The imaging of the near-surface features using earthquakes and ambient noise in the Tehran region
Seismic surface wave tomography of short-period dispersion curves is a useful method for studying the shallow structures of the Earth. In this research, the continuous records of ten seismographs of the Tehran Disaster Mitigation and Management Organization for a period of 8 months have been used to calculate the Green’s function for Love and Rayleigh waves. Dispersion curves are calculated using the cross-correlation of the ambient noise signal recorded at station pairs. In order to improve the ray coverage in the Tehran region, dispersion curves of Love and Rayleigh waves are derived from the seismic events recorded by a temporary network run by Parsian Company. The epicentral distance and magnitude of earthquakes are less than 100 km and larger than 1.5, respectively. The dispersion curves are calculated in the period range between 2 seconds and 5 seconds, which correspond to the top sedimentary cover. Surface wave tomography has also been performed to estimate the two-dimensional group velocity maps of Love and Rayleigh waves in the region. Based on the ray coverage inside the 0.1° × 0.1° cells in the region, the estimated minimum dimension of distinct heterogeneities was about 6 km. Based on the derived velocity model, the western and the central parts of the Tehran plain show low anomalies that could be due to the large thickness of alluvial sedimentary cover over the basement. The high-velocity anomaly in the southeastern part of the region can be attributed to the tapering of the alluvial cover towards the rock units where the southeastern mountains of Tehran are present.