## Rationale

A Grid of 10184 points has been defined on the basis of historical Tsunamis. The magnitudes selected range from 6.5 to 9.5 in steps of 0.25 (see Grid Development Methodology outlined below).

- To access the JRC Tsunami Grid Database: Grid Database
*(user/password required)* - For a higher resolution image of the grid: Click here (2.4 Mbytes)
- For a Google Earth visualization of the grid: Click here

The completion status of the grid calculations is shown in the table below.

## Grid Development Methodology

When a new seismic event occurs the known parameters are the position (lat/lon) and the magnitude. Later on (after some hours) also the fault form can be estimated by the composition of various p-wave seismic signals. Using the procedure outlined in the JRC on-line calculation system, the magnitude is extremely sensible for the results because it determines the fault form (width, length and height) which is then translated as initial condition for the Tsunami wave. It was shown that moving the epicenter location by 50 km, for relatively mild Tsunamis, may affect strongly the locations to be alerted (since the objective of the calculation tool is the identification of the locations which may be affected by dangerous wave heights).

The above considerations suggested to define a uniform grid of 0.5 degrees, corresponding to about 55 km to be considered as possible source of Tsunami. Considering the need to perform one calculation for each magnitude from 6.5 to 9.5 in steps of 0.25, it is easy to show that this corresponds to about 2.3 10^{6} calculations [1] Considering the maximum current calculation volume at JRC (500 calcs/day on 15 computers with peaks of 1300 calcs/day on 20 computers), it would mean 12 years of calculation time, which, of course, is not acceptable.

A method to reduce the number of calculations to a more reasonable number is to consider the historical Tsunamis and use these locations as possible Tsunami sources. The NOAA NGDC database reports the historical Tsunami sources and contains about 2300 sources data points. Selecting every data point in the database and building a regular grid (10x10) around each data point it is possible to build up a reduced not-uniform grid in which, most probably every new Tsunami source location will fall. If new Tsunami will not fall into the grid, it will be possible periodically to update the grid to include new data points.

In these conditions the number of data points reduces to 10185 for the whole world. Considering the current JRC capacity of calculations, the overall number of Tsunami calculations (132405) should be completed in about 8-9 months, thus in March-April 2008. The tables on the top show the current status of the calculations.

[1] Npoints=180x360/(0.5^{2}) =181440. Considering 30% of earth in the globe and the need to perform 13 magnitude calculations (one every 0.25 from 6.5 to 9.5), this corresponds to: 181440*0.7*13=2 358 720