3D shear-wave velocity structure for Oran city, northwestern Algeria, from inversion of ambient vibration single-station and array measurements

Abstract

The city of Oran experienced several earthquakes. Therefore, the characterization of its subsurface is crucial for a better evaluation of the seismic hazard. Using ambient vibration single-station and array measurements at 193 sites, the HVSR curves showed a variation of the fundamental frequency peak between 0.3 and 7.4 Hz, growing towards the west, with maximum amplitude of ∼6. The shallow structure has been explored by means of F–K analysis. Joint inversion of the HVSR and Rayleigh wave dispersion curves showed 3 layers of soft and stiff sediments of varying thicknesses overlying the bedrock. The shear-wave velocity (Vs) of the sediments varies between 280 and 1300 m/s and that of the bedrock can reach 2500 m/s. Cross sections show a decrease in sediments thickness from east to west where bedrock outcrops. The maximum depth of bedrock is 1050 m northeast of the city. The obtained Vs models support a soil classification ranging from stiff soil to hard rock.