Exam 1 Flashcards
Force has a ____ and _____ (vector quantity)
magnitude and direction
force equation
F = ma (newtons)
body force
work at a distance and depend on amount of material (ex: gravity)
surface force
works across surface of contact and depend on magnitude and area of surface
stress is the ____
intensity of force
stress on a _____ is a vector and is a ____ at a point
surface, tensor
stress equation
stress = F/a (Pa, MPa, GPa)
lithostatic stress
stress caused by the weight of the rock above a point
uniaxial stress
stress state where only one of the principial stresses is nonzero
convergent boundaries create
compression
divergent boundaries create
tension
transform boundaries create
shear
normal stress vector is…
perpendicular to the surface
shear stress vector is…
parallel to the surface
in a stress ellipse the stress is acting in…
all directions
stress ellipse shows…
the graphically the magnitude of stress
the long axis of ellipse is…
max principal stress
the short axis of ellipse is…
min principal stress
sigma 2 is the…
the intermediate principal stress axial
the center of a stress tensor can be considered a…
cube
if the center of a stress tensor is stable then shear stress…
on mutually perpendicular faces are equal
what if sigma 1 = sigma 2 = sigma 3
stress state is isotropic (hydrostatic stress or pressure)
deviatoric stress and mean stress are..
components of total stress
deviator stress causes…
permanent deformation
simple shear
deformation
pure shear
flattening and stretching
sub-simple (general) shear
deformation by rotation and flattening and stretching
how to measure 2D strains of a stretched pebble
- calculate area of ellipse
- find radius of circle w/ equivalent area
- strain is calculated from difference between ellipse length axis (final) and circle radius (initial)
rocks don’t fracture along…
planes of mx shear stress because internal friction
fracture initiation in tectonic settings
- increase differential stress
- increase pore fluid pressure
normal fault setting
push less from side “decrease sigma 3”
thrust fault setting
push more from side “increase sigma 1”
What causes an earthquake
- fracture ruptures
- fault develops
- earthquake happens when fracture develops
- when frictional limit is met stress is converted to tectonic to seismic waves and heat
draw a normal fault and label principle stress orientations
YAY!
divergent plate boundaries mean stress
generally lower because of principal stresses are orientated away from each other
(lower mean stress reduces the overall resistance to deformation)
divergent plate boundaries differential stress
-high due to the tensional stress, causing rocks to deform more easily along fractures and faults
convergent plate boundaries mean stress
-mean stress is higher due to the compression, making it more difficult for rocks to deform
convergent plate boundaries differential stress
-high stress results from compression, making rocks more resistant to deformation and more likely to fold or undergo plastic deformation
mean stress
represents the average or uniform stress experienced by a material in a particular direction
differential stress
the difference between the maximum and minimum principal stresses in a stress field
represents the intensity of stress acting within a material and is a measure of the deformation potential or strain
