Probabilistic Estimates of Seismic Hazard and Public Awareness in Japa

Shimazaki, K.

Earth-prints Repository

Probabilistic estimates of seismic
hazard and public awareness in Japan
Kunihiko Shimazaki,
Earthquake Research Institute, University of Tokyo
16:00-16:30, 04 June 2007
Ettore Majorana Foundation and Centre for Scientific Culture, Erice, Sicily
5th International Workshop on Statistical Seismology:
Physical and Stochastic Modeling of Earthquake Occurrence and Forecasting
Section 5. Living in an Uncertain World: Interfacing Statistical Seismology and Society
Earthquake mechanisms
1.Shallow crustal earthquakes
Interplate earthquakes
2.Subduction zone earthquakes
Deep intraplate earthquakes
Intraplate normal-fault eq.
Intraplate reverse-fault eq.
Japanese earthquakes can be classified into two type.
Distributed sources
Smaller-than-the
largest EQ
Unidentifiable ones
Identifiable sources
Shallow crustal EQSubduction-zone EQ
Distributed sources
Evaluation of earthquake potential
Time-dependent & time-independent
long-term forecasts 
For distributed sources, we sum up results of spatial smoothing
and zoning methods by using small & moderate eq.
Source interactions are alluded to but no probability is given
except for Tokai, Tonankai, Nankai earthquake sequence.
Distributed sources
Smaller-than-the
largest EQ
Unidentifiable ones
Identifiable sources
Shallow crustal EQSubduction-zone EQ
Distributed sources
Evaluation of earthquake potential
Time-dependent & time-independent
long-term forecasts 
For distributed sources, we sum up results of spatial smoothing
and zoning methods by using small & moderate eq.
Av.repeat time
~100yrs
Historical eq data
Av.repeat time
~1000yrs or more
Active fault survey
Source interactions are alluded to but no probability is given
except for Tokai, Tonankai, Nankai earthquake sequence.
Small probabilities for EQ on active faults
The figure taken from news
article of Kyodo News Agency
shows why much smaller
probabilities are obtained for
earthquakes on active faults
relative to earthquakes along the
oceanic trench.
Probability less than 10% 
tends to be neglected
by general public
Classification of small probabilities and verbal expression are
necessary because small probability does not mean safe.
 High probability relative to other active fault
zones: 3% or higher (30yr probability)
 Slightly high probability: 0.1-3%
 No comments: less than 0.1%
The largest probability is used when the range of probability is estimated.
The 30-yr probability could have been evaluated as only 0.02-8%, if the
estimate had been made just prior to the Kobe earthquake.
Earthquake Research Committee, 2003
Help to understand meaning of probability level
Earthquake Research Committee,
2003; translated by Midorikawa,
2006
      159 faults/faults segments               116 cases with 30-yr probability
Model
used
comment
NO DATA
Poisson
HIGH
NO COMMENT
HIGH
SLIGHTLY HIGH
SLIGHTLY HIGH
Poisson
INACTIVE
INACTIVE
NO COMMENT
NO DATA HIGH
SLIGHTLY HIGH
SLIGHTLY HIGH
Summary of earthquake forecasts for
the 98 major active fault zones
(159 faults/ fault segments)
Long-term Evaluation Subcommittee, 2005
30-yr
probability
30-yr probability
3% -, High
0.1 - 3%, Slightly High
- 0/1%
Unknown
Long-term forecasts for
the major 98 fault
zones was made public
by April 2005.
Long-term Evaluation
Subcommittee, 2005
30-yr
probability
30-yr probability
3% -, High
0.1 - 3%, Slightly High
- 0/1%
Unknown
Long-term forecasts for
the major 98 fault
zones was made public
by April 2005.
Binary response
safe or dangerous
take measures or not
We need recipe.
Various EQ
measuresprobability
uncertainty
Long-term
Evaluation
Subcommittee,
2005
Forecast summary of earthquakes
along the oceanic trenches
Identifiable source
    Time-predictable with disturbances        2
    Brownian Passage Time model            15
    Poisson Process (unknown last event)    2
Unidentifiable source
    Poisson Process                                  14
Tokyo
Osaka
50%
60-70%
The probability is
estimated on the basis of
the time-predictable
model with disturbances
Earthquake Research Committee, 2001
30-yr probability: Nankai Earthq
Earthquake Research Committee, 2001
30yr probability
Nankai eq 50%, Tonankai 60-70%
Seismic Intensity: Nankai + Tonankai  (Central Disaster Prevention Council, 2003)
M.M. Intensity
10, 11, 12
        9-10
Estimated number of collapsed buildings per km2
(Central Disaster Prevention Council, 2003)
Historical damaging earthquakes:
Identifiable and unidentifiable sources
 98 major active fault zones: identifiable source
 50% of inland damaging events which killed more than 50
 70% of those which killed more than 1,000
 Other identifiable source
 Most off-shore earthquakes which killed more than 50
 Unidentifiable source
 Earthquakes occurring away from active faults
 Smaller off-shore earthquake
 Deep earthquakes
 Earthquakes on active fault other than the 98 major
fault zones（Identifiable, but inaccurate forecast）
Statistics based on the past 200 year data
The 1995 Kobe
earthquake
The present
top issue is
existing
weak
houses and
buildings
Damaged
houses
Central Disaster Prevention Council
Built
before
1982
1982
and
after
Most of the collapsed
houses were built prior to
the 1981 building code
revision.
M
aj
or
 d
es
tr
uc
tio
n
Investigation shows that 64% of houses built,
following the former building code, before 
1982 were destroyed by the earthquake.
It is very important to retrofit these houses. 
Ministry of land, construction, 
and transportation, 2004
1998 2003
# of houses
Unsafe 
44M 47M
14M 11.5M
Wooden houses
Apartment buildings
How can we reach the goal?
What would be the best incentive to make people retrofit or rebuild
their dwellings?
Example
Tax deduction for earthquake insurance premium starts from this fiscal
year and two years later the present tax reduction for fire insurance
(fire caused by earthquakes is not insured) premium will be abolished.
GOAL:25% unsafe houses/buildings should be
decreased to 10% within 10 years.
Which weak house/buildings should we choose
for retrofit or rebuilding?
Probabilistic seismic hazard map answers this question.
2006 Version
Probability of Ground Motion Equal to or
Larger than JMA Intensity 6 weak (MM9-
10) Occurring within 30 years years
 Slightly
High
   High
  Probability
The first national
seismic hazard map is
produced ten years
after the Kobe eq. on
the basis of long-term
forecasts and empirical
attenuation
relationship.
Earthquake Research
Committee, 2006
Japan Seismic Hazard Information Station
( J-SHIS )
http://www.j-shis.bosai.go.jp/j-shis/index_en.html
Intensity estimate in Yokosuka city on its HP
JMA 7
JMA 6 weak
MM 9-10
Shake map for M7.2 Miura Peninsula Fault
Zone EQ
JMA 6 strong
MM 10-
http://www2.wagamachi-guide.com/yokosuka/apps/search/asp?GetChkFlg=miura
Nagoya
Tonankai-Nankai EQ
30-yr probability:60-70%
Itoigawa-Shizuoka
Tectonic Line fault zone
30-yr probability:14%
Number of collapsed
buildings / km2
Seismic Intensity
Earthquake Research Committee, 2002
Central Disaster Prevention Council, 2003
!"#$%&'$())*$+),)--".%$&($/0$1)2-'3)-4
5
6
7
8
Very
positive
 Positive
NoMaybe No
Matsumoto
 (Fault EQ 14% in 30yrs)
!"#$%"
&
'
(
)
positive
Nagoya
 (Subduction EQ 60-70% in 30yrs)
Very
positive
Do you feel the necessity
of earthquake measures?
Headquarters for Earthquake Research Promotion,
2006
General comments may not be
sufficiently persuasive to make people
prepare for earthquake disasters.
One way is to make statements very
specific. If you are told that your house
will collapse when a ceratain
earthquake hits, you would start to think
about it.
long-term earthquake forecasts,
realizable at the present level of our
knowledge, are helpful and the first
step towards our goal.
Retrofit Construction of ERI building 
February 2007


Probabilistic Estimates of Seismic Hazard and Public Awareness in Japan

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Probabilistic Estimates of Seismic Hazard and Public Awareness in Japan

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