On: 8.9 earthquake hits Japan

[mrcharles]

From Wikipedia:

The energy release of an earthquake, which closely correlates to its destructive power, scales with the 3⁄2 power of the shaking amplitude. Thus, a difference in magnitude of 1.0 is equivalent to a factor of 31.6 ( = (101.0)(3 / 2)) in the energy released; a difference in magnitude of 2.0 is equivalent to a factor of 1000 ( = (102.0)(3 / 2) ) in the energy released.[2]

[jules → mrcharles]

How does energy scale with distance from epicenter?

[wisty → jules]

Small earthquakes have a lot of energy in the higher end of the frequency scale, which is rapidly dissipated.

Larger earthquakes have more low-frequency energy, so they go further.

There's no simple equation, they just use regression to fit the attenuation as a factor of 1/r, 1/r^2 (...), and for magnitude, and for frequency.

You can start here: http://earthquake.usgs.gov/hazards/about/attenuation.php

[ars → jules]

Probably goes down by r^2

However earthquakes may be "flat", in which case it's by r (i.e. r^1). It's probably somewhere in between those.

[jules → ars]

Wouldn't it go down by r^2 if the earthquake is flat, and by r^3 if it's not?

[wisty → jules]

No. A circle with 2X the radius has 2X the diameter, thus the energy will be cut in half.

Unless you also expect a linear attenuation, due to energy loss through the bedrock.

[borism → mrcharles]

so the correct answer is that this one was 1000 times more powerful than Kobe, and also very shallow (depth of 24 km), but fortunately offshore (but unfortunately that means powerful tsunami).