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
