Sunday, March 7, 2010

Chile earthquake intensities

Below is another clip from the USGS Chile earthquake poster showing the Modified Mercalli intensities from the recent 8.8 magnitude quake. Recall that magnitude is a seismograph-based estimate of the energy released by a quake and will be more or less the same for all seismic stations that record the waves. Intensities are evaluated according to human reactions and effects on buildings, are highest near the epicenter, and fall off with distance. I was surprised to see that Santiago has almost 5 million residents, so lots of people that are at risk.  The intensity in Santiago was VII ("Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken") on a scale of I-XII.

This map of the intensity data is a little easier to read:

No doubt about it, this was an intense event.

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