Download Earthquakes

Earthquakes
Earthquake waves are called…
Seismic Waves
• The types are P, S, and L waves
P - waves
• Travel the fastest
• They arrive first and thus are called
primary waves
• Travel through solids, liquids and gases
• Are longitudinal waves with compressions
and rarefactions
S - Waves
• Travel Slower
• Arrive later and are thus called Secondary
waves
• Travel through solids but not liquids or
gases
• Are transverse (or shear) waves with
crests and troughs
P-waves & S-waves
L - Waves
• Are the slowest moving
• Arrive after the P and S waves
• Originate on the earths surface thus are
called surface waves
• Move in a circular motion like water waves
• Cause the most damage during an
earthquake because the bend and twist
the Earth’s surface
Focus and Epicenter
• The point underground where the earth
quake originates is called the focus.
• The place on the Earth’s surface directly
above the focus is called the epicenter.
A seismograph consists of a weight attached
to a spring or wire.
A pen attached to the weight records any
movement of the Earth on a sheet of paper
wound around a constantly rotating drum.
Seismograph
• Instrument that detects and measures
seismic waves
Richter Scale
• A scale used to compare the strength of
earthquakes
• Each number on the Richter scale
represents an earthquake 10 times
stronger than the number below it.
• Any number above 6 represents a very
destructive earthquake.
P and S waves originate at the epicenter (left).
P-waves travel fastest and through all types of
matter (solid, liquid and gas.)
S-waves travel slower and only through solids.
Is the crust all one piece?
• No, the crust is divided into many “plates”.
The boundaries between plates are
called “faults”.
Why does the Earth quake?
• The entire crust of the Earth is floating on
a liquid layer of mantle (even the oceans).
At the faults the plates can…
…slide past each other, pull away from each
other or push against each other.
The plates pushing together…
…can cause mountains to push up and
earthquakes.
Plates pulling apart can cause…
…deep trenches and volcanoes.
Plates sliding past each other…
…build up tension. When this tension is
released, earthquakes occur.
San Andreas
Fault
Continental Drift …
Is the theory that the continents are all
drifting continuously and that millions of
years ago the were in very different
locations.
Focus of Haiti Earthquake
The recent quake in Haiti
(Hispaniola) occurred along a fault.
Damage to buildings
Damage to buildings
Alaska
When you think of Alaska, you may not think
of Earthquakes…
…but Alaska has more earthquakes than
any other state.
In fact, Alaska has a magnitude 7 quake
almost every year.
Not much is heard about this because
human casualties are usually not too high as
not a lot of people live in the earthquake
zones.
Alaska had a 9.2 magnitude earthquake in
1964.
This is the most violent earthquake
ever recorded in the United States, but
only about 100 people died.
California is much better known for
earthquakes.
• They do have a lot
of quakes, but the
main reason is the
large population
that is affected.
The San
Francisco quake
of…
… 1906 killed
an estimated
3000 people.
The fire that followed destroyed 28,000
buildings and made 225,000 people
homeless.
The city hall was one of the casualties.
The San Francisco quake of 1989…
…killed 62 and left 12,000 people homeless.
The Bay Bridge collapsed upon itself.