Investigation of the Growth of Active Faults in the Tehran Metropolitan Employing Historical Aerial Photos and Photogrammetric Techniques

In highly populated urban areas such as Tehran, with over 17 million inhabitants, identifying active faults is essential to hazard and risk management. Tehran is located in central Alborz within the Arabia-Eurasia collision zone. The region is the manifestation of interplay between structural systems of the western and eastern Alborz. The study area focuses on the Lavizan and Babaei fault-related fold structures as the main Quaternary features of the Tehran piedmont. Tehran's rapid urbanization in the past few decades has made it impossible to access fault traces and the associated geomorphic features in the field. This research is the first study which uses photogrammetric methods to extract detailed 3D data and digital terrain model (DTM) from archival imaging. Historical aerial photographs were acquired from 1955-1965, before the city's development. A DTM with a spatial resolution of about 86 centimeters, an orthophoto-mosaic, and a three-dimensional model were created employing photogrammetric methods. The geomorphic analysis of the model reveals lateral unidirectional eastwards growth of the Lavizan and Babaei structures during Pleistocene and Holocene. The presence of wind gaps developed from water gaps, and sharp fault scarps in the upper Pleistocene and Holocene geomorphic surfaces testify this lateral propagation. This study presents a typical example for a long-lasting tectonic activity and its Holocene continuation on the E-W fault-related fold structures, which directly affect urban areas in the Iranian metropolitan.