probabilistic seismic hazard assessment & related topics for...

Dr. Teraphan Ornthammarath

Department of Civil and Environmental Engineering

Mahidol University

[email protected]

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Mw 6.1, Mae Lao earthquake

at 15 km from epienter

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at 28 km from epicenter

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Probabilistic Seismic Hazard Assessment &

Related topics for Tall Structural Design

(s)

Presentation Content:

• Probabilistic Seismic Hazard Analysis (PSHA)

• PSHA for Thailand

Where will future earthquakes occur?Basic Questions

What will be their size?

What will be their frequency of occurrence?

What will be the ground shaking intensity at the site produced by earthquakes of different size, focal depth, and epicentral location?

How will the ground motion be influenced by local soil conditions and geology?

What will be the earthquake hazards (landslide, liquefaction, etc.) produced at the site?

How about the susceptibility of buildings and structures to damage from the ground shaking and ground failures?

SEISMIC HAZARD x SEISMIC VULNERABILITY = SEISMIC RISK

Seismic Hazard Assessment

In principle, Seismic Hazard Assessment (SHA) can address any natural hazard associated with earthquakes, including ground shaking, fault rupture, landslide, liquefaction, or tsunami.

However, most interest is in the estimation of ground-shaking hazard, since it causes the largest economic losses in most earthquakes.

Moreover, of all the seismic hazards, ground motion is the predominant cause of damage from earthquakes; building collapses, dam failures, landslides, and liquefactions are all the direct result of ground motion.

The current talk, therefore, is restricted to the estimation of the earthquake ground motion hazard

Earthquake hazard: still can not be predicted in advance

What is PSHA and Why it is important?

PSHA: the current LONG-term strategic tool in many countries (e.g. USA, Italy, etc.)

Application of PSHA products:

National Seismic Design Code

Setting of Insurance premiums

Risk and Loss assessment studies

PSHA products:

PSHA maps for different strong ground motion parameters (e.g. Peak Ground Acceleration)

Uniform Hazard Spectrum (UHS), Disaggregation

22 February 2011 Mw 6.3 New Zealand earthquake at LPCC station (2 kms from epicenter)

Courtesy: GNS

Peak Ground Acceleration (PGA) = 8.9 m/s2 (0.91g)

Probabilistic Seismic Hazard Analysis

GLOBAL SEISMICHAZARDASSESSMENTPROGRAM

http://seismo.ethz.ch/gshap/

These maps are generally updated to reflect newly understanding in earthquake science and to keep pace with national seismic design code.

GSHAP (1999)

In estimating the parameters you may use:

1. PROBABILISTIC APPROACH –use statistical methods to

assess probability of exceeding a predefined level of

ground motion in some time period (earthquake return

period), based on earthquake history and geological data.

2. DETERMINISTIC APPROACH – use a predefined

earthquake and calculate its effects and parameters of

seismic forces on the construction site. This is very difficult

to do because the site is in the near-field (close to the

fault) and most of the approximations you normally use are

not valid.

3. A combination of the two

Seismic Hazard Analysis

PSHA maps and national seismic design code

Thailand national seismic design code

Manila seismic hazard map

Italian national seismic design code

In estimating the parameters you may use:

1. PROBABILISTIC APPROACH –use statistical methods to

assess probability of exceeding a predefined level of

ground motion in some time period (earthquake return

period), based on earthquake history and geological data.

2. DETERMINISTIC APPROACH – use a predefined

earthquake and calculate its effects and parameters of

seismic forces on the construction site. This is very difficult

to do because the site is in the near-field (close to the

fault) and most of the approximations you normally use are

not valid.

3. A combination of the two

Seismic Hazard Analysis

Mw = 6.5

Loss assessment in Chiang RaiAssumption:• Define moment magnitude 6.5 in the west of Chiang Rai city

Ground motion by census tracts (Clusters)

Basic Steps of Probabilistic Seismic Hazard Analysis

1). Identify all seismic sources (active faults, area sources, subduction zones, etc.)

2). Define the seismicity of these seismic sources

3). Select suitable ground motion prediction equations (GMPEs)

4). Determine probabilistic ground motion parameters at the site by a modified Cornell procedure

1). 2).

3). 4).

4 5 6 7

0.1g 0.2g 0.3g

High

Low

High

Low

Presentation Content:

• Probabilistic Seismic Hazard Analysis (PSHA)

• PSHA for Thailand

PSHA for ThailandThailand and its surrounding seismicity (1912 -2007)GSHAP (1999)

PGA for 475-year return period

Bangkok

Bangkok

Mw < 4.0 Earthquake activity rate inside BG-I

Earthquake activity rate outside BG-IMw > 3.0

Thailand’s Active fault data

Investigation of Active Faults: Fault Trenching in Taiwan

Geological Record found in a Fault Trench in Taiwan

Fault Trenching in Kanchanaburi, Thailand

Crustal Fault Source Model Parameters

Rupture Length (km)

NameNo. DipAngle

Width (km)

Characteristic magnitude

Slip rate (cm/yr) Logic tree weight Recurrence Int. (yr)

Information about crustal faults is mainly obtained from recent paleoseismic investigations

in Northern, Western, and Southern Thailand.

Selection of Suitable Attenuation Models (II)

For BG-I and BG-II, and for earthquakes from all active faults, three

Next Generation Attenuation (NGA) GMPEs developed for shallow

crustal earthquakes in active tectonic regions:

Boore and Atkinson (2008) w = 0.33

Campbell and Bozorgnia (2008) w = 0.33

Chiou and Youngs (2008) w = 0.33

For subduction zone earthquakes in SD-A, SD-B and SD-C, adopted

the subduction zone GMPEs:

Youngs et al. (1997) w = 0.00

Atkinson and Boore (2003, 2008) w = 0.10

Zhao et al. (2006) w = 0.90

Peak Ground Acceleration with 10 % Probability of Exceedance in 50 years

Peak Ground Acceleration with 2 % Probability of Exceedance in 50 years

Structural response induced by strong motion

Low Long structural period

Spectral Acceleration at 1.0 sec with 2 % Probability of Exceedance in 50 years

Spectral Acceleration at 0.2 sec with 2 % Probability of Exceedance in 50 years

2-4 story buildings 10-15 story buildings

National Standard DPT 1302:Seismic Resistant Design of Buildings and Structures

Issued by Department of Public Works and Town & Country Planning, Ministry of Interior

(2009)

Model Code: ASCE 7-05

Require the values of SA at 0.2 sec and 1.0 sec with 2 % probability of exceedance in 50 yr for defining Maximum Considered Earthquake (MCE) ground motion

Define most likely earthquake scenario that can affect tall structures in Bangkok

To determine the dominated earthquake source at considered sites

To assess possible building and economic damage need further risk and loss assessmentstudies

Subduction earthquakes pose highest threat to tall buildings in Bangkok

T(s) M R(km) ε แหลง่ก ำเนดิแผน่ดนิไหว

0.0 6.7 130 1.45 รอยเลือ่นศรสีวัสดิ์

0.2 6.8 97 1.30 รอยเลือ่นเจดยีส์ามองค์



1.5 8.5 850 1.45 โซนมุดตัวฝ่ังตะวันตกของพม่า



Earthquake scenarios for Bangkok at different

structural periods at 2475 year return period

Disaggreation Analysis

T(s) M R(km) ε แหลง่ก ำเนดิแผน่ดนิไหว

0.0 6.3 12.6 -0.54 แผน่ดนิไหวบรเิวณใกลเ้คยีง

0.2 6.7 33 0.68 แผน่ดนิไหวบรเิวณใกลเ้คยีง






Earthquake scenarios for Ratchaburi

at different structural periods at 2475 year

return period

Shallow crustal fault

Subduction Zone

Earthquake source

Shallow crustal fault

Subduction Zone

Earthquake source

0 50 100 150-0.2

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n(g

)

Peru, 5 Jan 1974, Transverse Comp., ZarateM = 6.6, rhyp = 118 km

0 50 100 150-0.2

-0.1

0

0.1

0.2

Acce

lera

tio

n(g

)

Montenegro, 15 April 1979, NS Component, UlcinjM = 6.9, rhyp = 29 km

0 50 100 150-0.2

-0.1

0

0.1

0.2

Acce

lera

tio

n(g

) Mexico, 19 Sept. 1985, EW Component, SCT1M = 8.0, rhyp = 399 km

0 50 100 150-0.2

-0.1

0

0.1

0.2

Time (sec)

Acce

lera

tio

n(g

)

Romania, 4 March 1977 EW Component, INCERC-1

M = 7.5, rhyp = 183 km

Acce

lera

tion

(g)

Acce

lera

tion

(g)

Time (s)

Mw 6.1, Mae Lao earthquake

at 15 km from epienter

Acce

lera

tion

(g) Mw 6.8, Tarlay earthquake

at 28 km from epicenter

T

Sa (g)

(s)

Representative Ground Motion Based on Disaggregation

Analysis

Long Distance Large Earthquake 1985 Mexico City Mw 8.1

SCT station spectra is very different than

UNAM spectra

Large energy in Long period (tall buildings)

Bangkok conditional mean spectrum (CMS) at bedrock at

2475-year return periodMw 6.7 Distance 130 km = 1.5

Mw 7.5 Distance 100 km = 1.0 Mw 7.5 Distance 150 km = 1.0

Mw 8.5+ Distance 700 km = 1.5


Mw 8.5 Distance 700 km = 1.2

Two different earthquake scenarios

- Large earthquake (M 6.5-7.5) from crustal earthquake at 100 km

- Very large earthquake (M 8+) from subduction zone at 600 – 800 km

- Greatly reduce seismic demand comparing to UHS


Mw 6.7 Distance 33 km = 0.8 Mw 6.7 Distance 46 km = 1.0




Ratchaburi spectrum at bedrock at 2475-year return period

Two different earthquake scenarios

- Large earthquake (M 6.5-7.5) from crustal earthquake at 50 km

- Very large earthquake (M 8+) from subduction zone at 600 – 700 km

- Greatly reduce seismic demand comparing to UHS

DPT 1302-09 Design Spectrum

Short period spectra controlled

by active faults in Karnchanaburi

Long period spectra controlled

by subduction zone in Myanmar

Conclusion

• PSHA provides realistic seismic demand for structural engineers.

• Different locations would have different earthquake scenarios.

• Subduction ground motion would have long period energy with longer

duration than crustal fault earthquakes. (More seismic demand)

• CMS spectrum provides structural engineer more realistic structural

demand compared to UHS spectrum.

• Selected and scaled ground motion to CMS spectrum provide realistic

structural demand for non-linear time history analysis

probabilistic seismic hazard assessment & related topics for...

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