GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.1 GNGTS 2024 Actve Transpressive Faultng Along the High Atlas Mountains: the 8 September 2023, M W 6.8, Morocco Earthquake D. Cheloni 1 , N. A. Famigliet 2 , R. Caputo 3 , C. Tolomei 1 , A. Vicari 2 1 Isttuto Nazionale di Geofsica e Vulcanologia, Rome, Italy 2 Isttuto Nazionale di Geofsica e Vulcanologia, Sezione Irpina, Italy 3 Department of Physics & Earth Sciences, Ferrara University, Italy The 2023 Morocco earthquake sequence started on September 8th 2023 with a MW 6.8 event in the western sector of the High Atlas Mountains (Fig. 1), triggering signifcant afershocks (including a M4.9 event). The earthquake caused extensive damage, claiming at least 2900 lives and afectng around 320,000 people. The seismicity in Morocco is atributed to the convergent moton between the African and Eurasian plates, with the Atlas region experiencing moderate seismic actvity. Morocco’s seismic history includes notable events like the 1994, 2014 and 2016 earthquakes in the Rif and Alboran Sea and the 1960 Agadir earthquake. The 2023 event, the strongest recorded in modern tmes, occurred in the High Atlas region. The seismic regime is characterized by a present- day compressional regime with actve deformaton along the High Atlas, accommodatng about 1.7 mm/yr of WNW-ESE shortening (Serpelloni et al. 2007). We employed Interferometric Synthetc Aperture Radar (InSAR) data from Sentnel-1 and ALOS-2 satellites to study ground displacement associated with the mainshock of the 2023 seismic sequence. The coseismic deformaton feld displayed a WSW-ENE elongated ellipse, suggestng a blind rupture. Two fault scenarios were investgated using geodetc modelling: an NNW-dipping fault in agreement with the focal mechanism and an SSW-dipping fault consistent with seismic data. We performed the geodetc modelling using the formulaton of Okada (1985), following a standard two-steps procedure (e.g. Atzori et al., 2009; Cheloni et al., 2020). Both models efectvely explained the observed data, indicatng ambiguity in fault identfcaton. Coulomb stress analysis implicated stress redistributon in afershock occurrence. Uncertaintes in fault dip directon persisted, with seismic databases showing discrepancies in afershock distributon. On the other hand, gravity and heat-fow data (Teixell et al., 2005), coupled with geodynamic consideratons, favoured the SSW-dipping fault model. The analysis suggests that the high-angle fault model is unrealistc based on rheological arguments and regional geodynamic constraints. Integratng interferometric analyses with geological, tectonic, and seismological data could be crucial for resolving ambiguites in satellite-based models. The study therefore