Portugal - Atlas do Ambiente I.10 - Intensidade Sísmica

Summary

The modern research dealing with the constitution of the interior of the Globe has revealed three main divisions: the terrestrial crust, the rocky mantle, and the central core composed of a fluid outer core and a solid inner Core. At the moment, the methods generally in use for geophvysical prospects are the gravimetrical, magnetical, electrical and radioactive ones. All of them are very important to geology for the detection of minerals, and to engineering for the emplacement of structural foundations, such as dams, bridges and viaducts. Within the geophysical methods the seismic prospects deserve a particular interest. The region inside the Globe where a seism takes place is named the hvypocentre and the correspondent point on the surface, the epicentre. The Wood-Neumann seale 18 the seismological scale generally in use. Such a seale of nwelve «seismical intensity» degrees was the one used for caracterizing the zones of maximum seismical intensity in Portugal. The effects of seisms ever affect and disturb the human environment, but the catastrophic ones affect and disturb the natural environmentitself. To minimize the seismical effects a search is on the way to find out a method to forecast the exact moment of oceurence of the phenomenon. The experts believe however that we are still very far away from sucha goal. In the Chart of the maximum seismical intensity zones, observed in the maintand of Portugal from 1901 to 1972, the isoseismals are drawn up aceordingto tie Wood-N