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Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 1 DE LA RECHERCHE À L’INDUSTRIE [EGU2020-5554] Tsunami hazard associated to earthquakes along the French Mediterranean coastslines A probabilistic approach (PTHA) 6 May, 2020 E.G.U. General Assembly 2020 Viviane Souty & Audrey Gailler [email protected], [email protected] Commissariat à l’énergie atomique et aux énergies renouvelables – www.cea.fr

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Page 1: Tsunami hazard associated to earthquakes along the French … · 2020. 5. 4. · 2. TSUMAP-NEAM project 3. TANDEM project. Sørensen et al. (2012) quantified the tsunami hazard in

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 1

DE LA RECHERCHE À L’INDUSTRIE [EGU2020-5554]

Tsunami hazard associated to earthquakes alongthe French Mediterranean coastslinesA probabilistic approach (PTHA)

6 May, 2020

E.G.U. General Assembly 2020 Viviane Souty & Audrey [email protected], [email protected]

Commissariat à l’énergie atomique et aux énergies renouvelables – www.cea.fr

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Outline

1. Introduction1.1 Two recent critical events1.2 Events within the Western Mediterranean Sea1.3 Previous studies1.4 Finding and response

2. Method2.1 Seismic hazard2.2 Tsunamis2.3 From seismic hazard to PTHA

3. Results: Tsunamis impacting Cannes area (z05)3.1 Extension of the period of observation3.2 A first overview of the magnitude uncertainties

4. Conclusions and perspectives4.1 Conclusions4.2 Perspectives

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 2

Page 3: Tsunami hazard associated to earthquakes along the French … · 2020. 5. 4. · 2. TSUMAP-NEAM project 3. TANDEM project. Sørensen et al. (2012) quantified the tsunami hazard in

About N.A.R.S.I.S.

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 3

New Approach to ReactorSafety ImprovementS

2017–2021

www.narsis.eu

The work I will present you is co-founded by Euratom H2020 NARSIS project and CEA. NARSIS

means New Approach to Reactor Safety ImprovementS. It is an European project involving 18

partners in 10 countries. The main objective of the project is to improve safety and reliability of

Generation II and III reactors. The project includes the characterization of potential physical threats

due to different external hazards and scenarios (WP1), especially using probabilistic hazard as-

sessment for tsunamis, extreme weather and flooding and their impacts on facilities and extreme

earthquakes effects.

Page 4: Tsunami hazard associated to earthquakes along the French … · 2020. 5. 4. · 2. TSUMAP-NEAM project 3. TANDEM project. Sørensen et al. (2012) quantified the tsunami hazard in

Outline

1. Introduction1.1 Two recent critical events1.2 Events within the Western Mediterranean Sea1.3 Previous studies1.4 Finding and response

2. Method2.1 Seismic hazard2.2 Tsunamis2.3 From seismic hazard to PTHA

3. Results: Tsunamis impacting Cannes area (z05)3.1 Extension of the period of observation3.2 A first overview of the magnitude uncertainties

4. Conclusions and perspectives4.1 Conclusions4.2 Perspectives

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 3

Page 5: Tsunami hazard associated to earthquakes along the French … · 2020. 5. 4. · 2. TSUMAP-NEAM project 3. TANDEM project. Sørensen et al. (2012) quantified the tsunami hazard in

IntroductionTwo recent critical events

26 Dec., 2004 Sumatra-Andamanearthquake and tsunami

➢ Mw9.1 Burma and Indian plates

➢ 250 000–300 000 dead people

➤ The deadliest one

11 March, 2011 Tohoku earthquake andtsunami

➢ Mw9.0 Pacific and Northern Honshu plates

➢ Low altitude of the Fukushima NPP

➤ Nuclear accident

Two time scales

✔ Warning time scale: starting with the triggering event in real time

✔ Historical time scale:❏ Study of past events and extrapolation to future events

❍ DTHA: conservative❍ PTHA: determination of the most affected zones, determination of the most

threatening zones➢ Evacuation plannification, building engineering

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 4

Since the major tsunamigenic earthquakes at Sumatra in December 2004 and Tohoku in March2011, the determination of the tsunami hazard is questioned worldwide.

The Sumatra tsunami is known as the deadliest tsunami within living memory (250 000–300 000dead people). The lack of information and communication is responsible for part of this situation(Okal, 2011).

The 2011 Tohoku tsunami caused a great deal of attention, strengthened by the Fukushima NuclearPower Plant accident. The reactors were stopped after the Mw9.0 earthquake, but the elevation ofthe NPP was too low in altitude to be preserved from the tsunami waves that exceeded 10 m-heightat the NPP place.

These two high-profile events illustrate the interest to correctly determine the tsunami hazardin order to communicate truthful analyses.

They also illustrate that the tsunami hazard must be studied at several time scales:1) the warning time scale, from the triggering event (often an earthquake), and2) the historical time scale.

At historical time scale, we study past events to extrapolate to probable future events. Two ap-proaches exist:1) The Deterministic Tsunami Hazard Assesment (DTHA) look for the worst probable scenario thatcan threaten a place.2) The Probabilistic Tsunami Hazard Assesment (PTHA) look for all probable scenarios. A weight isgiven to each probable scenario in order to get the probability of exceeding a threshold value ina return period (i.e. the maximum water elevation).

This study at historical scale is necessary to plan evacuation and design buildings.

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IntroductionEvents within the Western Mediterranean Sea

354 1̊5'

354 1̊5'

0 0̊0'

0 0̊0'

5 4̊5'

5 4̊5'

11 3̊0'

11 3̊0'

34 3̊0' 34 3̊0'

40 1̊5' 40 1̊5'

0 200 400

km

Tsunamigenic Earthquakes

Mw=6.0

Mw=6.5

Mw=7.0

Amplitude lower than 1m

Amplitude greater than 1m

Mw=7.5

Mw=8.0

1169

1365

1562

1564

1680

1693

1726

1742

1783 1783

1802

1804 1818

1818

1823

1846

1856

1887

1905

1908

1954

1980

2003

2003

79

Algiers

Andorra

Monaco

Rome

Tunis

Non-exhaustive list

N

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 5

Adapted from fig. 1 in Gailler et al. (2013)

Tsunamis in the Western part of the Mediterranean Sea are not frequent and little destructive atregional scale (i.e. Western Mediterranean Sea area).

However they exist. This map show most of the earthquakes that triggred tsunamis in this part ofthe Mediterranean Sea.

Yellow circles show earthquakes that generated less than 1m water elevation along the WesternMediterranean coastlines. Red circles show earthquakes that triggered tsunamis with waves locallyupper than 1m.

Especially, the Mw6.7 earthquake, that occured offshore in front of Imperia in 1887, impacted a lotthe coastlines along the Ligurian Sea.

The red dashed lines, on the map show the intensity distribution of the tsunami that was generatedby the Mw6.7 earthquake.The vertical lines show the wave heights that were observed in some cities along the coastlines.

Notably, waves have reached heigths between 1 m and 2 m at Cannes [3] and Antibes [4] cities.

The question of what is the risk naturally arises.

Here we focus on the characterization of the tsunami hazard that is a part of the risk.

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IntroductionFeb. 23, 1887 Mw6.7 earthquake, Imperia (Italy)

23 Feb., 1887, Mw6.7Tsunami effects

hmax : 0 < a < 0.5 m 0.5 < b < 1 m 1 < c < 2 m

Locations: 1, Marseille; 2, Fréjus; 3, Cannes; 4, Antibes;5, Nice; 6, St Jean-Cap-Ferrat; 7, Monaco; 8, Menton; 9, Ospedaletti; 10, San Remo; 11, Arma di Taggia;

12, Riva Ligure; 13, Imperia; 14, Oneglia; 15, Diano Marina; 16, Andora; 17, Alassio; 18, Genoa; 19, Bogliasco; 20, Recco; 21, Sestri Levante; 22, Livorno.

Dotted red lines: distribution of the intensity of the tsunami [intensity scale from Sieberg (1923) modified by Ambraseys (1962), compilation by A. Laurenti].

What’s next?

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 5

Adapted from fig 5 from Larroque et al. (2012)

Tsunamis in the Western part of the Mediterranean Sea are not frequent and little destructive atregional scale (i.e. Western Mediterranean Sea area).

However they exist. This map show most of the earthquakes that triggred tsunamis in this part ofthe Mediterranean Sea.

Yellow circles show earthquakes that generated less than 1m water elevation along the WesternMediterranean coastlines. Red circles show earthquakes that triggered tsunamis with waves locallyupper than 1m.

Especially, the Mw6.7 earthquake, that occured offshore in front of Imperia in 1887, impacted a lotthe coastlines along the Ligurian Sea.

The red dashed lines, on the map show the intensity distribution of the tsunami that was generatedby the Mw6.7 earthquake.The vertical lines show the wave heights that were observed in some cities along the coastlines.

Notably, waves have reached heigths between 1 m and 2 m at Cannes [3] and Antibes [4] cities.

The question of what is the risk naturally arises.

Here we focus on the characterization of the tsunami hazard that is a part of the risk.

Page 8: Tsunami hazard associated to earthquakes along the French … · 2020. 5. 4. · 2. TSUMAP-NEAM project 3. TANDEM project. Sørensen et al. (2012) quantified the tsunami hazard in

IntroductionPrevious studies

Sørensen et al. (2012)

✔ Tsunami hazard, due to earthquakes, in the Mediterranean Sea using PTHA

✔ Long-wave offshore to get peak offshore tsunami amplitudes

✔ Extrapolation to PCTAs using Green’s law

✔ Contribution to tsunami hazard per seismogenic zone

TSUMAPS-NEAM

✔ European project

✔ Tsunami hazard along European coastlines

✔ Peak offshore tsunami amplitude extrapolated to PCTAs using Green’s law

TANDEM

✔ French project

✔ Tsunami hazard along French coastlines (North Atlantic Ocean and French Channel)

✔ DTHA using high-resolution simulations

✘ Green’s law approximation are not accurate nearshore

✘ DTHA only look at the worst probable scenario

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 6

Several studies had the aim to study the tsunami hazard along the European coastlines. Amongother, we can cite1. The study of Sørensen et al. (2012)2. TSUMAP-NEAM project3. TANDEM project.

Sørensen et al. (2012) quantified the tsunami hazard in the Mediterranean Sea using PTHA. Theysimulated tsunamis using long-wave model to get the peak offshore tsunami amplitude andextrapolated it to Peak Coastal Tsunami Amplitude (PCTA) using Green’s law (Green, 1838) takenat low depth, generally around 1 m depth (e.g. Glimsdal et al., 2019; Selva et al., 2016).

TSUMAPS-NEAM was a European project with the objective to evaluate the tsunami hazard alongthe European coastlines (TSUMAPS-NEAM, 2020). In this project, peaks offshore amplitudes werealso extrapolated to PCTAs, also using Green’s law.

One of the objectives of the French project TANDEM was to estimate the tsunami hazard alongthe French coastlines, especially in the North Eastern Atlantic Ocean and in the French Channel(TANDEM). DTHA was used on high resolution grids.

However PCTAs obtained from Green’s law approximations provide a crude approximation of waveheights at the coast only, within a factor of 2 at best (e.g. Gailler et al., 2018).Also if the results from TANDEM project are more accurate, they only consider the worst probablescenario. However, smaller events can be significant, especially since they are more frequent.

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IntroductionFinding and response

✔ Few historical tsunamis along the French Mediterranean coastlines

✔ Few earthquakes can potentially generate a significant tsunami along theFrench Mediterranean coastlines on a human scale

✘ Large coastal populations: Cannes, Nice, Marseille...

✘ non-optimal adaptation of equipment

➜ Evaluation of the hazard down to the coastal level for large return times✘ Deterministic analysis: a large but far earthquake might generate lower water

height along the French coastlines than a small and close earthquake

✓ Probabilistic Tsunami Hazard Assessement (PTHA)

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 7

We foccuse on the tsunami hazard along the French Mediterranean coastlines that is due toearthquakes.

There are few historical tsunamis and few earthquakes can potentially generate a significanttsunami along the French Mediterranean coastlines on a human scale.

This is a great thing but it can also become a danger because there are large coastal populations,such as in Cannes, Nice, especially during summer holidays, that are not aware of the danger.Moreover there are few adaptations of equipments.

It is then necessary to determine the tsunami hazard along the French Mediterranean coastlinesdown to the coastal level (beaches, harbours).

A DTHA approach is not the most adapted due to the few occurence of great events.

We then use Probabilistic Tsunami Hazard Assessment to evaluate the hazard along theFrench Mediterranean coastlines down to coastal level.

Page 10: Tsunami hazard associated to earthquakes along the French … · 2020. 5. 4. · 2. TSUMAP-NEAM project 3. TANDEM project. Sørensen et al. (2012) quantified the tsunami hazard in

Outline

1. Introduction1.1 Two recent critical events1.2 Events within the Western Mediterranean Sea1.3 Previous studies1.4 Finding and response

2. Method2.1 Seismic hazard2.2 Tsunamis2.3 From seismic hazard to PTHA

3. Results: Tsunamis impacting Cannes area (z05)3.1 Extension of the period of observation3.2 A first overview of the magnitude uncertainties

4. Conclusions and perspectives4.1 Conclusions4.2 Perspectives

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 7

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MethodProcess overview

Seismic hazard per seis-mogenic zone

PCTAs per tsunami

Scaling

factor

Seismogenic

zones

Earthquake

datasets

Earthquake

catalog

per zone

Distribution

law per zone

PTHA

Fault

dataset

PCTA

Tsunami

simulations

Rupture

catalog

per zone

Concatenation

Synchronisation

Selection

Source

combination

CLIONAmulti-grid

shalow water

Calculation of

the magnitude

distribution

Keeping PCTA

from simulation

results

Aggregation

historical

instrumental

unity segments

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 8

Here is an overview of the method we use to determine tsunami hazard, due to earthquakes, alongthe French Mediterranean coastlines.

On the left side, we determine the seismic hazard, from the collect of the data to the distributionlaw of the magnitude.This is necessary as the probability of having a tsunami with a given intensity is directly linked tothe probability of the earthquake that can triggered that tsunami.

On the right side, we determine all the probable scenarios of rupture that can trigger a tsunami andsimulate these scenarios to get the PCTAs down to the coastal level.

Whether for seismic hazard or for tsunamis scenarios, we work by seismogenic zone (more detailsare given here after).

The distribution law of the magnitude and the PCTAs arethen combined to process the PTHA.

Page 12: Tsunami hazard associated to earthquakes along the French … · 2020. 5. 4. · 2. TSUMAP-NEAM project 3. TANDEM project. Sørensen et al. (2012) quantified the tsunami hazard in

MethodSeismic hazard

Catalogue of reference

−4000−2000 0 2000 4000

Elevation

m

1 2 3 4 5 6 7 8

Seismogenic zone

Mw1

Mw2

Mw3

Mw4

Mw5

Mw6

Mw7

Mw8

Offshore and <100km inland

Other

−5°45'

−5°45'

0°00'

0°00'

5°45'

5°45'

11°30'

11°30'

34°30' 34°30'

40°15' 40°15'

250 km

✔ Synchronization of several datasets∗

❏ Completeness, Magnitudeconversion?

✔ Seismogenic zones (Sørensen et al., 2012)

❏ Accuracy, Missing zones?∗CMT, EMEC, FCAT-17, ISC, NOAA, SHARE, USGS

Distribution law (Gutenberg-Richter)

4 5 6 7

Moment magnitude (Mw)

10−4

10−3

10−2

10−1

100

101

Annual

rate

(1/yr)

no magnitude conversion

Best distribution law per seismogenic zone

z01

z02

z03

z04

z05

z06

z07

z08

✔ Magnitude of completeness

❏ Method, Parameters?

✔ Distribution law

❏ Weichert’s method: parameters?(Weichert, 1980)

Seismogenic zones†

z01 Southeastern Spainz02 Nothern Moroccoz03 Northern Algeriaz04 Northern Tunisiaz05 Ligurian Coastz06 Western Italyz07 Sicilyz08 Calabria

†Sørensen et al. (2012)

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 9

The seismic hazard is the foundation of the PTHA and thus need to be carefully determined.Indeed an inaccurate catalog will lead to inaccurate determination of the probabilities of PCTA.

We need to synchronize various databasets of earthquakes because some have historical earth-quakes but stop more than 10 years ago (FCAT-17, SHARE) and others are dayly updated but haveonly instrumental records (USGS, EMEC,...). Morever all does not span worldwilde.Despite the synchronisation of the various databases, we need to be careful of the completenessof the synchronized catalogue (time, magnitude and space).

The occurrence of earthquakes depends on the seismotectonic context; i.e. the Sicily regiontriggers more earthquakes and stronger earthquakes than the Ligurian region.Then, we split the main earthquake catalogue into sub-catalogues depending on seismogeniczones in order to determine an accurate and consistent annual rate of a moment magnitude in eachseismogenic zone.These seismogenic zones must be determined consistently with the seismic rate and the faultingregime of each zone.We use the seismogenic zones proposed in Sørensen et al. (2012).The accuracy of these zone has to be questionned.Also some areas have earthquakes but are not part of a seismogenic zone, yet.

We assume here that the magnitude of the earthquakes within each zone follow a Gutenberg-Richeter law.The law is determine using Weichert’s method (Weichert, 1980), based on the maximum likehoodbetween a model and the data.The method includes seismic rates for periods of time (period of completeness) that depend onmagnitude.

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MethodTsunamis

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 10

−4 −2 0 2

Elevation

km

1 2 3 4 5 6 7 8

Zones

Reverse faultNormal faultStrike­slip fault

−5°

−5°

10°

10°

15°

15°

35° 35°

40° 40°

45° 45°

0 125 250

A) CENALT fault database

B) Rupture combination(Gailler et al., 2013)

−0.5

−0.4

−0.3

−0.2

−0.1

0.0

0.1

0.2

0.3

0.4

Wa

ter

ele

va

tio

n [

m]

0 20 40 60 80 100 120

Propatation time [min]

cannes [6.9810°E; 43.5438°N; ­201m]

hmax on crude gr id: 0.46m

hmax­apriori (z=1m):1.73m

C) Simulation on crude grid

0 2 4 6 8 10 12 14 16max(h_simu) [cm]

0

20

40

60

80

h_sim

u>=h

thr[1

cm] [

%]

h_thr=1cm

5cm

10 scenarios148 scenarios

(15cm,72%)

Scenarios having h_apriori<1cm but having max(h_simu)>=1cmZone z05

D) Selection ofsignificative eventsusing Green’s law

E) High resolution simulationsz05-001577-74-3u

6°57'

6°57'

7°00'

7°00'

7°03'

7°03'

43°30' 43°30'

43°33' 43°33'

43°36' 43°36'

0 1 2 3 4 5

Maximum water elevation

m

F) Peak Coastal Tsunami Amplitudes

z05-001577-74-3u

6°57'

6°57'

7°00'

7°00'

7°03'

7°03'

43°30'

43°30'

43°33'

43°33'

43°36'

43°36'

12

34

56

hm

ax

0

2

4

6

Maximum water elevation

m

(1) (2)

(3)

(4)

(5)

(A) We use the fault database of the French Tsunami Warning Center (CENALT) to build a cata-logue of ruptures. The fault database consists in a unit source function system which follow themajor structural trends of the Western Mediterranean basin seismogenic context (Gailler et al.,2013).

(B) We combine unit sources to build a rupture (20 km wide, 25 km length, 1 m slip, Gailler et al.(2013)).Lengths and widths of combined unit sources follow Wells and Coppersmith (1994) laws (fixingL = 200 km for Mw = 8.0) and the slip is scaled by a factor Fs in order to fit the moment magnitudeMw .The combination is controlled geometrically by the distance between two unit sources and theazimuth difference between these two sources. The distance between two faults is set between18.5 km and 37.5 km and the azimuth difference is set lower than 40◦.The available combinations of unit source in a seismogenic zone give the maximum moment mag-nitude in the zone.

(C) A first tsunami simulation of each rupture is done in a crude grid in order to collect Peak Off-shore Tsunami Amplitde (POTA) where the water depth is ∼100 m (CLIONA code, CEA). We thenuse the Green’s law (Green, 1838) to extrapolate each POTA to an a priori PCTA hmaxapriori (PCTA).

(D) We then select all rupture for which hmaxapriori is greater than or equal to 1 cm. This reducesthe number of high-resolution simulation to do, and thus reduces the computational time. Thismethod of selection was configure using high-resolution simulations, on Cannes area, of all rupturesin the Ligurian zone (z05), for magnitudes between 5.5 and 7.4.

(E) We run CLIONA code (CEA, e.g. A.Poupardin et al., 2018) using shallow water equations andnested-grid resolution down to the coastal level (10 m) for each rupture selected in (D). The lengthof the simulation is adapted for each seismogenic zone, here again to reduce the computational time.

(F) Last step, here consists in collecting the PCTAs. The resultant files are smaller and easier touse than grids.

Page 14: Tsunami hazard associated to earthquakes along the French … · 2020. 5. 4. · 2. TSUMAP-NEAM project 3. TANDEM project. Sørensen et al. (2012) quantified the tsunami hazard in

MethodFrom seismic hazard to PTHA

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 11

A) Seismic hazard

4 5 6 7

Moment magnitude (Mw)

10−4

10−3

10−2

10−1

100

101

Annual

rate

(1/yr)

no magnitude conversion

Best distribution law per seismogenic zone

z01

z02

z03

z04

z05

z06

z07

z08

B) Tsunamis

z05-001577-74-3u

6°57'

6°57'

7°00'

7°00'

7°03'

7°03'

43°30'

43°30'

43°33'

43°33'

43°36'

43°36'

12

34

56

hm

ax

0

2

4

6

Maximum water elevation

m

C) Probability of occurence of a rupture scenario

Pi =–

`

Mwi

´

Nscenario

`

Mwi

´

D) Probability of exceedance of a PCTA at a site of referecence

P`

(x , y )ref , PCTAref

´

=P

iPi

`

(x , y )ref , PCTA ≥ PCTAref

´

E) Hazard maps

2500-year return period

6°57'

6°57'

7°00'

7°00'

7°03'

7°03'

43°30'

43°30'

43°33'

43°33'

43°36'

43°36'

−1000−500

0Elevation

m

3060

9012

015

0

hmax

[cm

]

030 60 90 120 150

hmax

cm

Source zone: z05. Period of

observation to do the PTHA:

10000yr. Number of scenarii:

1577 scenarios. Number of

earthquakes: 80 earthquakes.

2020-04-08 14:26:37

F) Probability maps

50cm in a 2500-year return period

6°57'

6°57'

7°00'

7°00'

7°03'

7°03'

43°30'

43°30'

43°33'

43°33'

43°36'

43°36'

−1000−500

0Elevation

m

2040

6080

100

Pro

babi

lity

[%]

020 40 60 80 100

Probability

%

Source zone: z05. Period of

observation to do the PTHA:

10000yr. Number of scenarii:

1577 scenarios. Number of

earthquakes: 80 earthquakes.

2020-04-08 14:13:00

PTHA

(C) The annual probability P of each scenario i , during the period T , is given by the (A) annualrate of its moment magnitude Mw which is determined from the distribution law and by the (B)number of probable scenarios that can generate an earthquake of magnitude Mw .

The annual probability of each PCTA is equal tothe annual probability of its rupture scenario.

(D) The annual probability of exceeding a PCTA, at each place, is computed by aggregation ofany rupture scenario that can exceed a given PCTA, such that the annual probability is the sum ofthe annual probability of each rupture scenario triggering a tsunami that exceeds the chosen PCTAat the chosen place.

We can use these annual rates and this probabilities to plot (E) hazard maps, which give the maxi-mum water elevation in a return period, or to plot (F) probability maps, which show the probabilityof experiment a water elevation during a return pediod. Probability curves can also be given.

Page 15: Tsunami hazard associated to earthquakes along the French … · 2020. 5. 4. · 2. TSUMAP-NEAM project 3. TANDEM project. Sørensen et al. (2012) quantified the tsunami hazard in

Outline

1. Introduction1.1 Two recent critical events1.2 Events within the Western Mediterranean Sea1.3 Previous studies1.4 Finding and response

2. Method2.1 Seismic hazard2.2 Tsunamis2.3 From seismic hazard to PTHA

3. Results: Tsunamis impacting Cannes area (z05)3.1 Extension of the period of observation3.2 A first overview of the magnitude uncertainties

4. Conclusions and perspectives4.1 Conclusions4.2 Perspectives

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 11

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Results: Tsunamis impacting Cannes area (z05)Extension of the period of observation

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 12

1a) Hazard map using recorded events

500-year return period

6°57'

6°57'

7°00'

7°00'

7°03'

7°03'

43°30'

43°30'

43°33'

43°33'

43°36'

43°36'

−1000−500

0Elevation

m

2040

6080

100

hmax

[cm

]

020 40 60 80 100

hmax

cm

Source zone: z05. Period of

observation to do the PTHA:

827yr. Number of scenarii: 1

1

s c e n a r i o s . N u m b e r o f

earthquakes: 4 earthquakes.

2020-04-08 15:51:25

1b) Probability map using recorded events

20cm in a 500-year return period

6°57'

6°57'

7°00'

7°00'

7°03'

7°03'

43°30'

43°30'

43°33'

43°33'

43°36'

43°36'

−1000−500

0Elevation

m

2040

6080

100

Pro

babi

lity

[%]

020 40 60 80 100

Probability

%

Source zone: z05. Period of

observation to do the PTHA:

827yr. Number of scenarii: 1

1

s c e n a r i o s . N u m b e r o f

earthquakes: 4 earthquakes.

2020-04-08 15:55:30

2a) Hazard map using synthetic events

500-year return period

6°57'

6°57'

7°00'

7°00'

7°03'

7°03'

43°30'

43°30'

43°33'

43°33'

43°36'

43°36'

−1000−500

0Elevation

m

2040

6080

100

hmax

[cm

]

020 40 60 80 100

hmax

cm

Source zone: z05. Period of

observation to do the PTHA:

10000yr. Number of scenarii:

1112 scenarios. Number of

earthquakes: 36 earthquakes.

2020-04-08 16:35:57

2b) Probability map using synthetic events

20cm in a 500-year return period

6°57'

6°57'

7°00'

7°00'

7°03'

7°03'

43°30'

43°30'

43°33'

43°33'

43°36'

43°36'

−1000−500

0Elevation

m

2040

6080

100

Pro

babi

lity

[%]

020 40 60 80 100

Probability

%

Source zone: z05. Period of

observation to do the PTHA:

10000yr. Number of scenarii:

1112 scenarios. Number of

earthquakes: 36 earthquakes.

2020-04-08 16:46:38

43° 43°

44° 44°

z05

Cannes area

Mw6.1 (1644)

Mw6.3 (1854)

Mw6.7 (1887)

Mw6.3 (1963)

Historical earthquakes (Mw>6.0)

Recorded earthquakes

We now present some results of the PTHA along the coastlines in Cannes city area.

Earthquakes sources are located in the Ligurian Sea (z05). High-resolution simulations from otherseismogenic zones are not finished yet.

The hazard maps for a 500yr return period are shown on the left side, and the probabilityto experiment at least 1 tsunamic wave having hmax ≥ 20 cm in a 500yr return period onthe probability maps on the right side.At the top, results are given using only the 4 earthquakes, with Mw ≥ 6.0, recorded in thereal period of observation of 827yr. The 4 earthquakes are shown in the centered map.At the bottom, results are given for the 36 earthquakes of Mw ≥ 6.0 that can occur duringan extended period of observation of 10 000yr. This number of earthquakes is obtainedusing the distribution law (MBS+Weichert, dM0.2, dy1).11 scenarios correspond to the 4 recorded earthquakes, 1112 scenarios can generateearthquakes of Mw ≥ 6.0 in the Ligurian Sea seismogenic zone.

Looking at the hazard maps, we observe that the maximum water elevation is quite similar whetherwe choose to use the (1a) real period of observation or the (2a) extended period of observation.However, the probability of experiment at least one wave height equal to or greater than 20 cm in a500yr return period is different whether we choose to use the (1b) real period of observation or the(2b) extended period of observation.

Indeed the extension of the period of observation allows the model to take into account much moreprobable scenarios.

This first result illustrates that hazard maps are notself-suficiant to describe the tsunami hazard.

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Results: Tsunamis impacting Cannes area (z05)Extension of the period of observation

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 12

3a) Hazard map using recorded events

2500-year return period

6°57'

6°57'

7°00'

7°00'

7°03'

7°03'

43°30'

43°30'

43°33'

43°33'

43°36'

43°36'

−1000−500

0Elevation

m

2040

6080

100

hmax

[cm

]

020 40 60 80 100

hmax

cm

Source zone: z05. Period of

observation to do the PTHA:

827yr. Number of scenarii: 1

1

s c e n a r i o s . N u m b e r o f

earthquakes: 4 earthquakes.

2020-04-08 15:51:25

3b) Probability map using recorded events

50cm in a 2500-year return period

6°57'

6°57'

7°00'

7°00'

7°03'

7°03'

43°30'

43°30'

43°33'

43°33'

43°36'

43°36'

−1000−500

0Elevation

m

2040

6080

100

Pro

babi

lity

[%]

020 40 60 80 100

Probability

%

Source zone: z05. Period of

observation to do the PTHA:

827yr. Number of scenarii: 1

1

s c e n a r i o s . N u m b e r o f

earthquakes: 4 earthquakes.

2020-04-08 15:55:30

4a) Hazard map using synthetic events

2500-year return period

6°57'

6°57'

7°00'

7°00'

7°03'

7°03'

43°30'

43°30'

43°33'

43°33'

43°36'

43°36'

−1000−500

0Elevation

m

2040

6080

100

hmax

[cm

]

020 40 60 80 100

hmax

cm

Source zone: z05. Period of

observation to do the PTHA:

10000yr. Number of scenarii:

1112 scenarios. Number of

earthquakes: 36 earthquakes.

2020-04-08 16:35:57

4b) Probability map using synthetic events

50cm in a 2500-year return period

6°57'

6°57'

7°00'

7°00'

7°03'

7°03'

43°30'

43°30'

43°33'

43°33'

43°36'

43°36'

−1000−500

0Elevation

m

2040

6080

100

Pro

babi

lity

[%]

020 40 60 80 100

Probability

%

Source zone: z05. Period of

observation to do the PTHA:

10000yr. Number of scenarii:

1112 scenarios. Number of

earthquakes: 36 earthquakes.

2020-04-08 16:46:38

43° 43°

44° 44°

z05

Cannes area

Mw6.1 (1644)

Mw6.3 (1854)

Mw6.7 (1887)

Mw6.3 (1963)

Historical earthquakes (Mw>6.0)

Recorded earthquakes

We now increase the length of the return time of the analysis from 500yr to 2500yr.

The hazard maps for a 2500yr return period are shown on the left side, and the probabilityto experiment at least 1 tsunamic wave having hmax ≥ 50 cm in a 2500yr return periodon the probability maps on the right side.At the top, results are given using only the 4 earthquakes, with Mw ≥ 6.0, recorded in thereal period of observation of 827yr. The 4 earthquakes are shown in the centered map.At the bottom, results are given for the 36 earthquakes of Mw ≥ 6.0 that can occur duringan extended period of observation of 10 000yr. This number of earthquakes is obtainedusing the distribution law (MBS+Weichert, dM0.2, dy1).11 scenarios correspond to the 4 recorded earthquakes, 1112 scenarios can generateearthquakes of Mw ≥ 6.0 in the Ligurian Sea seismogenic zone.

Here the hazard maps are different whether we are looking at (3a) real period of observation or (4a)the extended period of observation.Indeed, the return time is now greater than the period of observation. It is then a non-sens tolook at the results from the real period of observation.The maximum water elevation is here biased because the same 11 scenarios are repeated hereto reach the 2500yr return period instead of creating earthquakes elsewhere in the seismogeniczone.

This also leads to inconsistent probabilities. Indeed according to the (3b) probability map, thereis almost no-probability to experiment a 50 cm in a 2500yr when considering only the recordedearhtquakes.Yet, when we look at the (4b) probability map when using the extended period of observation, theprobabiliy to experiment a 50 cm in a 2500yr is rarely lower than 30 %.

The bias induded by the period of observation can have a great impact on the PTHA and thuson civil and building engineering.

It is then necessary to enlarge the period of observation using distribution laws.

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Results: Tsunamis impacting Cannes area (z05)A first overview of the magnitude uncertainties

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 13

×100or more

Adding uncertainties tothe magnitude

Processing PTHA

Aggregation

We want to look at the sensibility of the model due to the uncertainty on magnitudes.

We then duplicate, let’s say 100 times, the catalogue of reference and add an uncertainty on themagnitude of each record.The uncertainty is added following a normal law where the mean is the recorded magnitude and thestandard deviation is the error on the magnitude. Here we have choosen a 0.2 uncertainty.

We then process the PTHA for each duplicated catalogue as described in the method section.

Finally, we aggregate the results.

In this example we choose to show the results as hazard curves.

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Results: Tsunamis impacting Cannes area (z05)A first overview of the magnitude uncertaintiesAggregation

CaseAnnual Probability of

probability (%) experiment1 (%)

Reference 5.72 94.74Mean 9.65 99.37

2nd percentile 5.72 94.7416th percentile 5.94 95.32Median 6.98 97.3284th percentile 13.60 99.9398th percentile 15.40 99.98

1Probability of experiment at least one wave tsunamiequal to or greater than 1 m in a 50-year return period.

✔ Annual probability of exceedance of amaximum water elevation at any placealong the coastline

➟ Work in progress...

➟ Annual probability of exceedance of amaximum water elevation at a chosenplace along the coastline

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At the top left, the curves in the show the annual probability of exceedance of a PCTA at anyplace along the coastlines of the studied area.

Each grey curve show the results from 1 duplicated catalogue.The cyan curve show the results from the catalogue of reference.The blue and red curves show the mean and mediane hazard curves, respectively, fromall the duplicated catalogues and the catatalogue of reference.

The median curve show that the probability to experiment a 1 m PCTA anywhere in the Gulf of LaNapoule (Cannes city area) in a 50-year return period is ∼97.32 %1 (annual probability of∼6.98 %).In the present case, it increases the probability in regards of the probability we would have usingonly the catalogue of reference (∼94.74 %, annual probability of∼5.72 %).

This work is still in progress, but a particular place could have been chosen to study the sensibilitydue to uncertainties on the magnitudes.

Sensibility analyses can also be done on other parameters during the PTHA process. Suchas the choice of the method to determine the distribution laws.

1P = 1 − (1 − pannual)T

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Outline

1. Introduction1.1 Two recent critical events1.2 Events within the Western Mediterranean Sea1.3 Previous studies1.4 Finding and response

2. Method2.1 Seismic hazard2.2 Tsunamis2.3 From seismic hazard to PTHA

3. Results: Tsunamis impacting Cannes area (z05)3.1 Extension of the period of observation3.2 A first overview of the magnitude uncertainties

4. Conclusions and perspectives4.1 Conclusions4.2 Perspectives

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 13

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Conclusions

Current results: Tsunami-earthquakes from Ligurian Sea impacting Cannes area

✓ Needs of synthetic catalog to improve the analysis

✓ Probability of experiment a 1 m PCTA anywhere in the Gulf of La Napoule in a 50-year return period❏ ∼94.7 % when considering no uncertainty on the magnitude❏ ∼97.3 % when considering uncertainties on the magnitude (median curve)

➟ Simulations in progress

Challenges

❏ Large amount of data to manage Earthquake entries, Results of the tsunami, Aggregation of the results

❏ Many uncertainties to take into accounts at different steps of the analysis Earthquake parameters, Distribution law,

Rupture scenarios, Tsunami simulations

❏ High number of high-resolution simulations: long computational time

Our answers

❏ Semi-automatic processing with structured data hierarchy (➟ work in progress)

❏ Sensibility analysis (➟ work in progress)

❏ Reduction of the number of the high-resolution simulations using Green’s law on low-resolutionsimulations (hmaxapriori)

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 14

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Perspectives

PTHA

❏ Highlighting the areas that can be the most affected at the level of a municipality

❏ Tracking the most threatening areas (deaggregation)

Other high-resolution maps (10 m)

❏ Antibes [5]

❏ Bandol [3]

❏ Leucate [1]

❏ Nice [6]

❏ Sete [2]2°

41° 41°

42° 42°

43° 43°

44° 44°

−2000 0 2000

Elevation

m

A

B1B2

B3

1

2

3

45

6

Application to the North Atlantic French coastlines

❏ Increase of the quantity of data

❏ Increase of the time of propagation to simulate

❏ Increase of the number of simulations

Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 15

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DE LA RECHERCHE À L’INDUSTRIE [EGU2020-5554]

Thank you for your attention.

6 May, 2020

E.G.U. General Assembly 2020 Viviane Souty & Audrey Gailler

Commissariat à l’énergie atomique et aux énergies renouvelables – www.cea.fr

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Commissariat à l’énergie atomique et aux énergies renouvelables Souty & Gailler | EGU2020-5554 | page 17