Soil characterization of Babol City using single-station ambient seismic noise method.

The interrelation between the local site conditions and the severity of destruction during earthquakes has increased the necessity for more investigations on soil characterization in recent years. In residential areas, where active seismic methods are problematic for defining soil properties, passive seismic methods have attracted considerable attention due to their cost-effective and non-invasive features. Therefore, we have utilized 35 single-station ambient seismic noise recordings in the seismically vulnerable city of Babol, Iran, to evaluate the site response (including azimuthal variation and resonance frequency), estimate the seismic vulnerability index (K g), and classify the soil based on the Vs 30 of the region. To address the aim, we extract Rayleigh wave ellipticities from ambient seismic noise using their polarization features and employ them to define the azimuthal variations, resonance frequencies, and K g values of the region. In each station, the ellipticity curve is inverted with the support of supplementary geotechnical information to obtain a shear velocity profile. The inversion results have good consistency with borehole and downhole test information. The study identifies a low resonance frequency of 0.9 Hz with a NE directivity for the majority of the city and a Vs 30 range of 180 m/s to 350 m/s. Moreover, the seismic bedrock of Babol City is represented by a 3D Vs model at a depth of 60 m. Our results reveal that the city is vulnerable to seismic hazards due to the thick and low-velocity deposits responsible for high amplification affecting the study region, which combines with a high seismic vulnerability index, particularly in the southern part. This work has applications for future structural design, urban development, and seismic hazard reduction. • The results represent that single-station ambient noise analysis is a cost-effective and reliable method for soil characterization. • Polarization methods are effective in extracting Rayleigh wave ellipticities from ambient noise recordings. • · The city is characterized by a low resonance frequency with an almost NE orientation and seismic bedrock at a depth of 60 m • · According to Iran's No. 2800 seismic code, the region classified as ground type III • · The soil characterization, high amplification and k g value make the region's southern part vulnerable to seismic shaking [ABSTRACT FROM AUTHOR]