Shallow S-Wave Velocity Structure in the Middle-Chelif Basin, Algeria, Using Ambient Vibration Single-Station and Array Measurements

Abstract

In order to better assess the seismic hazard in the northern region of Algeria, the shear-wave velocity structure in the Middle-Chelif Basin is estimated using ambient vibration single-station and array measurements. The Middle-Chelif Basin is located in the central part of the Chelif Basin, the largest of the Neogene sedimentary basins in northern Algeria. This basin hosts the El-Asnam fault, one of the most important active faults in the Mediterranean area. In this seismically active region, most towns and villages are built on large unconsolidated sedimentary covers. Application of the horizontal-to-vertical spectral ratio (HVSR) technique at 164 sites, and frequency–wavenumber (F–K) analysis at 7 other sites, allowed for the estimation of the ground resonance frequencies, shear-wave velocity profiles, and sedimentary cover thicknesses. The electrical resistivity tomography method was used at some sites to further constrain the thickness of the superficial sedimentary layers. The soil resonance frequencies range from 0.75 Hz to 12 Hz and the maximum frequency peak amplitude is 6.2. The structure of the estimated shear-wave velocities is presented in some places as 2D profiles to help interpret the existing faults. The ambient vibration data allowed us to estimate the maximum depth in the Middle-Chelif Basin, which is 760 m near the city of El-Abadia.

Liquefaction Potential and Vs30 Structure in the Middle-Chelif Basin, Northwestern Algeria, by Ambient Vibration Data Inversion

“…The stratigraphical column is composed of a succession of marine, continental, and lacustrine deposits. Lateral variations in facies were also reported [10,16], and further confirmed in [21], where important lateral variations in the shear-wave velocity were observed within the same formations. All these perturbations in the sedimentary cover reflect several instability periods with intense tectonic activities and different episodes of marine regression and transgression that conditioned the sedimentation process [10].…”

“…The aim was to determine the resonance frequencies of the ground, the shear-wave velocity structure of the sedimentary layers, and the bedrock depth, where the impedance contrasts with the sedimentary cover and may be the cause for ground shaking amplification during strong earthquakes. This work is a continuation of the ones carried out in the Middle-Chelif basin [20,21].…”

“…The Miocene series outcrop in succession on the hills that overlook the city of El-Abadia (Figure 2). The shear-wave velocity varies from 640 to 1450 m/s for the Miocene formations [21]. The Pliocene is divided in two stages, marine and continental, with alternations between sands, sandstones, and conglomerates [10,16].…”

“…In the present study, we used ambient vibrations data to characterize some geotechnical features and to estimate some dynamic properties of the soil column in the cities of El-Attaf, El-Abadia, and Ain-Defla. Ambient vibration-based techniques have been used previously in the Chelif Basin [18][19][20][21]. The aim was to determine the resonance frequencies of the ground, the shear-wave velocity structure of the sedimentary layers, and the bedrock depth, where the impedance contrasts with the sedimentary cover and may be the cause for ground shaking amplification during strong earthquakes.…”

Microzonation Site Effects and Shear Strain during Earthquake Induced Landslide Using HVSR Measurement in Ulu Mana Sub-District, South Bengkulu Regency Indonesia

“…(Layadi et al, 2016;Gosar, 2017). In particular, this method is used widely in many geological research, for instance, mapping of geological stratigraphy (Tebbouche et al, 2017) and sedimentary basin (Issaadi et al, 2021), ground characterization (Panzera et al, 2019), and ground structure interaction (Pazzi et al, 2016). In addition, this method is applied to the definition and characterization of landslides, where different spectral responses are associated with different landslide zones (stable and unstable) (Iannucci et al, 2020).…”