probabilistic seismic hazard assessment & related topics for...
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Dr. Teraphan Ornthammarath
Department of Civil and Environmental Engineering
Mahidol University
teraphan.orn@mahidol.ac.th
0 50 100 150-0.2
-0.1
0
0.1
0.2
Acce
lera
tio
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)
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
0.5 7.5 130 1.00 รอยเลือ่นศรสีวัสดิ์
1.0 7.5 150 1.00 รอยเลือ่นศรสีวัสดิ์
1.5 8.5 850 1.45 โซนมุดตัวฝ่ังตะวันตกของพม่า
2.0 8.5 850 1.50 โซนมุดตัวฝ่ังตะวันตกของพม่า
3.0 8.5 850 1.20 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
0.5 6.7 38 0.84 รอยเลือ่นเจดยีส์ามองค์
1.0 6.7 46 1.04 รอยเลือ่นเจดยีส์ามองค์
1.5 6.7 49 1.19 โซนมุดตัวฝ่ังตะวันตกของพม่า
2.0 8.5 750 1.67 โซนมุดตัวฝ่ังตะวันตกของพม่า
3.0 8.5 750 1.82 โซนมุดตัวฝ่ังตะวันตกของพม่า
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
-0.1
0
0.1
0.2
Acce
lera
tio
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 = 1.5
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 = 0.68
Mw 6.7 Distance 33 km = 0.8 Mw 6.7 Distance 46 km = 1.0
Mw 6.7 Distance 49 km = 1.2
Mw 8.5+ Distance 650 km = 1.67
Mw 8.5+ Distance 650 km = 1.82
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
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