Week 2 Flashcards
Rheology definition and two examples
Describes how rock will deform when subjected to a force and takes into account both the physical properties of the rock and the conditions at which it is deforming.
Elastic (for materials that deform like a spring).
Viscous (for materials that deform like a fluid).
Isostasy
Is the rising or settling of a portion of the Earth’s crust that occurs when weight is removed or added in order to maintain equilibrium between buoyancy forces that push the crust upward, and gravity forces that pull the crust downward.
The crust neither floats nor sinks within the ductile asthenosphere beneath.
The state in which pressure from every side are equal.
Visco-elastic
Visco-elastic materials may be both elastic and viscous, with stress being equal to the sum of strain-dependent deformation and strainrate dependent deformation.
Visco-plastic
Behavior of a material to exhibit both viscous and plastic characteristics
What drives crustal deformation?
Mantle convection, induces stresses within the lithosphere. In response, lithospheric rocks deform (change shape).
What is rheology??
What factors impact it list 8
How matter deforms and flows, including elasticity, plasticity and viscosity.
mineralogy
fluid content
chemistry
mineral grain size
melt fraction
temperature
pressure
differential stress conditions
Brittle-elastic
Behavior of rocks to deform elastically under stress (meaning they return to their original shape when stress is removed) up to a certain limit. Once the stress exceeds this limit, rocks will fracture or break, displaying brittle failure.
Lithosphere-Asthenosphere Boundary (LAB)?
Is the boundary between Earth’s rigid lithosphere and the more ductile, flowing asthenosphere below it. This boundary marks a change in mechanical properties, where the lithosphere behaves as a brittle, rigid layer, while the asthenosphere is weaker and can flow due to its partially molten state. The LAB depth varies, generally deeper under continents (up to 200 km) and shallower under oceanic crust (around 50-100 km).
What is hydrostatic pressure?
Is the pressure imposed on a layer of material by the weight of the overlying material.
Pascal’s Law
Within a fluid in static equilibrium, the hydrostatic pressure is the same on every point at the same elevation, the so-called surface of hydrostatic compensation.
What is Archimede’s Principle?
A body that is partially or completely submerged in a fluid, will experience an upwards buoyancy force that is equal to the weight of the fluid the body displaces.
What is Pratt’s model?
The Compensation Depth was a horizontal surface beneath mountains. Consequently, the density must vary laterally across a mountain range, with the higher altitudes underlain by rocks of lower density
What is Airy’s Model?
Continental crust has a uniform density. Consequently, the highest mountains must be supported by deep crustal roots that reach greater depths within the ductile mantle below.
What is flexural isostasy?
It is the deflection of lithospheric plates due to topographic loading or unloading.
When a mass (e.g. seamount) is placed atop a plate, it will bend/flex.
Orogeny, erosion and shield formation.
Draw the three main steps
Normal Fault
AKA dip-slip fault
Defined by hanging wall moving downwards relative to the footwall due to extensional forces.
45*
Earthquakes how do they work?
Stress accumulates at the fault surface, due to the differential motion of the plates either side of the fault.
When the accumulated tectonic stress exceeds the frictional strength of the fault, an earthquake rupture occurs.
The accumulated stress is released as seismic (elastic) waves and rock either side of the fault is permanently offset.
Reverse Fault
AKA Dip-slip fault
Hanging wall is forced upward driven by compressional forces.
45*
Strike-Slip Transverse
What are the two types?
Sidewards movement horizontally in the direction of the fault
left-lateral (sinistral)
right-lateral (dextral)
What are principal stress orientations?
Sigma 1 is defined as the greatest compressive stress
sigma 2 is the intermediate stress.
sigma 3 is the least principal stress
Stress directions of a normal fault
S1 red, S2 yellow, s3 blue
Stress directions of a reverse fault
S1 red, S2 yellow, s3 blue
Stress directions of a strike-slip fault
S1 red, S2 yellow, s3 blue
Mega-Thrust Fault
Is a large-scale fault that forms at subduction zones, where one tectonic plate is forced beneath another. These faults have low-angle dips and are associated with some of the most powerful earthquakes and tsunamis on Earth, due to the immense stress and energy release. Mega-thrust faults are typically found at convergent plate boundaries, such as along the Pacific Ring of Fire.
