Improving Ground Motion Forecasting for the 2023 Al-Haouz and 2004 Al-Hoceima Earthquakes (Morocco) by using the Mdesign Concept

Abstract

The performances of Morocco’s seismic hazard forecasts demonstrated severe shortcomings at the occurrence of the 2023 Al-Haouz earthquake (MW 6.8), evidencing the need for improved data and approaches. This study expands the Neo-Deterministic Seismic Hazard Assessment (NDSHA) to the use of the design magnitude (Mdesign) definition. We verified the approach through testing the performance of ground shaking maps computed for bedrock site conditions with respect to the 2023 Al-Haouz (MW 6.8) and the 2004 Al-Hoceima earthquakes (MW 6.4).Using three earthquake catalogues (all truncated to 2012), we generated NDSHA ground shaking maps. To account for the Mdesign concept, earthquakes magnitudes were incremented, according to the Panza-Rugarli law, by γEMσM=0.5 (γEM=2) and 0.7 (γEM=2.8) respectively, and the predicted peak ground accelerations were compared to recorded data. The results show that the Morocco catalogue with Mdesign increment values could significantly improve the recorded ground shaking forecast for the 2023 earthquake.The analysis demonstrates that NDSHA maps accounting for Mdesign may significantly reduce underprediction biases, especially for strong intraplate earthquakes, where the available information about past seismicity may well be incomplete and not representative of the seismogenetic potential of the region. We conclude that Mdesign is an essential prerequisite for reliable seismic hazard assessments, particularly in regions with sparse seismicity data, as it can enhance predictive capability and risk mitigation in Morocco and similar intraplate seismotectonic settings.