"The amplitude of the pattern is used to quantify the magnitude of an earthquake, using the formula M = log (A/T) + (source distance function) ; with A is amplitude and T is time. The source distance function is a correction factor for an individual seismic station. Because the scale is logarithmic, each ground motion unit represents an earthquake that is 10 times larger. But seismologists discovered that earthquakes radiate their energy over different time periods. As the amount of energy radiated by an earthquake is a measure of the potential for damage, seismologists also use radiated energy to describe the effects of an earthquake. Estimates of energy use the relationship, log10E = 11.8 + 1.5M. For example, an M=5 earthquake generates 2 x 1019 ergs, which is roughly equal to one atom bomb (or 20,000 tons TNT). A M=6 earthquake generation 6 x 1020 ergs, which is roughly equal to a hydrogen-fusion bomb, and~30x greater than a M=5 earthquake. This explain the rapid increase in destructive power of earthquakes as their magnitude only slightly increases. Comparing earthquake magnitude and energy released:

Magnitude Change
Ground Motion
(displacement)
Energy

1.0
10 times
32 times

.5
3.2 times
5.5 times

.3
2 times
3 times

.1
1.3 times
1.4 times"



"So, the energy release at an earthquake travels away like a 3-D ripple, in the form of both compression and shear waves. Consider a source near the surface of the Earth, say, and an earthquake in southern California. If there are discrete jumps in density, the path will show jumps in the velocity. The latter, a density increase with depth, is seen in the velocity of energy waves over much of the Earth's volume. The velocity changes do not always occur gradually. Relatively rapid increases occur at ~150 km, ~400 km and ~670 km. These steps indicate that there are changes in material properties at these levels.

A change occurs at ~2900 km depth, where we find that compression waves decrease in velocity and that shear waves have a velocity of zero. This major change in the Earth, the Gutenberg discontinuity separates the Earth's core from the Earth's mantle.

We see another jump in properties at ~5150 km depth, which means that the core is also layered. When we compare the properties of elastic waves through a material made primarily of Fe (like iron meteorites), it turns out that its characteristics match those of the core quite well. The variation in velocity of shear and compressive waves is fully explained by a liquid outer core and a solid inner core made up mostly of Fe, some Ni, and some heavily debated lighter elements such as H, O and S."


This is right on the boundary of too much science for me. I can just picture my highschool chem, bio and geology teachers starting at me waiting for an answer! LoL

[link to www.globalchange.umich.edu]