EGU General Assembly 2020
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the Creative Commons Attribution 4.0 License.

Tsunami hazard associated to earthquakes along the French coasts. A probabilistic approach (PTHA).

Viviane Souty and Audrey Gailler
Viviane Souty and Audrey Gailler
  • CEA, DAM, DIF, 91297 Arpajon Cedex, France

Probabilistic Tsunami Hazard Assessment (PTHA) is a fundamental tool for producing time-independent forecasts of tsunami hazards at the coast using data from tsunami generated by local, regional and distant earthquake source. If high resolution bathymetry and topography data at the shoreline are available, local tsunami inundation models can be developed to identify the highest risk areas and derive evidence-based evacuation plans to improve community safety.
This study takes part of the H2020-Euratom NARSIS project (2017-2021), which aims at making significant scientific updates of some elements required for the Probabilistic Safety Assessment, focusing on external natural events (earthquake, tsunami, flooding, high speed winds...). In this framework, we are developing a PTHA approach to estimate the tsunami hazard along the French Mediterranean coasts at a local level. The probability of occurrence of tsunamigenic earthquakes is the foundation of our work as wrong probabilities would lead to a wrong evaluation of the tsunami hazard. We first discuss the various uncertainties from the determination of the tsunami sources to the simulation of the propagation of the tsunami to the coast. We then present the results of tsunami hazard in the city of Cannes (French Riviera).

How to cite: Souty, V. and Gailler, A.: Tsunami hazard associated to earthquakes along the French coasts. A probabilistic approach (PTHA)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5554,, 2020

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Presentation version 1 – uploaded on 04 May 2020
  • CC1: Comment on EGU2020-5554, Yu-Chun Chang, 06 May 2020

    Hi Viviane

    Very great and informative work. Part of my works is also relevant to tsunami-height estimate but in the active volcanic islands in the Azores.  

    As Green's law was applied in part of your reserach, I was wondering how the ~100m water depth of POTA was determined? Is it becasue those events with risky potential occurred at such a non-deep zone? I also would like to know how you decide the water depth of PCTA. Did you use a constant shallow value or depends on the in-stu configuration? If the latter, how do you evaluate?

    Many thanks for your time.

    Yu-Chun (U of Manchester)  

    • AC1: Reply to CC1, Viviane Souty, 06 May 2020

      Hello Yu-Chun,

      I thank you for your interest.

      I am not sure I understand well your question.

      In fact I introduced the selection using the extrapolation of the POTA to PCTA very late. For now the point of reference is choosen manually, looking for a place where the water depth is about 100m. It is seems to be common depth used for extrapolations (e.g. Grezio et al. 2020, Lorito et al. 2015) but is not a rule. I think it depends on what you are looking for.

      The water depth of the PCTA of the selection (used to calculate hmax_apriori) is also chosen from common use. This remains subjective but has little impacts on my final results as my threshold to compute high resolution simulation is low. The threshold of hmax_apriori=1cm works well for earhquake-tsunami from the Ligurian (z05)  zone (only 10 scenarios have water heights exceeding 5cm along Cannes coastlines using high resolution simulations, there might be one or two places over the ~ 500 places). This 1cm threshold also works perfectly for tsunami-earthquakes from the North Algerian (z03) zone (not any high resolution simulation having water heights exceeding 5cm).

      PCTAs on high resolution simulations are taken for a 0-meter water depth.

      I hope I have answered your questions. Do not hesitate to contact me again.


      • CC2: Reply to AC1, Yu-Chun Chang, 06 May 2020

        Hello Viviane

        Thanks for your explanation. Perhaps I can describe a bit more about my question. 

        I have simulated tsunami wave-heights at source (triggered by submarine landslide), where the water depth of the headscarp or center of mass should be deep to 300-500 meter. I would like to have a quick test based on Green's law [A1/A2 =  (h2/h1)^0.25 * (B2/B1)^0.5] first to make a quick order guess about how high it could be once propagate to the coast line.

        If the width doesn't change so much as laoctaed at the open coast (?), can I directly covert the wave-height change from the source (300m) to the coast line (1m or lower?) based on the Green's law ? 

        Sorry I am not expert with this so you can see I still put some questions marks on the number I used. If I misunderstand the application way, please could you correct me. 

        Thanks again.

        • AC2: Reply to CC2, Viviane Souty, 07 May 2020

          Hello Yu-Chun

          The depth where to take the POTA and PCTAs should be adapted to the geometry of your sites and the resolution of the bathymetry you are working with.  There is no rule. Just try and check with a representative set of testing scenarios.

          You can look at this poster and the references inside to get more understanding. Be careful that the Green's law for tsunami-earthquakes might not work for tsunami-landslides.