# 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.

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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:
 PacificNorthwest(Washington & Oregon) Montana Washington California Yellowstone National Park Alaska (Another Alaska Map) California and Nevada Utah Hawaii (Island of Hawaii) Another California  site Wyoming and  Idaho Colorado

Although major earthquakes are infrequent, there are also active regions in southeastern Canada and in the MississippiValley.

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:

1. the amplitude of the ground movement
2. the time of first P-wave arrival
3. 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.