.. _ch:tsunamis:

Tsunami Simulations
===================

This part of our project conducts simulations of the March 11, 2011, M 9.1 Tohoku and the February 27, 2010 M 8.8 Chile tsunami events.
Details on historic tsunami events are available from the `NOAA/WDS Global Historical Tsunami Database at NGDC <https://www.ngdc.noaa.gov/hazard/tsu_db.shtml>`__.

.. figure:: data_6/cut.png
   :name: fig:cut

   Visualization of a vertical cut through the epicenter of the March 11, 2011, M 9.1 Tohoku earthquake event and Sõma.
   The bathymetry data was extracted from the GEBCO_08 Grid.

For our simulations, we use the respective epicenter as projection center for our map projections.
In preprocessing\ [1]_ the map projections project the data, typically given in terms of a reference ellipsoid, to a planar domain.
Using the epicenter as projection center reduces distortions of the used cylindrical map projection (transverse Mercator) in the vicinity of the epicenter.
Additionally, we use a scale factor of 0.9996 following the UTM mapping system.

For both events, preprocessed input data in the form of binary netCDF-files are `provided <https://cloud.uni-jena.de/s/CqrDBqiMyKComPc>`__.
As an example, :numref:`fig:cut` illustrates the bathymetry data for the Tohoku event.

.. [1]
   Details on the used preprocessing configurations are available from:
   https://github.com/breuera/tsunami/tree/master/geo_information/scripts/configs

.. _ch:tsunami_chile:

2010 M 8.8 Chile Event
----------------------

Bathymetry and displacement data for the February 27, 2010 `M 8.8 Chile earthquake and tsunami event <https://nctr.pmel.noaa.gov/chile20100227/>`__ are available as part of the provided archive.
You should be able to read them with :numref:`sec:netcdf input`'s ``setup::TsunamiEvent2d``.

.. admonition:: Tasks

   #. Make yourself familiar with the input data and visualize it.
   #. Simulate the tsunami event and visualize the output.
      Use different grid resolutions, e.g., 1,000m, 500m or 250m, and outflow boundaries for your simulations.

      *  How long (simulated time) do you have to run the simulations until the first waves leave your computational domain?
      *  What are the computational demands of your simulations (number of required cells and cell updates)?

      **Hint**: Use proper color maps for visualizing the bathymetry, e.g., the `ParaView XML color maps (converted from GMT) <https://www.earthmodels.org/date-and-tools/color-tables>`__.
      Note, newer ParaView versions additionally require wrapping the color maps in the XML-tag ``ColorMaps``.

.. _ch:tsunami_tohoku:

2011 M 9.1 Tohoku Event
-----------------------
Analogue to :numref:`ch:tsunami_chile`, bathymetry and displacement for the March 11, 2011, `M 9.1 Tohoku earthquake and tsunami event <https://nctr.pmel.noaa.gov/honshu20110311/>`__ are available in the linked archive.

.. admonition:: Tasks

   #. Simulate the tsunami event and visualize the output.
      Use different grid resolutions and outflow boundaries for your simulation.

      *  How long (simulated time) do you have to run the simulation until the first waves leave your computational domain?
      *  What are the computational demands of your simulations (number of required cells and cell updates)?

   #. Sõma is a town in Japan about 55 km south and 128 km west of the March 11, 2011, M 9.1 Tohoku event's epicenter.
      We are interested in the time between the earthquake rupture and the arrival of the first tsunami waves in Sõma.

      *  Find measured data for Sõma for the March 11, 2011, M 9.1 Tohoku earthquake and tsunami event.
      *  A cut (see :numref:`fig:cut`) of the bathymetry is located at the linked `location <https://scalable.uni-jena.de/assets/tsunami_lab/soma_epicenter_tohoku_2011_bathymetry.csv>`__.
         ``Points:0`` and ``Points:1`` are the :math:`x` and :math:`y` coordinates and ``z`` is the corresponding value for the bathymetry.
         The cut contains Sõma and the epicenter.
         Use the following rule of thumb to approximate the wave speed :math:`\lambda` and the travel time until the first waves reach Sõma:

         .. math:: \lambda \approx \sqrt{gh}

      * Add a station close to Sõma and measure the :math:`h`, :math:`hu` and :math:`hv` over time. Compare the results with your simulated tsunami arrival times.