So how powerful are these beasts?
Most of us are familiar with the Richter scale, which measures earthquakes in terms of the amplitude, or length of one wave cycle. The higher the amplitude, the more powerful the quake. This scale, now-defunct, was replaced by another in the 1970s called the Moment Magnitude Scale, whose values align similarly with the original.
It’s a logarithmic scale, meaning that a 2.0M quake is 32 times as energetic as a 1.0M event. Similarly, a 3.0M quake is 1,000 times more powerful than a 1.0M event. Technically, the scaling factor is 31.6, but I'm cheekily rounding up here.
Seismologists can use the seismic waves unleashed by these quakes to work out how many joules of energy they release. For a point of comparison, an apple falling a meter to the ground from a tree involves one single joule of energy.
The Valdivia quake, using the somewhat basic Richter formula, released 4.5 quintillion joules of energy in mere seconds. This was around 23 times more powerful than the most explosive nuclear weapon ever detonated, the Tsar Bomba. Make no mistake, these quakes are insanely powerful.
Some of you may have spotted a pattern here – all of these quakes took place on convergent plate boundaries. They’re what are known as “megathrust” quakes, which describes one fault sliding upwards relative to another on a gargantuan scale. Forget the fabled “Big One” due to rock San Andreas sometime soon – megathrusts are where the planet is at its most destructive.
To say these five quakes were devastating is a massive understatement. The release of so much energy triggered enormous landslides, turned the soil into a fast-flowing fluid, and cities were literally washed away. They were even powerful enough to ever-so-slightly change the length of a day by causing the planet to wobble on its axis.
It’s safe to say, however, that even these megathrust monsters could not literally crack open the crust though, and as far as geologists can tell, it’s never happened in the entire history of the world. But why?