Earthquakes and Volcanoes
when rock masses
in the Earth’s
faults. The rock
horizontally or in
point on the
Focus – The location on a
fault where the greatest
amount of movement is.
It is far underground.
Energy travels outward from the
focus in waves.
The intensity of an earthquake
can be expressed on the Richter
Types of Earthquake Waves
An “S Wave” (“shear” or “secondary”)
causes material to move up and down as it
A “P Wave (or “Primary” or
“Pressure” wave) consists of
compressions which move
straight through a material.
p & s waves animations
P waves can travel through solids, liquids
S waves can travel only through solids.
Earthquake waves are detected on a
Seismometers produce a seismograph
P waves travel faster than S waves.
The farther away from the
epicenter, the greater the
difference in arrival time of P and
This graph lets
arrival of P
and S waves.
An earthquake occurred on June
23, 1946 and these were recorded
times of P and S wave arrivals at
0 2 37
For example, the P/S time interval
in Saskatoon was 0 h, 2 min and
2 minutes and
about 1400 km.
A circle with a 1400 km radius
could be drawn on a map with
Saskatoon in the middle. The
epicenter would be somewhere
on this circle.
The procedure could be repeated for
all the other stations. The point where
all 5 circles overlap would be the
epicenter of the earthquake.
In a different example, circles were drawn
around 3 seismic stations.
Eg. All 3 circles
intercept at this
point, so this
would be the
location of the
High Risk Zones
1. They are located near
a plate boundary.
2. There is a history of
earthquakes in the
3. There are numerous
The West Coast of
North America has
More Information on
Earthquakes from National
way to the
Three types of Volcanoes
The lava is quite liquid and flows down the sides.
These volcanoes are very large but not very steep. An
example is Hawaiian volcanoes like Kilauea
form mainly from explosive eruptions of lava. Blown violently into the air,
the erupting lava breaks apart into fragments called cinders. The fallen
cinders form a cone around the volcano's central vent.
such as Mount St. Helens, build from both explosive and
slow flowing eruptions. Layers of tephra alternating with
layers of viscous lava flows create steep-sided, often
symmetrical cones that we think of as the classic volcano
have all these
More Information on Volcanoes
from National Geographic