Midterm 2
What is a hanging wall?
Block above the fault
What chemical is Limestone made of?
Calcium Carbonate
Where are conglomerates found?
Close to the sediment source
What is a strain?
Distortion or the response to stress
What kind of fold is a syncline?
Down Fold, limbs dip toward the hinge
Chemical Sedimentary Rock
Minerals precipitated directly from water solutions
What are surface features of sedimentary structures?
Mudcracks and ripple marks
Are earthquakes predictable?
No
Is the Earth a perfect sphere?
No. Spinning had caused the Earth to "bulge" around the Equator (This is due the fact that the Earth is comprised of many different chemicals)
Thrust Fault (What is the definition and stress regime?)
Reverse fault w low angle (less than 30º) Stress regime: Compressive (shortening/narrowed by movement of fault)
Foliated Rocks
Rock that contains parallel layers of flat and elongated minerals
Rayleigh Waves
Rolls in wave motion, surface waves
Types of Foliated Rock
Shale Slate, Phyllite, Schist, Gneiss Sharks Sometimes Play with Scientists and Grandmas
How deep in Earth do earthquakes occur in divergent boundaries?
Shallow
How deep in Earth do earthquakes occur in transform boundaries?
Shallow
How deep in Earth do earthquakes occur in convergent boundaries?
Shallow-Deep
How deep in Earth do earthquakes occur in collision zones?
Shallow-Intermediate
What is the geoid?
Shape the earth's surface would have if only gravity and rotation were involved, and other forces were absent
What are the limbs of a fold?
Sides or flanks of folds
What kind of fold is a bowl?
Syncline with center point
What are the 3 types of differential stress we considered?
Tensional Compressional Shear
What is a footwall?
The block of rock that forms the lower half of a fault
Love Waves
Undulates laterally, surface waves
Frost-cracking
Water in cracks might not freeze at exactly 0º C Water can migrate through porous material to freezing area.
Strike-Slip Fault
birds eye view, forward and backward motion
What are the 4 processes involved in metamorphism?
-Heat -Pressure -Shear (pressure/force with direction) -Hydrothermal fluids
What conditions affect the deformation behavior of rock?
1) Temperature- warmer temps are more likely to have plastic behaviors 2) Pressure- higher pressure likely to have plastic behavior 3) Deformation rate- slower deformation favors plastic behavior 4) Composition of rock- softer rock types are more likely to have plastic behavior
Within a convergent boundary, where would these metamorphic environments be found, and what rocks would be produced?
1) low-temperature, high-pressure 2) high-temperature, low-pressure 3) high-temperature, high-pressure
What pressure/temperature conditions and metamorphic rock types are associated with the following:
1) regional metamorphism in a mountain belt 2) contact metamorphism around a magma chamber 3) subduction zone metamorphism
What is 1 mm in microns?
1000 microns
Grain size of Silt
4-62 microns (gritty)
Grain size of Sand
62 microns - 2 mm (sandy)
Grain size of Clay
< 4 microns (creamy)
Grain size of Pebbles
> 2 mm
What is a fault?
A break in the earth's crust
Non-Foliated Rocks
A metamorphic rock that does not have parallel layers of mineral grains
How does particle shape vary with energy or transport distance?
A particle becomes more round with more transport distance
What is metamorphic grade?
A scale denoting the level of pressure and temperature involved in forming a particular metamorphic rock
What is a metamorphic aureole?
An area that surrounds rock that has been changed and undergone Metamorphosis
Where would the oldest rocks be found in a dome?
Anticline = Oldest rocks in the middle
What kind of fold is a dome?
Anticline with center point
Where is Sandstone found?
Beach Shore
Biochemical Sedimentary Rock
Cemented shells of organisms
Clastic Sedimentary Rocks
Conglomerate Breccia Sandstone Siltstone Shale Mudstone Can Bees Save Silver Sharks' Mouths
What can we do to protect ourselves from earthquake hazards?
Create buildings with reinforced corners
What are internal features of sedimentary structures?
Cross-bedding indicates deposited in flowing water or air in dunes or ripples Also... fossils
Where is Mudstone found?
Deep Marine
Where is Shale found?
Deep Marine
What does the moment depend upon?
Depends on energy released which depends on length and distance of rupture
How does the energy release of a Mw 7 compare with the energy release in a Mw 6 Earthquake?
Difference in 1 unit = 31 x more energy
How does the energy release of a Mw 7 compare with the energy release in a Mw 5 Earthquake?
Difference in 2 units = 1000 x more energy
How do we identify the location of an earthquake?
Difference in P Wave and S Wave arrival times at 3 different sources
Where is there a better potential for geothermal energy?
Differences in tectonic settings Plate boundary on the west, but the east coast is passive margin
What are the 3 deformation styles that occur in response to differential stress?
Displacement Change in orientation (rotation) Change in shape (distortion)
What is the moment (M0) of an earthquake?
Energy released
How are metamorphic rocks from deep in the crust ever exposed on the surface?
Exhumation - from collision or erosion
Where is it fatter—around the equator or the poles?
Fatter around the equator Reference spheroid has radius 6378 km around equator and 6357 km around poles
How much does lithostatic pressure increase with depth?
For every ~3km in depth, pressure increases by ~1 kbar
How common are great earthquakes (Mw > 8)? How frequent are lower magnitude Earthquakes?
Great ones aren't so common, lower magnitude EQs are EXTREMELY common
What are some hazards from earthquakes?
Ground shaking- building damage Landslides and rockfall Sediment Liquefaction: Fire Tsunamis
Normal fault (What is the definition and stress regime?)
Hanging wall moves down (below) relative to the footwall Stress regime: Extension (lengthened/expanded by movement of the fault)
Reverse fault
Hanging wall moves up (above) relative to footwall Stress regime: Compression (shortened/narrowed by movement of fault)
What are the 3 main causes (drivers) of metamorphism
Heat, Pressure, and Hydrothermal fluids
We can assess hazard from
History of earthquakes Monitoring of earthquakes Monitoring plate motion Understanding plate tectonics context and subsurface structure
Types of Non-Foliated Rock
Hornfels (silicates) Quartzite (quartz) Marble (calcium carbonate)
Hydrothermal Fluids
Hot water with dissolved ions and volatiles
Oxidation/hydration cracking
In biotite tetrahedral sheets Iron oxidises and biotite expands
What is the moment magnitude (Mw) of an earthquake?
Index is called Moment Magnitude Mw Reported on logarithmic scale
Oxidation
Iron reacts with water to make iron oxides
What causes sediments to mobilize?
Landslides, rock fall, debris flows and creep
What is a shield?
Large area of exposed Precambrian crystalline igneous High-grade metamorphic rocks that form tectonically stable areas.
Breccia
Large clasts compiled together (Angular)
Conglomerate
Large grains compiled together (Rounded)
What is foliation?
Layers (visible in gneiss or schist) or alignment in rock form by a preferred orientation (in metamorphic rocks) Alignment of platy minerals (alternating light and dark minerals)
Exfoliation jointing
Like an onion skin, joints are fracture planes. Unloading is erosion taking load off rock. Created by erosion unloading; only found in strong, otherwise flawless rock.
Biochemical Sedimentary Rocks
Limestone and chert
Pattern of sedimentary bedding that shows transgression?
Limestone, Shale, Sandstone
Organic Sedimentary Rock
Made of carbon-rich relicts of plants or other organics
Clastic Sedimentary Rock
Made of particles from other rocks
Metamorphic Rock
Metamorphic rock is rock formed from pre-existing rock (the protolith), by solid state change (no melting), in response to changes in its environment.
Where are metamorphic rocks generally found?
Metamorphic rocks are formed mainly in the lithosphere, wherever there is high pressure and high temperature. ... Metamorphic rocks are most abundant at convergent plate boundaries, but can occur in other areas where there are increased pressures and/or temperatures
Dissolutions
Minerals dissolve in water producing salt solutions and often clay minerals.
Where would the oldest rocks be found relative to the fold axis in a Syncline?
Oldest on the limbs, youngest on the axis
Where would the oldest rocks be found relative to the fold axis in an anticline?
Oldest rocks on the axis, youngest on the limbs
In short, why do earthquakes occur repeatedly on the same failure surface?
Once a failure has occurred, that location is a plane weakness, makes it more likely for another failure to occur there, easiest place for a slip to be accommodated
What does "protolith" mean?
Original rock before change in property occurred
Chemical Weathering Products
Oxide minerals & Clay minerals
What does it mean when rocks are red?
Oxidizing, most likely on land
Which is the faster of the two body waves?
P waves are faster than S waves
What are the four kinds of seismic waves?
P-waves S-Waves Love Waves Rayleigh Waves
Differentiate plastic deformation and brittle deformation
Plastic: Recoverable deformation Brittle: Unrecoverable deformation
What is the hypocenter (or focus) of an earthquake?
Point underground where earthquake occurred
Lithification
Process of sediments compacting under pressure.
Sedimentary Rock
Rocks made of fragments of other rocks cemented together. Minerals precipitated from water solutions at Earth's surface.
What is the typical organization of sedimentary units from shoreline beaches to deep ocean?
Sandstone Siltstone Shale Mudstone
Pattern of sedimentary bedding that shows regression?
Sandstone, Shale, Limestone
How are sedimentary rocks formed?
Sediment undergoes lithification
Where is Limestone found?
Shallow Marine
Where is Siltstone found?
Shallow Marine
What chemical composition does chert have?
Silica
What kind of fold is a monocline?
Simple bend makes it not horizontal Only one limb Product of a reverse fault that occurred deep in the crust
How does grain size vary with energy or transport distance?
Size decreases with more transport distance and lower energy
What do we mean by geologic structure?
Small scale deformation of earth's crust
How does sorting vary with energy or transport distance?
Sorting will increase with more transport distance and lower energy
Thermal expansion cracking
Spikes in surface temperature cause rock to expand (caused by fire, solar radiation, air temp)
What is the epicenter of an earthquake?
Spot above hypocenter above ground
What is stress, and how does it differ from force?
Stress = Force acting over an area
Where would the oldest rocks be found in a bowl?
Syncline = Oldest rocks on the outside
How is it possible to accumulate thousands of meters of sediments in an area?
Tectonic shifts that cause rifts, basins, and any other thinning of the crust tend to shift some of the mantle out of the way, creating space for sedimentation
What does dip measure?
The acute angle that a rock surface makes with a horizontal plane.
Why doesn't the low spot fill with sediment?
The asthenosphere that is below the sediment, deforms from the weight of the sediments above.
How do we know about the Cretaceous Interior Seaway?
The bottom of the seaway had very little oxygen, which meant that any of the unique sea creatures that died were fossilized
What does strike measure?
The direction of the line formed by the intersection of a rock surface with a horizontal plane
What is the axis of a fold?
The intersection of the axial plane with one of the strata of which the fold is composed
What is non-permanent deformation of rocks/surfaces?
The rock can return to its original shape when the stress is removed
What is permanent brittle deformation?
The rock cannot return to its original shape when the stress is removed
What is elastic deformation?
The rock returns to its original shape when the stress is removed
What is an earthquake?
The vibration of Earth produced by the rapid release of energy
What does it mean when rocks are black/blue?
They are organic rich with little to no oxygen
Biological processes
Tree roots, fungal hyphae growing towards and through minerals.
What kind of fold is an anticline?
Up Fold, limbs dip away from the hinge
Tectonic Jointing
Uplift and displacement of the crust breaks rock, forming faults and pervasive sets of fractures called joints.
What is a marine regression?
Water levels fall away from the shore
What is a marine transgression?
Water levels rise towards the shore
Sediment Liquefaction
When pressure in the water in the pores push sediment grains apart so that they become surrounded by water and no longer rest against each other, and the sediment becomes able to flow like a liquid
What is the hinge line of a fold?
Where the limbs of the fold meet
What is Colorado's state rock?
Yule marble
S-Waves
back and forth, body waves, secondary waves, slower than p-waves
Types of sedimentary rocks
clastic, chemical, organic and biochemical
Oblique slip fault
combination of strike-slip and dip-slip
What does geothermal gradient mean, and what is a typical geothermal gradient?
geothermal gradient = change in temperature with depth dt/dz (t is temp in C, z is depth in km) Usually about 25 C/km, but it varies from place to place Typically, west US has higher geothermal gradients
Left Lateral Fault
straddle fault→ Left foot comes towards you
Right Lateral Fault
straddle fault→ Right foot comes towards you
P-Waves
up and down, body waves, primary wave, travels through all layers of earth
