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.