Acta Geodynamica et Geomaterialia

Title: AMBIENT NOISE FOR DETERMINATION OF SITE DYNAMIC PROPERTIES AT HURGHADA AND SAFAGA CITIES, RED SEA, EGYPT
Authors: Toni Mostafa, Abd el-aal Abd el-aziz Khairy and Mohamed Gad-Elkareem A.
DOI: 10.13168/AGG.2016.0004
Journal: Acta Geodynamica et Geomaterialia, Vol. 13, No. 3 (183), Prague 2016
Full Text: PDF file (4.8 MB)
Keywords: Shear wave velocity, H/V spectral ratio, surface wave dispersion curves, SPAC, frequency-wavenumber, thickness of sediments
Abstract: Recording ambient noise at the surface is increasingly used for the assessment of site response and has become a fundamental task for seismic risk reduction in urbanized areas. Methods based on the measurement of seismic noise, which typically are fast, non invasive, and low cost, have become a very attractive option in microzonation studies. In the current work, we use the ambient noise recordings collected by single seismic stations and two‐dimensional arrays to determine the response of the near-surface soil at the two touristic cities of Hurghada and Safaga which are located at the Red Sea coast in Egypt. Based on the horizontal-to-vertical (H/V) spectral ratio Nakamura’s technique, recordings of the single stations are analyzed to estimate the fundamental site frequency (f0). Using the raw noise signals recorded by two arrays, we present a joint inversion scheme for surface wave dispersion curves. In particular, the Rayleigh wave dispersion curves and the H/V curves are combined in a joint inversion procedure. We present inversion procedure based on the computation of high-frequency correlation functions between arrays’ stations. The calculation of Rayleigh wave phase velocities is based on the frequency-domain SPatial AutoCorrelation (SPAC) and frequency-wavenumber (f-k) methods. Constitutively, a tomographic inversion of the travel-times estimated for each frequency is performed, allowing the vertically varying 1-D shear wave velocity structure below the array to be retrieved. Following the relationship between resonance frequency (f0) and thickness of sediments, the thickness of unconsolidated sediments at the investigated sites are determined.