Seismic vulnerability assessment in the new urban area of Diriyah Governorate, Riyadh, Saudi Arabia
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ORIGINAL PAPER
Seismic vulnerability assessment in the new urban area of Diriyah Governorate, Riyadh, Saudi Arabia Kamal Abdelrahman 1,2 & Mohammad Fnais 1,3 & Enayat Abdelmonem 2,4 & Khaled Magram 5 & Abdullah Bin saadoon 5
Received: 6 June 2017 / Accepted: 21 September 2017 # Saudi Society for Geosciences 2017
Abstract Nine seismic refraction profiles were conducted and processed to study the near-surface sediments in the new urban area of Diriyah. The 2D geoseismic models illustrate two layers: a surface layer of soft sediments and weathered to hard limestone bedrock. Moreover, microtremor measurements were performed at 38 sites for 40 min using three-component seismographs and processed to assess the peak spectral amplitude and the corresponding fundamental resonance frequency. The seismic vulnerability index at each measurement site was estimated. These results correlate well with the geotechnical borehole data. The north-western zone is highly vulnerable due to the great thickness of the soft sediments. Keywords Microtremors . Seismic refraction . Geotechnical data . Vulnerability assessment . Riyadh . Saudi Arabia
Introduction Seismic refraction is broadly used to delineate shallow subsurface structures, depth to bedrock, and fractures.
* Kamal Abdelrahman [email protected]
1
Geology and Geophysics Department, College of Sciences, King Saud University, Riyadh, Saudi Arabia
2
Seismology Department National Research Institute of Astronomy and Geophysics, Cairo, Egypt
3
Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia
4
Al-Farabi colleges, Riyadh, Saudi Arabia
5
Undergraduate students, Geology and Geophysics Department of, King Saud University, Riyadh, Saudi Arabia
Moreover, in areas characterized by complex geological structures, the seismic refraction technique has played a vital role in building a precise geological model of the subsurface because it provides full coverage of the exploration area. Many researchers have used seismic refraction to depict the bedrock and subsurface structures for engineering constructions (Redpath 1973; Dutta 1984; Bennett 1999; Palmer 2001; Rucker 2000; Sirles et al. 2006; Alhassan et al. 2010; and Adeoti et al. 2013). Because microtremors are natural ground vibrations generated mostly by natural processes, these motions change the site response effects and are representative of the soil characteristics. Microtremor analysis is used to get evidences for soil vibration properties of sites. The seismic wave-trapping phenomenon leads to intensified vibration amplitudes that might increase hazards at sites with soft soil. Several investigations illustrated that each site has its own resonance frequency at which the ground motion gets amplified (Mukhopadhyay and Bormann 2004). Kanai and Takana (1961) were the first to propose the application of microtremors. Nakamura method (H/V) has been applied at several locations worldwide where it has been confirmed that the measurement and processing of microtremor data are efficient and rapid and have low
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