TY - JOUR
T1 - Growth of exfoliation joints and near-surface stress orientations inferred from fractographic markings observed in the upper Aar valley (Swiss Alps)
AU - Ziegler, Martin
AU - Loew, Simon
AU - Bahat, Dov
N1 - Funding Information:
This research is part of the Paraglacial Rock Slope Mechanics project supported by the Swiss National Science Foundation ( SNF 135184 ). We thank KWO Kraftwerke Oberhasli AG, Innertkirchen, for providing access to their data archive, drill cores, and for stress measurement data. Marc Hugentobler (ETH) helped us substantially with collecting data in the field. We gratefully acknowledge many fruitful discussions with Florian Amann and Keith Evans (both ETH). We thank T. Engelder and S. Martel very much for their constructive inputs to our manuscript.
Publisher Copyright:
© 2014 Elsevier B.V.
PY - 2014/1/1
Y1 - 2014/1/1
N2 - Granitic rock mass of the upper Aar valley (Grimsel area, Switzerland) contains distinct generations of exfoliation joints, which formed during different stages of the Pleistocene, subparallel to distinct glacial valley palaeotopography. The bulk of exfoliation joints shows prominent, common fractographic features: (1) radial plumose structures with distinct plume axes; (2) arrest marks superimposed by plumose striations; and (3) gradually-developing en échelon fringe cracks.Multiple arrestmarks reveal that exfoliation joints formed incrementally and, togetherwith the absence of hackle fringes, suggest stable, i.e., subcritical fracturing conditions. Smooth transitions fromplumose structures on the parent plane to en échelon fringe cracks, combinedwith nonsystematic stepping senses of fringe cracks, suggest local (vs. temporal) stress field variations. Assuming that plume axes formed parallel to the maximum principal compressive stress (σ1) enables us to infer near-surface palaeostress orientations and compare them with classical borehole-based in-situ stress data. The majority of plume axes suggest (1) persistently subhorizontal to slightly inclined σ1 orientations at trough valley slopes and (2) near-surface variability of σ1 orientations originating from topographic perturbation caused by glacial valley erosion superimposed on the regional stress field. Our investigations of fracture surface morphologies yield unique insights into exfoliation fracture formation, such as directional trends of fracture propagation and associated palaeostress orientations within Alpine valley slopes.
AB - Granitic rock mass of the upper Aar valley (Grimsel area, Switzerland) contains distinct generations of exfoliation joints, which formed during different stages of the Pleistocene, subparallel to distinct glacial valley palaeotopography. The bulk of exfoliation joints shows prominent, common fractographic features: (1) radial plumose structures with distinct plume axes; (2) arrest marks superimposed by plumose striations; and (3) gradually-developing en échelon fringe cracks.Multiple arrestmarks reveal that exfoliation joints formed incrementally and, togetherwith the absence of hackle fringes, suggest stable, i.e., subcritical fracturing conditions. Smooth transitions fromplumose structures on the parent plane to en échelon fringe cracks, combinedwith nonsystematic stepping senses of fringe cracks, suggest local (vs. temporal) stress field variations. Assuming that plume axes formed parallel to the maximum principal compressive stress (σ1) enables us to infer near-surface palaeostress orientations and compare them with classical borehole-based in-situ stress data. The majority of plume axes suggest (1) persistently subhorizontal to slightly inclined σ1 orientations at trough valley slopes and (2) near-surface variability of σ1 orientations originating from topographic perturbation caused by glacial valley erosion superimposed on the regional stress field. Our investigations of fracture surface morphologies yield unique insights into exfoliation fracture formation, such as directional trends of fracture propagation and associated palaeostress orientations within Alpine valley slopes.
KW - Alpine valley slope
KW - Brittle fracture propagation
KW - Fractographic analysis
KW - In-situ stress measurements
KW - Palaeostress analysis
KW - Topographic stress perturbation
UR - http://www.scopus.com/inward/record.url?scp=84922002472&partnerID=8YFLogxK
U2 - 10.1016/j.tecto.2014.03.017
DO - 10.1016/j.tecto.2014.03.017
M3 - Article
AN - SCOPUS:84922002472
SN - 0040-1951
VL - 626
SP - 1
EP - 20
JO - Tectonophysics
JF - Tectonophysics
IS - 1
ER -