Investigation of seismicity, morphology and focal mechanism of important earthquakes of Tehran

The Iran plateau is located in the seismic belt of the world. Sustainable development in seismic regions of the world depends on having a comprehensive bank of all destructive seismic historical events, seismic events of recent centuries and their careful analysis for the reliable design of important buildings and structures. Owing to the occurrence of historical and instrumental earthquakes in the Central Alborz region, this region is known as a high seismic active region.    In this study, the waveforms of all earthquakes recorded at existing seismic stations in Central Alborz were used in order to determine the location of earthquakes and their causative faults, accurately. The studies conducted in this area show that activity of faults in Tehran results in the occurrence of significant earthquakes. Furthermore, the calculated focal mechanisms are consistent with the geometry of the faults. The density of morphological evidence, features and landforms observed in the northern and northeastern regions were higher than the southern and northwestern regions. Moreover, accumulation of the epicenters in the northern and northeastern regions is more than the other areas. This indicates that in these areas, there are high tectonic activities which affects on the morphology of the areas strongly. The folds created between the faults indicate the compressive zone of the reverse faults and the remaining deposits indicate the existence of tension between the normal faults. Focal mechanism of high quality and reliable seismic events of the area show different compressive, strike-slip and normal mechanisms. Compressive and strike-slip mechanisms have the dominant trends in the region. Strike-slip components have a more pronounced characteristic than the other components or have always been seen alongside the other components. Small components of traction are also observed among the obtained mechanisms. This shows the existence of traction mechanisms in this area. Therefore, the effect of tensile stresses should be considered in future studies about the tectonic seismic regime of this area. Considering the seismic complexity of fundamental trends in Alborz region and a lack of common opinion among researchers about the focal mechanism of faults in the region, calculating the focal mechanisms of more seismic events can complement and confirm the results of this study. It provides more accurate interpretation of seismic characteristics and geomorphology of the region. The results of this study confirm the importance of proper station coverage in the region and the need to monitor seismic events. Installation of dense seismic networks, even temporarily and with longer deployment times around faults in the area, is necessary to collect more seismic data and record micro-earthquakes.