Dynamic Earth Exam 2
Types of plate margins and most highlighted examples of each
o Divergent: mid-ocean ridges, continental rifts can transition to become oceanic rifts o Convergent: edge of continent/continents colliding (continental collision zone). When at least one of the converging plates is oceanic, an oceanic plate will descend into the mantle (subduction). Volcanic arcs occur at subduction zones. o Transform: lateral slip. Oceanic transforms: transform faults and fracture zones (inactive). Left-lateral and right-lateral motion is the opposite of what one would assume. Transform faults create no volcanoes and do not create mountains, shallow earthquakes only. San Andres Fault
About how fast do plates move (cm/yr, m/yr, km/yr)?
o 1 to 15 cm/yr
Order of the five horizons in soil (Furthest down to surface)
o C Horizon, B Horizon, E Horizon, A Horizon, and O Horizon
Where are volcanic arcs formed? Know highlighted examples
o Convergent subduction zones, Hawaiian Islands,
Most abundant mineral in crust of the Earth
Feldspar
What is refraction?
Like light, seismic waves bend (refract) when their velocity changes. Rays refract toward the boundary when they speed up.
How is metamorphism different from igneous processes?
Metamorphism is the recrystallization in the solid state where igneous processes are rocks solidified from magma
What controls the mineralogy of a metamorphic rock?
Mineralogy is due to the starting mineral (parent rock/protolith) and conditions of metamorphism.
Recognize five kinds of folds in photos or diagrams
Monocline (not pictured): looks like a stair step and is commonly draped over a fault break.
What layers within the Earth are liquid?
Only the outer core
The geologic time scale: knowing geologic time scale elements as requested in class (boxes and circles in red and blue in power point slides)
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Three kinds of unconformities; recognize in pictures.
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What makes a good metamorphic "index mineral"? (be able to distinguish good and poor index minerals on a diagram)
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Which is more explosive, basaltic magma or rhyolitic magma? Why?
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Is there a P-wave shadow zone?
Yes, if the density of the Earth increased gradually with depth all the way to the center, the shadow zone would not exist, bc rays passing through the interior would reach every point on the surface. The presence of this shadow zone means that deep in the earth, a major interface exist at which seismic waves abruptly refract downward, implying that the velocity of the wave suddenly decreases. This interface is know as the core-mantle boundary.
What is the Moho?
boundary between crust and mantle
Where do we find metamorphic rocks in SD?
Black Hills
Brittle versus plastic deformation
-Brittle Deformation: Forming the joints and the fault involved cracking and breaking rock. -Plastic Deformation: A fold that formed when rock changed shape without breaking
Know what sedimentary rocks are clastic, chemical, biochemical, and organic
-Clastic: Conglomerate, Breccia, Sandstone, and Mudstone or Shale -Chemical: Rock-salt, rock gypsum and some limestone and cherts -Biochemical: Most limestones made of fossil fragments and bedded cherts made of microscopic silica shells -Organic: Coal and Oil shale(partly clastic too)
Four classes of sediment/sedimentary rocks
-Clastic: Pieces of rock or mineral grains - Chemical: ions coming out of solution to create minerals -Biochemical: organisms remove atoms from water, air, soil, and the hard parts become sediments -Organic: plants remove atoms from water, air, soil, and plant matter becomes sediment
General aspects of the two highlighted ways in tectonics creates sedimentary Basins
-Foreland Basins: "Thrust" faulting at the continental margin thickens crust. Crustal thickening flexes down adjacent crust crating a basin. Ex. The Appalachian Basin and Powder River Basin. -Continental Rift Basin: Tectonic extension causes normal faulting in which some blocks are down-dropped relative to others. Ex. Newark Basin and Connecticut River Valley.
Basics of two "environments" of metamorphism discussed in lecture
-Contact Metamorphism: Increase in heat/ temp due to an igneous intrusion, it develops without a change in pressure and without differential compression or shear. Develops adjacent to the contact between an intrusion with its rock wall. -Regional Metamorphism: During the development of mountain ranges bc of convergent boundaries or continental collision, regions of crust undergo compression and large slices of crust slip up over other portions of crust. As a result the rock that was once near earths surface ends up at great depth beneath the mountain. The protolith changes in three ways 1) heats up bc of geothermal gradient and igneous activity 2) endures greater pressure bc of the weight of overburden 3) undergoes compression and shearing
Know two sedimentary structures that can be used to determine paleocurrent directions (and be able to tell direction based on a picture of cross beds)
-Crossbedding: Formed by a series of dunes or ripples, forests slope in the direction of paleocurrent -Ripples: Formed in current of wave oscillations, current ripples asymmetric with steep surface dipping (sloping) in direction of paleocurrent.
Characteristics of earthquakes at different plate tectonic boundaries
-Divergent (Mid-Oceanic Ridges): Along spreading segments, stretching generates normal faults, whereas, along transform faults, strike-slip displacement occurs. Occur very shallow (<10km) and weak. -Transform: one plate slides past another without producing or consuming oceanic lithosphere, most of the time causing a strike-slip motion. Are usually shallow and can be powerful. -Convergent: Where one plate subducts under another, tend to host several different kinds of earthquakes. Specifically, as the downgoing plate begins to subduct, it bends, causing normal faults to develop in the downgoing plate, seaward of the trench. Then, where it scrapes along the base of the overriding plate, large thrust faults form, defining the contact between the downgoing and overriding plates. Shear on these faults can produce disastrous, shallow earthquakes. Thrust faults in the accretionary prism may also slip. In some cases, shear between the downgoing plate and the overriding plate also triggers shallow faulting in the overriding plate within and on both sides of the volcanic arc. lithosphere
Know the highlighted feature of rocks distinctive of each of the following paleoenvironments: dunes, glaciers, streams, swamps, deep open oceans, and arid lakes
-Dunes: Thick layers of well sorted sandstone, large cross beds -Glaciers: Extremely poorly sorted boulder conglomerate -Streams: Conglomerates -Swamps: Coal -Deep Ocean: Shales and bedded Cherts -Arid Lakes: Rock salts and Gypsum
Epicenter vs. focus (hypocenter)
-Focus: The location where seismic ways first begin to be generated, for earthquakes associated with faulting the focus represents the point in the ground where the slip on a fault initiates. -Epicenter: The point on the surface of the earth that lies directly above the focus of the earthquake.
What do plunging folds look like on a map or aerial photograph?
-Foldings don't have to be horizontal, not horizontal= plunging -Plunging Folds produce a fold pattern that appears on the earth's surface.
How does foliation orientation relate to directions compressional tectonic stresses?
-Foliation: the alignment of platy minerals -Foliation and banding forms perpendicular to tectonic compressive stress -
How are joints and faults different?
-Joints are planar fractures in rock, with no slip. Weathering accentuates joints. -Faults: are also planar fractures but on which sliding occurs, and slip events or faulting can generate earthquakes.
Difference between magnitude and intensity?
-Magnitude: represents the amount of energy released from the seismic source indicated by the amount of up and down or back and forth motion of the ground Intensity: the degree of ground shaking at the locality. Varies with location for a given earthquake. Intensity depends on subjective observation of damage and how the shaking felt, not a direct measurement with an instrument.
Know plausible protoliths for marble, quartzite, and amphibolite
-Marble: Limestone -Quartzite: Sandstone -Amphibolite: Basalt
Characteristics of different types of seismic waves
-P-Waves (Primary): Compressional body waves(pass through the interior of the earth) that arrive first bc they are the fastest, particles of wave move like a spring, coils expand and compress. -S-Waves (Secondary): Shear body waves, the second to arrive and travel at about 60% of the speed of a P-Wave. Particles move up and down, perpendicular to the wave direction. Like sending a wave through a rope by whipping it. -Surface Waves: Consists of two waves Rayleigh and Love waves, they travel along the earths surface and are the slowest. Rayleigh waves are like an ocean wave without the crest. Love waves cause the ground to shimmy back and forth perpendicular to the wave.
Concepts of radioactive decay, parent/daughter, half-life
-Radioactive Decay: Some isotopes of some elements are unstable and undergo spontaneous change releasing energy. -Parent/daughter: ^ this change produces a new isotope of a different element. -Half-life (t1/12) The time required for 1/2 of the quantity of an isotope to undergo decay.
Stresses responsible for different normal vs. reverse faults
-Reverse Faults: shortening of crust, as happens during continental collision -Normal Faults: stretching of Earth's crust, as happens in rifting.
Recognize schist vs. gneiss vs. quartzite in pictures
-Schist: Visible grains that make it very shiny -Gneiss: composed of alternating dark- and light- colored banding -Quartzite: White, tan, pink that looks glassier than sandstone and does not have the graining sandpaper-like surface of sandstone.
What kind of stresses cause folding?
-Some layers wrinkle up or buckle in response to end-on compression. -Other folds develop where shear stress gradually shifts one part of the layer up and over another part. -Still, others form when a new slip on a fault causes a block of basement to move up so that the overlying sedimentary layers must warp. -Lastly, some result from the movement of rock layers up and over step-like bends in an underlying fault, for layers must curve to conform to the fault's shape as they move.
Stress versus strain
-Strain is the change of shape in something which is caused by stress -Stress is the force applied to a structure
What are strike and dip?
-Strike: the angle between the imaginary horizontal line (the strike line) on a plane and the direction of true north. or line where a geologic plane intersects a horizontal plane. -Dip: the angle at which a plane enters the earth.
Principles used to document relative age and correlation of geologic units
-The principle of uniformitarianism: As we've seen, the principle of uniformitarianism means that physical processes we observe operating today also operated in the past, at roughly comparable rates. -The principle of original horizontality: Sediments on the Earth settle out of fluids in a gravitational field. The surfaces on which sediments accumulate (such as flood plains or the seafloor ) are fairly flat. Therefore, layers of sediment, when first deposited, are fairly horizontal. If sediments collect on a steep slope, they typically slide downslope before lithification, so they will not be preserved as sedimentary rocks. With this in mind, we conclude that folding, tilting, and faulting of sedimentary beds must occur after the beds were deposited. -The principle of superposition: In a sequence of sedimentary rock layers, each layer must be younger than the one below, for a layer of sediment cannot accumulate unless there is already a substrate on which it can collect. Thus, the layer at the bottom of a sequence is the oldest, and the layer at the top is the youngest. -The principle of lateral continuity: Sediments generally accumulate in continuous sheets within a given region. When you see a sedimentary layer cut by a canyon, you can assume that the layer once spanned the area and was later eroded by the river that formed the canyon -The principle of cross-cutting relations: If one geologic feature cuts across another, the feature that has been cut is older. The principle of inclusions: A rock containing an inclusion (fragment of another rock) must be younger than the inclusion.
Two settings in which we find extensive exposures of metamorphic rocks
-The towing cliffs in the interior of a mountain range -Continental shields: broad region of long lived, stable continental crust where sedimentary cover either was not deposited or has been eroded away so that Precambrian bed rocks are exposed.
In order, what are the two most abundant elements in the crust and the Earth as a whole?
1. Oxygen 2. Silicon
What are the grain size boundaries for sand/sandstone (in mm)?
1/16-2mm
How many seismometers are required to locate and earthquake?
3
Age of the Earth
4.565
What horizons constitute "topsoil"
A and O Horizons
Recognize map patterns of synclines and anticlines based on ages of rocks or strike and dip symbols
Anticlines: older in the middle, rocks dip away Synclines: younger in the middle, rocks dip to center.
The "low velocity zone (LVZ") corresponds to what mechanical layer?
Asthenosphere
How are unconformities interpreted?
Breaks in the geologic record; missing time.
What are the two aspects of lithification, turning sediment into sedimentary rocks?
Compaction and Cementation
What causes large local variations in shaking by earthquakes (e.g. the San Francisco Bay area in the 1989 earthquake)
Damage patterns may be complex bc of the amplification of seismic waves in sediment, Geology of land is different, different geologic materials respond differently to having the same energy pass through them.
Use of seismic reflection studies
During the past half century, geologists have found that by exploding dynamite , by banging large weights against the Earth's surface , or by releasing bursts of compressed air into the ocean, they can produce artificial seismic waves that propagate down into the Earth and reflect off the boundaries between layers of rock in the crust. By recording the time at which these reflected waves return to the surface , geologists can determine the depth to these boundaries. With this information, they can produce a cross-sectional view of the crust called a seismic-reflection profile. This image can define subsurface bedding, stratigraphic formation contacts, folds (bends in layers), and faults. Oil and gas companies use seismic -reflection profiles despite their high cost, to identify likely places where energy reserves have accumulated underground .
Most fatal, most costly, and most powerful earthquakes.
Earthquakes in subduction zones.
What modern technology can track deformation in "real time"
GPS (geographic position system) can measure real time (mm/year) movements.
How much more energetic is an earthquake 1 magnitude more than another? Difference of 2? Etc.
If energy from one quake to the next goes from mag 7 to 8 (32x), how much would the energy difference be from 7 to 9: 1000 (32x32)
What does the S-wave shadow zone tell us?
It means that S-Waves cannot pass through the core at all. If they could, an S-wave headed straight down through the earth should reach the ground surface on the other side of the planet. S-waves are shear waves, which by nature can only travel through solids. So this means that the earths core, or at least part of it, consists of liquid.
Several parts of the US are most subject to tsunami hazards, where?
Mostly the Pacific Northwest such as Oregon, Washington and Cali bc of the cascadia subduction zone. Alaska and Hawaii are also threatened.
What kind of structure is responsible for the Basin and Range landscape in the western U.S.?
Normal faults: divergent, system bound ranges (horsts) and valleys (grabens)
How good are we at forecasting the specific timing of earthquakes?
Not very good, we have short term warning systems. Seconds to minutes for seismic waves to arrive allowing opportunity for minimal response
Basics of damaging secondary effects of earthquakes
Notes
Know parent-daughter element pairs Highlighted in class that are used for age dating
Potassium -> Argon Carbon -> Nitrogen Uranium -> Lead
The concept of uniformitarianism; simple examples of its application
Processes we see active today were active in the geological past and explain analogous characteristics observed in rocks.
Recognize faults: normal, reverse, left-lateral and right-lateral strike- slip in photos or diagrams
Right-Lateral:
What kind of seismic waves are not transmitted through a fluid/liquid?
S-Waves
Earthquake in U.S. that did tremendous damage via fire
San Francisco 1909, Mag 7.9. 25,000 building destroyed and around 700-2,800 killed. Ruptured natural gas lines susceptible to ignition
What are the three elements of long-range earthquake forecasts?
Seismologists base long-term earthquake predictions on two pieces of info: the identification of seismic belts and the recurrence interval. Seismic belts are regions where many earthquakes happen, therefore are regions with greater seismic risk. To identify a seismic belt, seismologists produce a map showing the epicenters of earthquakes that have happened during a set period of time. The Recurrence Interval is the average time between successive events of a specified size.
What does seismic tomography tell us?
Seismologists can distinguish locations where seismic waves travel faster than expected from the regions where the waves travel slower than expected. Tomographic studies can display these variations in maps, cross sections, or three-dimensional models. Researchers interpret the slower regions to be warmer regions of the mantle , and faster regions to be cooler regions , for as rock gets hotter and softer , it can't transmit seismic waves as rapidly . The occurrence of warm and cold regions is a consequence of convection in the mantle , so seismic tomography has led researchers to picture the inside of the Earth as a dynamic place.
Know the sequence of four metamorphic rocks created by progressive metamorphism (low-grade to high-grade) of a shale parent rock
Slate, Phyllite, Schist, Gneiss
At what kind of plate tectonic boundary are the greatest tsunami's generated? Why? (two basic reasons)
Subduction Zones
Be able to interpret the relative ages of two geologic features in a photo or diagram
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Be able to roughly determine distance from an earthquake using seismometer record.
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Different ways that we learn about the interior of the Earth
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How do we interpret grain size in igneous rocks?
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Know the four components of the definition of a "mineral" used in lecture
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Origin of mafic versus felsic magma
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Where is the greatest concentration of intraplate earthquakes in the US (away from other geologic activity)? Why there?
The New Madrid Seismic Zone, Missouri Area. Three quakes with mag est. at 8.0-8.5. Over failed rifts of the precambrian and Mesozoic era.
How do seismic waves refract when they speed up?
The angle at which a reflected ray bounces off a boundary is always the same as the angle at which the incoming , or inci dent , ray strikes the surface . The angle by which a refracted a ray bends at a boundary , however , depends on the contrast in wave velocity between the two materials in contact at the boundary , and on the angle at which a ray hits the boundary . As a rule , if a ray enters a material through which it will travel more slowly , the ray bends down and away from the interface (Fig. ). ( To see why , picture a car driving from a paved surface diagonally onto a sandy beach - the wheel that rolls onto the sand first slows down, relative to the wheel still on the pavement , causing the car to veer toward the sand .) For example, the light ray in Figure D.3b bends down when hitting the air-water boundary because light waves travel more slowly in water Alternatively , if the ray were to pass from a layer in which it travels slowly into one in which it travels more rapidly , it would bend up and toward the boundary
What are thrust faults? Where are fold and thrust belts found in the US (two areas highlighted)?
Thrust faults are low angle (<30 degrees) reverse faults. Fold and thrust belts from during collisions and subduction zones causing mountain building events called orogenies. Ex. Appalachians, Rockies.
What defines a specific element?
To As specimens; physical properties o More fundamentally, underlying physical properties, chemical properties
What are transgressions and regressions? Be able to recognize them in a sequence of sed rocks as presented in lecture.
Transgression: When relative sea level rises, the shoreline migrates inland. Regression: When relative sea level falls, the coast migrates seaward.
Highlighted techniques other than radiometric dating that yield numerical ages
Tree Rings, Varves (annual lake beds), and annual ice layers in glaciers.
Most fatal recent earthquake (last 10 years)
magnitude-9.1 quake struck off the coast of Japan on March 11, 2011, triggering a tsunami as high as 90 feet in some areas. Killing at least 15,000 people Fukushima Daiichi nuclear plant cooling system failure meltdown.
Volcanism, earthquakes, and mountains at different types of plate margins + hotspots (info in the table shown in lecture)
o Divergent: mid-ocean ridges, continental rifts can transition to become oceanic rifts o Convergent: edge of continent/continents colliding (continental collision zone). When at least one of the converging plates is oceanic, an oceanic plate will descend into the mantle (subduction). Volcanic arcs occur at subduction zones. o Transform: lateral slip. Oceanic transforms: transform faults and fracture zones (inactive). Left-lateral and right-lateral motion is the opposite of what one would assume. Transform faults create no volcanoes and do not create mountains, shallow earthquakes only. San Andres Fault
What is the difference between a theory and a hypothesis?
o Hypothesis: an explanation for observations to be tested (can be supported or not confirmed). o Theory: an explanation for observations that have been tested many times and is supported by evidence.
Know what defines the three rock types and their corresponding rock-forming processes
o Igneous: the freezing of molten rock o Metamorphic: when pre-existing rock change character in response to a change in temperature, pressure, or chemical environment. o Sedimentary: form either by the cementing of fragments (grains) that had been broken off pre-existing rocks, or by the precipitation of mineral crystals out of water solutions at or near the earth's surface.
What are the key nutrients in soil
o Nitrogen, Phosphorus, Potassium
The outer two mechanical layers of the Earth, what is special about them? And, how do they relate to the compositional layers?
o The Lithosphere is the outer layer of the earth that cannot flow. The Asthenosphere behaves like a soft plastic and is able to flow. o The Lithosphere consists of the crust and the uppermost part of the mantle, the Asthenosphere consists of the rest of the upper mantle as well as the lower mantle.
Differences between continental and oceanic crust?
o The oceanic crust underlies the seafloor is a thin (7-10 km) but dense layer, consists of basalt and gabbro or Mafic in composition. o Continental crust generally has a thickness of 35-40 km but can go up to 70 km, it contains a great variety of rock types so the density is overall less dense than the oceanic crust. Felsic or intermediate in composition.
