Whenever a quake happens we always hear all kinds of discussions regarding how to measure intensity. While I am not a trained seismologist I have always had an interest in the subject and thought I’d offer a little mini primer. There are a number of different scales for measuring quake impact.
The most commonly used is the Richter scale. As many have discussed the Richter scale is logarithmic. There are two ways that this comes into play.
In terms of shaking intensity it is a base 10 scale. In other words a 5.0 quake is 10 times as intense as a 4.0 quake. A 6.0 quake would be 100 times more intense than a 4.0 (10 times 10).
In terms of energy released it is roughly a base 32 scale (actually 31.6 to be precise). So that means a 5.0 quake would release 31.6 times more energy that a 4.0 and a 6.0 quake would release about 1,000 times more energy that the 4.0 shock (31.6 times 31.6).
The Haitian quake measured around 7.0 on the Richter scale while this shock was 8.8
So on the Richter scale the quake in Chile would be about 100 times as intense but would have released about 1,000 times as much energy.
Another system is the Modified Mercalli intensity scale which focuses more on the intensity of the shock.
We don’t have firm figures yet on the MM scale but it seems likely that the shock measured in the 9 or 10 region.
Another issue is how deep the quake was under the ground. If the shock is shallow then it can cause greater damage even with lesser intensity. In the case if the Chile quake it was about 22 miles deep versus only 8 for the Haitian quake so that could mean that the intensities were somewhat similar.
Distance is another factor. Here it seems Chile may have somewhat dodged the bullet. The Haitian quake struck within 30 miles of the capital city while in this case the larger cities were 70-200 miles away. That could help with the death toll.