Transcript Chapter 19 - Earthquakes

Chapter 19 - Earthquakes
19.1- Forces within Earth
Earthquakes


Result of movement of crust produced by
Plate tectonics
Stress = total force acting on crustal rocks



Builds up overtime
Overcomes strength of rocks and causes
movement along fractures in rock
Earthquake = vibrations caused by
movement in crust
http://earthquake.usgs.gov/learning/kids/sciencefair.php
Stress

Three types




Compression – decrease volume of material
Tension – pulls material apart
Shear – causes material to twist
Strain = deformation of material in a
response to stress
Deformation

Elastic – when a material is compressed,
bent, or stretched

at low stress
Material can return to “normal” when stress is
zero

Example: Pulling on a rubber band

Deformation



Plastic – stress builds up past elastic limit
Permanent deformation – stays changed
even when stress is zero
Point of Rupture = failure

Example: Pulling rubber band until it breaks
Deformation

Most materials exhibit varying degrees of
plastic and elastic deformation
http://www.uwsp.edu/geo/faculty/ritter/images/lithosphere/Earth_Structure/plastic_deformation.jpg
Faults

Any fracture or system of fractures along
which Earth moves


Happens along weak regions
Fault plane = surface along which
movement takes place
http://facweb.bhc.edu/academics/science/harwoodr/Geol101/study/Images/ReverseFault.gif
Faults



Reverse Fault – form as a results of
horizontal and vertical compression that
squeezes rock
Seen near convergent plate boundaries
Two areas end up closer together after
faulting
http://facweb.bhc.edu/academics/science/harwoodr/Geol101/study/Images/NormalFault.gif
Faults

Normal fault – movement partly horizontal
and partly vertical



Horizontal movement pulls rocks apart and
stretches crust
Vertical movement causes one side of rock to
move down relative to the other side
Two areas end up farther apart after
faulting
http://facweb.bhc.edu/academics/science/harwoodr/GEOL101/Study/Images/StrikeSlipRLFault.gif
Faults

Strike-slip fault – caused by horizontal
shear

Movement is mainly horizontal in opposite
direction


Example: San Andreas Fault
Creates offset features after movement
Earthquake waves

Seismic waves = vibration of the ground
produced during an earthquake


Primary waves = squeeze and push rocks in
same direction wave is traveling
Secondary waves = cause rocks to move at
right angles relative to wave direction


Slower than P waves
Surface waves = cause most destruction and
take longest to past

Slowest wave, only travel of Earth’s surface
Seismic Waves
http://www.seismo.unr.edu/ftp/pub/louie/class/100/waves.GIF
Earthquake


Focus = point where waves originate
Epicenter = point on surface directly above
focus
http://stevekluge.com/geoscience/images/epicenter.jpg
In-Class Assignment/Homework