Towards a New Seismic Hazard Zoning Map for Tehran

This study is conducted to find a new seismic hazard zoning for the Tehran region. The return period for which the calculations are performed in Iranian Seismic Code (Code2800, 4th edition; 2014) has been 475 years. The first step for calculating seismic hazard in an area is preparing a uniform catalogconsists of all historical and instrumental events. All of magnitude scales was unified by using regional conversion equations between mb, Ms, ML and Mw and convert tomagnitude in Mw scale. The uniform catalog of earthquakes has provided a reliable and most complete collectionof available information for seismic study in this region. It emerges from temporal and spatial completeness study of the catalog that significant variation in data survival in historical, early instrumental and modern instrumental time periods. The seismicity of the region of Tehran might be described on the reported and recorded earthquakes during the history in this region. Very recently, we could find some activetrends in the region which their activity relate to eastern part of the region especially theNorth Tehran, Parchin, Pishva, Mosha and the Garmsar faults. Also, we observed strong historical earthquakes in this zone. Historical earthquakes showed that the east of Tehran is more active that the west. Released seismic energy map of the region showed the main active zones with high energy values for microearhquakes data in the east of the region.There is 13 milions day time population of which about 3 milions live on the actie fault zones. The new zoning comprises the improvement of historical seismicity (since 230 BC),the data concluded from paleoseismological studies (indicated 7 major earthquakes of M6-7.2 in the last 30000 years, of which 2 occurred in the last 8000 years), and the new data of instrumental seismicity since 1995. A Mmax (M7.5) on the North Tehran Fault is estimated based on a "landslide" caused by a major earthquake of M7.5 over this fault. The results of new site effects studies in differemt regions of Tehran indicate that the new assesments of seismic hazard values for the urbanised region of Tehran increased about 20 to 30% comparing to previously obtained values.

کلیدواژه ها:

actie fault zones ، seismic energy map ، paleoseismological studies