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What is stress?
A force exerted on an object.
What is confining stress (or pressure)?
Equal from all sides. Reduced volume without deformation.
What is directed stress?
Stresses mostly in one direction.
What are the 3 types of directed stress?
Compressive, Extensional, and Shear Stress.
What is compressive stress?
Deforms rock and shortens distance between 2 points. Occurs at convergent plate boundaries.
What is extensional stress?
Fractures rock and lengthens the distance between 2 points. Occurs at divergent plate boundaries.
What is shear stress?
Acts in parallel but opposite directions. (Like a transform fault or transform plate boundaries)
What factors control how a rock responds to stress?
1. The nature of the rock 2. Temperature ( higher temp > tendency to deform plastically) 3. Pressure (greater pressure favors plastic behavior) 4. Time (long time stress favors plastically more than SUDDEN stress).
What is a geologic structure?
Any feature produced by rock deformation.
What are the 3 types of structures tectonic stress creates?
1. Fold 2. Fault 3. Joint
What are the 3 characteristics of folds?
1. Results from compressive stress. 2. Folding always shortens the horizontal distances in rock. 3. Usually occurs as part of a group of many similar folds.
What are the 5 common fold types?
Syncline, anticline, assymetrical anticline, overturned anticline, and recumbant folds.
What are the sides of a fold called?
What is a circular or elliptical anticline called?
A dome or a basin.
How do a dome or basin form?
By the sinking or rising of continental crust, in response to vertical movements of the underlying mantle.
What is a fault?
A fracture along which rock on one side has moved relative to rock on the other side. (may be gradual or sudden earthquake)
What is a fault-zone?
Numerous closely spaced fractures.
Why does rock move repeatedly along many faults and fault zones?
1. Tectonic forces commonly persist in the same place over long periods of time (Ex. tectonic plate boundaries). 2. Once a fault forms, it is easier for rock to move again, along the same fracture, then for a new fracture to develop nearby.
Where does a normal fault form?
Where extensional stress stretches the Earth's crust, pulling apart.
What happens in a reverse fault?
Hanging wall moves up relative to the footwall, as tectonic force squeezed the rock horizontally.
What is a thrust fault?
A special type of reverse fault that is nearly horizontal.
What is a strike-slip fault?
A vertical fault in which the rocks on opposite sides move horizontally.
What is a joint?
A fracture in rock (similar to a fault) and has rocks on either side of the fracture have not moved.
What is orogeny?
The process of mountain building including tectonic forces.
What processes thicken the crust?
1. Plutons and volcanic rocks thicken the continental rocks by adding volumes of new material to it. 2. Magnetic activity heats the lithosphere, above subduction zones, causing it to expand and become thicker. 3. Underthrusting (2 continents colliding) can double the thickness of continental crust in the collision zone. 4. Compressive forces squeeze the crust horizontally to increase its thickness.
What is an island arc?
A volcanic mountain chain that forms where 2 plates carrying oceanic crust coverage.
What is an earthquake?
A sudden motion or trembling of the Earth caused by the abrupt release of energy that is stored in rocks.
What is a seismic wave?
Waves that travel through rock.
What is seismology?
The study of earthquakes and the nature of the Earth's interior based on evidence from seismic waves.
What is the focus?
The initial rupture point, where abrupt movement creates an earthquake (typically lies below the surface).
What is the epicenter?
The point on the Earth's surface directly above the focus.
What is a p wave?
A compressional elastic wave that causes alternate compression and expansion of the rock. They are called primary waves because they are so fast that they are the first seismic waves to reach an observer.
What is an s wave?
A shear wave, it arrives after P and are secondary to an observer.
What are body waves?
Waves that travel through the Earth's interior and carry some of the energy from the focus to the surface. Including p and s waves.
What are surface waves?
An earthquake wave that travels along the surface of the Earth, or along a boundary between layers within the Earth.
What is the most important factor that determines the speed of a p wave?
The elastic properties of the medium in which the wave travels.
What is the interpreted cause of the low-velocity zone?
A zone of partial melting in the mantle.
What is the primary kind of stress that caused the dip-slip fault shown below?
Compressive stress.
Rocks that are deformed "blank" store energy that can be released by earthquakes.
What is the basis for the Mercalli Intensity Scale?
Surface effects of earthquakes.
Which was a major contributing factor to the damage experienced from both the 1989 Loma Prieta and 1985 Mexico City earthquakes?
Liquification of sediments.
The average elevation of the continents above sea level is greater than the average depth of the ocean floor below sea level.
Areas are continental crust are higher than those of oceanic crust because continental crust is:
Thicker and less dense than oceanic crust.
Which 2 geologic processes can lead to isostic uplift?
Crustal thickening and erosion.
Where would one find the oldest crust?
Interiors of continents.
A thickening of the crust will lead to what geologic response?
How does mountain building relate to the growth of continents?
Middle (old) and then spreads out and gets younger.
What are the 2 main reasons mountains disappear?
1. Erosion 2. Crust can only get so thick.
What is a Benioff Zone?
An inclined zone of Earthquake activity that traces the upper portion of a subducting plane in a subduction zone.
Where do seismic waves travel faster, the mantle or the crust?
The mantle
What is the Moho discontinuity?
The boundary between the crust and the mantle identified by a change in the velocity of seismic waves.
What is the zone called where seismic wave velocity changes?
660kilometer discontinuity , seismic wave velocities increase because pressure is great enough that the minerals in the mantle recrystallize to form denser materials.
What is the metallic core composed of?
Iron and Nickel.
Where is the Earth's magnetic field generated from?
The outer core.
What are the 2 types of motion that occur in the Earth's outer core?
1. Liquid metal convects (because the outer core is much hotter at its base than at its surface). 2. These convecting spinning liquid conductors are thought to generate the Earth's magnetic field. (the rising and falling metals are detected by the Earth's spin)
What is weathering?
The process that decomposes rocks and converts them to loose gravel, sand, clay, and soil.
What is mechanical weathering?
It reduces the solid rock to small fragments but does not alter the chemical composition of rocks and minerals.
What is chemical weathering?
When air and water chemically react with rock to alter its composition and mineral content.
What 5 different processes can cause mechanical weathering?
Pressure-release fracturing, frost wedging, abrasion, organic activity, and thermal expansion and contraction.
What is pressure-release fracturing?
Fracturing of rock that occurs when pressure decreases and the rock expands as tectonic forces raise it from a depth of several kilometers and erosion removes overlying rocks.
What is frost wedging?
When water accumulates in a crack and then freezes causing expansion to pull the rock apart.
What is abrasion?
The mechanical weathering of rocks by friction and impact.
What are the most important processes of chemical weathering?
Dissolution, hydrolysis, and oxidation.
What is the only rock-forming silicate mineral that does not weather to form clay?
Quartz, because it dissolves extremely slow and only to a small extent.

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