Lessons from Tohoku: why earthquake hazard maps often fail and what to do about it

1
Lessons from Tohoku why earthquake hazard maps
often fail and what to do about it
Seth Stein, Northwestern University Robert
Geller, University of Tokyo Mian Liu,
University of Missouri 
CNN
NY Times
Tohoku, Japan March 11, 2011 M 9.1
2
Tools in preparing for natural disasters include
- Long term forecasts 1-2500 yr (earthquakes),
100 yr (climate change), 1-10 yr (hurricane,
volcano) - Short term predictions days
(hurricanes), days to months (volcano), hours
(tornado) - Real time warnings (hours to
minutes) tsunami, earthquake shaking, hurricane,
tornado, flood Sometimes these work, sometimes
they fail
3
FAILURES False negative - unpredicted
hazard Loss of life property False positive
- overpredicted hazard Wasted resources, public
loses confidence Authorities typically ignore,
deny, excuse, or minimize failure More useful to
analyze failures to improve future performance
4
2008Hurricane Ike predicted to hit Miami
5
Ikes actual track
6
Ikepredicted to bring certain death
7
Actual deathslt 50 of 40,000Error 800x
8
If it had been a weekday, Major cost
9
K. Emanuel CNN 8/26/11
NYT 8/28/11
10
Economic loss ? What if weekday?
11
Science News 6/15/91
The local economy collapsed, said Glenn Thompson,
Mammoth Lakes' town manager. Housing prices fell
40 percent overnight. In the next few years,
dozens of businesses closed, new shopping centers
stood empty and townspeople left to seek jobs
elsewhere. (NYT 9/11/90)
12
Expensive seawalls - longer than Great Wall of
China -proved ineffective 180/300 km swept away
or destroyed In some cases discouraged evacuation
NY Times 3/31/2011
13
Japan spent lots of effort on national hazard
map, but 2011 M 9.1 Tohoku, 1995 Kobe M 7.3
others in areas mapped as low hazard In
contrast map assumed high hazard in Tokai gap
Geller 2011

14
Hazard map crucial for mitigation
strategy Optimal level of mitigation minimizes
total cost sum of mitigation cost expected
loss for given mitigation
level Expected loss ? (loss in ith expected
event
x assumed probability of that event)
Less mitigation decreases construction costs but
increases expected loss and thus total
cost More mitigation gives less expected loss
but higher total cost
Because assumed probability taken from hazard
map, inaccurate map biases mitigation - too
little or too much
Stein Stein, 2012
15
Including uncertainty Consider marginal costs
C(n) benefits Q(n) (derivatives)
More mitigation costs more But reduces
loss Optimum is where marginal curves are equal,
n
Benefit (loss reduction)
cost
Uncertainty in hazard model causes uncertainty in
expected loss. We are risk averse, so add risk
term R(n) proportional to uncertainty in loss,
yielding higher mitigation level n
Crucial to understand hazard model uncertainty
Stein Stein, 2012
16
Choosing policy involves politics, economics,
geoscience Too expensive to rebuild for 2011
sized tsunami gt100 B for new defences only
slightly higher than old ones In 30 years there
might be nothing left there but fancy breakwaters
and empty houses.
NY Times 11/2/2011
17

• Hazard maps fail because of
• - bad physics (incorrect description of
  earthquake processes)
• bad assumptions (mapmakers choice of poorly
  known parameters)
• bad data (lacking, incomplete, or
  underappreciated)
• bad luck (low probability events)
• and combinations of these (Tohoku!)

18

Detailed model of segments with 30 year
probabilities
Off Sanriku-oki North M8 0.2 to 10
Off Sanriku-oki Central M7.7 80 to 90
Assumption No M gt 8.2
Off Miyagi M7.5 gt 90
Off Fukushima M7.4 7
Off Ibaraki M6.7 M7.2 90
Sanriku to Boso M8.2 (plate boundary) 20 Sanriku
to Boso M8.2 (Intraplate) 4-7
Expected Earthquake Sources 50 to 150 km
segments M7.5 to 8.2 (Headquarters for
Earthquake Research Promotion)
J. Mori
19

Giant earthquake broke five segments
2011 Tohoku Earthquake 450 km long fault, M
9.1
Expected Earthquake Sources 50 to 150 km
segments M7.5 to 8.2 (Headquarters for
Earthquake Research Promotion)
(Aftershock map from USGS)
J. Mori
20
Planning assumed maximum magnitude 8 Seawalls
5-10 m high
NYT
Stein Okal, 2011
Tsunami runup approximately twice fault slip
(Plafker, Okal Synolakis 2004) M9
generates much larger tsunami
CNN
21
Didnt consider historical record of large
tsunamis
NYT 4/20/11
22
Lack of M9s in record seemed consistent with
model that M9s only occur where lithosphere
younger than 80 Myr subducts faster than 50 mm/yr
(Ruff and Kanamori, 1980)
Disproved by Sumatra 2004 M9.3 and dataset
reanalysis (Stein Okal, 2007) Short record at
most SZs didnt include rarer, larger
multisegment ruptures
Stein Okal, 2011
23
NY Times 3/21/11
Why?
24
Hazard maps are hard to get right success
depends on accuracy of four assumptions over
500-2500 years
Where will large earthquakes occur? When will
they occur? How large will they be? How strong
will their shaking be?
Uncertainty map failure often result because
these are often hard to assess
25
2010 M7 earthquake shaking much greater than
maximum predicted for next 500 years
2001 hazard map
http//www.oas.org/cdmp/document/seismap/haiti_dr.
htm
Including GPS would have predicted higher hazard
26
2008 Wenchuan earthquake (Mw 7.9) was not
expected map showed low hazard based on lack of
recent earthquakes
Didnt use GPS data showing 1-2 mm/yr ( Wasatch)
27
Maps are like Whack-a-mole - you wait for the
mole to come up where it went down, but its
likely to pop up somewhere else.
28
What to do
Continue research on fundamental scientific
questions (geoscience communitys
job!) Realistically assess map uncertainties and
present them to help users decide how much
credence to place in maps how to use them given
uncertainties Develop methods to objectively test
hazard maps - which hasnt been done despite
their wide use - and thus guide future
improvements
29
Comparing map predictions shows the large
uncertainties (3X) resulting from different
assumptions
Stein et al, 2012
Newman et al, 2001
30
Testing analogy evidence-based medicine
objectively evaluates widely used treatments,
often with embarrassing results Although more
than 650,000 arthroscopic knee surgeries at a
cost of roughly 5,000 each were being performed
each year, a controlled experiment showed that
"the outcomes were no better than a placebo
procedure."
31
Test maps by comparison to what happened after
they were published.
Bad luck or bad map? Compare maximum
acceleration observed to that predicted by both
map and null hypotheses. A simple null
hypothesis is regionally uniformly distributed
hazard. Japanese map seems to be doing worse
than this null hypothesis.
Geller 2011
32
Avoid biases from new maps made after a large
earthquake that earlier maps missed.
Before 2010 Haiti M7
After 2010 Haiti M7
4X
Frankel et al, 2010
33
A posteriori changes to a model are "Texas
sharpshooting shoot at the barn and then draw
circles around the bullet holes.
34
Possible problem Overparameterized model
(overfit data)Given a trend with scatter,
fitting a higher order polynomial can give a
better fit to the past data but a worse fit to
future dataAnalogously, a seismic hazard map
fit to details of past earthquakes could be a
worse predictor of futureones than a less
detailed mapHow much detail is useful?
Linear fit
Quadratic fit
35
Challenge Users want predictions even if
theyre poor Future Nobel Prize winner Kenneth
Arrow served as a military weather forecaster. As
he described, my colleagues had the
responsibility of preparing long-range weather
forecasts, i.e., for the following month. The
statisticians among us subjected these forecasts
to verification and found they differed in no way
from chance. The forecasters themselves were
convinced and requested that the forecasts be
discontinued. The reply read approximately
"The commanding general is well aware that the
forecasts are no good. However, he needs them for
planning purposes." Gardner, D., Future Babble
Why Expert Predictions Fail - and Why We Believe
Them Anyway, 2010
36
(No Transcript)
37
What to do given that earthquake hazard maps
often fail
Seth Stein, Northwestern University Robert
Geller, University of Tokyo Mian Liu,
University of Missouri 
CNN
NY Times
Tohoku, Japan March 11, 2011 M 9.1