Using Ambient Array Method in Evaluating the Shear Wave Velocity Profile of a Site in Tehran

Document Type : Geotechnical Earthquake Engineering




In order to evaluate the capability of ambient array method for estimating the underground shear wave velocity (Vs) profile, a series of microtremor array measurement was performed in a site in Tehran. Fifteen seismometers were used simultaneously as 3 concentric circles with a radius of 25, 35 and 50m and the data were recorded continuously for 15 hours. Using the Nakamura H/V technique, the records of each station were processed individually and the natural period of the site was evaluated. The frequency wave number (F-K) and Spatial Autocorrelation (SPAC) methods were used to process the ambient array records and the extracted results were compared with the previous down hole and PS logging results. To obtain the shear wave velocity profile of subsurface layers, inversion of dispersion curve was performed using the neighborhood algorithm. Based on the obtained average results from F-K and ESPAC processing methods, it seemed that the Vs profile derived from ESPAC technique was more consistent with previous site investigation results. It was also concluded that by using multi layer model for the site with at least the layer number as the real, the extracted Vs profile fits better with previous investigations. By increasing the suggested layer number from real one, little variation can be shown in the Vs profile of the site.