Turkey Earthquake Risk Model

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Turkey Earthquake Risk Model

• Financing the Risks of Natural Disasters
• World Bank
• Washington, DC , June 2-3, 2003
• Dennis E. Kuzak
• Senior Vice President, EQECAT, Inc

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Overall Model Components
Turkish Census and building stock data, plus TCIP
information
Portfolio of Insured TCIP Exposures
Professor Erdik, USGS Research Papers, historical
catalogs
Seismotectonic Model - fault/source locations,
magnitudes, frequencies
Attenuation Functions,Local Soil Conditions
Seismic Hazard - Ground Shaking
Historical Building Performance, Engineering
Analysis, Turkish construction practices
Vulnerability
Policy Deductibles, Limits
Damage and Financial Loss
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Seismic Hazard Modeling Methodology
The location, size, and frequency of rare
catastrophic earthquakes and their associated
ground shaking are modeled using a Probabilistic
Seismic Hazard Analysis (PSHA), which is composed
of the following elements

• Source zonation model (location)
• Recurrence model (size and frequency)
• Ground motion model (ground shaking)
• Hazard curve (ground shaking vs. probability)
• Soil model (ground shaking amplification)

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Tectonic Setting of Turkey
White
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Quaternary Faults of Turkey
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Earthquakes in Turkey, 1904-1992
Legend M 5.0-5.9 (purple) M 6.0-6.9 (blue) M
7.0 (red)
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Earthquake Sources of Turkey
White
Source Erdik et al. (1999), Assessment of
earthquake hazard in Turkey and neighboring
regions, Annali di Geofisica, Vol. 42, pp.
1125-1138.
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Seismic Hazard Map of Turkey
PGA (g) with a 10 Probability of Exceedance in
50 Years (475-year Return Period) on soft rock
Black
Sea
Istanbul
Ankara
Sea
Mediterranean
Source Erdik et al. (1999), Assessment of
earthquake hazard in Turkey and neighboring
regions, Annali di Geofisica, Vol. 42, pp.
1125-1138.
White
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EQECAT Source Zonation Model

• Basic area-source model from Erdik et al. (1999)
• Large characteristic earthquakes (M ? 6.5)
• North Anatolian Fault (NAF)
• Northern NAF (NNAF Marmara Sea)
• Southern NAF (SNAF south of Marmara Sea)
• Distributed faulting on NNAF and SNAF
• Smaller earthquakes included as NAF, NNAF and
  SNAF background seismicity zones

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Marmara Sea Region
NNAF
NAF
SNAF
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North Anatolian Fault System (NAF)

• Potentially the largest contributor to seismic
  hazard in Istanbul and northwestern Turkey
• Ruptures in a sequence of large earthquakes
• Previously known rupture sequences occurred in
  967-1050 and 1254-1784
• Latest sequence began in 1939 and is still in
  progress
• Latest events in current sequence are the 1999M
  7.4 Izmit and M 7.2 Duzce earthquakes
• Next event in sequence is likely to be in Marmara
  Sea (Yalova and/or Princes Islands Faults?)

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Rupture History of the NAF to 1992
Note Mean repeat time is now estimated to be
225 years east of NNAF/SNAF split and 280 years
west of this split (Stein, personal comm., 2000
Parsons et al., 2000)
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EQECAT Recurrence Model

• Area and background sources
• Fault sources
• North Anatolian Fault (NAF)
• Northern NAF (NNAF Marmara Sea)
• Southern NAF (SNAF south of Marmara Sea)

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Recurrence Area and Background Sources

• Earthquake catalog from regional sources
• All magnitudes converted to moment magnitude
• Foreshocks, aftershocks and swarms removed
• Corrected for incompleteness
• Exponential (Gutenberg-Richter) recurrence law
• Maximum magnitude from seismicity/tectonics

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Recurrence Fault Sources

• Characteristic earthquake recurrence law
• Recurrence rates from previous historic events
• Magnitudes on NAF from last historic event
• Magnitudes on NNAF from length/historic events
• Magnitudes on SNAF from largest historic event
• Time-dependent probability on NAF and NNAF

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EQECAT Time-Dependent Model

• Definition of Time-Dependent Probability
• Time-dependent probability is the conditional
  probability that an earthquake will occur on a
  fault within some specified period of time in the
  future (i.e., 2000 to 2030), given that a similar
  earthquake has occurred on this fault at some
  known time in the past

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Causes of Time-Dependent Behavior

• Secular stress increase due to long-term strain
  accumulation
• Permanent stress increase or decrease due to
  stress interaction from an earthquake on a nearby
  fault
• Transient stress increase or decrease due to
  stress interaction from an earthquake on a nearby
  fault (decays with time)

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Time-Dependence from Secular Stress Lognormal
Probability Model
PARAMETERS Te Elapsed Time?T Exposure Period
A
Conditional Probability A/(A B)
B
Last Earthquake
Note We use recurrence intervals of 225 years
east of NNAF/SNAF split and 280 years west of
split exposure period of 1 year elapsed time
from last historic event
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Time-Dependence from Secular StrainSensitivity
to Total Variability
Note We use ? 0.5
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Time-Dependence from Fault InteractionTransient
Stress for NAF
Source Parsons et al. (2000)
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Time-Dependence from Fault Interaction?
Progressive Effect of1939-1992 Earthquake
Sequence
Source Stein et al. (1997)
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Time-Dependence from Fault Interaction ?
Effect of 1999 Izmit Earthquake
Source Parsons et al. (2000)
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Time-Dependence from All EffectsFaults within
50 km of Istanbul
Source Parsons et al. (2000) Our results give
50 smaller probability
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Time-Dependence from All EffectsIstanbul
Earthquake Probabilities of M ? 7 for
Faults within 50 km of Istanbul Beginning in May
2000 (Interaction includes Secular and
Interaction Stress Effects)
Note 30-year time-averaged (Poisson)
probability is 20 ? 10
Source Parsons et al. (2000) Our results give
50 smaller 1-year combined probabilities
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EQECAT Ground Motion Model

• Four attenuation relationships for shallow
  crustal earthquakes
• Abrahamson and Silva (1997)
• Boore et al. (1997)
• Campbell (1997)
• Sadigh et al. (1997)
• One attenuation relationship for subduction
  earthquakes
• Youngs et al. (1997)
• 1999 Izmit earthquake validation

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PGA Estimate for 1999 Izmit Event
Note PGA in g Values are consistent with
limited strong-motion recordings
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EQECAT Soil Model

• NEHRP soil classifications (A-E) were derived
  from a 1500,000-scale geologic map of Turkey
• Correlation with geology was based on extensive
  studies relating shear-wave velocity and geologic
  units in California
• PGA amplification factors were based on empirical
  and theoretical studies relating shear-wave
  velocity and amplification

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Turkish Soil Map
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EQECAT Hazard Results

• Seismic hazard curves
• Istanbul (Bakirkoy)
• Izmit
• Ankara
• Seismic hazard maps
• All of Turkey
• Marmara Sea Region

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Seismic Hazard Curves

• Lowest hazard in Ankara, located in more stable
  central region of Turkey
• Hazard in Izmit is approximately the same as that
  in Istanbul (Bakirkoy) because
• Time-dependent probability effects have increased
  hazard in Istanbul
• Time-dependent probability effects have decreased
  hazard in Izmit

Soft Rock
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Seismic Hazard Map for Turkey
PGA with 10 Probability of Exceedance in 50
Years (475-year Return Period)
Soft Rock
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Seismic Hazard Map for Marmara Sea
PGA with 10 Probability of Exceedance in 50
Years (475-year Return Period)
Soft Rock
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Building Vulnerability

• Good building codes- poor construction practices
• Non ductile concrete frames, soft story
• Limited/No claims data for residential
  multi-family
• EQECAT approach- use aggregate residential damage
  data from Izmit, select damage curve consistent
  with Izmit data.

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Summary

• Turkish Model incorporates current research on
  time-dependent studies of North Anatolian Fault
• Raises hazard in Istanbul
• Lowers hazard east of Izmit epicenter
• Recognizes uncertainty in NAF location in the
  Marmara Sea
• Incorporates poor building practices into
  vulnerability assumptions
• Fully probabilistic damage and loss model
  consistent with other EQECAT earthquake models
  for the US, Japan, Taiwan, etc.

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TCIP RISK ANALYSIS RESULTS
Portfolio exposures estimated as of 31-10-2002
Estimated Annual Damage .138 (1.38 per mill)