failure slope, of all

Debris slide

Toppling and rock fall

Plan failure, arc failure and wedge failure

Others


items reported are as shown in Fig.12 and Fig.13. The distribution of the slope angle

compared relatively well with the distribution of the types of the slope failure, because

typically the debris slide and toppling/rock fall would occur at the slope with steep slope

angle. Due to the extensive slope failures caused by the earthquake, tremendous amount of

landslide materials deposited in the up-stream areas of watershed, and were prone to induce

the secondary hazard. Measures for the secondary hazard prevention and further hazard

reduction including the rating of landslide potential, field investigation and rating of possible

debris flows, and emergency remedial measures for slope stability were taken.

GROUND MOTION AND SEISMIC ZONATION

The ground motions are directly related to the seismic forces acting on structures, and hence

seismic zoning for ground motion addresses one of the most fundamental aspects of seismic

hazard. Zoning for ground motions is therefore an essential part for hazard reduction caused

by the earthquake. The seismic codes for building called for the exceeding probability of 10%

for 50 years, which corresponded to a return period of 475 years for the design earthquake.

Based on the statistic of the earthquake records prior to the Chi-Chi earthquake, the seismic

zonation was determined as shown in Fig.14(a). After the Chi-Chi earthquake, the detailed

mapping of the Chelungpu fault was conducted, and the peak ground acceleration (PGA) data

were traced by National Center for Research on Earthquake Engineering from records of 387

strong motion stations. The PGA contour of motion caused by the main shock is shown in Fig.

15. By taking into account the ground motion records of the Chi-Chi earthquake in the

statistic model, the seismic codes were revised, and the new seismic zonation for design

earthquake called for 2 zones with peak ground accelerations of 0.23g and 0.33g, respectively,

as shown in Fig.14(b). The seismic codes for building were revised again in July, 2005, in

(a) (b)

Figure 14. Seismic zonation of Taiwan (a) before Chi-Chi Earthquake (4 zones), (b) revised

after Chi-Chi Earthquake (2 zones). (NCREE, 2000)


Figure 15 Distribution of peak ground acceleration (PGA) of the Chi-Chi Earthquake (Mean).

(NCREE, 2000)

which for the maximum earthquake with return period of 2500 years, ductility requirement of

structure, and other additional requirements were supplemented. During the Chi-Chi

earthquake, it was found that the ground motion is strong for area next to the fault, and

decreases rapidly with distance as illustrated in Fig.15. When reviewing the foundation

failures caused by the earthquake, it was found that the building failure immediately in the

vicinity of the Chelungpu fault was caused major by the faulting action. For buildings far

from the fault, the most important geotechnical factor causing damages to the buildings was

soil liquefaction. The first cause could be mitigated by detailed mapping of the fault and

regulations on building construction; therefore, the problem of the soil liquefaction is of major

concern. The landslide caused by the earthquake is also a major concern due to the

extensiveness of failure and the potential of causing the secondary hazard after the earthquake.

In fact, ground motion is the most important factor causing soil liquefaction and landslides.

CONSIDERATIONS OF LIQUEFACTION POTENTIAL

Soil liquefaction is one of the major factors for causing damages of buildings during

earthquake. If the liquefaction potential of each area could be evaluated in advance, it would

be possible to plan for earthquake hazard mitigation program. The preliminary liquefaction

potential maps were developed by NCREE(2001) to provide as a basic reference for drafting

of hazard mitigation policy. Data from more than 8000 boreholes were collected and analyzed

using method such as Modified Simplified Procedures proposed by Seed, et.al. (1985).

Liquefaction potential map displayed according to the evaluation results of borehole data is as

shown in Fig. 16 for Taipei Basin. Contours of liquefaction potential index are also generated

as shown in Fig. 17 for areas with sufficient density of borehole data. For the liquefaction

potential mapping of an over-all area, the sedimentary history and geomorphological factors

can be used, which would provide a reasonably good comprehensive result (Youd and Perkins,


1978; Lin and Dai, 2005).

For the liquefaction potential analysis, the codes for building foundation require that for the

design earthquake, either the liquefaction analysis can base on the laboratory testing results or

methods based on the field penetration test results such as the Simplified Procedures using

standard penetration test blow count or methods using cone penetration test tip resistance. The

overall liquefaction potential can be evaluated using relative thickness of soil layers proposed

by Ishihara (1985), or the liquefaction potential index proposed by Iwasaki et. al., (1982). For

the newly designed building susceptible to soil liquefaction, the foundation should be

properly designed to withstand the possible damages caused by soil liquefaction, and a

reduction factor is applied to the soil parameters. The reduction factor such as that proposed

by Japan Road Association (1996) can be used. For the buildings damaged by soil

liquefaction during the earthquake, both the repairing and reinforcing techniques can be

applied. The repairing technique is referred to the methods for retrofitting of the damaged

buildings. The retrofitting methods such as underpinning, foundation reinforcement and

jacking were used for the buildings damaged during the Chi-Chi earthquake. The reinforcing

technique is referred to improvement of the ground stability to withstand the possible soil

liquefaction. Such techniques include grouting, dynamic compaction, stone column,

compaction pile, etc. For the buildings damaged in the Chi-Chi earthquake, grouting method

was one of the most commonly used techniques.

Figure 16. Liquefaction potential map

of Taipei Basin. (NCREE,2001)

Figure 17. Contours of liquefaction potential

index of Taipei City. (NCREE, 2001)


SEISMIC SLOPE STABILITY

Due to the extensiveness of slope failure induced by the earthquake and the potential of

causing secondary hazard, the landslide caused by the earthquake is also a major concern.

Typically, analyses of dynamic slope stability are performed using three different methods:

the pseudo-static method, the Newmark’s method, and ground response analysis. The

pseudo-static method adopted the critical equilibrium concept to calculate the factor of safety

using a pseudo-static force acting on a slope under horizontal acceleration (Chen &

Snitbhan,1975; Seed, 1979). Newmark (1965) proposed a sliding block model to simulate

slope behavior under seismic forces, and calculate the block movement when acceleration

exceeded the critical acceleration of the slope. However, these two methods do not take into

account the dynamic slope behavior and soil amplification. With the help of numerical

methods, the ground response analysis using the finite element method and/or finite

difference method (Clough & Chopra, 1966) can take into account the dynamic ground

responses as well as the nonlinear behavior of soil, and the elastic-plastic constitutive laws

can be applied. For the earth dam, the shear beam method (Ambraseys & Sarma, 1967)

simplifies a 2-dimensional dam into a 1-dimensional analysis, and acceleration along the

height of dam can be obtained quickly.

Although it was suggested that the pseudo-static analysis might not be able to represent the

seismic slope behavior, and the safety factor might not be a good indication of seismic slope

stability (Seed, 1979), the method appeared to provide reasonable results for the dynamic

slope analysis if the failure surface was shallow and close to the toe of slope (Huang and Lin,

2003). For the Newmark’s method, the failure of the slope was assessed by the permanent

displacement of the sliding block. The threshold displacement of 5-10 cm was suggested by

Jibson (1993). Based on the analyses performed on the landslide cases induced by the Chi-Chi

earthquake, the displacement of 10 cm appeared to be a reasonable threshold value (Lin and

Kao, 2005) for causing failure of the slope.

0

20

40

60

80

100

120

140

160

180

150-250 250-350 350-450 450-550 550-650 650-750 750-

Mean PGA (gal)

Cas

e

Fig. 18 Distribution of the geometric mean PGA of the earthquake induced slope failures


0

50

100

150

200

250

0-100 100-200 200-300 300-400 400-500

Vertical PGA ( gal )

Case

Fig. 19 Distribution of the vertical PGA of the earthquake induced slope failures

Figure 20. Distribution of the rated potential debris flow rivers in the Central Taiwan.

From the field data collected on landslides induced by the Chi-Chi earthquake, it was found

that most of the landslides were with small to medium size and were typically shallow debris

slide of steep slope. The statistical analysis of the data (Lin, Wang, and Chen, 2000) indicates

that the slopes subjected to ground motion with horizontal mean PGA larger than 150 gal, and

vertical PGA larger than 200 gal are likely to be susceptible to landslide as illustrated in Fig.s

18 and 19. Generally, the failure surface appeared to be quite shallow, in somewhat circular

shape, and close to the crest of slope. Thus, the horizontal peak ground acceleration of 150 gal,

and a vertical PGA of 200 gal appear to be appropriate conditions to adopt in the seismic

slope analysis. Research by Chen, Lin, and Hung (2004) also suggested that for the slope

located near to the epicenter or fault, the vertical ground acceleration could have a significant

effect on the slope stability, and the strength of the material would range somewhere between

the peak strength and residual strength. It could be concluded that for the earthquake induced


shallow landslides, ground motion might be the most important factor.

Due to the severe slope failures caused by the Chi-Chi earthquake, the slope material was

loosened and with fissures and cleavages. New landslides, rock falls and debris flow may be

easily triggered by other earthquakes or rainfall. Field investigations were conducted to

identify the potential debris flow rivers, and models for evaluation of hazard potential and risk

were developed. Potential analysis of the debris flow rivers of the Central Taiwan areas were

performed and the debris flow rivers were rated as with high, intermediate, and low potential

as shown in Fig. 20. Emergency remedial and reinforcing measures for slopes and debris flow

rivers identified with high potential were conducted before the typhoon season in order to

prevent further damages and secondary hazard.

In 2001, typhoon Toraji caused severe landslide and debris flow hazard, and it was found that

most of the landslides and debris flows occurred at locations identified with previous

landslides caused by the Chi-Chi earthquake as illustrated in Fig.21. In 2004, typhoon

Mindule again caused severe landslides and debris flow hazard in the Central Taiwan area.

The reconnaissance report again indicated that a close relationship between the hazard

induced by the typhoon Mindule and landslides induced by the Chi-Chi earthquake as

illustrated in Fig.22. Thus, the landslide induced by a large magnitude earthquake could cause

severe and prolonged secondary hazard such as subsequent landslides and debris flows.

Mitigation efforts are required in order to reduce the effects of such secondary hazard.

Figure 21 Landslides and debris flows induce by typhoon Toraji in 2001 versus landslides

induced by the Chi-Chi earthquake


Figure 22 Landslides and debris flows induce by typhoon Mindule in 2004 versus landslides

induced by the Chi-Chi earthquake

CONCLUSIONS

The Chi-Chi earthquake with a magnitude of 7.3 caused all kinds of severe geotechnical

hazard. Based on the reconnaissance results, three major types of failure were discussed, i.e.

soil liquefaction, foundation failures, and slope failures, respectively. For all types of the

failures, ground motion appeared to be the most important factor, and liquefaction and slope

failures were the geotechnical hazard of more concerns for causing extensive damages and the

potential of causing secondary hazard.

Based on the data of the Chi-Chi earthquake, the seismic zonation of building codes was

revised, and more requirements on ductility of buildings were proposed. For area susceptible

to soil liquefaction, methods for potential analysis and reduction factor for the soil parameters

were used in general practice. In addition, mapping of the liquefaction potential could provide

preliminary information for hazard mitigation. For the seismic slope stability, analysis could

be performed using different methods, which would all provide reasonable results when

applied with discretion. Further mitigation of the potential secondary hazard is very important

when a catastrophic earthquake strikes and extensive slope failures are induced. In view of the

scale of the hazard and lessons learned from the Chi-Chi earthquake, more efforts are needed

for researches in seismic geotechnical engineering, and for reduction of secondary hazard

effects for years to come.

REFERENCES

Ambraseys, N. N., and Sarama, S. K., (1967), “The Response of Earth Dams to Strong

Landslides and debris flows

Earthquake scars


Earthquakes”, Geotechnique, Vol. 17, 181-213.

Central Geological Survey, (2000), Active Fault Map.

Chen, T. C., Lin, M. L., and Hung, J. J., (2004), “Pseudo-static Analysis of Tsao-Ling

Rockslide Caused by Chi-Chi Earthquake”, Engineering Geology, Vol. 71, 31-47.

Clough, R. W., and Chopra, A. K. (1966), “Earthquake Stress Analysis in Earth Dams”,

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