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Back-analysis of rock landslides to infer rheological parameters
Published in Xia-Ting Feng, Rock Mechanics and Engineering, 2017
S. Martino, M. Della Seta, C. Esposito
A detailed study of relict intra-vallive erosional surfaces starting from their remnants hanging at different heights upon the present-day valley-floor was performed aimed at: i) recognizing former base-levels; ii) estimating the timing of their deactivations; and iii) reconstructing the stages of landscape evolution. Remnants of the relict surfaces were firstly selected starting from the 5 × 5 m Digital Terrain Model (DTM) as the areas with a slope angle <15°, which are clustered to break the steep slopes along the valley-sides. The final selection was made through a detailed field-based geomorphological analysis that allowed us to discard litho-structural sub-planar surfaces and man-made surfaces. Field surveys were useful to confirm the presence of strath terraces (sensu Bull, 1990). Strath terraces were identified as fluvial erosional surface of the Tasso-Sagittario fluvial system (when it was connected), carved directly on bedrock and/or on alluvial-to-slope deposits (i.e. fill-cut terraces of Bull, 1990 as reinterpreted in Nesci et al., 2012). Whatever their typology, along the fluvial system draining the Apennine chain was demonstrated that strath terraces staircases formed in response to period of prevalently fluvial lateral erosion separated by tectonically-induced downcutting (Wegmann & Pazzaglia, 2009; Gioia et al., 2011; Nesci et al., 2012), the latter being often related to highrate of regional uplift, coseismic uplift, and local faulting. Therefore, the intra-vallive location of strath terraces and their along-valley correlation is useful for reconstructing the past base-levels of erosion and, thus, the former levels of valley-floor. Correlations among the remnants of relict surfaces was performed after having projected them on the stream long-profiles of the Tasso-Sagittario fluvial system, as shown in Figure 5, where a good spatial continuity can be observed among surface remnants and knickpoints along the river profile, both testifying for ancient base levels (Della Seta et al., 2016). Age constraint of the relict surfaces allowing their use as geomorphic markers was inferred indirectly, by taking information from the most recent official geological map available for the area and from associated notes (Carta Geologica d’Italia at the scale of 1:50.000, Sheet 378 “Scanno”, available at the website: http://www.isprambiente.gov.it/Media/carg/). In particular, the age of each relict surface was inferred based on its relative height upon the present valley-floor and on its along-valley distribution, on the correlation with Quaternary geological units of known age and on the age of the deposits they are carved into in the case of fill-cut terrace typology.
Paleoseismology of the Akatore Fault, Otago, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2020
Briar I. Taylor-Silva, Mark W. Stirling, Nicola J. Litchfield, Jonathan D. Griffin, Ella J. van den Berg, Ningsheng Wang
We also note that a radiocarbon age was obtained by I.C. McKellar (unpublished data, 1966) from a log within a carbonaceous clay lens in the hanging-wall of the Akatore Fault at Nobles Stream. We interpret the clay lens to be within the fluvial terrace gravels resting on the schist strath. This age of 9486 ± 127 14C yr BP (NZ 714; 11,160–10,300 cal. yr BP) is slightly younger than the OSL age obtained from the silt lens in the Big Creek Trench (14,900–11,500 yr BP; 68% uncertainty), but does provide some supporting evidence that they are broadly >10 ka in age.
Uplift and fault slip during the 2016 Kaikōura Earthquake and Late Quaternary, Kaikōura Peninsula, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2023
Andrew Nicol, John Begg, Vasso Saltogianni, Vasiliki Mouslopoulou, Onno Oncken, Andrew Howell
The location of the ABF in Figures 2 and 4 is based on our interpretation of the D-lidar data. The fault coincides with two deeply incised gullies and a northeast-trending step in the topography up to 45 m in height (Figures 2 and 3). The northwest side of the step in topography is higher than the southeast and the up-step direction is in the same sense as the uplift and modelled 2016 displacement on the ABF. For the interpretations of Ota et al. (1996) and Duffy (2020) the highest three marine terraces (I/1, II/2 and III/3) were not correlated across the topographic step. Here, we propose that the poor correlation of the older marine terraces across the topographic step is due in part to slip on the ABF (either at the surface and/or at depth, as occurred in 2016), which raised the northwest side of the fault relative to the southeast side. We propose that marine terraces II/2 and III/3, previously interpreted to be separate terraces cut during different MISs, are the same terrace that has been vertically displaced by 23 ± 5 m on the ABF at the ground surface (Figure 3). In support of this argument, we have mapped marine-terrace and sea-cliff couplets immediately adjacent to the fault. Counting back from the Holocene marine-terrace and the associated Holocene sea-cliff on each side of the fault, we find that previously mapped marine terraces II/2 and III/3 occupy the same stratigraphic position in the flight of terraces, supporting our new proposed correlation. In addition, re-examination of stratigraphic auger holes from Ota et al. (1996) on their terraces II and III show that the cover bed thickness is 3–3.5 m on both terraces. Finally, the cover beds on both terraces are comparable and comprise ∼0.5 m of pebble to fine cobble gravel (clasts 1–4 cm diameter) at the base of the sequence and resting on the bedrock strath, which supports the view that these two terrace surfaces could have formed synchronously.