Contents:
5.3- Surface Phenomena
5.3.1 - Landslide and Extrados Fractures
5.3- Surface Phenomena (Traction, σ3 negative)
5.3.1 - Landslide and Extrados Fractures
Landslides and extrados fractures are created by an extensional tectonic regime (σ1 vertical), but with a σ3negative, that is to say by traction) as illustrated in fig. 300.
Fig. 300- Extrados fractures should not be confounded with normal faults associated with anticlines. Indeed, they with a single bed and above the neutral surface, i.e. the area extended. Normal faults affect several beds and are not contemporaneous of compressional structures.
5.3.2- Folds and Faults associated with Gravity
Folds and faults can be associated with slumping (gravity) as illustrated in fig. 301.
Fig. 301- These faults, which are normal up-dip and reverse down-dip, have been labelled listric (Selley), term coming from the Greek listron, which means shovels. Indeed, in the toe of a slumping, there is development of a local compressional tectonic regime responsible by the shortening of the sediments to be accommodate to the new volume conditions (see fig. 302).
The next seismic line illustrates a reverse fault associated to gravity sliding. The reverse faults are associated with local tectonic stresses; they are the seaward continuation of normal faults.
Fig. 302- The sedimentary gliding, probably due to a slope instability, created a curvilinear fault plane with a normal geometry (extension up-dip) and a reverse geometry (compression) down-dip. This kind of faulting develops in areas where the confinement pressure is relatively small, i.e. and near the surface.
Additional reading:
Bally, A. W. , R. Catalano, J. Oldow, 1985- Elementi di Tettonica Regionale, Pitagora Editrice, Bologna.
Berest, P., 1988- La thermomécanique des roches, Manuels et Methodes nû16, BRGM.
Canadian Society of Petroleum Geologists, 1982, Special reprinting, Series 3.
Goguel , J. 1965- Traité de Tectonique, Masson et Cie, Editeurs.
Goguel J.,.1983- Etude mécanique des déformations géologiques. Mauels et Methodes nû6, BRGM.
Guidon M., 1987- Les structures Tectoniques, Mauels et Methodes nÐ15, BRGM.
Price, N. J. and J.W. Copsgrove, 1990- Analysis of Geological Structures. Cambridge University Press.
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Last update: August 2014, May 2022