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<p>On February 24, 2021, an earthquake of M<sub>w</sub> 4.7 struck near the Soubella Dam in the Hodna Mountain Chain of northeastern Algeria. Focal mechanism solutions indicated two possible fault planes: an E–W-striking reverse fault dipping north and an E–W-striking thrust fault dipping south, both parallel to the major Chott El Hammam Fault (CH-HF). This study investigates the seismotectonic setting, source dynamics, and seismic response of the dam using waveform data from the Algerian Digital Seismic Network (ADSN) and recordings from four strong-motion accelerometers operated by the Agence Nationale des Barrages et Transferts (ANBT) and installed within the dam. Time-domain moment tensor inversion based on full waveform modeling indicates a reverse-faulting mechanism with a seismic moment of M₀ = 1.49 × 10<sup>1</sup>⁶ Nm (M<sub>w</sub> 4.7) and a centroid depth of 6.2&#xa0;km. The causative structure is interpreted as either (1) a ramp-flat-ramp fault system associated with the Chott El Hammam Fault (CH-HF) or (2) a segment of the major tectonic contact between the Tellian allochthonous units of Djebel Boutaleb and the autochthonous Miocene formations of the Hodna Basin. Both interpretations are consistent with the regional compressional tectonic regime and provide new constraints on active faulting in southern Tellian Atlas. Dynamic source parameters were estimated using the Empirical Green’s Function (EGF) method, yielding a corner frequency ratio fc(P)/fc(S) of 1.03, indicative of in-phase far-field P- and S-wave radiation. The mean source duration is approximately 0.22&#xa0;s, consistent with the derived corner frequencies. The rupture is characterized by a small fault radius and a relatively high stress drop, reflecting localized faulting. The frequency-independent quality factor (Q) values were relatively low (Q<sub>P</sub> = 22–132, Q<sub>S</sub> = 22–184), indicating strong seismic attenuation in the study area. Strong-motion recordings, a peak ground acceleration (PGA) of 0.27&#xa0;g near the Soubella Dam, approaching design-level values despite the moderate magnitude of the event. This observation raises concerns regarding the adequacy of existing seismic design assumptions. Given the proximity of the dam to an active fault system, the results underscore the need for enhanced structural reinforcement to improve resilience against future near-fault earthquakes.</p>

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The 2021 Soubella earthquake (Mw4.7), Northeast Algeria: seismotectonic insights, source parameters from empirical green’s function and seismic response spectra analysis

  • 期刊论文

  • 发表日期：

    2026年3月25日

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  • Oualid Boulahia,
  • El-Mahdi Tikhamarine,
  • Issam Abacha,
  • Sofiane Taki-Eddine Rahmani,
  • Hichem Bendjama,
  • Fethi Semmane,
  • Khaled Roubeche,
  • Hamoud Beldjoudi

摘要

On February 24, 2021, an earthquake of Mw 4.7 struck near the Soubella Dam in the Hodna Mountain Chain of northeastern Algeria. Focal mechanism solutions indicated two possible fault planes: an E–W-striking reverse fault dipping north and an E–W-striking thrust fault dipping south, both parallel to the major Chott El Hammam Fault (CH-HF). This study investigates the seismotectonic setting, source dynamics, and seismic response of the dam using waveform data from the Algerian Digital Seismic Network (ADSN) and recordings from four strong-motion accelerometers operated by the Agence Nationale des Barrages et Transferts (ANBT) and installed within the dam. Time-domain moment tensor inversion based on full waveform modeling indicates a reverse-faulting mechanism with a seismic moment of M₀ = 1.49 × 101⁶ Nm (Mw 4.7) and a centroid depth of 6.2 km. The causative structure is interpreted as either (1) a ramp-flat-ramp fault system associated with the Chott El Hammam Fault (CH-HF) or (2) a segment of the major tectonic contact between the Tellian allochthonous units of Djebel Boutaleb and the autochthonous Miocene formations of the Hodna Basin. Both interpretations are consistent with the regional compressional tectonic regime and provide new constraints on active faulting in southern Tellian Atlas. Dynamic source parameters were estimated using the Empirical Green’s Function (EGF) method, yielding a corner frequency ratio fc(P)/fc(S) of 1.03, indicative of in-phase far-field P- and S-wave radiation. The mean source duration is approximately 0.22 s, consistent with the derived corner frequencies. The rupture is characterized by a small fault radius and a relatively high stress drop, reflecting localized faulting. The frequency-independent quality factor (Q) values were relatively low (QP = 22–132, QS = 22–184), indicating strong seismic attenuation in the study area. Strong-motion recordings, a peak ground acceleration (PGA) of 0.27 g near the Soubella Dam, approaching design-level values despite the moderate magnitude of the event. This observation raises concerns regarding the adequacy of existing seismic design assumptions. Given the proximity of the dam to an active fault system, the results underscore the need for enhanced structural reinforcement to improve resilience against future near-fault earthquakes.