Marrakech – A new study reveals Morocco’s largest dam faces serious seismic risks, with researchers predicting a 100% probability of moderate-magnitude earthquakes exceeding 4 Mw striking the Al Wahda Dam watershed within the next 25 years.
The research, published Monday in the Engineering Geology journal, developed a probabilistic model analyzing earthquake patterns in the region over the past century. The study examined seismic data from 1923 to 2023, integrating neotectonic information to assess risks to this critical infrastructure.
“The findings reveal a distinct spatial distribution of seismic activity, with higher earthquake densities observed near the extremities of the dam,” the researchers report. This concentration of seismic events poses particular concerns for dam safety and regional hazard management.
Led by Ayyoub Sbihi and a team of international researchers, the study identifies major fault lines as key contributors to the area’s seismicity. The Jebha Fault and the Nekor Fault, which cross the dam’s watershed, appear particularly active.
The investigation reveals the basin has experienced 392 earthquakes between 1 and 5.8 on the Richter scale during the study period. More concerning, seismic activity has increased dramatically in recent decades, with over 230 earthquakes recorded in just the last twenty years.
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While most recorded earthquakes range from low to moderate magnitudes (2.0-4.9 Mw), the researchers caution that higher-magnitude events cannot be dismissed. The study calculates a substantial probability of earthquakes up to 5 Mw occurring within 25 to 50 years.
“This research provides actionable insights for engineering geologists by identifying vulnerable zones, estimating earthquake recurrence intervals, and supporting geotechnical planning for infrastructure safety,” the paper states.
Morocco’s largest hydraulic structure, the Al Wahda Dam stands 88 meters tall and sits atop relatively weak Quaternary deposits. These geological conditions potentially increase vulnerability to seismic events.
Technical analysis shows the reinforced concrete dam possesses a dynamic amplification value of 0.72, indicating it can absorb up to 75% of seismic energy. However, this still leaves the structure exposed to considerable forces during moderate earthquakes.
“The spatial clustering of seismic activity near the dam and its embankments highlights the urgent need for enhanced monitoring and structural reinforcements,” the researchers warn.
The study compares two methodological approaches – the Cornell-McGuire method and Bayesian analysis – to estimate recurrence probabilities and return periods for earthquakes of various magnitudes.
This innovative combination of instrumental seismicity data with geodynamic parameters produces practical insights for hazard mitigation and could prove valuable for similar assessments in other seismically active regions worldwide.
The findings carry particular weight following recent global incidents like the Turkey-Syria dam failures, which demonstrated the devastating consequences of overlooking seismic risks in vulnerable infrastructure.
