The Midelt earthquake of November 17th 2019, and its implications on the present-day tectonics of the junction of the High and Middle Atlas (Morocco)

Abstract

The Midelt area in Morocco, located between the Middle Atlas and the High Atlas, was shaken on November 17th, 2019, by a strong earthquake that was felt with intensity VI MSK. The epicenter was at 32.677°N; 4.126°W, with a depth of 2.1 km. The event was followed by a series of aftershocks and another series of small events later in February 2020. Moment tensors of the main event mainly show strike-slip faulting with a P-axis oriented NW-SE. The review of the available seismic data around the epicentral area encompassing the Middle Atlas, the Eastern High Atlas, and the Missour basin shows three main clusters located in the Southern Middle Atlas, the north-eastern Middle Atlas, and the Central High Atlas, while the Missour basin is almost devoid of seismic activity. The available focal mechanisms and moment tensors show various tectonic regimes, mainly transpression and thrusting, while the Tabular Middle Atlas is undergoing transtension. Detailed review of neotectonic data leads to the conclusion that the area is tectonically active, as witnessed by the deformations of the Mio-Plio-Quaternary foreland formations especially at the master border faults. The review of all data including GPS measurements shows good accordance between tectonics, seismicity, and block motions with respect to fixed Nubia. Transtension in the Tabular Middle Atlas may be explained by a change of kinematics across the Northern Middle Atlas Fault. Comparison of various models set for the Eastern Meseta suggests that the whole area from the Anti-Atlas to the Tabular Middle Atlas is undergoing transpression and/or shortening.