Epicenter: The location where the seismic waves of an earthquake first appear on the surface, usually almost directly above the focus.
Fault: A crack running through rock that is the result of tectonic forces.
Focus: The underground location of the seismic event that causes an earthquake.
Modified Mercalli scale: A scale used to compare earthquakes based on the effects they cause.
Richter scale: A scale used to compare earthquakes based on the energy released by the earthquake.
Seismic waves: Classified as body waves or surface waves, vibrations in rock and soil that transfer the force of the earthquake from the focus into the surrounding area.
Thursday, December 18, 2008
Thursday, December 11, 2008
earthquakes
The border near Arkansas and Missouri was the site of an extraordinary series of earthquakes in 1811 and 1812 that included four earthquakes estimated to be magnitude 7.0 or larger. These earthquakes changed the course of the Mississippi River and even caused the river to flow backwards for several hours.
Hawaii has had its many earthquakes, two in 1868, one in 1871 and one more in 1975. MOst of these occured on or near 'Big Island' where there are active volcanoes.
In Alaska the rocks of the Pacific Ocean are being subducted underneath the continental rocks of Alaska. This activity has created at least twelve magnitude 7.0 or larger earthquakes in just the last 30 years.
Hawaii has had its many earthquakes, two in 1868, one in 1871 and one more in 1975. MOst of these occured on or near 'Big Island' where there are active volcanoes.
In Alaska the rocks of the Pacific Ocean are being subducted underneath the continental rocks of Alaska. This activity has created at least twelve magnitude 7.0 or larger earthquakes in just the last 30 years.
Earthquake Distruction
This image shows what can happen outside during an earthquake. This photograph shows a street in Healdsburg, California, following the 1906 San Francisco earthquake.Friday, December 5, 2008
San Andreas Fault
The San Andreas Fault is situated in California in the United States. The San Andreas Fault is a deep crack in the Earth's crust, where the North American Plate and the Pacific Plate slide past each other.
The average range of motion along the San Andreas fault zone is about 2 inches per year, about the same rate of growth of human fingernails.
The San Andreas fault is not one single fault, but a series of faults called a fault zone. Movement can occur along one section along the fault zone at any time. This fault zone is over 800 miles long, and up to 10 miles deep.
credits for this image go to berkeley.edu.com
Some Facts about Earthquakes
1. In 1769, the earliest reported earthquake was felt by Spanish explorers. It took place about 30 miles southeast of Los Angeles.
2. The magnitude of an earthquake is the measure of how big an earthquake is. It does not vary with location. However, the intensity of an earthquake is how much shaking is generated by an earthquake. The intensity does vary with location.
3. Every year, southern California has an average of about 10,000 earthquakes. The majority of these quakes are minor and go unnoticed by the general public. Only a few hundred of these quakes are above an M3.0, and about 15-20 are greater than M4.0. If a large earthquake takes place, the aftershocks will continue for many months.
5. The typical depth of an earthquake is about 50 miles below the earth's surface.
5. European settlers first experienced an earthquake in America in 1663.
2. The magnitude of an earthquake is the measure of how big an earthquake is. It does not vary with location. However, the intensity of an earthquake is how much shaking is generated by an earthquake. The intensity does vary with location.
3. Every year, southern California has an average of about 10,000 earthquakes. The majority of these quakes are minor and go unnoticed by the general public. Only a few hundred of these quakes are above an M3.0, and about 15-20 are greater than M4.0. If a large earthquake takes place, the aftershocks will continue for many months.
5. The typical depth of an earthquake is about 50 miles below the earth's surface.
5. European settlers first experienced an earthquake in America in 1663.
Thursday, December 4, 2008
Friday, November 28, 2008
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