Multiple ruptures on the North-Sofia fault at Gorni Bogrov from scarp profile and shallow geophysics

Pages: 
pp. 65-74
Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria; National Institute of Geophysics, Geodesy and Geography, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 3, 1113 Sofia, Bulgaria
Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
Abstract: 

The seismic hazard assessment across the densely urbanized region in the Sofia Basin in Bulgaria can be improved through using fault data, in search of which we first aim to attain to a better knowledge on the past earthquake ground ruptures. Currently focused on the North-Sofia fault, we investigated whether, and how, the fluvial system responded to fault displacements at a site located near the village of Gorni Bogrov. At the studied site, a scarp delimits a distal alluvial fan on the upper surface from an alluvial plain on the lower surface. Although the scarp forms a complex structure that resembles a breached relay ramp, its fault origin is questionable, because the basin axial stream could have caused lateral erosion approaching the toe of the fan. The electrical resistivity profiles that we measured imply that recent deposits are associated with fault displacement. A fault located beneath the middle slope juxtaposes Neogene sand layers, covered by an alluvial fan in the footwall, with colluvial deposits laterally merged with deposits from the alluvial plain in the hangingwall. The scarp also contains a non-tectonic component related to lateral erosion affecting mainly the lower slope. Breaks on the scarp profile are interpreted to have originated through erosion repeatedly renewed due to multiple fault displacements in recent times. The interseismic intervals of the North-Sofia fault are inferred to be in order of thousands of years but not longer. The inferred interseismic intervals correspond approximately to those of the adjacent South-Ihtiman and distant Chirpan faults; however, they are noticeably shorter compared to the adjacent Zlatitsa and distant Krupnik faults. It seems likely that faults in a broad region on the Balkans release strain at remarkably different rates, independently from their proximity.

Keywords: 

tectonic geomorphology, ERT, North-Sofia fault, Sofia Basin, Balkans

DOI: 
10.52321/GeolBalc.52.2.65

VOLUME 52 (2)/August 2023

Department of Paleontology, University of Vienna, Josef-Holaubek-Platz 2 (Geozentrum), 1090 Vienna, Austria; Austrian Archaeological Institute ÖAI, Austrian Academy of Sciences, Quaternary Archeology, Hollandstraße 11-13, 1020 Vienna, Austria
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Department of Geology, Aristotle University, School of Geology, 54124 Thessaloniki, Greece
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VERA Laboratory, Faculty of Physics, University of Vienna, Währinger Straße 17, 1090 Vienna, Austria
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VERA Laboratory, Faculty of Physics, University of Vienna, Währinger Straße 17, 1090 Vienna, Austria
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National Museum of Natural History, Bulgarian Academy of Sciences, 1 Tsar Osvoboditel Blvd, 1000 Sofia, Bulgaria

Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, Saint-Petersburg, Russian Federation
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria

Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria

Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria; National Institute of Geophysics, Geodesy and Geography, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 3, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria

Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria

Ministry of Defense, 227-231 Mesogeion Avenue, Cholargos, 15561, Greece
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Cyient Ltd., Hyderabad, 500039, India

Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria
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Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria

Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 24, 1113 Sofia, Bulgaria