نادیا طاهرنیا - دانشگاه آزاد اسلامی واحد تهران شمال
محمدرضا قیطانچی - دانشگاه تهران، موسسه ژئوفیزیک

The hypocenters of about ٣٧٣٥ earthquakes recorded by global seismic stations during the last ٤٠ years were analyzed. The region of study was divided into sub squares of each ٠,٥×٠,٥ degree. The energy released for each earthquake was evaluated from energymagnitude relation and the energy of earthquakes in each square for each time interval were sum up and the maps of seismic energy released in ٤ time intervals of ١٠ years between ١٩٦٥ and ٢٠٠٤ and ١ time interval for the past ٤٠ years were provided and over lapped on the fault map. the time- frequency and magnitude- frequency diagrams for Iran were provided. The graph of accumulated energy released in ٥ years intervals from ١٩٦٤ to ٢٠٠٤ for active zones in Iran were calculated. As expected, the rate of seismic energy in Zagros is larger than other parts of Iran. The result indicated that the most parts of Iranian plateau were seismically active during the past ٤٠ years. Alborz and Lut regions were seismically active, characterized by significant earthquakes. Zagros had a more regular pattern of seismic activity and experienced moderate and small earthquakes. The different seismic patterns suggest that the physical properties of fault systems are different in different regions and the crust is inhomogeneous in Iranian plateau. The comparison of seismic energy maps indicates that the seismic gaps in early intervals were filled up by the seismic activities during the following time intervals.