7/25/2023 0 Comments Definition of viscosity in geology![]() The level of stress at which deformation becomes irreversible is called the elastic limit. The principle can also be applied to most sediments and rocks. The principle was developed by Robert Hooke– Hookes Law (1660) the classic physics experiment involves a spring. The scale is logarithmic, such that a magnitude of 4 (10 4) is 100 times smaller and less energetic than M6 (10 6).Įlastic behaviour : This rheological behaviour describes materials that respond to stress by deforming but can return to their original state when the stress is removed. M is expressed as a number (M1.8, M4.6, M7.8) up to a maximum of 10. Cf epicentre.Įarthquake magnitude : Magnitude (M) reflects the severity of ground roll and shaking, and on seismograms the amplitude of the signal (usually of surface waves). Duplexes can take several geometric forms.Įarthquake focus : The actual point beneath the surface where an earthquake is focused. Duplexes represent progressive, incremental formation of ramps and bending folds (anticline-syncline pairs). ![]() Ductile deformation of rock is enhanced under conditions of high confining pressures, high temperatures, and low strain rates.ĭuplex: An imbricate stack of horses bound above and below by through-going thrusts these are the roof and floor thrusts. Materials that deform ductily appear to flow or bend. Drape folding can occur in soft sediment or as ductile deformation in indurated rock.ĭuctile deformation (flow): Deformation (strain) beyond a material’s elastic limit that is permanent (not reversible), but does not result in fracturing (brittle failure) – i.e. They are useful ( kinematic) indicators of fault displacement.ĭrape fold: Strata deformed as folds over pre-existing structures or topography. For example, boudinage of thinly bedded sandstone-shale will involve brittle failure and translation, and possibly rotation of sandstone boudins, and ductile flow of the mechanically less competent shale.ĭrag fold : Folds produced during faulting as a result of shear strain distributed beyond the fault plane into the adjacent rock. ![]() Hogbacks and Flatirons are usually identified by their dip slopes.ĭistortion (kinematics): Non-rigid body deformation involving a change of shape commonly by ductile flow. The grain size range is >0.1 mm and 30-40°. Ductile flow.Ĭataclastite : Fine ground-up bedrock produced by grinding during faulting. Brittle deformation is also enhanced by low confining pressures and low temperatures – these are the conditions that lead to faulting and fracturing during an earthquake. If the strain rate is high, this deformation will take place as sudden fracturing (e.g. Blind thrust tip points (tip lines) typically contain fault propagation fold pairs.īranch point: Locations along a thrust where branching or fault splays are generated.īrittle behaviour (rheology): Most Earth materials behave elastically up to their elastic limit, beyond which deformation is irreversible. thrust plane dip is towards the foreland.īlind thrust : A thrust that does not breach the surface at the time of its formation. In many cases back thrust vergence will be towards the hinterland, i.e. Riedel shears.īack thrust: A thrust that has vergence opposite the dominant trend of a thrust system. Antithetic and synthetic faults commonly occur in parallel arrays. Opposing subsidiary structures are synthetic where the displacement has the same shear sense as the master fault. They occur in extensional regimes (such as accommodation in the hanging wall of listric faults), compressional regimes as back-thrusts, and strike-slip faults. Synform.Īntithetic faults: Subsidiary or minor faults that have a sense of displacement opposite that of a master fault or principal deformation zone. ![]() If younging direction is known, the name anticline is used. antiform, syncline.Īntiform : Convex upward folds the name is reserved for folds where stratigraphic younging, or facing directions are unknown. angle of repose.Īnticlin e: Convex upward or outward folds, where layers are stratigraphically younger in the convex direction. It is an essential parameter in the quantification of rock deformation. Angle of internal friction: A rock or material property that refers to its ability to resist deformation, and is measured as the angle between the normal stress and a resultant stress at the point where shear begins.
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