Soil site characterization of Rabigh city, western Saudi Arabia coastal plain, using HVSR and HVSR inversion techniques

Abstract

Rabigh city located along the coastal plain of the Red Sea in western Saudi Arabia is economically significant. This pioneering study assesses the site characterization of Rabigh city based on integrated geological, geotechnical, and seismological data. These datasets include geotechnical data from 100 boreholes, 127 microtremor records, and detailed geologic maps of the area of study. The grid interval for microtremor sites is 1 km. The fundamental resonance frequency (fo) and maximum amplification factor (Ao) are identified from the horizontal-to-vertical spectral ratio (HVSR) curves from the recorded data. The distribution map of fo displays three distinct zones, high fundamental frequency (greater than 1 Hz), moderate (0.5 Hz– Hz), and low (less than 0.5 Hz), while the obtained Ao ranges between 2 and 4.2. The horizontal-to-vertical spectral response inversion technique has been conducted for 40 microtremor records in the frequency band 0.2–5 Hz to evaluate the shear-wave velocity for 30 m depth (Vs30). The computed values of Vs30 range from 208.5 m/s to 516 m/s. According to the National Earthquake Hazard Reduction Program (NEHRP) soil site characterization, Rabigh city is differentiated into two soil classes, C and D. The detailed geotechnical investigations for sabkhah sediments are highly recommended for reducing their environmental risks to urban facilities and economic projects in Rabigh area.