Click here
for a lower graphics version
Investigating Earthquakes
Learner Outcomes
By completing these activities, the learner will:
-
determine patterns in earthquake locations
-
use seismograms to measure earthquake magnitudes
-
investigate seismograms from significant events
-
locate epicenters using distance/time formulas and procedures
-
compare and contrast the feasibility of an Earthquake Alert System
Exploration
 |
Earthquakes
occur all over
the world.
The vast majority are too weak to be felt; but they can be measured using
seismographs. |
.
National Map
of Earthquakes Recorded in the Last 14 Days
As you can see, most of the earthquakes
occuring in the US are in the
western
portion. This includes:
Although major earthquakes are infrequent, there are also active regions
in southeastern Canada
and in the MississippiValley.
More Earthquake
Maps on the Web
Seismo-surfing
the Internet
Concept Introduction
1. Seismographs
are used to measure the magnitude of an earthquake.
This is done by measuring the amount of ground movement. The output of
a seismograph is a seismogram.
Current seismograms can be seen in Los
Angeles, CA, Reno,
NV, and Orange
County, CA.
The three most important parts of a seismogram are:
-
the amplitude of the ground movement
-
the time of first P-wave arrival
-
the time of first S-wave arrival
The difference in arrival times indicates how far away the epicenter is
located. This is because P-waves propogate through the Earth much faster
than S-waves propogate. Note the first P-wave arrival and the first S-wave
arrival as shown on the seismogram below. (Make your own seismogram
by clicking here).
2. Earthquake epicenters are pinponted by at least three stations calculating
radial distance.
Determine
the location of a "virtual" earthquake.
3. The shape of the amplitude disturbance also indicates the type of
earthquake. Underground nuclear tests can also be monitored in this way.
Concept Application
-
Use NIH Image to determine the distance
from the epicenter to each recording station A, B, E, and F.
Assessment
Extensions
-
Read the Earthquake
Alert System background material. This is a feasibility study being
done for the San Francisco, California area. Write an essay explaining
why such a system is necessary in this area, and how successful you think
it will be. Examine a population density map in an atlas along with a map
showing plate boundaries. Make a list of large urban areas that are close
to potentially active plate boundaries.
-
Explore how tsunami's
are related to earthquakes.
