A geological interpretation of the faulting mechanism is also proposed. The existence of a new unknown source in an intermontane area is problematic. The role of inherited alpine structures seems more important today than in the past. The strike of the two new seismogenic sources, responsible for the two strongest events of the 2021 earthquake succession, differs from the previously known active faults. This forces us to reconsider older views on the direction of development of active faults and the orientation of the stress field. | Turkish Journal of Earth Sciences Turkish J Earth Sci 2021 30 851-861 http earth TÜBİTAK Research Article doi yer-2110-6 Recent earthquake activity of March 2021 in northern Thessaly unlocks new scepticism on Faults 1 2 3 Spyros B. PAVLIDES Sotirios P. SBORAS 1 Department of Geology School of Geology Aristotle University of Thessaloniki Thessaloniki Greece 2 Institute of Geodynamics National Observatory of Athens Lofos Nymfon Thessio Athens Attica Greece 3 Hellenic Survey of Geological and Mineral Exploration Acharnae Attica Greece Received Accepted Published Online Final Version Abstract This short opinion article presents and highlights new and old problems related to active geological faults as seismic sources after the experience of the last March 3 and 4 2021 and respectively Tyrnavos-Elassona earthquakes in northern Thessaly Greece. Although the active faults in the area are very well studied demonstrating typical geomorphic features that intensely affect the morphological relief it seems that the earthquakes were produced by unknown faults emerging in the mountainous area alpine basement . Primary coseismic ruptures however were also observed northwards along the Titarissios valley. A geological interpretation of the faulting mechanism is also proposed. The existence of a new unknown source in an intermontane area is problematic. The role of inherited alpine structures seems more important today than in the past. The strike of the two new seismogenic sources responsible for the two strongest events of the 2021 earthquake succession differs from the previously known active faults. This forces us to reconsider older views on the direction of development of active faults and the orientation of the stress field. Concerns are being raised about how new structures can be detected and their role in seismic hazard assessment especially when located near or within the urban fabric in cities
