Seismic hazard describes the ground shaking level which can be produced by an earthquake. Seismic hazard assessment is thus the basic action to assess the actual risk.
The four basic elements of modern Probabilistic Seismic Hazards Assessment (PSHA) are:
- Earthquake catalogue: a catalogue of seismicity is created for earthquakes occurred in historical (before 1900) and instrumental (after 1900) periods of earthquake documentation and recording;
- Earthquake source characterization: it implies the definition of zones with similar seismic behaviour and space/time sequence of earthquakes (frequency, depth, focus);
- Strong seismic ground motion: studying ground shaking in relation to the distance to the source (hypocentre) generates as an output the macroseismic maps which describe the damages occurred during the different earthquakes;
- Computation of seismic hazard: calculation of the probability that an earthquake occurs in a given area.
The main effort to assess seismic hazard worldwide was made by the Global Seismic Hazard Assessment Program (GSHAP) launched in 1992 by the International Lithosphere Program (ILP) with the support of the International Council of Scientific Unions (ICSU) and endorsed as a demonstration program in the framework of the United Nations International Decade for Natural Disaster Reduction (UN/IDNDR).
The primary goal of GSHAP was to create a global seismic hazard map in a harmonized and regionally coordinated manner, based on advanced methods in probabilistic seismic hazard assessments (PSHA).
The GSHAP strategy was to establish Regional Centres responsible for the coordination and realization of the four basic elements of modern PSHA mentioned above. Website: http://www.seismo.ethz.ch/GSHAP/