Revised classification criteria for glacially induced faults

<p>Glacially triggered faulting is the release of stresses induced by the advances and retreats of ice sheets in addition to other stresses that accumulated in the lithosphere. The faulting typically occurred along pre-existing faults or weakness zones before, during or after the last ice melting. This type of faulting is mainly recognized in intraplate regions but is also proposed for some plate boundary areas. Past reactivations were probably accompanied by large-magnitude seismic events triggering hundreds of landslides and seismically induced soft-sediment deformation structures (SSDS) in the region surrounding the glacially induced faults (GIFs).</p><p>Classification criteria were developed in the 1980s and 1990s to correctly identify a GIF and distinguish it from the vast number of other faults around the globe. Reliable field evidence for reactivated faults in and (even) around many formerly glaciated areas has considerably increased the number of confirmed and probable GIFs in recent years, which were recently unified in an international database (Munier et al., 2020). It has been generally thought that GIFs, especially the so-called postglacial faults in northern Fennoscandia, were developed during a short period of time towards the end of and shortly after the deglaciation, however, new dating results from Fennoscandia documenting several episodes of fault rupture within the past 14,000 years (Ojala et al., 2018; Olesen et al., 2021) and even connected to the begin of glaciation (Sutinen & Middleton, 2021) challenge this idea. The youngest fault scarp was formed less than 600 years ago (Olesen et al., 2021).</p><p>The new findings warrant a discussion of the classification criteria. We introduce revised classification criteria for GIFs, modified from the previous criteria and for easier application expressed as a checklist, see also Steffen et al. (2021).</p><p> </p><p><strong>References</strong></p><p>Munier, R., Adams, J., Brandes, C., et al. (2020). International database of Glacially Induced Faults. PANGAEA, https://doi.org/10.1594/PANGAEA.922705.</p><p>Ojala, A. E., Markovaara-Koivisto, M., Middleton, M., Ruskeeniemi, T., Mattila, J., Sutinen, R. (2018). Dating of paleolandslides in western Finnish Lapland. Earth Surface Processes and Landforms 43(11), 2449–2462, https://doi.org/10.1002/esp.4408.</p><p>Olesen, O., Olsen, L., Gibbons, S., Ruud, B., Høgaas, F., Johansen, T., Kværna, T. (2021). Postglacial faulting in Norway – Large magnitude earthquakes of the Late Holocene Age. In H. Steffen, O. Olesen, R. Sutinen, eds., Glacially-triggered faulting. Cambridge University Press, pp. 198– 217, https://doi.org/10.1017/9781108779906.015.</p><p>Steffen, H., Olesen, O., Sutinen, R. (2021). Glacially-triggered faulting – A historical overview and recent developments. In H. Steffen, O. Olesen, R. Sutinen, eds., Glacially-triggered faulting. Cambridge University Press, pp. 3–19, https://doi.org/10.1017/9781108779906.003.</p><p>Sutinen, R., Middleton, M. (2021). Porttipahta end moraine in Finnish Lapland is constrained to Early Weichselian (MIS 5d, Herning stadial). Geomorphology 393, 107942, https://doi.org/10.1016/j.geomorph.2021.107942.</p>