stress on the crust “listen…you think you have it bad! i am under more stress than you can...
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Stress on the CrustStress on the Crust“Listen…you think YOU have it bad! I am under more
stress than you can possibly imagine. I lead a really hard life you know.”
Mr. Rock
stress- a force that acts on crust rocka force that acts on crust rock
1. compression- push together- push together
2. tension- pull apart- pull apart
3. shear- side by side tearing - side by side tearing
Deformations- “Strain” Deformations- “Strain”
deformation- any change in the shape or volume of Earth’s crust in response to a stress.
Types of Deformations:Faulting (breaking), folding (bending),
tilting, sliding, weathering, erosion
FoldingFolding
result of compressionresult of compression Types of Folds
1. monocline
2. anticline
3. syncline
Folding- Folding- Las Vegas Las Vegas
NevadaNevada
FaultingFaulting fault- a break in the earth’s crust - a break in the earth’s crust
where movement has occurredwhere movement has occurred Parts of Faults
1. Fault plane- fracture / break line fracture / break line
2. Hanging wall- rocks above fault plane rocks above fault plane
3. Footwall- rocks below fault plane rocks below fault plane
HWHW
HWHW
FWFW FW FW
Types of FaultsTypes of Faults1. Normal- - hanging wall moves downwardhanging wall moves downward
• cause = tension = tension
2. Reverse- - hanging wall moves upwardhanging wall moves upward• cause = compression = compression• Thrust Fault- HW rides up and over rides up and over FW
3. Strike-Slip- side by side movementside by side movement• cause = shear = shear• fault plane verticalfault plane vertical
“Oh no!! The ground shakes again!!
The gods must be angry with us!
Quick.…sacrifice something!!”Panicking Villager
Earthquakes!!!Earthquakes!!!
Earth’s Crust in Motion!Earth’s Crust in Motion!Earthquake:
shaking of the Earth’s crust caused by a shaking of the Earth’s crust caused by a release of energy.release of energy.
Ex.Ex. erupting volcanoes, plate movement erupting volcanoes, plate movement
How Earthquakes Happen…How Earthquakes Happen…
1. Friction keeps plates from moving.
2. Stress builds up.• plates “deform”• plates reach their elastic limit
• (amount of stress something can absorb)
3. Rocks rupture (break) at weakest point.• plates move suddenly- earthquake!
4. Plates “rebound”
Parts of an EarthquakeParts of an Earthquake
focus- the spot along the fault where - the spot along the fault where rock rock slippage (break) occurs occurs
epicenter- the point on the earth’s - the point on the earth’s surface directly above the surface directly above the focus
Review: Seismic WavesReview: Seismic Waves1. Body Waves
a. P-Waves- (Primary) 5-14 km/s
• compresses and stretches crust (compression wave)
b. S-Waves- (Secondary) 3.5-8 km/s
• vibrates crust side to side (shear wave)
2. Surface Waves- “L-Waves” 2.5-4.5 km/s
• combination of P & S waves• travel along the surface; cause most
damage; slowest
Locating an EarthquakeLocating an Earthquake
Seismographdevice used to detect seismic wavesdifferent wave types = different
seismographs
Locating an EarthquakeLocating an Earthquake P, S, L waves travel at different speeds
• each then arrives at the seismograph at different times
• time difference between P and S waves used to calculate distance to epicenter
• distance to epicenter = radius of a circle drawn around the station
Need 3 seismograph stations at 3 different locations.
Measuring EarthquakesMeasuring Earthquakes1. Mercalli Intensity Scale: I to XII
• based on intensity- amount and type of damage caused
2. Richter Magnitude Scale: 1 to 10+
• based on magnitude- amount of energy released (9.5 biggest)
3. Moment Magnitude Scale:• based on the size of many types of seismic
waves, amount of movement, size of rupture, and rock strength along the fault.
Earthquakes EffectsEarthquakes Effects
AftershocksAftershocks- - small EQ’s after a major EQ; small EQ’s after a major EQ; due to the release of more stressdue to the release of more stress
LiquefactionLiquefaction- - ground becomes “soft”; ground becomes “soft”; creates mudslides and landslidescreates mudslides and landslides
Fault ScarpsFault Scarps- - a cliff made by an EQa cliff made by an EQ
TsunamisTsunamis
TsunamiTsunami ocean wave caused by earthquakes, ocean wave caused by earthquakes,
massive landslides, meteor impactsmassive landslides, meteor impacts Japanese for “Japanese for “harbor wave””
• In deep water: low / very fast movinglow / very fast moving
• In shallow water: slows down due to drag on bottomslows down due to drag on bottom increases in height- up to 90+ ftincreases in height- up to 90+ ft
Earthquake ZonesEarthquake Zones”Seismic Belts””Seismic Belts”
1. Circum-Pacific Belt…“Ring of Fire”
2. Mediterranean-Asian Belt
3. Mid-Ocean Ridges
Earthquake Prediction Earthquake Prediction
Earthquake-Recurrence Rate (history)Animal Behavior Seismic Gap Theory- “Strain Accumulation”
areas along a fault where few EQ’s have occurred could be areas where A LOT of stress is building up.
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