A critique review and update of the earthquake surface fault rupture hazard in the northern zone of Tehran metropolis, Iran

Abstract

 The megacity of Tehran, the capital of Iran, is located on the southern slope of the central part of the Alborz Mountain range. The earthquake risk assessment studies in the Tehran metropolis have been focused mainly on earthquake data and technical aspects of buildings and structures. In the meantime, the data on the fault that can cause earthquakes and the related triggered fracture system, like the potential of direct surface rupture that can be developed or occur as the result of an earthquake faulting, have not been significantly updated during the last two decades for mountain front foothills. The land use changes and the growth of the metropolis of Tehran during the last two decades, especially in the city's northern half, with the lack of any regulatory action on the fault zone, are escalating the risk of surface rupture. In this regard, the need to update the fault map and establish a fault zone regulatory act is paramount to importance. By reviewing the existing information and combining it with new satellite data, an updated map of the faults in the northern zone of Tehran city has been presented. The vital point in this map is to recognize the continuation of the fault trends that were introduced before, but their end was unknown. Also, a vast network of fractures or subsidiary faults belonging to the North Tehran fault system has been mapped, especially in its hanging wall part, which has not been published before. The result of the overlapping faults with urban structures and building areas shows that in the lack of regulation, the fault zone's ignoring continues in the new constructions of the Tehran metropolis. It is estimated that more than twenty hospitals, many of which are newly built, along with other strategic and sensitive structures, are in danger of surface rupture, and it is indispensable to think of a solution for them.

Additionally, many important buildings are in danger of fault rupture. We recently found that large ancient mega-landslides exist in the northern foothills of Tehran that are under more investigation. In the end, this research emphasizes the special attention to the lateral investigation of thrusts located in the north of Tehran between the North Tehran fault and the Masha fault, especially the Imamzadeh Dawood, Kigah and Pourkan faults.

Keywords: fault surface rupture, fault setback, earthquake, seismic hazard, Tehran, North Tehran Fault