Aim: What is an earthquake?
Do now: In your notes, explain where most
earthquakes occur and Why?
I. Earthquakes
- are vibrations in the
crust caused by moving
crustal plates.
A. Focus - the origin (starting point) of the
earthquake underground.
B. Epicenter – the location on the surface
directly above the focus.
II. Causes of Earthquakes
• the release of potential energy stored
in rock.
• energy is released in all directions
A. Elastic Rebound Hypothesis
- Deformation of rocks (stressing/bending)
cause them to build up pressure (energy).
- When they break, the stored energy is
released which results in the vibrations.
Why would someone think that most
earthquakes cause little damage and little
loss of life?
- Because most occur in
areas that are not
populated by people or
Tokyo, Japan
AIM: How are Earthquakes
Do now:
If you were asked to measure a
recent Earthquake, what information/
observations/data would you try to
I. Measuring Earthquakes
• Seismology – the study of earthquake
waves (energy).
*Seismos = earthquake
• Seismographs –
instruments that
record earthquake
waves (energy).
• Seismogram – a graph produced by recording
the ground motion on a seismograph.
Creation of Seismogram
• Richter Scale: Measures the magnitude
(strength) of an earthquake from the
II. Types of Seismic Waves
(earthquake waves)
• created at the time
the earthquake
• help scientists
theorize about the
inside of Earth and
it’s structure.
1. Body Waves
- Travel through the Earth’s interior.
P- Wave
-Travels through
solids and liquids.
- Cannot go through
- Travel Faster
Travel Slower
P & S Wave Animation
• P-waves (Primary/Compression Waves)
- push-pull waves that compress and expand
the ground in the direction that the waves
• S-Waves (Secondary/Transverse Waves)
- move the ground at right angles (up and
down)to the direction that they travel.
2. Surface Waves –seismic waves that travel
along the Earth’s outer layers (crust).
- Follow P and S waves
- Most destructive since they are on the
3. Aftershocks and Foreshocks
movements of the crust that follow a
major earthquake called aftershocks.
small vibrations called foreshocks come
before a major earthquake.
Anchorage, Alaska
III. Earthquake Zones
The “Ring of Fire” is the area
that surrounds the Pacific Plate
which is marked with volcanoes
and earthquakes.
Aim: How do we locate Epicenters?
Do Now:
1) From the side table obtain the two
white worksheet.
2)Describe the causes of earthquakes.
Earthquakes are caused by the rapid release of
energy stored in rock that has been subjected to
great forces (at plate boundaries where plates
This releases of energy causes the vibrations of
an earthquake.
I. Locating an Earthquake
• The difference in arrival times of P and S
waves helps to locate the epicenter.
• The greater the difference, the greater
the distance to the earthquakes epicenter.
Take a worksheet
from the top bin
to practice
subtracting P and
S wave times.
II. Distance to Epicenter
A) Find the difference in arrival time
between the first P wave and the first S
wave on the seismogram.
S-wave Arrival
P-wave Arrival
B) Using ESRT page 11 and a piece of scrap
paper, we can find the equivalent distance.
**ESRT Page 11 and a piece of scrap paper **
S-wave – P-wave =
1) Use the time axis to
mark off this difference
in time. Always use 0
to start.
2) Slide the scrap
paper up the chart to
match the P and S
wave lines with the
marks you made.
3) Once they are
matched, as close as
you can, read down
from this intersection
to find the equivalent
“Spread Technique”
III. P- Wave
Travel Time
(or s-wave travel
-Use the distance
from the previous
step to find the travel
- Move up to the
wave you are
looking for. (either P
or S)
IV. Origin Time
-The origin is when the earthquake began.
- Subtract the arrival time from the travel
Origin (start)
Travel Time
Arrival (end)
V. Epicenter Location
• Data from three or more seismographs
must be used to find the exact location
of an earthquake epicenter.
- Use the distance
to epicenter value
and a protractor to
draw these circles.