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.
Highlights
Northern Algeria is characterized by a series of Neogene basins (e.g., Constantine Basin, Hodna Basin, Soummam Basin, Tizi-ouzou Basin, Mitidja Basin, Medea Basin, and Chelif Basin), elongated in an E–W direction, and surrounded by the Tellian Atlas mountain belts, which act as a substratum for their sedimentary covers [1,2,3]
The Neogene basins, in the western part of Algeria, stretch parallel to the Mediterranean coast and lie within the septentrional and meridional Tellian Atlas mountain belts, which belong to the southern branch of the Alpine chain [1,31]
The inversion of the horizontal-to-vertical spectral ratio (HVSR) curves allows for the retrieval of the shear-wave velocity values for the sedimentary layers, along with the bedrock depths of our study area
Summary
Northern Algeria is characterized by a series of Neogene basins (e.g., Constantine Basin, Hodna Basin, Soummam Basin, Tizi-ouzou Basin, Mitidja Basin, Medea Basin, and Chelif Basin), elongated in an E–W direction, and surrounded by the Tellian Atlas mountain belts, which act as a substratum for their sedimentary covers [1,2,3]. TThhee CChheelliiff BBaassiinn hhaass bbeeeenn tthhee ssuubbjjeecctt ooff sseevveerraall ggeeoollooggiiccaall aanndd ggeeoopphhyyssiiccaall ssttuuddiieess. TThhee mmaajjoorriittyy ooff tthheessee ssttuuddiieess hhaavvee bbeeeenn ddoonnee oonn tthhee LLoowweerr--CChheelliiff BBaassiinn,, aanndd oonnllyy aa ffeeww ooff tthheemm hhaavveeiinncclluuddeeddththeewweestseternrnpparatrot fotfhteheMMididdlde-lCe-hCehliefl.iIft. wItaws aosnloynalyt tahtetehnedeonfdthoef 1th9e601’9s6t0h’satthtahtethCeGCGG(GCo(CmopmapgangieniGe éGnéénréarlealededeGGéoépophhysyisqiquue)e)ccaarrrrieieddoouutt aa ggeeoopphhyyssiiccaall ppssttrrrroouussccppStteuueicncrrteteciiennooggftfhtctchehaaeemm19ssppee8adad0iiiiggEmmnnle-ebAbnnyyttsaaneerrllayyeemccddttrereeiippcacoormmtsshiieettqtssthuh[[oo7a7d]kd]..ses,iinnantthhdeetMhMeiidddddallmee--aCCghheeeillitiffcPPalulaasiinendiin,ntoohrreddMeerrittdoodssltteuu-dCdyyhetthhlieef region has been the subject of a multitude of geological and geophysical studies. The Woodward Clyde Consultants carried out a complete geotechnical and geological study in eight cities of the Chelif region, including Oued-Fodda, El-Attaf, and El-Abadia, where several boreholes were drilled. Ambient vibration measurements using single-station and array techniques were used to estimate the shear-wave velocity for the sedimentary layers, and to map the bedrock structure in the Middle-Chelif Basin. They can be used for seismic hazard mitigation studies, such as strong ground motion simulation, soil liquefaction studies, and for the updating of the Algerian seismic code
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