Active seismogenic faulting in the Tehran Region, north of Iran; state-of-the-art and future seismic hazard assessment prospects

Abstract

This study summarizes the state-of-the-art investigation into active-seismogenic faulting in the Tehran Region, and presents new complementary data to provide an overall view on potential seismic sources to strike the capital of Iran. The study region lies in the central portion of the Arabia-Eurasia collision zone. The Tehran Region is located in a transitional zone between the seismically active regions of Central Iran to the south and Alborz to the north and exhibits a tectonic context characterized by both dip-slip and strike-slip E-striking fault systems such as the Mosha, Parchin, Garmsar and North Tehran faults. Seismic catalogues record numerous strong and moderate earthquakes in the Tehran Region. Although the mapping of active faults and paleoseismological records have defined the seismic sources of several historical and prehistorical earthquakes, still many of them need to be constrained. Based on successive fault displacements and related microseismicity, five previously unknown or poorly understood major active seismogenic fault zones in the Tehran Region were introduced. From the west to the east, and in both near- and far-field contexts, the Qezel Hessar, Mahdasht-South Karaj, Kuhak-Lavizan, Arakuh, and Kajan define the fault zones. Critically, in the last decades, the rapid urban development in Tehran, including the new settlements of Karaj, Hashtguerd, Pardis, and Parand, has covered some of the surface expressions of these fault zones. The Kuhak-Lavizan fault zone, however, is known to cut across inner city parts of Tehran. Within the Tehran Region, seismicity on these faults demonstrates ongoing active structural evolution. The active faults of Tehran City are generally discussed in three northern, central and southern ∼E-striking basement zones. The major zones, which contain deep-seated faults, are capable of producing moderate to strong seismic events near and within the metropolitan areas of Tehran and Karaj and nearby settlements.