Download Earthquakes

DO NOW REVIEW FROM BEFORE THE VACATION
1- Name the three type of plate boundaries, describe
their direction of movement and what they create.
Convergent – plates come together and form mountains,
volcanos and trenches.
Divergent – plates move apart and cause the sea-floor to spread
and create new oceanic crust.
Transform – plates move parallel (side by side) and create
earthquakes and faults (cracks).
2- Explain what causes the plates to move around Earth.
Convection currents within the mantle (asthenosphere)
cause the plates to move. This is occurs as hot material
rises and the cooler material sinks causing a circular
flow.
Aim: What is an earthquake?
Do now: In your notes, explain where most
earthquakes occur and Why?
Japan
I. Earthquakes
- are vibrations in the
crust caused by moving
crustal plates.
California
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.
Closure:
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
cities.
Tokyo, Japan
AIM: How are Earthquakes
Measured?
Do now:
If you were asked to measure a
recent Earthquake, what information/
observations/data would you try to
use?
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
seismogram.
II. Types of Seismic Waves
(earthquake waves)
epicenter
• created at the start
of the earthquake.
What do you notice
about the waves in
the diagram?
• The waves motion
through Earth has helped
scientists theorize about
the inside of Earth and
it’s structure.
A. Body Waves
- Travel through the Earth’s interior.
1. P-waves (Primary/Compression Waves)
- push-pull waves that compress and expand
the ground in the direction that the waves
travel.
How would you describe the motion of this wave?
2. S-Waves (Secondary/Transverse Waves)
- move the ground at right angles (up and
down)to the direction that they travel.
How would you describe the motion of this wave?
P & S Wave Animation
P- Wave
S-Wave
-Travels through
solids and liquids.
- Cannot go through
Liquids.
- Travel Faster
- Travel Slower
- Arrives First
- Arrives Second
B. 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
surface
China
C. 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?
Based on the diagram, how many seismograph station locations
are necessary to find the epicenter of an earthquake?
I. Locating an Earthquake
Epicenter
• The difference in arrival times of P and S
waves help 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 (with
one wave)
Using the ESRT page 11 we can translate the
time into a distance.
… we can also use the same ESRT page to
translate a distance into a time.
Examples:
1)
2)
3)
4)
A P-wave takes how long to travel 2600 km?
An S-wave travels how far in 4 min?
After 8 min and 20 sec. a P-wave travels?
An S-wave travels 4.0 x 103 km in…
Get an Earthquake P and S wave
Travel Time worksheet from the
top back bin.
Work on questions 1 - 8 ONLY!
• III. Distance to
Epicenter (with
two waves)
“Spread Technique”
Ex: S-wave – Pwave = 00:04:45
1) Use the time axis to
mark off this difference
in time.
2) Match the P and S
wave lines with the
marks you made.
3) Read down from
this intersection to find
the equivalent
distance.
Complete the worksheet
IV. P- Wave
Travel Time
(or s-wave travel
time)
-Use the distance
from the previous
step to find the travel
time.
V. Origin Time
-The origin is when the earthquake began.
(start)
- Subtract the arrival time from the travel
time
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.
Epicenter
- Use the distance
to epicenter value
and a protractor to
draw these circles.