Evaluation of ground motion prediction equations and their corresponding shakemaps in northern Morocco

The production of intensity maps (shakemaps) is a critical step following major earthquakes to assess the distribution of damage across affected areas. However, this process is often time-consuming and resource-intensive. It typically begins with expert teams conducting field surveys in impacted regions and concludes with the classification of zones based on the earthquake's intensity. Despite this, decision-makers require rapid estimates of losses to facilitate timely victim assistance and compensation, such as through the EVCAT scheme.

This need has led to the development of intensity maps based on the Mercalli scale (MMI) and their comparison with observed maps. The approach involves converting earthquake magnitude into ground acceleration values (PGA or SA) using ground motion prediction equations (GMPEs), followed by a transformation into MMI using established formulas (Worden et al., 2012). Each GMPE is typically calibrated for a specific region, reflecting its tectonic and seismic characteristics. When GMPEs are unavailable for a given area, similar reference zones are used as proxies.

In Morocco, where dedicated GMPEs are lacking, equations corresponding to nearby tectonic settings are employed. This study aims to evaluate and compare various GMPEs applicable to northern Morocco to identify the most suitable models. We selected two earthquakes with distinct characteristics—Al Hoceima (2004) and Nekkour (2023)—and performed stress tests based on specific criteria, including fault geometry and depth.

For the methodology, we utilized parameters published on the USGS platform for both events and performed calculations using the OpenQuake engine developed by GEM. The results revealed the convergence of four GMPEs, which we recommend applying to northern Morocco with equal weighting.

Keywords: Earthquake; Magnitude; MMI; Shakemap; PGA; GMPE; USGS; OpenQuake.