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Unit 4 Geology
Terms in this set (109)
What is the elastic rebound theory?
explains the energy in rocks that allows them to go back to original "straightness" after energy is released
the displacement of distance traveled
What is another name for slip amount?
What is the difference between focus and epicenter?
Focus: the point where the real "failure" happened
Epicenter: the geographic point on Earth's surface directly above the focus
What are the common focal depths?
The longer the fault rupture
the longer the fault slip
little vibrations after BIG earthquake (little earthquake)
What is the rule of thumb for aftershocks?
largest aftershock is one magnitude under main-shock
little vibrations before Big earthquake (small earthquake)
Difference between seismograph & seismogram?
Seismograph: instrument that records the seismic waves
Seismogram: the actual recording
What does a seismograph record and what is another name for it?
P & S waves (can be vertical or horizontal)
Other Name: Seismic Signal Detection Device
What is the seismic signal?
Sends to surrounding signal (goes into ground too)
What are the 2 types of seismic waves?
Body Waves & Surface Waves
Do body waves travel fast or slow?
Do surface waves travel fast or slow?
Slow but cause most damage
What are the 2 types of body waves?
1. P wave
2. S wave
What type of wave (compressive or shearing) is a p wave?
What do p & S waves stand for?
P = primary
S = secondary
What is the fastest seismic wave & what does it travel through?
P wave (6 km/second); SOLID & LIQUID
What speed do S waves travel & what do they travel through?
Half the speed of P wave & through SOLID ONLY
What wave does the push-pull motion & what wave does the shearing motion?
Push-Pull = P waves
Shearing = S waves
What are the 2 types of surface waves?
1. Rolling motion (elliptical)
2. Shakes ground sideways (left→right)
What are the 3 mechanisms for seismic wave travel?
1. Compressional waves
2. Shear waves
What are the 2 characteristics of compressional waves?
move from contractions & expansions
What way do shear waves move?
What do the time of arrival of P & S waves depend on?
Depend on distance waves traveled
Longer the interval → Longer the distance traveled
How do you determine the exact location of focus & epicenter?
Calculate the time & distance traveled, then draw 3 circles to find intersecting point
What is the Richter scale?
logarithmic scale of 1 to 10 which increases by 10X magnitude
What type of scale is the Richter scale (magnitude or intensity)?
What is the Modified Mercalli Scale?
Determines what was felt & amount of damage done
What type of scale is the Modified Mercalli Scale (magnitude or intensity)?
What do seismic actives in the earth's crust correlate with?
correlate with known plate boundaries
Where do most earthquakes occur?
on plate boundaries
Where do the deepest earthquakes occur?
convergent plate boundaries (especially oldest & coldest)
Are seismic wave paths straight lines?
Do seismic waves travel faster through dense rock (like the core)?
Yes, and they bend as they go through
What is the P wave shadow zone?
bends slightly down as it goes towards core (105 → 142)
What is the S wave shadow zone?
does not travel through outer core!! (105 → 105)
What is lava?
material on earth's surface that comes from magma chambers
What are the 3 factors that determine the type of lava?
1. chemical composition
2. gas content
3. temperature of melting
What are the 3 types of lava?
What are the factors for viscous lava?
High silica content & low temps
What are the characteristics of basaltic lava?
mafic, dark-colored, low silica content, very fluid, moves fast and far (1000-1200 degrees celsius)
What is the characteristic for andesitic lava?
What are the characteristics for rhyolitic lava?
felsic, light-colored, high silica content, less fluid (viscous), solidifies much quicker than basaltic (800-1000 degrees celsius)
What are the 2 advantages of volcanoes?
1. source of economic minerals
2. sources of fertile soil
What are the 3 disadvantages of volcanoes?
1. loss of human lives & properties
2. covers the sun
3 ashes cover fertile fields
Where does Lava come from?
mostly near the boundary between crust & mantle
What are the 2 types of on-land basaltic lava?
Pahoehoe & Aa
Characteristics of pahoehoe basaltic lava
a thin skin forms @ the very top; the fast-moving liquid underneath drags the skin into twisted coiled folds (like rope)
What is the Hawaiian name for Pahoehoe?
Characteristics of Aa
a thick skin forms later that resembles moist plowed earth, then breaks into jagged blocks
What is pillow basaltic lava?
underwater mechanism that forms pillow-like blocks
The more gas lava contains...
the more violent the eruption
What are pyroclasts?
fragments of various sizes thrown into air in explosive way
volcanic ash size
2 mm or less
volcanic breccia size
2 mm or more
What are the characteristics of shield volcanoes?
-layer after layer of thin basaltic lava
What is an example of a shield volcano?
Mauna Lou (Hawaii)
What are the characteristics for a volcanic dome?
-felsic & steep
-looks like a dome
-viscous (not fast) felsic lavas pile up over vent
What is an example of a volcanic dome?
Mount St. Helens (Washington)
What are the characteristics of a cinder-cone volcano?
-layers of pyroclastics
-steep, but stable slope
-the crater @ the summit
What is an example of a cinder-cone volcano?
Cerro Negro (Nicaragua)
What are the characteristics of a stratovolcano?
-alternating layers of pyroclastic & lava
-every volcanic eruption = 2 layers
-lava/pyroclastic flow & steep
What is an example of a stratovolcano?
Mount Fuji (Japan)
What are the characteristics of a caldera?
-collapsed feature, leaving a large steep-walled basin
-volcano opening with collapsed features
What is an example of a caldera?
Crater Lake (Oregon)
What are the 7 volcanic features?
Phreatic eruption/steam eruption
Hot springs & geysers
Phreatic/Steam Eruptions occur when and where?
occur when hot, gas-charged magma encounters water making steam; can be mainland or in ocean
What are diatremes (shiprock)?
gas-charged magma shoots in air (pyroclastic) and feeder channel forms with solidified magma and erodes
What is a fissure eruption?
long lines of lava flowing; main style of volcanism along mid-ocean ridges where new oceanic crust is formed
What are flood basalts?
fissures that result in a pretty flat plateau
What are lahars?
volcanic mudflows made up of everything: water, mud, lava, pyroclastic, etc
What are hot springs & geysers?
hot water fountains that spouts steam with great force
What are hot spots?
volcanos developed over mantle plumes that are a much deeper, cylindrical, narrow course of magma
What is the class definition of plate boundaries?
Lithosphere that is broke into 13 different plates
How many major plates are there?
What happens when 2 plates collide?
They bend & crush to form heat energy
What is the lithosphere?
all of crust & part of mantle above athenosphere
Is the lithosphere a continuous shell?
What is net displacement?
1/2 distance from one plate + 1/2 distance from another plate
What is the mechanism of plate movement?
concept of mantle convection
What is the concept of mantle convection?
mantle rises → plates diverge → plate moves on hot material
What is the process of subduction?
When one plate descends beneath the other
What are convergent boundaries?
plates collide & lithosphere destroyed; one plat recycle into mantle
Does plate area increase or decrease with convergent boundaries?
What are divergent boundaries?
plates separate & lithosphere is created by rising magma (plate area increases)
Does plate area increase or decrease with divergent boundaries?
What are transform boundaries?
plates slide past each other; lithosphere neither created nor destroyed
What happens to plate area in transform faults?
stays the same
What was Edward Suess's theory called and what did it explain?
Gondwanaland = idea of giant landmass consisting of all the continents on the southern hemisphere
What did Edward Suess support?
Continental drift: concept based on jig-saw puzzle fit of continents
When did Alfred Wegener come our with his plan of Pangea? What is Pangea?
Pangea: supercontinent that existed about 200 mypb consisting of all the continents in the world
What are the 4 evidences of Pangea?
1. continental fit
2. fossil evidence
3. glacial feature (striations)
4. structural similarity
What happened in the early 1960s for plate boundaries research?
proposal of sea floor spreading mechanisms along the center of the Atlantic Ocean (MAR)
What is our proof of seafloor spreading?
Magnetic Pole Reversal
What are the 2 types of divergent plate boundaries?
Mid Oceanic Ridge & Rift Valley
What is the Mid Oceanic Ridge (MOR)
Only seen in divergent plate boundaries, an undersea mountain chain that exhibits earth quakes, volcanism, & rifting from mantle convection
What is a Rift Valley?
deep valley formed by rising & cracking similar to MOR but on land
What are the 3 types of convergent boundaries?
1. Ocean - Ocean
2. Ocean - Continent
3. Continent - Continent
What is an ocean - ocean boundary?
the one which is slightly heavier, subducts; forms trenches & volcanic island arcs from water rising to athenosphere to melt & form
What is an ocean - continent boundary?
ocean plate usually subducts & forms mountain belts/trenches
What is a continent - continent boundary?
not a true subduction; crust crumples to form mountains & and a wide plateau
As you go towards center of continent/plate...
What are the 4 ways we can determine plate velocities?
1. age of rocks on seafloor
2. magnetic pole reversal
3. plates over hot spots
4. satellite data
How does rock assemblage occur in divergent plate boundaries?
Ophiolite Suites: an assemblage of rocks, characteristic of the sea-floor but found on land, consisting of deep-sea sediments, submarine basaltic lavas, & magic igneous intrusions
What happens in ophilite suites?
Half goes to right, Half goes to left & some gets pushed into other plates
How does rock assemblage occur in convergent plate boundaries?
What are the 2 possible driving mechanisms for plate tectonics?
entire/whole mantle convection & upper mantle convection
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