Ambient noise for determination of site dynamic properties at Hurghada and Safaga cities, Red Sea, Egypt

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 (f 0 ). 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 (f 0 ) and thickness of sediments, the thickness of unconsolidated sediments at the investigated sites are determined. ARTICLE INFO

Estimation of seismic site effect at the new Tiba City proposed extension, Luxor, Egypt

“…The HVSR method is the most applicable technique for estimation the soft sedimentary cover thickness (e.g. Ibs-von Seht and Wohlenberg 1999;Parolai et al 2002;Fäh et al 2003;Hinzen et al 2004;Toni et al 2016aToni et al , 2016bTrevisani et al 2017;Trevisani and Boaga 2018;Abd El-aal 2018). The basic concept of Nakamura's technique can be described in a simplest case ( Figure 5), in a onedimensional soft sedimentary layer (soil: denoted as subscript "s") above bedrock (denoted as subscript "b").…”

Simulation of strong ground motion parameters of the 1 June 2013 Gulf of Suez earthquake, Egypt

“…This zone is covered mainly by Quaternary deposits, Sabkha deposits (fine sand, silt, evaporates), and recent Wadi (Valley) deposits (detritals of sand, silt, and gravel) (EGSMA, 1981;Conoco, 1987;Said, 1990). At Hurghada, Zafarana, and Suez, the site amplification has been calculated by using shear wave velocity profiles obtained in Hurghada by Toni et al (2016a), in Zafarana by Abd el-aal et al (2016), and in Suez by Mohamed et al (2016). An example of the shear wave velocity profiles used in the determination of site amplification in the current study is depicted in Fig.…”

“…The site amplification functions were determined from the shear wave velocity-site amplification relationship (Tamura et al, 2000). The shear wave velocity is taken from the previous work in Hurghada (Toni et al, 2016a), Zafarana (Abd el-aal et al, 2016), and Suez (Mohamed et al, 2016). In Ras Gharib and Ain Sokhna, a field survey of microtremor single station has been carried out to estimate the site effect using H/V spectral ratio method (Nakamura, 1989).…”

“…The site response is estimated in the studied areas by using microtremor data that have been collected from Ain Sokhna and Ras Gharib. For Hurghada, Zafarana, and Suez, geotechnical information used in site effect estimation is taken from Toni et al (2016a), Abd el-aal et al 2016, respectively. According to site response, the investigated areas are classified into two zones: Zone A and Zone B, where Zone A is characterized by higher site amplification than Zone B.…”