Faults Flashcards
Stress
the force exerted per unit area
Force applied to an object, typically dealing with forces within the Earth.
Strain
The deformation that results from application of a stress.
Strain in rocks can be represented as…..
-Change in rock volume and/or rock shape
-Fracturing the rock
-
3 Types of Stress
Tensional
Compressional
Shear
Tensional Stress
Stresses that pull objects apart into a larger surface area or volume; stretching forces.
-which results in strain that stretches and thins rock.
What stress?
Tensional Stress
Compressional Stress
Stresses that push objects together into a smaller surface area or volume; contracting forces.
(Forces Pushing Together)
shows up as rock folding and thickening.
What stress?
Compressional Stress
Shear Stress
Stress within an object that causes a side-to-side movement within an internal fabric or weakness.
the strain shows up as opposing blocks or regions of material moving past each other
What kind of stress?
Shear Stress
What plate boundary is associated with tensional stress?
Divergent
What results from tensional stress?
Stretching and thinning
What type of fault is associated with tensional stress?
Normal Fault
What plate boundary is associated with compressional stress?
Convergent
What’s the result of compressional stress?
Shortening and thickening
What fault is associated with compressional stress?
Reverse Fault
What kind of plate boundary is associated with shear stress?
Transform
What results from shear force?
Tearing
What fault is associated with shear stress?
Strike-slip
If stress is the force applied to a rock, then strain is ______.
the deformation of the rock that results
Stress leads to resulting strain by changing the physical shape of the rock.
When rocks are stressed, the resulting strain can be__________
Elastic
Ductile
Brittle
Deformation
A strain that occurs in a substance in which the item changes shape due to a stress.
Elastic deformation
A type of deformation that reverses when the stress is removed.
For example, when you stretch a rubber band, it elastically returns to its original shape after you release it
Ductile deformation
A bending, squishing, or stretching style of deformation where an object changes shape smoothly.
occurs when enough stress is applied to a material that the changes in its shape are permanent, and the material is no longer able to revert to its original shape.
For example, if you bend a metal bar too far, it can be permanently bent out of shape.
Yield Point
An amount of strain where the substance has a maximum amount of elastic deformation and switches to ductile deformation.
Brittle deformation
A style of strain in which an object suddenly breaks, fractures, or otherwise fails in a different way than ductile deformation.
The type of deformation a rock undergoes depends on__________
on pore pressure strain rate rock strength temperature stress intensity time confining pressure
Pore Pressure
Pore pressure is exerted on the rock by fluids in the open spaces or pores embedded within rock or sediment.
Strain rate
Strain rate measures how quickly a material is deformed.
For example, applying stress slowly makes it is easier to bend a piece of wood without breaking it.
Rock strength measures_____________
Rock strength measures how easily a rock deforms under stress.
Removing heat or decreasing the temperature makes materials more ___________
Removing heat, or decreasing the temperature, makes materials more rigid and susceptible to brittle deformation.
Heating materials make them more ____________
heating materials make them more ductile and less brittle
How will a rock respond if it is subjected to high heat and pressure?
Bend
Rocks are more ductile at higher temperatures. With heat and pressure, the rock will most likely bend.
If you snap a “green” stick (freshly removed from a tree) into two pieces, it will first undergo __________ deformation, then __________ deformation.
If you snap a “green” stick (freshly removed from a tree) into two pieces, it will first undergo ELASTIC deformation, then BRITTLE deformation.
You will notice that you can bend a green stick before breaking it, and the stick can return to its previous shape after pressure is released if the stick is not broken, elastically. But if it breaks, it exhibits brittle behavior.
What is the resulting strain in ductile deformation?
permanent change in shape
Folds
A rock layer that has been bent in a ductile way instead of breaking (as with faulting).
Faults
A rock layer that has been bent in a ductile way instead of breaking (as with faulting).
Formations
An extensive, distinct, and mapped set of geologic layers.
Each formation on the map is indicated by a color and a label.
This symbol represents what?
Strike Slip
showing strike of N30oE and dip of 45 to the SE.
The short trunk represents the dip and the top line represents the strike.
Dip
Dip is the angle that a bed plunges into the Earth from the horizontal.
A measure of a plane’s (maximum) angle with respect to horizontal, where a perfectly horizontal plane has a dip of zero and a vertical plane has a dip of 90°.
Strike
A measure of a geologic plane’s orientation in 3-D space. Used for beds of rocks, faults, fold hinges, etc. Using the right hand rule, dip is perpendicular, and to the right 90° of the strike.
If a rock layer has a dip of 90 degrees, how is that rock layer oriented relative to a horizontal plane?
Vertical (perpendicular to level ground)
What does the strike and dip of a rock represent?
Dip is the angle of greatest inclination down from horizontal and strike is the angle from true north or true south of a horizontal line on the stratum.
Geologists define a geological formation as ______________________?
A recognizable, mappable rock unit
Faults
Faults are the places in the crust where brittle deformation occurs as two blocks of rocks move relative to one another.
Normal and reverse faults display vertical, also known ________
Normal and reverse faults display vertical, also known as DIP SLIP
Dip-slip
Faulting that occurs with a vertical motion.
Dip-slip motion consists of relative up-and-down movement along a dipping fault between two blocks, the hanging wall and footwall.
Footwall
On a dipping fault, the part of the block that is below the fault. Moves down in normal faulting, up in reverse faulting.
Hanging Wall
On a dipping fault, the side that is on top of the fault plane. Moves down in normal faulting, up in reverse faulting.
Fault Scarp
Place where fault movement cuts the surface of the Earth.
Slickensides
are polished, often grooved surfaces along the fault plane created by friction during the movement.
Joint
A break within a rock that has no relative movement between the sides. Caused by cooling, pressure release, tectonic forces, etc.
A brittle deformation
What type of fault?
Normal Fault
Normal faults move by_______
by a vertical motion where the hanging-wall moves downward relative to the footwall along the dip of the fault.
Grabens, horsts, and half-grabens are______
Grabens, horsts, and half-grabens are blocks of crust or rock bounded by normal faults
Grabens
A valley formed by normal faulting.
drop down relative to adjacent blocks and create valleys.
Horsts
Uplifted mountain block caused by normal faulting.
rise up relative to adjacent down-dropped blocks and become areas of higher topography.
Half-grabens
A valley formed by normal faulting on just one side.
Half-grabens are a one-sided version of a horst and graben, where blocks are tilted by a normal fault on one side, creating an asymmetrical valley-mountain arrangement
Do normal faults continue clear into the mantle?
No
What type of fault?
Normal Fault
What type of fault?
Normal Fault
What type of fault?
Normal Fault
Reverse Fault
compressional forces cause the hanging wall to move up relative to the footwall
Thrust Fault
A thrust fault is a reverse fault where the fault plane has a low dip angle of less than 45°.
Thrust faults carry older rocks on top of younger rocks and can even cause repetition of rock units in the stratigraphic record.
Convergent plate boundaries with subduction zones create a special type of “reverse” fault called a _______
Convergent plate boundaries with subduction zones create a special type of “reverse” fault called a MEGATHRUST FAULT
What fault causes the largest magnitude earthquakes yet measured and commonly cause massive destruction and tsunamis?
Megathrust
What plate subducts with a megathrust fault?
A megathrust fault is where denser oceanic crust drives down beneath less dense overlying crust.
What type of fault?
Thrust Fault (Which is a type of reverse fault)
Strike-Slip Faults
Strike-slip faults have side-to-side motion
Faulting that occurs with shear forces, typically on vertical fault planes as two fault blocks slide past each other.
They do not move up or down
How is the direction of strike-slip movement determined?
The direction of strike-slip movement is determined by an observer standing on a block on one side of the fault. If the block on the opposing side of the fault moves left relative to the observer’s block, this is called sinistral motion. If the opposing block moves right, it is dextral motion.
sinistral
A strike-slip or transform motion in which the relative motion is to the left. As viewed across the fault, objects will move to the left.
dextral
Movement in a transform or strike-slip setting which it toward the right across the fault. As viewed across the fault, objects will move to the right.
transpression
A segment along a transform or strike-slip fault which has a compressional component, sometimes creating related thrust faulting and mountains.
transtension
A place along a transform or strike-slip fault with an extensional component, sometimes including normal faulting, basin formation, and volcanism.
What type of fault is San Andreas Fault?
dextral, right-lateral strike-slip fault
What type of fault is the Dead Sea fault in Jordan and Israel
sinistral, left-lateral strike-slip fault
Flower Structure
A small area along a strike-slip or transform fault with branching structures of transpression/transtension, causing local hills or valleys.
What type of fault is this?
Strike-Slip
Right or Dextral
What type of fault?
Strike-Slip
Left or sinistral
What type of fault?
Dextral
Right lateral
What time of fault?
Reverse Fault
In which type of fault does the hanging wall move down relative to the footwall?
Normal
In normal faults, produced by tension, the hanging wall moves down relative to the footwall.
Which fault type is the result of compression?
Reverse/thrust
Compression shortens and thickens material, creating reverse faults; thrust faults are low-angle reverse faults.
Which fault type would be most prominent at a transform plate boundary?
Strike-slip
Transform plate boundaries are dominated by shear forces, which create strike-slip faults.
What type of fault?
Normal fault
What type of fault?
Reverse Fault (thrust fault)
What type of fault?
Reverse Fault (thrust fault)
What type of fault?
Strike Slip Fault
What kind of fault is indicated by this focal mechanism?
Strike Slip Fault
What kind of fault is indicated by this focal mechanism?
Reverse Fault
What kind of fault is indicated by this focal mechanism?
Normal Fault
