Ambient Noise Rayleigh Wave Shallow Tomography in the Tehran Region, Central Alborz, Iran

Abstract

The Tehran region is one of the most densely concentrated areas of seismic activity in northern Iran. This region is dominated by the central Alborz Mountains belt and a large composite cone, the Damavand volcano. Located in the foothills of the Alborz Mountains, the city of Tehran, with a population of ∼15 million, is subject to high seismic risk (Jackson 2006; Berberian 2005). It is also surrounded by many active faults that have caused destructive earthquakes in the past (Berberian and Yeats 2001). Recent seismicity studies ( e.g. , Mottaghi et al. 2010) indicate that this region is under t|he threat of some major and yet unresolved active faults. Strong ground motion due to amplification of seismic energy by shallow velocity structure can be responsible for serious property damage (German and Beroza 2008). In order to accurately predict ground motion through waveform modeling, it is necessary to accurately image the shallow crustal seismic velocity. The local tomographic images available in the Tehran area come from body-wave earthquake tomography ( e.g. , Mostafanejad et al. 2011) and do not allow precise control of the near-surface (depth < 5 km) velocity structure. Furthermore, this model is affected by a variety of factors such as the effect of uneven source (or station) distribution and potential errors in identifiable seismic sources. We address these limitations by using the information extracted from ambient seismic noise. The present study uses continuous data recorded at a variety of sensors to investigate shallow crustal structure surrounding Tehran. We extract inter-station Green’s functions (GFs), with Rayleigh waves as the largest component, from beams of ambient noise cross-correlations at stations in and around the city of Tehran. We first estimate group velocity dispersion curves in the period band between 2 and 4 sec for each station-pair to invert for the 2D …