The stats for this earthquake are mind-blowing even today. It is still the largest quake ever recorded. The rupture was 1000 km long. There was as much as 40m of fault slip in some places!

But also: this happened in the era before we'd fully worked out plate tectonics.

[1/7] https://twitter.com/USGS/status/1263820720980873219

Now we know that deep trenches found off the coast of places like Chile are the surface expressions of giant faults that dip shallowly into the Earth: subduction zones where oceanic crust is returned to the mantle.

We didn't know that then. [2/7]

The recipe for giant earthquakes: fast plate motion across a long fault with a huge surface area that stays shallow and cold enough to fracture, rather than flow, when stressed. This is where the Earth cooks almost all of them.

We didn't know that then, either. [3/7]

We also didn't know that because the trenches are where these massive faults reach the seafloor, a large rupture pushes up a massive bulge of water that then rapidly collapses outwards - a tsunami. This amplifies and extends the deadly reach of the giant earthquakes. [4/7]

This earthquake, and another large subduction earthquake in Alaska 4 years later, provided the key evidence for large horizontal motions on large thrust faults at subduction zones - a building block of what became plate tectonics. [5/7] https://www.sciencenewsforstudents.org/article/quake-shook-geology-Alaska-1964

But they also helped us to understand earthquake hazards much more clearly. We still can't predict when big earthquakes will happen, but now we can understand where they happen, and what they do. This means we can save lives - before, during, and after big earthquakes hit. [6/7]

Today, an event like the Valdivia earthquake would still be shocking, and devastating. But, at some level, we can at least comprehend that is it something the planet can do, in places like this.

We've come a long way since 1960. [7/7]