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Structural continuity across an oblique rift and a transform zone in southwest Iceland.

Yohann Chatelain 1, Joël Ruch1, Elisabetta Panza1, Nicolas Oestreicher1, 2, 3

  • Affiliations:  1 Department of Earth Sciences, University of Geneva, Genève, Switzerland ; 2 WSL Institute for Snow and Avalanche Research SLF, Switzerland ; 3 Climate Change, Extremes and Natural Hazards in Alpine Regions Research Centre CERC, Davos, Switzerland 

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 154

  • Programme No: 3.5.13

  • Theme 3 > Session 5

Abstract

The South Iceland Seismic Zone (SISZ) and the Reykjanes Peninsula, located along the active plate boundary between the North American and Eurasian plates, exhibit distinct tectonic behaviors. The Reykjanes Peninsula, an oblique rift zone, experiences volcanic, and seismic activities, whereas the SISZ, a transform fault zone, is characterized by significant seismic activity (up to Mw 7) nucleating on NS-oriented faults but lacks volcanism. Both regions form a 140 km long E-W left-lateral shear zone oriented N070, with NS right-lateral strike-slip faults, indicative of a common tectonic mechanism. Structural continuity between the two zones remains uncertain, raising concerns about potential large earthquakes propagating toward the Reykjavik area. We used drone photogrammetry to map and analyze NS fault systems, producing high-resolution DEMs and orthophotos. We examined fault populations to obtain detailed structural maps. We found that 20 NS fault zones distributed in both areas exhibit comparable en-echelon fractures and compressional push-ups, supporting a structural continuity between the SISZ and Reykjanes. We then combined our results with seismic data and observed a westward decrease of fault segment lengths, earthquake magnitudes and epicenter depths. We suggest that these structural differences in the faults' systems are likely influenced by a plate boundary rotation. An angle exceeding approximately 20° between the boundary and the spreading direction, due to a higher normal component,  may promote volcanic activity. This activity increases the geothermal gradient, thereby expanding the ductile area and reducing the risk of large earthquakes, which is crucial for assessing seismic hazards in this densely populated region.