Abstract
The city of Oued-Fodda is located in north-central Algeria on the margins of the Middle-Cheliff Basin. This region has suffered several destructive earthquakes. The strongest was the 1980 El-Asnam earthquake (Ms7.3), whose causative fault was located about 1 km north of the city of Oued-Fodda. Therefore, a good knowledge of the soil characteristics in this city may allow a better evaluation of the seismic risk and help to minimize damages in the future. With this objective, a detailed microzonation study of Oued-Fodda has been carried out in this study. For that, the horizontal-to-vertical spectral ratio (HVSR) method has been applied on 102 sites along the city, estimating the soil fundamental frequencies and their corresponding amplitudes. Besides, the Rayleigh wave ellipticity inversion has been accomplished in order to estimate the corresponding Vs profiles and provide two cross-sections of the geology under the city. In the central part of the city, high-frequency peaks are observed, between 12.5 and 15 Hz, which correspond to impedance contrasts at shallow depth (<20 m). In the surrounding plain, two clear peaks are identified in the ranges 1.8–3.5 Hz (fundamental frequencies) and 6.5–15 Hz (secondary peaks).
Highlights
The north of Algeria is characterized by moderate to high seismicity, as a result of the convergence between the African and Eurasian plates. This seismicity is mainly concentrated on the margins of the Neogene basins [1]
The city of Oued-Fodda is situated in the western margins of the Middle Cheliff Basin (Figure 1)
The shear-wave velocity for the topmost layer of the zone Z1, which consists of Holocene alluviums, ranges between 280an m/s and 330 m/s
Summary
The north of Algeria is characterized by moderate to high seismicity, as a result of the convergence between the African and Eurasian plates. This seismicity is mainly concentrated on the margins of the Neogene basins [1]. In the Cheliff Basin, located in the northwestern part of Algeria, between the northern and southern Tellian Atlas mountain belts and lying parallel to the Africa-Eurasia plate boundary, in the approximately E-W direction, the active deformation is mainly expressed by reverse faults oriented in a NE-SW direction [1,2]. The city of Oued-Fodda is situated in the western margins of the Middle Cheliff Basin (Figure 1)
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