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NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
J Miguel MirandaCGUL / IDL
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
“Tsunamis, earthquakes, hurricanes, volcanoes and other natural disasters now pose a greater global threat than war and terrorism. Finding ways of reducing the impact of natural disasters is vital.”
The European Commission supports the UN Disaster Reduction Conference in Kobe - IP/05/51- Brussels, 17 January 2005
Earthquakes with less then 30,000 victims
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
Why the phocus on natural hazards suddenly developed ?
1946, Havai
1883, Krakatoa
1992, Ilha Flores2004, Sumatra
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
In the Iberian geo-environment tsunamis are rare (but violent) phenomena.
Historical (red stars) and instrumental (black dots) events.
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
Plato wrote about the destruction of the legendary city - new evidence suggests he was writing about a devastating tsunami: "There occurred violent earthquakes and floods...the island of Atlantis disappeared in the depths of the sea." That was how Greek philosopher Plato described the destruction of the legendary city.
"... nor could the martial tribes of the Lusitanians and Cantabrians escape; no more could the ocean, with its tide (the ebb-tide, ebb and flow), which yet was terrible to the ancient inhabitants; at least, until where the Pillars of Hercules extend..." (FLAVIO JOSEPHUS Memories, translated by Georgeos Díaz-Montexano, 2002)
Even Atlantis is “located” here and there are large historical traditions.
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
The 1st November 1755 earthquake and tsunami started modern hazard studies.
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
Monitoring and Warning versus Hazard and Risk assessments.
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
LANDSLIDES
LANDSLIDES
LANDSLIDES
EARTHQUAKES
EARTHQUAKES
EARTHQUAKES
Where do they come from?
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
> The maximum wave elevation (MWE);
The maximum run-up
The maximum run-in
The velocity and the flow depth
What are the most important parameters ?
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
What are the relevant processes for tsunami impact ?
)()cos()cos(
12
DC
ugvf
guvuuu xyxt
u
)()cos(
12
DC
vgufgvvvuv yyxt
u
0)cos()()()cos(
1 yxt vDuDu
25.0
s
o
h
hk
SHALLOW WATER
RUN UP
ELASTIC DEFORMATION
Okada EHS equations
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
If the source is known the propagation can be accurately computed
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
If the source is known the propagation can be accurately computed
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
Determinist approach: the worst case (easy in the case of the stronger yet credible event). However,
we need for probability descriptions (can tsunamis risk be mitigated by intervention on the “building code” side?)
How rare are tsunamis? How can we characterize the occurrence model?
How to compute tsunami hazard in SW Iberia?
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
EARTHQUAKES LANDSLIDES
SEA SURF DISTURBANCE
PROPAGATION
COASTAL INTERACTION
PEOPLE + CONSTRUCTION + ...
What are the main phenomena ?
+ TIDES
Efficiency
Model reliability
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
Deterministic Tsunami Hazard Approach
The case of the stronger yet credible event for the UK (DEFRA study). Variability of hazard is only a function of local morpological conditions.
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
What can be learned from earthquake statistics?
In case tsunami sources are far away from the risk areas run-up is mainly a function of local topography and if earthquakes are the main tsunami generation mechanism we can build a statistical model using a more common phenomenon (earthquakes).
Gutenberg Richter relationship:
0
200
400
600
800
1000
1200
1400
1600
1800
2000
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
Earthquakes with M>=5
)MM(M
M
T
eee
NN
)M(F 0
01
Not all earthquakes generate tsunamis
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
What can be learned from earthquake statistics?
5,5 6,0 6,5 7,0 7,5 8,0 8,51E-4
1E-3
0,01
0,1
1
10
1E-4
1E-3
0,01
0,1
1
10
Freq
uênc
ia A
cum
ulad
a (a
no-1
)
Magnitude
0,1 1
Zona Oceânica Portuguesa
Altura da Onda (m)
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
Observations follow always a GR-like relationship?
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
What is the physical mechanism ?
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
Probabilistic seismic hazard assessment?
GENERATION
ATTENUATION
SITE EFFECTS
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
jn
jj EP.E|yYPyYP
1
Cornell’s approach is based on the assumption that the probability of excedance of an effect Y in a study area can be obtained by adding the effect of all possible seismogenic contributions
dRdM)M|R(f).M(f.R,M|yYPE|yYP jjjj
Chosing as random variables the magnitude and hipocentral distance
n
ijE|yYPyYP
1
1
Assuming that earthquake generation follows an homogeneous Poisson process;
n
ijEyYP
ano eyYP 1|
1 1
RyRlogyMyyylog 3210
If atenuation is given by;
)MM(
M)r,y(m
Uee
)r,y(mF)r,y(mMPrR|yYP0
0
11
11
We have for a specific place:
Probabilistic seismic hazard assessment?
200 400 600 800 1000 1200 14002
4
6
8
10
12
MS
K I
nte
nsi
ty
Distance (km)
OBS Oliveira (1984) Sousa (1996) Baptista (1998) Levret (1991)
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
The homogeneous source areas
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
What are the main results of PSHE ?
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
Probability tsunami hazard evaluation (PTHE)
In case tsunami wave heights can be predicted (as a consequence of seismic hazard or independently) than inundation and associated effects can be predicted by deterministic numerical simulation.
Ex for Oregon in http://pubs.usgs.gov/ds/2006/236/figures/f_100-500cont.shtml
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
Can we forget the source ? Extreme value theory ?
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
PTHE must be meaningfull
DIscriminate between different levels of danger to people and goods;
Allow the design of mitigation strategies, including land management rules;
Allow the design of building codes;
NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA
THANKS !
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