Planet Earth Lecture Exam II

Stress vs strain

stress - applied force per area (the push/pull)

strain - the rocks response (shape change)

What does deformation produce?

deformation changes a rock

1. displacement - moves from A to B

2. Rotation - tilt or twist of layers

3. Distortion - stretch/flatten

Brittle

rock breaks (creates faults and joints) ed: nutrigrain bar

Ductile

rocks are flexible (creates folds and foliations) ex. taffy

compress (type of stress)

rocks are squeezed tg

tension (type of stress)

rocks are pulled apart

shear (type of stress)

rocks slide past each other

joint

rock cracking from stress & weathering

veins

fluid fills the joint and eventually turns into minerals

faults

are fractures in the earth where blocks of rock have moved

Normal fault

hanging and foot wall are pulling apart (hanging wall falls from gravity)

reverse fault

hanging wall moves upward (common in mountain ranges)

strike slip fault

plates are moving horizontal (saint andres fault line)

anticline

fold compresses upwards (looks line an A)

syncline

fold compresses downwards (looks like U)

subduction

one plate (usually oceanic) dives beneath another

what is geophysics?

allows us to scan the earth or fine details

seismology

study of seismic waves

global seismology

tells us about earth’s structure — crust, core, mantle

• velocity contrasts map entire layers of planet

regional seismology

maps finer details of faults and potential earthquakes

• used for rapid solutions and early warning/response

satellite gravimetry

monthly gravity changes from satellites tell us about environmental patterns

• water fluctuations, droughts, floods, ice shifts

magnetics

• magnetic field of earth is studied through magnetism

• reveals history of plate tectonic movement and magnetic rich deposits

electro magnetics (EM)

• senses conductivity changes in earth

• salt water, fresh water, clays, minerals — all have different electrical conductivities

• critical for mapping drinking water

• excellent for rapid mapping without disturbing the ground

induced polarization

a specific kind of electrical method studies the tiny electrical interactions on surfaces

• has advanced critical mineral and remediation studies

• a geophysical imaging and prospecting technique that measures the chargeability of subsurface materials

satellite remote sensing

remote sensing tracks greenhouse gases, air pollution, and long term climate changes

combining geophysical methods

a toolbox, useful when combined

• major societal decisions and integrity rely on geophysical studies

what are earthquakes

sudden rupture on a plate releases stored strain as seismic waves

hypocenter

energy radiates outward from the hypocenter (focus)

the exact point inside the Earth where an earthquake originates

epicenter

• the point on the Earth's surface directly above the underground location where the earthquake actually starts

• sits directly above it at the center

P wave (compression)

fastest, travels, through solids, liquids, gases

S wave, (shear)

slower, travels through solids only, twists

Rayleigh wave

moves like ocean wave

love wave

wave moves side to side

seismograph

• track ground motions

• a scientific instrument used to detect, measure, and record ground vibrations

seismogram

a visual or digital graph produced by a seismograph

intensity (earthquakes)

tracks shaking and damage

magnetitude

tracks amplitude and size

• scales are logarithmic — M6 is 10x stronger than M5

megathrust earthquakes

• plates moving together cause this

• enormous energy results in massive tsunamis

intraplate earthquakes

• form away from plate boundaries

• occur from ancient weaknesses and regional stress

liquefaction

loose sediment often becomes saturated with water and leads to more quake damage

tsunami

• caused by rapid displacement of the seafloor

• whole water column is pushed, not just the surface

• often caused by earthquakes far deep in the ocean

How do we detect/warn in time?

• seismic networks flag likely sources, catastrophe modelers forecast arrival times

• deep ocean pressure sensors (seafloor) confirm waves

plate tectonics

explains mountains, earthquakes, volcanoes, and ocean basins

*connects deep earth to surface landscape and hazards

divergent boundary

move apart (new crust forms at mid ocean ridges)

convergent boundary

move together (subduction, trenches, mountains)

transform

slide past (fault zones and earthquakes)

Alfred Wegner

• continental drift theory, found evidence

• pieced tg rocks/continents like puzzle

rejected:

• wegner assumed earth’s spin plowed oceans (wrong, lacked physics, hypothesis failed

glacial deposits

show up in tropical continents today

• places too warm show clear ice age fingerprints

climate fossilization

tropical corals, reefs, and deserts all act as fossils for the past

fossils and matching rocks

split by sea, continental drift

sonar

used to map ocean floor after WWII for nuclear threats, effective for ocean mapping

• showed us that mid ocean ridges ring the globe (volcanic seamounts/fracture zones as evidence)

ocean crust

thinner and younger than continental, due to heat flow being highest at ridges where new crust forms

seafloor spreading

magma rises and cools, creating new lithosphere as plates move apart

• old ocean crust sinks at trenches (subduction)

magnetic stripes

basalt records the position of the poles as they cool at ridges

• heat activates magnetism in these iron rich rocks

• record past seafloor spreading

crust density

crust age increases with distance from ridges

• sediment thicknesses also increases away from ridges

wilson cycle (ocean recycling)

new crust is formed at ridges, while old crust is destroyed in subduction, lifecycle for oceans/continents

1. rifting

2. seafloor spreading

3. subduction

4. collision

GPS

• measures plate movement

• hotspot tracks - show movement overtime

plate movement

Stage 1 – a continent stretches

and faults

• Stage 2 – spreading opens a

narrow ocean

• Stage 3 – continued spreading

widens the ocean

normals faults (plate tectonics II)

let blocks drop downward

grabens

the dropped blocks

red sea (triple junction)

arabian, nubian, somalian plates meet 3 diverging boundaries form a triple junction

accretionary prism

sediment is scraped off the sinking plate

• sediment piled up (bulldozer pushing a wedge sand)

ocean - ocean subduction

builds island arcs (aleutians)

ocean - continent subduction

builds continental arcs (Andes)

Continent - continent collision

buoyant continental crust resists sinking
- compression folds, faults, and thickens crust | mountain grow (ex: himalayas)