## Wednesday, March 16, 2011

### The Most Powerful Thing on Earth

On Monday, the recent earthquake in Japan was recalculated to be a 9.0 on the moment magnitude scale. This is not the Richter scale, which is based off of the horizontal shaking amplitude of an earthquake. Instead, the moment magnitude scale is based off of the sheer amount of energy released. As it turns out, this scales to about 3/2 the horizontal amplitude, and as such is calibrated to match closely to the Richter scale.

What does the recalculation from 8.9 to 9.0 mean? Well, the Richter scale itself is a logarithmic scale on base 10; a step of 1 relates to 10x the displacement. However, the moment magnitude scale, while logarithmic as well, is calibrated so that a step of 1 means about 32 times the energy was released.  A magnitude 2 points higher had a whopping 1,000 times the energy. As such, this lowly adjustment of .1 on the scale actually denotes around 40 percent more energy.

This got me thinking, what does this actually mean? Well according to the USGS, the earthquake released 39 zettajoules. What's a zettajoule? You've heard of the prefix mega-? giga-? tera-? peta-? exa-? This is bigger than all of those, zetta- is reserved for 1021.

Well, that's a big number, but it's probably meaningless, right? Here's why that's insane.

First off, the world's largest nuclear weapon ever detonated, the Tsar Bomba, had a 50 megaton yield. That means it had the equivalent force of detonating 50 megatons of TNT. How much energy is that? One megaton of TNT would produce 4.184 petajoules when detonated, so this comes out to 209.2 petajoules. It'd take 186,000 of them to match the energy of the earthquake. Fat Man, the bomb dropped on Nagasaki, was a paltry 20 kilotons in comparison, 2,500 times smaller. Even the 1883 eruption of Krakatoa, which was heard 3,000 miles away, had an estimated force the equivalent of only 200 megatons of TNT.

In comparison to our current capabilities, according to World Nuclear News there were 2,558 terawatt-hours of energy produced by the world's nuclear reactors in 2009. That comes out to 9.2 exajoules. That means every nuclear reactor in the world would take four and a quarter millennia to match the earthquake's output.

In fact though, nuclear reactors provide only a small portion of the world's energy: we consumed 484 exajoules overall in 2008. At that rate, if we could have harnessed all the energy from Japan earthquake, we could last on it for 82 years. And yet the earthquake only took 5 minutes to release it.

The even more amazing part: this number is nothing compared to the Sun. The Sun outputs 384.6 yottajoules every second. What's a yottajoule? It's 1,000 zettajoules. So in a single second the Sun outputs nearly 10,000 times the energy produced by the earthquake. Though, to be fair, the Earth only receives a small portion of that output, 174 petajoules a second. And at that rate, it'd still take 2 months to match the earthquake's raw power.

The moral of the story? Never doubt the power of mother nature. To think this is just one of six to break 9.0 on the moment magnitude scale in the past 100 years, not including the 8.8 in Chile last year and the 8.5 in Sumatra in 2005.  After all, this planet is both breathtakingly awesome and entirely terrifying in the forces it can unleash.

#### 1 comment:

1. Wow, great writeup to put that power in perspective...I had no idea exactly how massive the earthquake was. Super info, VP.