Study of Seismic Hazard and Risk Using Classical Probabilistic Seismic Hazard Analysis (PSHA) in the Rif Chain using Openquake Engine

Abstract. This study presents a probabilistic seismic hazard assessment (PSHA) for the Rif region in northern Morocco, using the OpenQuake Engine to incorporate both fault-based and distributed seismic sources within a unified modeling framework. Active faults were modeled using moment-balanced truncated Gutenberg–Richter distributions, while background seismicity was represented through nine distributed zones derived from local catalogs and characterized by incremental magnitude-frequency distributions (MFDs). A logic tree was used to combine source models and ground motion prediction equations (GMPEs) relevant to active shallow crustal regions.

Hazard calculations were performed for peak ground acceleration (PGA) at exceedance probabilities of 50%, 10%, 5%, and 2% in 50 years. The results show that several cities, including Al Hoceima, Fès, and Meknès, are subject to significantly higher ground shaking than prescribed by the Moroccan seismic design code (RPS v2011). Mean PGA values at 10% exceedance exceed 0.35 g in these areas, compared to the 0.14–0.18 g ranges specified in the code. These discrepancies suggest that the current national zonation underestimates seismic hazard in several tectonically active regions.

The model developed in this study is intended to shed light on the need to revise and enhance Morocco’s seismic hazard framework. By integrating detailed fault geometries, updated seismicity data, and regionally calibrated ground motion prediction models, the study provides a scientifically grounded perspective that can guide and support future improvements to national seismic zonation. These insights contribute to more accurate seismic risk assessment and the development of resilient, risk-informed design standards.