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Transcript for Hidden Fury, segment 04 of 11
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The great San Francisco earthquake in nineteen oh six matched the power of the strongest New Madrid shock. It had a Richter magnitude of eight point three, enough to devastate San Francisco. Beyond the city, the quake had a damage area of twelve thousand square miles. That's twenty times smaller than the area of damage for the New Madrid earthquakes.
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Earthquakes are normally seen as a California concern, and while quakes are not as common in the New Madrid Earthquake Zone, their enormous damage areas put millions of people at risk in the central United States.
Damage areas are so large partly because of the zone's relation to global plate tectonics. The zone lies at the core of the North American tectonic plate, one of twelve major plates that form the outer skin of our planet. The plates are floating on molten material below, forcing them to crash together or pull apart at the edges. Over ninety percent of all earthquakes occur where plates meet, but the plates' cores or critons have remained relatively stable for billions of years. They have become rigid. When earthquakes strike, seismic waves travel great distances through this dense, solid rock.