Identification of soil characteristics using Vp & Vs tomograms for hazard assessment: case study from Ain Sokhna area, Egypt

Abstract

This study presents a detailed geotechnical characterization of an industrial development site in Ain Sokhna, Egypt, a strategic location within the new industrial zone of the Suez Canal, using integrated P-wave (Vp) and S-wave (Vs) tomography. The seismic velocity models reveal three subsurface layers, starting from unconsolidated wadi sediments at the surface to compacted sandstone bedrock at depth. Compressional wave Vp values ranging from 400 m/s in the near surface to 3500 m/s in the deepest layer, while shear wave Vs values rise from as low as 130 m/s to approximately 1896 m/s, reflecting a marked enhancement in material stiffness with depth. From these velocity profiles and estimated densities, the dynamic elastic moduli were derived. The shear modulus (G) increases from about 0.069 up to 7.91 GPa, and Young’s modulus (E) from 0.043 to 14.2 GPa, attended by a rise in bulk modulus (K) from the order of 0.01 to 10 GPa with depth. These high moduli values in the bedrock layer indicate a highly stiff, well-consolidated ground. Geotechnical parameters including stress ratio, material index, concentration index, standard penetration resistance (N-value), ultimate bearing capacity, and settlement were also calculated to measure soil and rock competence. The results indicate an increase in bearing capacity and decreasing settlement in deeper layers, consistent with the transition from loose soil to strong bedrock. Notably, the time-averaged Vs to 30 m depth (Vs₃₀) is consistently high across the site (800–1100 m/s), leading to a NEHRP Site Classification of B (rock/very stiff soil). This integrated geophysical-geotechnical approach provides a comprehensive assessment of subsurface conditions, yielding critical parameters for seismic hazard evaluation and safe foundation design in the Ain Sokhna region on the coastal side of the Gulf of Suez (GOS).