BACKGROUND:
 Earthquakes have occurred for as long as the Earth has
had a solid crust. They will continue until the Earth turns into a solid
rock. Our great grandchildren will have to live with the possibilities of
earthquakes. Students should realize that earthquakes generally recur in the
same locations. It is reasonable to assume that if one earthquake strikes an
area, there will probably be more.
Earthquakes are caused by stresses from plate
movement. Most earthquakes thus occur at plate boundaries, where pieces of
the lithosphere converge, diverge, or slide past each other. This is also
true for most volcano related earthquakes, as most volcanoes form at plate
boundaries as well. In particularly, earthquakes and volcanoes are very
common along the "Ring of Fire", the belt of converging plate
boundaries that circles the Pacific Ocean.
PROCEDURE:
- Explain to the class that earthquakes tend to recur in the same areas,
and that these areas are usually at or near plate boundaries. Explain
the map on the worksheet to the class. This global map shows all the
large earthquakes that occurred between 1904 and 1980. The Richter Scale
magnitude of each earthquake is listed for each event.
- Have the students complete the worksheet. You may want the students to
trace the general area where large earthquakes have historically
occurred. This looks particularly dramatic with a colored pencil or pen.
You may want to trace along with the class.
- Ask the students if these areas will have earthquakes again. The
answer is yes, because where plates meet there will be stress until they
stop moving.
- Instruct the students to write about the areas that are free from
earthquakes, and to explain why no earthquakes occur there.
- If you have a relief map of the world, point out that the areas that
have many earthquakes often have high mountains: these are either
volcanoes or compressional mountain ranges. The latter form at
converging plate boundaries.
ANSWERS:
- Many earthquakes have occurred along the rim of the Pacific Ocean,
especially in the following areas: Southern Alaska, Japan, and
Chile. The area between China and India also has had many large
earthquakes (This is the Himalaya Mountains, a compressional
mountain range).
- Large earthquakes are not likely to occur in Australia, the
eastern coast of North America and South America, and in the
interior of Africa.
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