The dataset shows earthquake intensity zones in accordance with the 1956 version of the Modified Mercalli Scale (MM). The intensity describes exclusively the effects of an earthquake on the surface of the earth and integrates numerous parameters (such as ground acceleration, duration of an earthquake, subsoil effects). It also includes historical earthquake reports. The risk grading is based on expectations for a period of 50 years, corresponding to the mean service life of modern buildings. The probability that degrees of intensity shown on the map will be exceeded in 50 years is 20 per cent. This probability figure varies with time; i.e., it is lower for shorter periods and higher for longer periods.
In ARC/INFO, the item ZONE in the polygon attribute table (PAT) contains the following earthquake intensity values:
Zone Probable maximum intensity once in 50 years (MM Scale)
0 V and below
1 VI
2 VII
3 VIII
4 IX and above
10 indicates main waterbodies