The Iranian territory is situated at the middle of Alpine-Himalayan orogenic-seismic belt, and is among the most active seismic regions in the world. The plate tectonic models, based on the analysis of world-wide ocean floor spreading patterns, fault systems, and slip vector of faults, indicate that the Arabian shield is moving with a rate of 30 to 40 mm per year toward Eurasian plate. The consequence of this convergence is shortening of the Iranian crust, and development of the Zagros Mountains (in the southwestern part of Iran), the Alborz (in the north) and abundant earthquakes in the Iranian plateau.
Among the hazardous phenomena, devastating earthquakes are responsible for the most casualties and financial damages. Unfortunately, the number of casualties in developing countries is more than developed ones. The number of homeless people in developing countries is 40 times more than the rest. The negative effect of earthquake on the developing countries economy is very strong. Investigations indicate that the direct and indirect effects of earthquake on the economy of developing countries are about 3% to 4% of annual GNP (Gross National Product). It is obvious that urbanization and population increase will expand the hazardous conditions of earthquakes. At present, many people are living in the seismic territories on the Earth. Of course, capital and major cities are subjected to more risk. Many cities of our country such as Tehran, Tabriz, Mashhad, Kerman, Qazvin, Semnan, Karaj and most of the cities in northern part of country are encountering this great risk. One of the fundamental data regarding the hazard and risk assessment of earthquake is the familiarity with the seismicity background, the seismotectonic character of each region and deep investigation on earthquakes history (ancient, historical, 20th and 21st century). To assess to seismotectonic properties, earthquakes history has to be compiled and examined for a long period. If earthquakes events are studied for a short period of time (i.e. earthquakes after 1900), seismic regions may represent aseismic or of low seismicity in investigation process for the earthquakes return periods. For example, before the earthquake of Shahrivar 1979 in Tabas (Golshan) (Io=X, mb=6.4, Ms=7.3), no history was available from great earthquakes for about 11 centuries.