Which of the following is NOT a piece of evidence that shows the Earth is composed of tectonic plates?
1) Past climates
2) Jigsaw puzzle fit
3) Distributon of fossils
4) Width of the oceans
Answer = #4
Striatons are scratches on a rock surface produced by a glacier moving across it. (T/F?)
The geologic community agreed with Wegener's continental drift idea. (T/F?)
False. They thought he was absolutely nuts.
A lithospheric plate consists of what???
The crust and uppermost part of the mantle.
The oldest oceanic plate on the surface of Earth is about 200 Ma years old. (T/F?)
The thickest ocean sediment is found near mid-ocean ridges and the thinnest ocean sediment is found away from the ridge. (T/F?)
The picture below represents a magnetic profile across a mid‐ocean ridge. Where is the ridge axis?
It's between wherever the big gap on the diagram is.
A reversal in the Earth's magnetic field will happen again in the future. (T/F?)
True. Our planet changes everyday and there is no telling when it might happen, but if it does, we're screwed.
Following WWII, Harry Hess determined that oceans are younger than continents based on ______.
The thickness of the ocean floor sediment.
The oldest continental plate on the surface of Earth is about 4 billion years old. (T/F?)
True. The Ocean Continental Plate is about 200 ma.
Continental plates are heavier (i.e. more dense) than oceanic plates. (T/F?)
False. Oceanic Plates are heavier causing them to go under.
-Oceanic Plates are composed of basalt and gabbro
-Continental Plates are composed of granite
Pieces of the Lithosphere = Plates
The Himalayan Mountains are an example of what type of plate boundary?
The mid‐Atlantic ridge is an example of what type of plate boundary?
Divergent: Ocean-Ocean Plates
The East Africa Rift is an example of what type
of plate boundary?
Volatiles carried into the Earth at subduction zones lead to the formation of volcanoes. (T/F?)
The San Andreas fault (shown in the picture) is a _____ lateral‐fault.
Divergent plate boundaries are also known as _______ plate boundaries.
Constructive. They make new plate materials.
The Wilson Cycle describes how plates rift apart and collide together again repeatedly over time. (T/F?)
What is the basic driving force behind plate tectonics?
Hotspots move location to location over time. (T/F?)
False. They stay put where they're at.
The point on the surface of the Earth above where an earthquake happens is called the ______.
Deep focus earthquakes tend to be the most destructive. (T/F)
What type of fault would you expect to find in a mid-ocean ridge (diverge) environment?
What type of fault would you expect to find in a mountain building (convergent) environment?
What type of fault would you expect to find near a subduction zone environment?
As strain/energy builds up in rocks, it cause the rock to PERMANENTLY deform. (T/F?)
If you have a slow gradual movement along a (i.e. fault creep) you tend not to have earthquakes. (T/F?)
It is possible for humans to induce earthquakes. (T/F?)
What type of seismic wave will travel the fastest and will be the first to arrive at a seismometer?
What type of seismic wave tends to cause the most damage to human-made structures?
The minimum number of seismic records needed to locate an earthquake is _________. How many?
The Richter Scale is the best and most accurate scale used for measuring earthquake size. (T/F?)
Which dot color on a map would mark the deepest earthquakes (i.e. Wadati-Benioff Zone)?
The force that deforms the layer of rock is called __________.
Changes to different rocks result from _____________.
When a deck of cards is push forward at the top, the cards look horizontal slanted after that. What stress is that?
If stress is applied slowly, materials tend to exhibit brittle deformation. (T/F?)
Ductile deformation in rocks occurs at high temperatures and pressures. (T/F?)
Fracturing (creating a joint or fault) is a type of ______________ deformation.
Brittle and Plastic
Which type of fold points upwards and has the oldest rocks in the center?
When you snap a twig in half, breaking it down into two pieces, you have caused ______________ deformation.
Folds are generally created by which types of stress?
Foliation indicates that a rock has experienced brittle deformation. (T/F?)
Given the principle of isostacy, the taller the mountain, the thicker the crust beneath it. (T/F?)
Cratonic shields are Precambrian rocks covered by a thin layer of sediment. (T/F?)
What was Wegener's evidence for continental drift include?
He explained what happened, but didn't say how it happened.
- Continents plow through oceanic crust
- Forces from Earth's rotation
- Continental rocks fairly weak compared to oceanic rocks
- Rotational forces too small to move massive chunks of land
• "Jigsaw puzzle" fit of the continents
• All assembled-could fit into one large landmass
• Evidence of past glaciations
• Striations: scratches on rock produced by ice moving over it.
• Locations of glacial deposits not in polar locations
• Striations pointed outward from a common point
• Correlation of geologic units
• example: rocks in the Appalachian Mts. resemble rocks found in mountains in Scandinavia and Great Britain
Where are the thick and thinnest sediment located at?
Thin sediments are located at mid-ocean ridges and thick sediments are located away from the ridge.
Explain some characteristics of "Sea-Floor Spreading." What are they?
• new ocean crust made at mid‐ocean ridges (thin sediment); gets older as it moves away (thick sediment)
• Sea floor consumed at trenches
• Driving force for continental drift
That's how they make new oceanic plates
Be able to explain Earth's magnetic record (normal versus reversed polarity) and how to use a magnetic record to identify mid-ocean spreading centers.
Normal polarity is small and wide on the diagram. Also, to identify mid-ocean spread centers using magnetic records, look for symmetrical lines.
State the Earth's compositional layers. What are they?
• oceanic and continental
• below crust, surrounds core
• plastic (not molten) consistency
• solid inner core
• liquid outer core
• both composed mostly of iron and nickel
State the Earth's rheological (mechanical) layers. What are they?
• crust and upper mantle
• rigid; brittle
• mantle down to 660 km
• plastic; flows very slowly
• not molten!!!
What does the "Plate Tectonics Theory" state?
It states that pieces of the lithosphere move relative to one another, moving over the asthenosphere.
They explain that:
• Earth's major surface processes
• distribution of ancient organisms and mineral deposits
• geologic distribution of earthquakes, volcanoes, and mountains
How are plate boundaries identified?
By looking for a lot of volcanoes on a diagram. Black lines to be more specific.
What are the three types of plate boundaries?
What is a divergent boundary?
A plate boundary where two plates are moving away from one another (spreading center). They have mid-oceanic ridges (separation of two oceanic plates) and continental rifts (separation of two continental plates).
What is a convergent boundary?
A plate boundary where two plates are running into one another. They have Ocean-Ocean Continent Convergences (Where the oceanic plates subduct under continental plates because of being much heavier with basalt and gabbro) and Continent-Continent Convergences (Mountain Building).
Convergent Boundaries are also known as __________ boundaries.
Destructive. They destroy plate material.
What is a transform boundary?
A plate boundary when two plates are moving past one another, side-by-side. Plate material is neither created nor destroyed. They contain right and left lateral strike slip faults as relative motions of the plate boundaries.
How are "hotspots" developed?
Hotspots develop under oceanic plates and even continental plates too. Yellowstone for example. Hawaii too.
State the difference between "Active Margin" and "Passive Margins." What is the difference?
Active Margins are edges of continents where you have an active plate boundary (subduction or mountain building going on).
Passive Margins are transitional areas between oceanic and continental crust with minimal tectonic activity.
What is the "Wilson Cycle?"
It describes how continents rift apart and then come back together again through time.
What does "slab pull," "slab suction," and "ridge push" mean? Extra note: They are the related forces of Mantle Convective Flow.
• Slab pull - Weight of subducting plate
• Slab suction - Induced mantle flow
• Ridge push - Material squeezing out at divergent boundaries
How is plate motion measured?
They are measured in relation to hotspots. Hotspots don't move. They are stationary.
What is an earthquake?
A shaking of the Earth caused by a sudden release of energy.
What are the focuses of the Earthquakes?
Shallow‐focus: <70 km
Intermediate‐focus: 70‐300 km
Deep‐focus: >300 km
Which of the earthquakes are more destructive? Shallow or deep earthquakes?
Shallow‐focus earthquakes are generally the most destructive.
Where do earthquakes tend to occur at?
They occur at EVERY type of Plate Boundary. China, Memnon, Zeus, Haiti, Alabama, Chile, etc.
What is a fault?
Fractures/cracks along which movement has occured. That's how many earthquakes tend to develop. It's a release of energy during movement.
State the two types of faults. What are they?
Dip-Slip and Strike-Slip Faults.
In a dip-slip fault, what is the difference between the hanging wall and the footwall?
Hanging wall is the rock surface above the fault.
Footwall is the rock surface below the fault.
State the 4 categories of Dip-Slip Faults. What are they?
Does the hanging wall move down or up in a normal fault?
Down. It also accommodates extensional forces.
Does the footwall move down or up in a reverse fault?
Down. It accommodates compressional forces.
Does the hangwall move < or > 45 Degrees in a thrust fault?
It moves less than 45 degrees. It also accommodates compressional forces.
How does oblique motion move?
It moves as components of horizontal as well. It accommodates compression or tension forces.
What does strike-slip faults accommodate and compose of?
They are composed of Right and Left Laterals and accommodate horizontal motion.
What is a transform boundary?
They are also a type of strike-slip faults. They are very large and cut through the lithosphere. They accommodate motion between 2 plates.
What is the "Elastic Rebound Theory?"
• It was developed by Harry Fielding Reid following the 1906 San Francisco earthquake
• It describes how energy builds up and is released during an earthquake
It was on a high friction of right lateral strike-slip faults.
What is displacement?
It's when movement/displacement occurs in fault segments.
What are the three ways that displacement can occur?
- Fault creep: slow, gradual displacement
- Numerous, small earthquakes (periodic energy release)
- Store up energy until major earthquake occurs
State some points about foreshocks and aftershocks of earthquakes. What are they?
• Small earthquakes before the major event are called foreshocks (generally in days or months leading up to the main earthquake); fault is starting to move
• Adjustments after a major earthquake can generate small earthquakes called aftershocks
What is the story behind "earthquake triggering?" State some points.
• Earthquakes set‐off far away from the main earthquake (outside aftershock area)
• Landers: triggered earthquakes up to ~1300 km away
State the two types of seismic waves. What are they?
- Compressional (P) waves-They move one behind the other.
- Shear (S) waves-Up & Down motion movement
• Surface Waves
- Rayleigh waves-Roller Coaster Movement
- Love waves-Side to Side Movement
P Waves are also known as ____________ (________) waves, Two answers here.
S Waves are also known as ____________ (________) waves. Two answers here.
P-Waves don't move through the outer core. (T/F?)
S-Waves don't move through the outer core. (T/F?)
In the diagram of the Earth's Seismic Velocity, does the increased temperature decease or increase velocity?
In the diagram of the Earth's Seismic Velocity, does the increased pressure decease or increase velocity?
What is a "rayleigh wave?"
• Named for Lord Rayleigh, who mathematically predicted this type of wave in 1885
• Also known as "ground roll"
• Counter‐clockwise elliptical particle motion that decreases with depth
What are "love waves?"
• Named for a A.E.H. Love, a mathematician who worked out the model for this type of wave in 1911
• Side‐to‐side particle motion that also decreases with depth
What is the difference between the seismometer and a seismogram?
-Seismometer is an instrument used to measure the intensity, direction, and duration of an earthquake.
-Seismogram is a record of the ground motion at a measuring station as a function of time.
How can an earthquake be located?
Earthquake locations can be determined using the S‐P time from several seismograms.
What are the patterns of earthquake depth?
- Ranges from 5-700 km
• classified as:
- Shallow (< 70 km)
- Intermediate (70 to 300 km)
- Deep (> 300 km)
- Patterns Exist
• Shallow: along oceanic ridge systems
• Deep: subduction zones
What does "Wadati-Benioff Zone" mean?
Dipping seismic zones common to convergent plate boundaries where one plate is subducted beneath another.
What does magnitude mean?
A measure of the energy released during an earthquake; several different scales.
Dr. Charles Richter came up with the "Richter Magnitude." It uses the maximum amplitude of shear waves recorded on a specific type of seismometer.
Magnitude scales are logarithmic, so this means that for every ONE POINT increase on the scale, the amplitude of the ground motion increases TEN TIMES! (T/F?)
What are some Earthquake Hazards?
What is the "Mercalli Intensity Scale?"
• It's based on data gathered from people who experienced the event
• Quantifies the effects of an earthquake on humans and man‐made structures; based on a scale from I‐XII.
Can earthquakes be predicted?
NO! Because of fault frictions and fault interactions that occur.
What is Deformation?
When rocks are folded, tilted, and faulted.
• Cause: Plate tectonics
• Effect: "Crustal deformation"
• Structural Geology
What is Stress?
Force acting on a rock unit.
What is Strain?
The result of stress = change in size or shape.
What are the different types of stress?
1. Confining Stress (Equal stress in all directions)
2. Differential Stress (Stress larger in one direction)
-Compressional (Convergent) Stress
-Tensional (Divergent) Stress
-Shear (Transform) Stress
Where are the different types of stress found?
What are the different types of strains?
1. Elastic deformation: Reversible, like a rubber band.
2. Plastic deformation: Irreversible, once the elastic limit of the rubber band is surpassed.
What are some differences between something being ductile and something being brittle?
1. Environment (temperature/pressure):
What are some factors that determine how a rock deforms?
1. Temperature and Pressure Conditions
2. Amount of time that Stress is applied
3. Rock Composition/Strength
What are faults like in regards to deformation?
It's brittle deformation.
What are joints?
They are the result of brittle deformation.
-Different than faults
-Fractures in which NO movement has taken place; "natural cracks."
-Tends to occur in groups
-Help advance chemical weathering
What are folds?
They are a result of ductile deformation and compressive stress. They are described as a series of wave-like undulations
What are different types of folds?
Large-scale, Small-scale, Anticlines, Synclines, Domes (Upwarped rock layers), and Basins (Downwarped rock layers).
What is a strike?
The compass direction of the line produced by the intersection of a rock layer or fault with a horizontal plane. An angle relative to the north. Clockwise angle.
What is a dip?
It's perpendicular to a strike. It's the angle of inclination of a rock unit or fault measured from the horizontal plane. It includes an angle measurement and a direction.
What is "foliation?"
An alignment of mineral grains due to differential (directional) stress; ductile deformation
Remember the metamorphic grade. What was the four rocks in order?
Slate, Phyllite, Schist, Gneiss. Low to high metamorphic grade from top to bottom. The further down, the more increasing of the temperature.
What type of plate tectonic boundary is most often associated with metamorphism and high levels of ductile deformation?
How is metamorphic grade related to deformation?
Higher metamorphic grade = more extensive ductile deformation.
What is orogenesis?
A term used to describe an episode of mountain building.
What is isostasy?
• gravitational balance between the lithosphere and the asthenosphere
• tectonic plates "float" at a height dependent on their thickness and density
• Iceberg example
What is isostatic rebound?
The regaining of isostatic equilibrium/balance
What is the "Internal Continential Structure?" (Craton, Shield, and Platform)
• Craton: crust that hasn't experienced an orogeny for at least 1 billion years
Parts of the Craton include:
• Shield: where Precambrian igneous and metamorphic rocks are exposed
• Platform: where Precambrian rocks covered by thin later of sediment