Episodic activity of a dormant fault in tectonically stable Europe: The Rauw fault (NE Belgium)

• Published in: Tectonophysics 2017-03, Vol.699, p.146-163
• Main Authors: Verbeeck, Koen, Wouters, Laurent, Vanneste, Kris, Camelbeeck, Thierry, Vandenberghe, Dimitri, Beerten, Koen, Rogiers, Bart, Schiltz, Marco, Burow, Christoph, Mees, Florias, De Grave, Johan, Vandenberghe, Noël
• Format: Article
• Language: English
• Subjects: Alluvial deposits; Alluvial terraces; Campine Basin; Clay; Confluence; Displacement; Dormancy; Earthquakes; Electron paramagnetic resonance; Electron spin; Electron spin resonance dating; Fault detection; Fault lines; Faults; Geological faults; Geomorphology; Geophysics; Graben; Gravel; History; Identification; Neogene; Optical dating; Paleoseismology; Pleistocene; Pliocene; Rauw fault; Rupturing; Seismic activity; Seismicity; Seismology; Solifluction; Spin resonance; Stable continental region; Stratigraphy; Trenches (pipelines); Valleys
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2017.01.023

Our knowledge about large earthquakes in stable continental regions comes from studies of faults that generated historical surface rupturing earthquakes or were identified by their recent imprint in the morphology. Here, we evaluate the co-seismic character and movement history of the Rauw fault in Belgium, which lacks geomorphological expression and historical/present seismicity. This 55-km-long normal fault, with known Neogene and possibly Early Pleistocene activity, is the largest offset fault west of the active Roer Valley Graben. Its trace was identified in the shallow subsurface based on high resolution geophysics. All the layers within the Late Pliocene Mol Formation (3.6 to 2.59Ma) are displaced 7m vertically, without growth faulting, but deeper deposits show increasing offset. A paleoseismic trench study revealed cryoturbated, but unfaulted, late glacial coversands overlying faulted layers of Mol Formation. In-between those deposits, the fault tip was eroded, along with evidence for individual displacement events. Fragmented clay gouge observed in a micromorphology sample of the main fault evidences co-seismic faulting, as opposed to fault creep. Based on optical and electron spin resonance dating and trench stratigraphy, the 7m combined displacement is bracketed to have occurred between 2.59Ma and 45ka. The regional presence of the Sterksel Formation alluvial terrace deposits, limited to the hanging wall of the Rauw fault, indicates a deflection of the Meuse/Rhine confluence (1.0 to 0.5Ma) by the fault's activity, suggesting that most of the offset occurred prior to/at this time interval. In the trench, Sterksel Formation is eroded but reworked gravel testifies for its former presence. Hence, the Rauw fault appears as typical of plate interior context, with an episodic seismic activity concentrated between 1.0 and 0.5Ma or at least between 2.59Ma to 45ka, possibly related to activity variations in the adjacent, continuously active Roer Valley Graben. [Display omitted] •Low slip rate, normal Rauw fault demonstrated on geophysics and in a trench•The 7m offset occurred between 2.59Ma and 45ka, most of it between 1 and 0.5Ma.•Micromorphology of the fault gauge indicates fast, co-seismic rupturing.•Activity of the Rauw fault is episodic and it is dormant at present.