NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA J Miguel Miranda CGUL / IDL

NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA

J Miguel MirandaCGUL / IDL


“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


Why the phocus on natural hazards suddenly developed ?

1946, Havai

1883, Krakatoa

1992, Ilha Flores2004, Sumatra


In the Iberian geo-environment tsunamis are rare (but violent) phenomena.

Historical (red stars) and instrumental (black dots) events.


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.


The 1st November 1755 earthquake and tsunami started modern hazard studies.


Monitoring and Warning versus Hazard and Risk assessments.


LANDSLIDES

LANDSLIDES

LANDSLIDES

EARTHQUAKES

EARTHQUAKES

EARTHQUAKES

Where do they come from?


> 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 ?


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


If the source is known the propagation can be accurately computed


If the source is known the propagation can be accurately computed


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?


EARTHQUAKES LANDSLIDES

SEA SURF DISTURBANCE

PROPAGATION

COASTAL INTERACTION

PEOPLE + CONSTRUCTION + ...

What are the main phenomena ?

+ TIDES

Efficiency

Model reliability


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.


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


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)


Observations follow always a GR-like relationship?


What is the physical mechanism ?


Probabilistic seismic hazard assessment?

GENERATION

ATTENUATION

SITE EFFECTS


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)


The homogeneous source areas


What are the main results of PSHE ?


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


Can we forget the source ? Extreme value theory ?


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;


THANKS !

Documents

NEW CHALLENGES CONCERNING GEO-HAZARD EVALUATION – J M MIRANDA J Miguel Miranda CGUL / IDL