Earthquake prediction is not possible as current scientific studies include activities aiming to understand the mechanisms of seismicity and to assess the probability of an earthquake in a given area, with a given magnitude and in a given time period; an earthquake prediction is thus only possible in probabilistic terms.
Based on the relevant studies in this field, we know:
- Where seismic areas are localised;
- the most dangerous earthquakes experienced historically in such areas;
- the most energetic (magnitude) earthquakes in the areas;
- the type of earthquake sequence typical for different areas (i.e. the seismic style);
- the seismic pattern and sequences over the time in the different areas.
However, we often still don’t know:
- Where exactly the next earthquake will occur (ipocentre / epicentre).
- When exactly the next earthquake will strike.
- Which will be the energy released (magnitude).
- Which will be the preferred diffusion direction of the waves (as underground rocks have different composition, mechanic behaviour, etc.).
- Which will be the surface site effects (due to surface rocks and morphological conditions).
The assessments and evaluations of seismic risk are mainly based on:
- the study of the dynamics of the geological system in the area;
- the study of the seismic history for that area (number, type, impact of earthquakes in pre-historical and historical times up today);
- the assessment of the probability of different earthquake magnitudes and impacts;
- the identification and detailed analysis of areas and sites at risk;
- the study of the quality and quantity of buildings and of the other exposed elements (industries, social activities) in order to assess their vulnerability to Earthquake and their exposed value.
The search for safety in seismic areas also uses tools to simulate earthquakes of different nature and violence to estimate consequent losses. Loss estimates should include the following main elements of knowledge:
- physical damage expected for buildings of different nature (commercial, schools, residential, critical facilities, infrastructure and lifelines);
- economic losses deriving from job loss, business interruption, costs for repair and reconstruction;
- social consequences for people exposed to earthquakes: displaced people need shelter for the first emergency.
Such pre-disaster estimates are very important to develop mitigation policies and prepare the civil protection organization for emergency, response and recovery.
Nevertheless, there are experimental projects aimed at trying to predict short term earthquakes. One of those is the recent “INGV-DPC Project S3” developed in the framework of the agreement between the Italian National Department of Civil Protection (DPC) and the Italian National Institute for Geophysics and Volcanology (INGV). Its goal is to identify and evaluate effective procedures for short term (from hours up to some months) forecasting of destructive earthquakes (see the project’s web page for more details).
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/