Earthquakes and the Richter Scale

Humans have been trying to describe the strength of earthquakes for almost forever — I imagine the initial attempt began soon after the first caveman got knocked on his or her butt. It wasn’t until 1935, however, that an American seismologist by the name of Charles Richter proposed a scientific and mathematical way to quantify the amount of energy released during a seismic event, and began to unravel and understand the enormous forces involved.

Hoping to develop a functional scale that would actually have some value (and withstand the rigors of common usage), Richter wanted it to have small numbers — preferably ten or less — that would at the same time cover the full extent of all possible earthquakes.

An ambitious goal, to say the least!

Unfortunately, the variation between the amount of energy released by a small quake as opposed to a large one is extraordinary: millions, even billions of times difference between a baby rattler and a legitimate thumper.

What now? Well — as all good scientists will do when forced to move beyond the expected — he cheated (or became creative, if you prefer).

Instead of using a linear increase in values, Richter next tried a logarithmic scale (click here for an earlier post that touches on the difference between linear and non-linear math). And when that still didn’t give him the compressed range of values he was aiming for, he modified the logarithmic scale to suit his observations, and ended up making each value approximately thirty times (30X) greater or lesser than the number next to it.

 (BTW: This multiplier continues to change as more data are collected. At the time of this post, the accepted value is approximately 31.623… but since it’ll continue to change anyway, rounding to 30X seems reasonable — and I always try to be conservative in my estimates…)

Whatever. What this means is that a 7.0 quake is not just a little bit stronger than a 6.0, it’s approximately thirty times stronger. Another way of looking at it would be to say that you would need thirty earthquakes with a magnitude 6.0 on the Richter scale to release the same amount of seismic energy as a single quake with a magnitude of 7.0.

How about an 8.0? It sends out sixty times more energy than a 6.0, right?

Wrong! The way the math works it’s actually 30 times 30. You’d need somewhere around 900 temblors with a magnitude of 6.0 to equal a single 8.0. And 27,000 of them to equal a 9.0 — like I indicated, it gets real big, real fast. (And who can blame Charlie for this wee bit of subterfuge: without his chicanery, any quake worth talking about would have a magnitude measured in the billions.)

Still confused? Let’s try it another way. A single 8.0 quake sends out approximately 15 megatons (MT) of energy, with an 8.5 temblor equivalent to approximately 85 MT, and a 9.0 around 480 MT.

A release of 15 MT is equal to the largest H-Bomb ever detonated by the United States, with just over 500 MT of energy (a skosh over a 9.0 on Dr. Richter’s scale) being converted by all testing during the heady days of nuclear proliferation.

It is sobering to note that the main 9.1 seismic rupture during the 2011 Tōhoku event off the northeast coast of Japan (the quake that nuked the Fukushima power plant) released nearly as much energy as all the nuclear testing ever done by humankind.

The condensed version is that there is a colossal difference between a 5.8 and a 9.2, and when the truly great quakes occur it is probably the most overwhelming natural force that can impact us here on the surface.

We have been so lucky in the United States, even though our entire west coast — not to ignore the New Madrid fault zone in Missouri and surrounding areas — are sitting on top of seismic time bombs!!

The only credible contender to a massive thumper would be a Giant Rock From Space. Smaller rocks, like smaller quakes, happen all the time to no great effect — it’s the big ones that matter. One of the last GRFS to seriously impact the biosphere was approximately sixty-five million years ago and contributed to the extinction of the dinosaurs. It was a relatively small speck of space dust but moving really fast, and the energy release has been estimated at 100,000,000 MT… about a 12.5 on the Richter scale.

Chew on that for a bitsy…