C. C. LinC. C. LinCentral Geological SurveyCentral Geological Survey

Email: Email: lincc@moeacgs.gov.twlincc@moeacgs.gov.twWeb: http://Web: http://www.moeacgs.gov.twwww.moeacgs.gov.tw

Introduction toIntroduction toGeological Disasters of TaiwanGeological Disasters of Taiwan

mailto:lincc@moeacgs.gov.tw

IntroductionIntroduction

1.1. The active tectonic movement and mountain building The active tectonic movement and mountain building process have resulted in highprocess have resulted in high--rise mountains and rise mountains and strongly deformed rock formation in Taiwan.strongly deformed rock formation in Taiwan.

2.2. People are threatened by a variety of geological People are threatened by a variety of geological hazards, such as earthquakes, landslides, land hazards, such as earthquakes, landslides, land subsidence, coastal erosion, and tsunami. Among subsidence, coastal erosion, and tsunami. Among them, earthquakes and landslides are the most them, earthquakes and landslides are the most disastrous and extensive.disastrous and extensive.

3.3. Various Various geoscientificgeoscientific research and monitoring research and monitoring programs have been proceeded to provide programs have been proceeded to provide comprehensive information for disaster mitigation.comprehensive information for disaster mitigation.

In the part of the most active plate boundary with frequent earthquakes and

Where do we live in? Where do we live in?

a belt with most active volcanoes, being called Ring of FireTAIWAN

Tectonic Setting of TaiwanTectonic Setting of TaiwanPart of the CircumPart of the Circum--Pacific Pacific Seismic Belt, active tectonic Seismic Belt, active tectonic movement induced frequent movement induced frequent earthquakesearthquakesLocated along the convergent Located along the convergent boundary between Philippine boundary between Philippine Sea and Eurasian platesSea and Eurasian plates Philippine Sea plate Philippine Sea plate subductedsubducted

toward N in NE Taiwan toward N in NE Taiwan Eurasian plate Eurasian plate subductedsubducted

toward E in SE Taiwantoward E in SE Taiwan Phil. Sea plate collided with Phil. Sea plate collided with

Eurasian plate in Central E Eurasian plate in Central E Taiwan Taiwan

Being the junction of Ryukyu Arc Being the junction of Ryukyu Arc and Luzon Arcand Luzon Arc

TopographyTopography

Geologic settingGeologic setting

Geologic hazards of TaiwanGeologic hazards of Taiwan

TaiwanTaiwan may be the place on Earth most vulnerable may be the place on Earth most vulnerable to natural hazards, with 73 percent of its land and to natural hazards, with 73 percent of its land and population exposed to three or more hazards;population exposed to three or more hazards;More than 90 percent of the populations of More than 90 percent of the populations of Bangladesh, Nepal, the Dominican Republic, Burundi, Bangladesh, Nepal, the Dominican Republic, Burundi, Haiti, Haiti, TaiwanTaiwan, Malawi, El Salvador, and Honduras live , Malawi, El Salvador, and Honduras live in areas at high relative risk of death from two or more in areas at high relative risk of death from two or more hazards;hazards;

----Natural Disaster Hotspots: A Global Risk Analysis, Natural Disaster Hotspots: A Global Risk Analysis, March 29, 2005, World Bank March 29, 2005, World Bank

Geologic hazards of TaiwanGeologic hazards of Taiwan

EarthquakesEarthquakes causing the most severe and extensive damagecausing the most severe and extensive damage the most hazardous geologic processes in Taiwan the most hazardous geologic processes in Taiwan

Landslides Landslides among the most wideamong the most wide--spread geologic hazardsspread geologic hazards Landslides associated with typhoon pose fatalities and Landslides associated with typhoon pose fatalities and

property lossesproperty lossesSubsidence and coastal erosionSubsidence and coastal erosion occurred very slowlyoccurred very slowly being deteriorated by human activitiesbeing deteriorated by human activities

Volcanic Volcanic erutpionerutpion no volcanic eruption record in historyno volcanic eruption record in history

Coastal erosionCoastal erosionMost of the coastal line is Most of the coastal line is subjected to erosion, due to:subjected to erosion, due to: Over excavation of river Over excavation of river

sediments to support the sediments to support the massive demand for aggregate massive demand for aggregate of concrete has reduced the of concrete has reduced the supply of coastal sandssupply of coastal sands

Land reclamation from the sea Land reclamation from the sea for industry parks and for industry parks and construction of seaports construction of seaports interfere the distribution the interfere the distribution the sediments along coast.sediments along coast.

Dams for water supply or debris Dams for water supply or debris flows control retain the flows control retain the sediments behind the dams.sediments behind the dams.

Land subsidence along the Land subsidence along the coastcoast

Land subsidenceLand subsidenceNatural compaction of sedimentsNatural compaction of sedimentsExcessive withdrawal of Excessive withdrawal of groundwater for fish farms in groundwater for fish farms in lowlow--lying areas speeding up the lying areas speeding up the subsidence ratesubsidence rateMostly occurred in coastal areasMostly occurred in coastal areas

Land subsidenceLand subsidenceCumulative subsidence since 1970s (cm) Annual subsidence rate (cm/yr)

LandslidesLandslides

Landslides include many types of downhill earth movements, ranging from rapidly moving catastrophic rock avalanches and debris flows in mountainous regions to more slowly moving earth slides and other ground failures.Thousands of landslides can be triggered by a single severe storm or earthquake, causing spectacular damage in a short time over a wide area.

Landslide distributionLandslide distributionSlope failures Debris flows

Causal factors of landslidesCausal factors of landslides

LithologyLithologyshale, conglomerate, slate, and schist are highly shale, conglomerate, slate, and schist are highly susceptible to landslide susceptible to landslide StructuresStructuresbedding, bedding, foliation,jointsfoliation,joints, fractures, cleavage, , fractures, cleavage, and faults etc. and faults etc. TopographyTopographyangle, aspect, shape of slopesangle, aspect, shape of slopesImproper landImproper land--useuseremoval of downremoval of down--slope supportingslope supporting

Triggering factors of Triggering factors of landslideslandslides

Heavy rainfallsHeavy rainfallsEarthquakesEarthquakesVolcanic eruptionVolcanic eruptionChange of water levelChange of water levelSnow meltingSnow melting

Annual precipitation(unit: 1,000 mm)

LandslidesLandslides

People living in People living in mountainous area are mountainous area are endangered by slope endangered by slope failures and debris failures and debris flows flows

Landslide disastersLandslide disasters

Landslide disasters occurred in Landslide disasters occurred in the surroundings of urban areasthe surroundings of urban areasTriggered by heavy rainfallsTriggered by heavy rainfallsMost of them can be avoidedMost of them can be avoided

Case of landslide Case of landslide triggered by typhoon triggered by typhoon

rainfallsrainfalls

Date: 25/08/2004Date: 25/08/2004Hazard type: landslideHazard type: landslideTriggered by: Typhoon Triggered by: Typhoon AereAereLosses: Losses: Some 20 houses buriedSome 20 houses buried 22 deaths22 deaths

Area of sliding: 5.8 hectaresArea of sliding: 5.8 hectaresVolume of sliding: 1 million mVolume of sliding: 1 million m33

Water crisis caused by extensive landslidesWater crisis caused by extensive landslides

Extensive landslides in Extensive landslides in the the catchmentcatchment area of area of ShihmenShihmen ReservoirReservoirLarge amount of Large amount of sediments being carried sediments being carried into the reservoir, raising into the reservoir, raising the turbidity of the turbidity of impoundment.impoundment.Causing crisis of lacking Causing crisis of lacking water for daily use of water for daily use of millions people for 19 millions people for 19 days.days.

Cases of earthquake induced landslide (1)Cases of earthquake induced landslide (1)TsaolinTsaolin

Date: 21/09/1999Date: 21/09/1999Hazard type: landslideHazard type: landslideTriggered by: earthquakeTriggered by: earthquakeLosses: Losses: 4 houses 4 houses 36 deaths36 deaths

Area of sliding plus debris piling Area of sliding plus debris piling up: 522 hectaresup: 522 hectaresVolume of sliding mass: 120 Volume of sliding mass: 120 million mmillion m33

Geology: Dip slope consists of Geology: Dip slope consists of sandstone overlying on thick sandstone overlying on thick soft shalesoft shale

Cross sections of Cross sections of TsaolinTsaolin landeslidelandeslide

DateDate Triggering factorTriggering factor18611861 earthquakeearthquakeM 6M 6--7712/17/194112/17/1941 earthquakeearthquakeM 7.1M 7.18/10/19428/10/1942 heavy rainfallsheavy rainfalls8/15/19798/15/1979 heavy rainfallsheavy rainfalls9/21/19999/21/1999 earthquakeearthquakeM 7.3M 7.3

Historical landslide events of Historical landslide events of TsaolinTsaolin

Case of earthquake induced landslide (2)Case of earthquake induced landslide (2)ChiufenershanChiufenershan

Date: 21/09/1999Date: 21/09/1999Triggered by: ChiTriggered by: Chi--Chi earthquakesChi earthquakesArea: 159 hectaresArea: 159 hectaresVolume: 36 million mVolume: 36 million m33

Losses: Losses: 14 houses buried14 houses buried 39 deaths39 deaths

Dip slope composed of lateDip slope composed of late--Miocene sandstone and shale Miocene sandstone and shale alternationalternation

Debris flowsDebris flows

Case of debris flow disaster (1)Case of debris flow disaster (1)

Date: 03/07/2004Date: 03/07/2004Hazards: floods and debris flowsHazards: floods and debris flowsTriggered by: Rainstorm after Triggered by: Rainstorm after Typhoon Typhoon MindulleMindulleLosses:Losses: 30 dwelling houses totally destroyed30 dwelling houses totally destroyed 1 death, 1 injury, 2 missing1 death, 1 injury, 2 missing

Landslide occurrence after the 1999 Landslide occurrence after the 1999 ChiChi--Chi earthquakeChi earthquake

In central Taiwan, the ChiIn central Taiwan, the Chi--Chi earthquake had Chi earthquake had triggered 25,845 landslides of varied scale, with a total triggered 25,845 landslides of varied scale, with a total slide area of some 16,000 hectares, 8 times compared slide area of some 16,000 hectares, 8 times compared with landslides before earthquake.with landslides before earthquake.Changes of occurrence of landslides and debris flows:Changes of occurrence of landslides and debris flows: Increase the frequency of landslides and debris flows;Increase the frequency of landslides and debris flows; Increase the magnitude of landslides and debris flows;Increase the magnitude of landslides and debris flows; Remarkably reducing the threshold precipitation needed Remarkably reducing the threshold precipitation needed

to trigger landslides and debris flows ;to trigger landslides and debris flows ;Typhoon Typhoon TorajiToraji (30/07/2001) posed severe landslide (30/07/2001) posed severe landslide and debris flow disaster for eastern and central and debris flow disaster for eastern and central Taiwan, caused 240 deaths and/or missing. Taiwan, caused 240 deaths and/or missing.

Landslide Hazards Mitigation Strategies

Restricting development in landslide-prone areas.Standardizing codes for excavation, construction, and grading.Protecting existing development.Utilizing monitoring and warning systems.

Landslide susceptibility mapLandslide susceptibility mapFirst step to landslide hazard assessments

Statistic methods are being developed to prepare landslide susceptibility map

Active Faults & Earth QuakesActive Faults & Earth Quakesthe destiny of people in Taiwanthe destiny of people in Taiwan

Historical disastrous earthquakes

Last century, Earthquakes Last century, Earthquakes have killed some 8,000 peoplehave killed some 8,000 peopleThere were 7 earthquakes with There were 7 earthquakes with M>7M>7Most of disastrous earthquakes Most of disastrous earthquakes occurred on land and were occurred on land and were accompanied with surface accompanied with surface rupturesruptures

Locations of disastrous earthquakes occurred in Taiwan area for the past 100 years

19991999ChiChi--Chi earthquakeChi earthquake

Main Shock

Time: Sep. 21, 1999Magnitude: MW 7.6, ML 7.3Deaths : 2,494Injuries : 11,305Houses damaged: 107,002Nominal property losses :

US$11.5 billions

Damage caused by ground ruptures Damage caused by ground ruptures

Damage caused by ground motionDamage caused by ground motion

liquefactionliquefaction

Active fault investigationActive fault investigation

42 active faults being classified 42 active faults being classified into 3 categories:into 3 categories: Holocene active faultHolocene active fault

activated in the Holocene; activated in the Holocene; offset manoffset man--made structures; made structures; relate to historical earthquakes; relate to historical earthquakes; offset the recent alluvium; offset the recent alluvium; show the creeping phenomena show the creeping phenomena from the recent geodetic surveyfrom the recent geodetic survey

Pleistocene active faultPleistocene active faultactivated within 100,000 years;activated within 100,000 years;offset the terrace deposits.offset the terrace deposits.

Suspect faultSuspect faultby now without definite by now without definite information to classify into information to classify into appropriate categoryappropriate category

FAULT ZONESEGMENTATION

RECURRENCEMODELS

GEOLOGIC DATA

Slip RateRecurrence IntervalElapsed TimeDisplacement / EventFault Geometry

Rupture Length

MaximumEarthquake LONG-TERM

EARTHQUAKE POTENTIAL Hazard Model Probability of Occurrence

From Schwartzand Coppersmith(1986)

Geologic data (mainly Geologic data (mainly paleoseismologicpaleoseismologic) needed for ) needed for Seismic Hazard AssessmentsSeismic Hazard Assessments

Active fault research programActive fault research programFault geometryFault geometry Detail mappingDetail mapping Geophysical exploration (seismic reflection, electric Geophysical exploration (seismic reflection, electric resistivityresistivity)) DrillingDrilling

Slip rateSlip rate Short termShort termmonitoring horizontal and vertical displacementmonitoring horizontal and vertical displacement Long termLong termpaleoseismologypaleoseismology

Recurrence intervalRecurrence interval PaleoseismologyPaleoseismology Historical recordsHistorical records

Elapsed timeElapsed time PaleoseismologyPaleoseismology Historical recordsHistorical records

DisplacementDisplacement Short termShort termmonitoring horizontal and vertical displacementmonitoring horizontal and vertical displacement Long termLong termpaleoseismologypaleoseismology

Surface investigation and mapping Surface investigation and mapping

Seismic reflectionSeismic reflection

0.0

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Two-W

ay Time (second)

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37

77

123

173

224

281

338

397

459

521

583

645

711

781

852

922

992

1066

1143

1220

1296

1373

1450

1527

Dep

th (

m)

N

470

430

390

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70

Distance (m) STTC-HL04P

820

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Seismic reflection profileSeismic reflection profile

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37

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583

m)

N

470

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390

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Distance (m) STTC-HL04P

820

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Two-W

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37

77

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338

397

459

521

583

m)

0

37

77

123

173

224

281

338

397

459

521

583

m)

N

470

430

390

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70

Distance (m) STTC-HL04P

820

780

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1060

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860

N

470

430

390

350

310

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190

150

110

70

Distance (m) STTC-HL04P

820

780

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700

660

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550

510

1060

1020

980

940

900

860

ResistivityResistivity profile across active faultprofile across active fault

0 50 100 150 200 250 300 350 400 450 500DISTANCE (m)

0 50 100 150 200 250 300 350 400 450 500

TTC-HL03E

-100

-50

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EVAT

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(m)

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-50

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ELEV

ATIO

N (m

)

1.0 1.5 2.0 2.5 3.0 3.510 100 100031 316 3160RESISTIVITY (OHM-M)

520 470 420 370 320 270 220 170 120 70 20

N S

520 470 420 370 320 270 220 170 120 70 20

L

LRA

AA

A

1935

A

Active fault monitoringActive fault monitoring

GPS High Precision Leveling

Reference Point

Leveling showing a 40 mm elevation change across the Changhuaactive fault between the year 2002 and 2004.No significant change found across the Chelungpu fault

Elevation change Elevation change across active fault (1)across active fault (1)

The leveling survey delineates a uplifting rate of 12 mm/yr for the Tainan tableland.The eastern margin of the tableland is bordered by a west-dipping back-thrust.

Reference Point

Elevation change Elevation change across active across active faultfault (2)(2)

GPS velocity field (1)GPS velocity field (1)

GPS velocity field (2)GPS velocity field (2)

Showing the variation Showing the variation of velocity field across of velocity field across the active faultsthe active faults

Trenching of CLP fault Trenching of CLP fault

S1

S2

S2

S3

S3

S3

S4

S4

S5

S5

S6

S7

Another Trench Another Trench of CLP faultof CLP fault

Before the 921 Chi-Chi earthquake, there had been 3 to 4 paleo-seismic events occurred within the latest 1800 years according to the result of C14 dating. The recurrence of fault activation are calculated around 450 years. The latest one (the one before Chi-Chi) occurred between 150 to 430 years (elapsed time) before present.

Combination of trench and boreholesCombination of trench and boreholes

ProbablisticProbablistic seismic seismic hazard assessmenthazard assessment

Probabilistic hazard assessment has been performed using the available geologic data collected from the active faults investigation, incorporated with seismic catalogue. (map showing the PGA of 10% probability of exceedancein 50 years) .

Earthquake precursors and predictionEarthquake precursors and predictionA variety of earthquake precursors are under A variety of earthquake precursors are under

studied, including: studied, including: Measurable changes in rock Measurable changes in rock Minute cracks developed in rocks, and dilation of rocks Minute cracks developed in rocks, and dilation of rocks Changes in groundwater levelChanges in groundwater level Changes in the electrical Changes in the electrical resistivityresistivity of rocksof rocks Increases in radon gas levels of ground waterIncreases in radon gas levels of ground water Decrease in the P wave/S wave speed ratio Decrease in the P wave/S wave speed ratio Variation of electromagnetic intensityVariation of electromagnetic intensity

Seismological variationsSeismological variations

Sum up (1)Sum up (1)1. Landslides are a significant component of many major

natural disasters, but the damage caused by landslide is often reported as a result of a triggering event, such as floods (rainstorm) and earthquakes.

2. Landslide losses are increasing in Taiwan as development expands under pressures of increasing populations. The resulting invasion of developments into hazardous areas, expansion of transportation infrastructure and deforestation of landslide-prone areas may lead to continually increasing landslide losses.

3. The increase in the cost of landslide hazards can be restrained through better understanding and mapping of the hazards and improved capabilities to mitigate and respond to the hazards.

4. Landslide inventory and susceptibility maps and other data are a critical first step and are prerequisite to producing probabilistic hazard maps and risk assessments, but the susceptibility maps are not yet available in Taiwan.

5. Statistic methods are being developed to landslide susceptibility map.

Sum up (2)Sum up (2)

Sum up (3)Sum up (3)6.6. Earthquakes result in catastrophic disasters every tens Earthquakes result in catastrophic disasters every tens

years, government and general public are expecting the years, government and general public are expecting the success in shortsuccess in short--term prediction of earthquakes. term prediction of earthquakes.

7.7. Earthquake is nothing but a physical phenomenon. The Earthquake is nothing but a physical phenomenon. The rapid progress in measuring and information handling rapid progress in measuring and information handling technologies make the prediction promising. technologies make the prediction promising.

8.8. A variety of research and monitoring programs on A variety of research and monitoring programs on earthquake precursors are in progress in Taiwan.earthquake precursors are in progress in Taiwan.

Sum up (4)Sum up (4)9.9. International cooperation is necessary for developing International cooperation is necessary for developing

earthquake prediction technologies. earthquake prediction technologies. 10.10. Before earthquake prediction becoming practical, seismic Before earthquake prediction becoming practical, seismic

hazard assessments are the fundamental information for hazard assessments are the fundamental information for earthquake disaster reduction. Detailed active fault earthquake disaster reduction. Detailed active fault investigation and investigation and paleoseismologicalpaleoseismological research are research are requirement for hazard assessments.requirement for hazard assessments.

Introduction to Geological Disasters of TaiwanIntroductionWhere do we live in? Tectonic Setting of TaiwanTopographyGeologic settingGeologic hazards of TaiwanGeologic hazards of TaiwanCoastal erosionLand subsidenceLand subsidenceLandslidesLandslide distributionCausal factors of landslidesTriggering factors of landslidesLandslidesLandslide disastersCase of landslide triggered by typhoon rainfallsWater crisis caused by extensive landslidesCases of earthquake induced landslide (1)TsaolinCross sections of Tsaolin landeslideHistorical landslide events of TsaolinCase of earthquake induced landslide (2)ChiufenershanDebris flowsCase of debris flow disaster (1)Landslide occurrence after the 1999 Chi-Chi earthquakeLandslide Hazards Mitigation StrategiesLandslide susceptibility map First step to landslide hazard assessmentsActive Faults & Earth Quakesthe destiny of people in TaiwanHistorical disastrous earthquakes1999 Chi-Chi earthquakeDamage caused by ground ruptures Damage caused by ground motionliquefactionActive fault investigationGeologic data (mainly paleoseismologic) needed for Seismic Hazard AssessmentsActive fault research programSurface investigation and mapping Seismic reflectionActive fault monitoringElevation change across active fault (1)Elevation change across active fault (2)GPS velocity field (1)GPS velocity field (2)Trenching of CLP fault Another Trench of CLP faultCombination of trench and boreholesProbablistic seismic hazard assessmentEarthquake precursors and predictionSum up (1)Sum up (2)Sum up (3)Sum up (4)