ANSWERS Finding an Earthquakes Epicenter
Background
Earthquakes occur because of a sudden release
of stored energy. This energy has built up
over long periods of time as a result of tectonic
forces within the earth. Most earthquakes take
place along faults in the upper 25 miles of the
earth's surface when one side rapidly moves
relative to the other side of the fault. This
sudden motion causes shock waves (seismic
waves) to radiate from their point of origin
called the focus and travel through the earth.
The epicenter is the point on the surface directly above the focus. It is these seismic waves that
can produce ground motion which people call an earthquake.
The rocks that seismic waves travel
through quickly organize the waves into
two types; longitudinal and transverse.
The longitudinal waves, also known as
primary or P waves, travel fastest, at
speeds between 1.5 and 8 kilometers per
second in the Earth's crust. The
transverse waves, also known as
secondary or S waves, travel more slowly,
usually at 60% to 70% of the speed of P
waves.
Since waves travel outward from the
source in all directions, it is possible to
track an earthquake back to its source. The
greater the earthquake damage an area suffers, the closer the area is to the earthquakes epicenter.
One way to measure and track this damage is the modified Mercalli scale.
Purpose
the epicenter of an earthquake using the Mercalli scale.
Materials
pencil and colored pencils
To find
A
Procedure
1. Use the modified Mercalli scale to rate the severity of the earthquake in each location
listed in the data table. Write the Roman numeral rating for each in column 3 of the
data table.
2. Draw lines on the map connecting areas of matching earthquake severity. Label each
zone
3. Color each zone with a different color
ANSWERS Finding an Earthquakes Epicenter
Analysis and Conclusions
1.
-
What cities were nearest the epicenter of the earthquake? A. Tacoma is the epicenter
Tacoma is the epicenter
Issaquah and Seattle
Olympia and Sumner
2. Where was the focus of the Earthquake?
- Directly underneath the epicenter (Tacoma) on the fault line
3. Explain the process that causes seismic waves.
- Earthquakes occur because of a sudden release of stored energy. This sudden motion causes
shock waves (seismic waves) to radiate from their point of origin called the focus and travel
through the earth
4. Earthquake waves travel out from the focus in all directions
5. Earthquakes happen because of a release of stored energy
6. Transverse earthquake waves are called Secondary Waves
7. Longitudinal earthquake waves are called Primary Waves
8. Explain 3 ways the picture below is similar to what happens during an earthquake.
1. Waves Travel outward in all directions
2. Epicenter where the wave is the strongest
(earthquake – the spot where faults moved)
(pond its where the bobber hit the water)
3. Energy disturbance that is traveling through a medium
(pond-water)
(earthquake-land or earth)
4. Transverse waves – waves are traveling at a right angle