Site response assessment of an urban extension site using microtremor measurements, Ahud Rufeidah, Abha District, Southw
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ORIGINAL PAPER
Site response assessment of an urban extension site using microtremor measurements, Ahud Rufeidah, Abha District, Southwest Saudi Arabia Sattam Almadani & Kamal Abdelrahman & Elkhedr Ibrahim & Abdulaziz Al-Bassam & Awad Al-Shmrani
Received: 18 November 2013 / Accepted: 17 March 2014 # Saudi Society for Geosciences 2014
Abstract Microtremor horizontal-to-vertical spectral ratio (HVSR) method has been conducted at 33 sites in Ahud Rufeidah urban expansion zone in order to assess the fundamental frequency and the corresponding amplitude of the sediments. Clear HVSR peaks have been identified in the majority of the surveyed area. The eastern and northern parts of the area are characterized by two well-separated peaks which indicate distinct shallow and deep impedance contrasts. The frequency map of sediments shows a distribution in the range of 0.86–3.13 Hz. The observed frequencies can be related to the total thickness of Quaternary alluvial sediments (sand, gravel, and shale) deposited over the gneiss bedrock. Lower resonance frequencies are attained at sites in the northern part, while the higher values are attained at sites in the southern part. The amplitudes of HVSR peaks are in the range 3–15. In general, the higher peak amplitudes are identified at lower frequencies. Since low fundamental frequencies are related to bedrock, this can be an indication of highimpedance contrast between alluvial sediments and gneiss bedrock. The results of this study represent one step for S. Almadani : K. Abdelrahman (*) : E. Ibrahim : A. Al-Bassam : A. Al-Shmrani Geology and Geophysics Department, College of Science, King Saud University, Riyadh, Kingdom of Saudi Arabia e-mail: [email protected] A. Al-Bassam Geology and Geophysics Department, College of Science, King Saud University, Riyadh, Kingdom of Saudi Arabia E. Ibrahim Geology Department, Faculty of Science, Mansoura University, Mansoura, Egypt K. Abdelrahman Seismology Department, National Research Institute of Astronomy and Geophysics, Helwan, Cairo, Egypt
seismic hazard assessment and risk mitigation of this urban area where great damage can be attained in case of strong earthquakes. Hence, these results should be taken into consideration before establishing the new urban constructions in the area of study. Keywords Site response . Urban zone . Fundamental frequency . Maximum amplitude
Introduction The local geology and topography can significantly control the scale and distribution of damages due to strong earthquakes. The maximum amplitude of earthquake ground motion by local site conditions has important implications in urban planning and development. In areas characterized by soft sediments, the maximum amplitude of ground motion is common that lead to enhanced seismic hazard and risk. Local site response can be evaluated by empirical and theoretical methods. The theoretical method allows detailed analysis of the parameters used in the evaluation; however, it requires detailed geotechnical information about the materials through which the sei
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