Comment: 03:26 - 04:36 (01:10)
Source: Annenberg/CPB Resources - Earth Revealed - 9. Earthquakes
Keywords: earthquake, "San Andreas Fault", California, plate, "North American Plate", "Pacific Plate", fault, "Richter Scale", Iran, Armenia, China, "James Sadd"
Our transcription: Earthquakes often occur here on the San Andreas Fault in California.
This fault is actually the boundary between two tectonic plates, the North American and Pacific Plates.
In 1857 this segment of the San Andreas caused a massive earthquake.
The ground on either side of the fault shifted suddenly and violently, moving as much as four meters.
Instruments to measure the strength of the quake didn't exist at the time, but estimates based on eye witness accounts of the damage range as high as 8.2 on the Richter Scale.
Since then, California has experienced several devastating earthquakes; in fact, thousands of earthquakes on hundreds of different faults shake California each year.
But earthquakes are not just a California story, they occur throughout the world.
In regions that are densely populated and where construction practices are primitive, the destruction and loss of life from a powerful earthquake can be almost incomprehensible.
In 1990, 50,000 people died in Iran.
The year before 25,000 people were killed in Armenia, and in China, hundreds of thousands of people were killed in a single earthquake in 1976.
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