EUROPEAN-MEDITERRANEAN SEISMIC HAZARD MAP
European Seismological Commission
UNESCO-IUGS International Geological Correlation Program Project no. 382 SESAME
Editors: D. Giardini, M.-J. Jiménez and G. Grünthal
Seismic hazard is defined as the probable level of ground shaking associated with the recurrence of earthquakes. The assessment of seismic hazard is the first step in the evaluation of seismic risk, obtained by combining the seismic hazard with local soil conditions and with vulnerability factors (type, value and age of buildings and infrastructures, population density, land use). Frequent, large earthquakes in remote areas result in high seismic hazard but pose no risk; on the contrary, moderate earthquakes in densely populated areas entail small hazard but high risk.
Minimization of the loss of life, property damage, and social and economic disruption due to earthquakes depends on reliable estimates of seismic hazard. National, state and local governments, decision makers, engineers, planners, emergency response organizations, builders, universities, and the general public require seismic hazard estimates for land use planning, improved building design and construction (including adoption of building codes), emergency response preparedness plans, economic forecasts, housing and employment decisions, and many more types of risk mitigation.
The basic elements of modern probabilistic seismic hazard assessment can be grouped into four main categories:
1. Earthquake Catalogue: the compilation of a uniform database and catalogue of seismicity for the historical (pre-1900), early-instrumental (1900-1964) and instrumental periods (1964-today).
2. Earthquake Source Model: the creation of a master seismic source model to describe the spatial-temporal distribution of earthquakes, integrating the earthquake history with evidence from seismotectonics, paleoseismology, mapping of active faults, geodesy and geodynamic modeling.
3. Strong Seismic Ground Motion: the evaluation of ground shaking as a function of earthquake size and distance, taking into account propagation effects in different tectonic and structural environments.
4. Seismic Hazard: the computation of the probability of occurrence of ground shaking in a given time period, to produce maps of seismic hazard and related uncertainties at appropriate scales.
Seismic hazard depicts the levels of chosen ground motions that likely will, or will not, be exceeded in specified exposure times. Hazard maps commonly specify a 10% chance of exceedance (90% chance of non-exceedance) of some ground motion parameter for an exposure time of 50 years, corresponding to a return period of 475 years. This map depicts Peak Ground Acceleration (PGA) with a 10% chance of exceedance in 50 years for a firm soil condition. PGA, a short-period ground motion parameter that is proportional to force, is the most commonly mapped ground motion parameter because current building codes that include seismic provisions specify the horizontal force a building should be able to withstand during an earthquake. Short-period ground motions affect structures with corresponding short-period resonance vibrations (e.g. one-to-three story buildings, the largest class of structures in the world). The map colors chosen to delineate the hazard roughly correspond to the actual level of the hazard; the cooler colors represent lower hazard while the warmer colors represent higher hazard. Specifically, white to green correspond to low hazard (0-8% g, where g equals the acceleration of gravity), yellow and orange to moderate hazard (8-24% g); reds to high hazard (> 24% g).
Over the past eight years three main project frameworks have aimed at improving regional seismic hazard assessment in the European-Mediterranean region, by integrating earthquake catalogues, seismic source zoning and hazard assessment.
The Global Seismic Hazard Assessment Program (GSHAP), a UN/IDNDR demonstration project, produced the first seismic hazard map for the European-Mediterranean region as part of the Global Seismic Hazard Map (Giardini, 1999), based on the compilation and assemblage of hazard results obtained independently in different test areas and multinational programs (Adria, Ibero-Maghreb, Central-Northern Europe, Fennoscandia, Turkey and Greece, Caucasus, Near East, the Balkans).
The International Geological Correlation Program project n.382 Seismotectonics and seismic hazard assessment of the Mediterranean basin (SESAME) developed in 2000 the first integrated seismic source model and homogeneous hazard mapping for the Mediterranean region.
Finally, the European Seismological Commission (Working Group on Seismic Hazard Assessment) has completed the first unified seismic source model and seismic hazard mapping for Europe and the Mediterranean, presented here. The unified seismogenic source model for the whole region consists of a total of 463 seismic sources (455 shallow and 8 intermediate-depth) and is depicted in the right panel. Each source is characterized by seismicity parameters in terms of earthquake activity rates and maximum magnitude.
The ESC-SESAME model for the European-Mediterranean region allows the generation of hazard maps expressing ground motion in different parameters, for different soil conditions and probability levels through a homogeneous computational procedure. This map is computed using the PGA attenuation laws of Ambraseys et al. (1996), Musson (1999), and Papaioannou and Papazachos (2000); areas not covered by the ESC-SESAME seismic source model (Iceland and Russia) are taken from the GSHAP Global Seismic Hazard map.
Financial support from the International Lithosphere Project (ILP), the International Council of Scientific Unions (ICSU), UNESCO, the International Association of Seimology and Physics of the Earth Interior, the European Council, NATO (ARW Ct.95-1521), INTAS (Ct.94-1644), the National Institute of Geophysics and Volcanology of Italy and the Swiss Federal Institute of Technology Zurich is acknowledged. Many research agencies supported the participation of their scientists in the different programs.
Hazard computation was carried out with SEISRISK III (Bender and Perkins, 1987) and with software developed by R. Musson of the British Geological Survey.
This map was printed with the contribution of the Swiss Federal Institute of Technology Zurich, the Swiss Federal Office for Water and Geology, the Swiss Geophysical Commission, the Swiss Pool of Earthquake Insurance, the Spanish Ministry of Science and Technology (AE00-0365), the Institut Cartogrŕfic de Catalunya and UNESCO.
M. Erdik (Turkey), M. García-Fernández (Spain), D. Giardini (Switzerland), G. Grünthal (Germany), M.-J.Jiménez (Spain), R. Musson (UK), C. Papaioannou (Greece), A. Shapira (Israel), D. Slejko (Italy).
D. Giardini (Switzerland), M. García-Fernández (Spain), K. Makropoulos (Greece), S. Riad (Egypt).
Y. Alpay-Biro (Turkey), A-Q. Amrat (Jordan), V. Avirax (Israel), S. Balassanian (Armenia), A.A. Barka (Turkey), G. Birgoren (Turkey), C. Bosse (Germany), T. Camelbeeck (Belgium), I. Cecić (Slovenia), M. Chadi (Tunisia), A. Drumya (Moldova), D. El Foul (Algeria), M. El Khoubbi (Syria), A. El Sayed (Egypt), M. Erdik (Turkey), L. Feldman (Israel), M. García-Fernández (Spain), J.-C. Gariel (France), D. Giardini (Switzerland), S. Gregersen (Denmark), G. Grünthal (Germany), P. Gülkan (Turkey), B. Guterch (Poland), P. Halldorsson (Iceland), W. Hays (US), M. Herak (Croatia), A. Hofstetter (Israel), E. Ibrahim (Egypt), M.-J. Jiménez (Spain), P. Labak (Slovakia), J. Lapajne (Slovenia), W. Lenhardt (Austria), C. Lindholm (Norway), K. Makropoulos (Greece), P. Mäntyniemi (Finland), J.-M. Martínez-Solares (Spain), L. Matias (Portugal), D. Mayer-Rosa (Switzerland), L. Mendes-Victor (Portugal), B. Muço (Albania), R. Musson (UK), C. Papaioannou (Greece), G. Papakyriacou (Cyprus), L. Peruzza (Italy), A. Rebez (Italy), B. Reich (Israel), S. Riad (Egypt), P. Scandone (Italy), V. Schenk (Czech Republic), Z. Schenkova (Czech Republic), S. Sellami (Switzerland), K. Setseyan (Turkey), G. Shamir (Israel), A. Shapira (Israel), D. Slejko (Italy), C. Sousa-Oliveira (Portugal), M. Stucchi (Italy), E. Sulstarova (Albania), B.-A. Tadili (Morocco), P. Teves-Costa (Portugal), V. Ulomov (Russia), T. van Eck (Netherlands), R. Verbeiren (Belgium), R. Wahlström (Sweden), B. Zabukovec (Slovenia), T. Ziros (Hungary), M. ivčić (Slovenia), P. Zupančič (Slovenia).