- The Focus
- The focus is the point beneath the surface where the breaking, or slipping, of rocks actually happened. This may be more than 400 miles deep but is probably less than 35 miles deep.
- The Epicenter
- The epicenter is the point on the Earth's surface directly above the focus.
It's usually regarded as the "center" of the earthquake. Scientists locate
the epicenter by studying the time earthquake waves arrive at several
recording stations.
- Aftershocks
- After the initial rock movement causing the quake, other movements occur as neighboring rocks adjust to the new arrangement. These aftershocks are usually smaller than the first shock but can be quite strong and can occur long periods after the initial quake.
- Damage
- When rocks deep within the Earth crack or slip, they release stored energy that radiates through the solid Earth as waves. There are three basic types of waves: P-waves, S-waves, and surface waves.
P-waves are longitudinal and similar to sound waves except they have extremely long wavelengths. These waves are a series of pushes. Imagine standing in single file with a large group of people when someone at one end is pushed forward hitting the next person. The energy of the "push" travels from person-to-person through the line. S-waves are transverse waves similar to those snake-like (sine) waves you can make with a length of rope.
S and P-waves move very fast and are important to geologists studying earthquakes and the Earth's interior structure. They do not, however, cause much damage. Earthquake damage is the result of the more complex, and slower moving, surface waves. The waves are similar to waves in water where the Earth moves with a rolling action.
- Environmental Damage
- Ecologically, earthquakes are important in at least two distinct ways. First, earthquakes can cause changes in local ecosystems by altering the topography and changing the flow of local waterways. In the long term, earthquakes, over vast periods, modify the physical environment to which organisms must then adapt.
Earthquakes can also raise environmental issues. Gas and oil pipelines can be broken dumping large quantities of fuel into neighboring ecosystems. Dams can be cracked causing widespread flooding. What design considerations have been implemented to minimize such damage? Were earthquakes considered when pipelines were constructed in Alaska?
Thanks to Bill Einsig of SEE Flash for this explanation. The Science, Environment and Ecology (SEE) Flash is an email newsletter sponsored by Keystone Outdoors magazine and the Pennsylvania Department of Education with support of the Science Teacher's Resource Center at Penn State York. Its purpose is to provide an exchange of information and instructional ideas for the outdoor community as well as teachers of elementary and secondary education. Questions, comments, and requests for changes to the mailing list should be sent to wxe1@psu.edu. There no fees and new subscribers are always welcome.
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