midterm 2 Flashcards
earthquakes and their causes, what Have we used from them?
an earthquake is an episode of groundshaking
causes:
- fault motion **MAIN
- fracking (rock-breaking detonations)
- explosions (underground nuclear detonations)
- meteor impact
- landslides
- re-arrangment of atoms in minerals (in subduction zones bc of pressure
used seismic waves to understand the earth’s deep structure
elastic rebound theory
under pressure rocks will bend until they break, when they break they go back to their original shape but with a fracture
faults and their terminology
a fault is a fracture in the ground where one body has slid relative to the other due to forces in the earth
(ex: Istanbul Highway (TEM) near Ankara, Turkey)
head block: block of rock on top
footwall block: block of rock on the bottom
fault vs joint
joint: fracture in rock has no slippage
fault: fracture in rock, there is slippage
types of force that cause faults
compression: force from both sides (left and right), crust gets thicker vertically (crustal thickening)
tension: pulling apart the crust, crust gets thinner vertically, can cause mountains to form because creates basins separated by ranges
ex: SW usa, east african rift
shear: side to side motion, crust gets pulled angularly (rectangle to parallelogram), aka transform boundaries
ex: San Andreas fault
types of faults
normal faults:
- head block moves down
- force = tension
reverse faults:
- head block moves up
- force = compression
earthquake depth vs boundary
divergent & transform: shallow
convergent: deep
New Madrid Earthquakes
in/around missouri ~200 years ago (winter of 1811-1812)
maybe an old rifting spot that stopped
3 BIG shakes (8 or 9 Richter)
weird things: geyers of sand, silt erupting from ground
earthquakes that are not at boundaries
- adjusments to lithosphere to volcanism
- ancient collision zones
- ancient rift zone
what caused the 2011 VA earthquake
slippage at an old reverse fault from formation of Pangea
body waves, surface waves, types and order
P => S => R & L
body:
- P (compressional) solid & liquid
- S (shear) solid
surface:
- R (rayleigh) like ocean
- L (love) side to side
types of earthquake scales
mercalli: very qualitative, based on what happens (feels like truck driving, liquids disturbed)
seisogram: depicts vert & horiz waves when they arrive (P, S, surface)
richter: base intensity on largest amplitude of each wave; logisitic scale
how can you determine location of earthquake from seismogram?
S-P interval (time between arrival P & S waves) is used to determine distance from the station. incr time = incr distance.
distance is drawn as a circle around the station => epicenter (specific location) is found from intersection of 3 circles
US Geological Earthquakes Hazards Map
- Alaska: & Oregon OC-CC (reverse)
- West Coast: transform boundary (shearing)
- Utah: active rift (normal)
- Wyoming: hotspot
- Missouri/Arkansas: ancient rift (normal)
- Appalachain Mts: old reverse faults
- New York: glacial rebound earthquakes
- South Carolina: hotspot where pangea rifted
- Hawaii: hotspot
when rocks break how is energy released?
body and surface waves
deformation
the bending, breaking, stretching of rock
ex: Interior Plains (mid west) is super flat and undeformed [shales, sandstones, & limestones] can infer there used to be a shallow ocean
types of deformation
brittle (breaking):
- composition: covalent bonds
- lower pressure
- high rate of force (fast)
- lower temp
ductile (bending):
- composition: ionic bonds (ex: NaCl, micas)
- higher pressure
- slow rate of force (long time)
- higher temp
- strain = change in shape
- ex: clasts in quartzite stretched
types of ductile folds
folds are larger scale strain
anticline: old layer in coming thru middle, young layer sandwich
syncline: young layer middle, old layer hotdog
plunging: bump in carpet, but at a slope
how did appalachian mountains form?
formed from 3 collisions that created fold and thrust belt => reverse faults and plunging folds
why does granite form large joints at high altitude?
granite is formed under high pressure, when exposed to low pressure it cracks
relative age uses and types
- original horizontality: sediment deposited horizontally
- lateral continuity: sediment layers are continuous
- super position: youngest layer on top, oldest on bottom
- cross cutting: geology that crosscuts rock is newer then the rock
- inclusions: inclusions in rock are older than the rock
unconformities
gaps in dating of rocks (200ya, 300ya, - , 500ya)
causes: no sediment (no source material like mountains), erosion of gap layer
absolute dating
- most based on radioactivity
- C14 decay
- U decay (U = parent, Pb = daughter)
- Rb (Rb = parent, Sr = daughter)
=> when feldspar in GRANITE forms, it grabs rubidium thinking its K - needs minerals that:
===> don’t have any of the daughter element to start
===> trap the parent & daughter forever
ex: Zircon for U & Pb
half life formula and meanings
N = N_0*(e)^(-λt)
N = # of parents now
N_0 = # of parents initially
λ = ln(2)/half life
t = years passed
wats da geo period order
phanerozoic
protozoic
archaen
hadean
phanerozoic:
0 - cenozoic - 64
64 - mesozoic - 252
252 - paleozoic - 541
cenozoic:
- quarternary => 0.02 modern humans
- neogene
- paleogene => 30 Alps, 40 India, 66 K-Pg event
mesozoic:
- cretaceous
- jurassic
- triassic
paleozoic:
- permian
- carboniferous
- devonian
- silurian
- ordovician
- cambrian
youngest
oldest
varves
annual bands of seasonal deposition in lakes
layers:
- coarse sand
- fine silt, clay, organics
- coarse sand
- fine silt, clay, organics
- repeated^^
influences: floods from melted snow => more coarse sand, using radioactivity (bomb pollution) to date sediment
why is papau new guinea significant to jim?
small region but over 800 langauges b/c separation by mnts. => SEPARATION BREEDS DIVERSITY
ice age
10% of earth covered in ice
what caused the devonian explosion?
continental continental collision created hella mountains => separation => diversity
what conditions for hydrocarbon formation?
- dead plankton
- calm water (so they^ settle)
- very low O2 (so reaction doesn’t reverse)
- a lot of sediment (ex: clay) (buries plankton)
=> when this layer gets buried and reaches 80C, its trnasformed into a source rock (ex: shale) w/ kerogen
==> when kerogen reaches 120C, it turns into oil; unless the source rock has a cap rock on top, the oil floats to the surface
<0.1% of all marine organic matter will become a viable petroleum resource
what is the geological timeline for a perfect hydrocarbon formation environment
continental rifting => new ocean (warm & shallow) & sediment => perfect for hydrocarbon
ex: mesozoic rifting of pangea in Middle East
oil shale
basically source rock, dirty & smelly, mostly black, kerogen wasn’t heated to oil
coal
black, brittle, sedimentary rock [carbon, quartz, clay from a SWAMP]
type:
pete (plant matter) => ligmite => bituminous => anthracite (high grade)
- high grade = generates most energy
- difficult to mine, dirty to burn
- TERRESTRIAL deposit, edge of continents
why was the paleozoic good for coal formation?
- collisions to make coal high grade
- high oxygen for plants
- continental flooding (buries swamps w/ sediment)
both fossil fuel qualities
both aka Coal & Hydrocarbons
- limited supply
- mining & extraction disasters
- changes atmosphere composition
- also coral bleaching (CO2 makes H2CO3 which is an acid)
why was the eastern usa in carboniferous good for coal formation
- near equator so hella warm & swampy
- gets buried w hella sediment from flooding
- crashes into africa (goof for high grade)
Uranium as an energy source
pros:
- a lot left
- little/no greenhouse emissions
- naturally occurring
- more energy potential than coal
cons:
- waste rock
- needs hella water
- nuclear waste
- human error
strong force (nuclear energy term)
force holding together nucleus, released by firing neutrons at nucleus
ore
rock with concentrated metal-rich minerals (must be concentrated enought to be valuable to mine)
- biological processes & climate change create valuable ore
aluminum
- 8% of crust
- 10% of felsic and intermediate rocks
- hydrolysis will dissolve feldspars in granite and leave Al ore
- needs hella rain, warm climate, expose felsic igneous rock for hella long
- bauxite is the primary Al ore (ancient tropical soils developed on felsic igneous rock)
iron
- 6% of crust
- 30-60% of rock
- first massive deposits created because photosynthesis started (HELLA O2 in water)
- BIF = Proterozoic Banded Iron Formations (layers of magenetite and red hematite)
sulfide deposits
valuable metals (Pb, Cu, Au, Zn) bond with sulfur and form sulfide minerals
magmatic:
sulfide minerals crystallize quickly and sink to the bottom of the magma chamber
ex: mine in Admiralty Island, Alaska
black smokers:
sulfide minerals in heated up seawater ejects from “chimneys” underwater, at divergent boundary
placer deposits
ore rock erodes, clasts containg native metals fall into a stream, stream concetrates the ore by separating the grains
chemical weathering to make aluminum
primary rock + CO2 + water
= residual clay mineral + soluble stuff that leaches away (esp Si)
residual clay mineral + leaching = Al2O3
mass wasting
erosion whose sole transport is gravity
creep: gravity acting on particles, slow, on every sloping surface
angle of repose
loose granular material assumes a slope because of friction, the angle of repose is the steepest slope it can have
influenced by water content, grain size, shape
causes of creep
bioturbation (animal burrowing), freeze/thaw (ground rising&falling), rainsplash (rain loosens particles)
controls on mass wasting
water:
- depending on amount
- binds particles with surface tension
- saturated sedimenet will flow
slope
climate
cohesion
vegetation
what makes coastal cali susceptible to mass wasting hazards
semi arid climate
=> when it rains, BIG problem
emergent coastlines
=> tectonically active region, coastline gets lifted and terraced, creates erosion structures
earthquakes
whose fault was La Conchita, CA? avocado ranch bc they didnt drain rainwater properly
