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Last sync:2023-01-18 08:15
Today's earthquakes in Indonesia sparked fear and panic in southeast Asia and scary memories for the rest of the world, and no one can be blamed for being alarmed.

The first quake lasted three or four minutes and had a magnitude of 8.6. Another strong jolt, magnitude 8.2, soon followed.

For a while, many feared a repeat of the infamous 2004 earthquake which struck the same region, the west coast of northern Sumatra, triggering a tsunami that killed over 200,000 people and displaced a million more.

So why did these two very similar quakes have such different results? For starters, if you're rounding up, 8.6 rounds to 9, and 9.1 also rounds to 9, so they seem like they should be in the same neighborhood. But the fact is they're, you know, like orders of magnitude apart.

The earthquake magnitude scale uses a logarithm based on the amplitude of the waves caused by the quake. By this logarithm, each whole number on the scale represents an amplitude 31 times the number below it. So a 9.0 quake is 31 times stronger than an 8.0 quake, and some 961 times stronger than a 7.0 quake.

But even more important in this case is the difference in the geophysics between the 2004 quake and this week's. The 2004 quake took place along a subduction fault, where one plate in the Earth's crust slides under another. In that instance, the movement of the bottom plate pushed the top plate up, and the displacement of that plate caused a displacement of the water above it, which caused the tsunami.

But boundaries between plates have different kinds of faults, and today's happened along a strike-slip fault, which is where the plates move side to side, rather than up and down. With that kind of earthquake, it hardly displaces any water; the waves that reached the Sumatran coast were measured at just 80 centimeters.

Though the geophysics went our way this time, but we know it's going to happen again. Indonesia is literally surrounded by plate boundaries, many of which are subduction zones. But at the very least, this was an excellent real world test. We know now that important lessons have been learned from 2004: wave detecting buoys triggered tsunami alerts, and entire towns were evacuated immediately. The system worked.

I hope that this helped you understand the world's news a little bit more. If you have questions about this week's earthquake or earthquakes in general, you can reach us through Facebook or Twitter or, as always, in the comments below. Goodbye.