r/GeologyExplained

On Wednesday evening, the ground southeast of Yumare ruptured in a magnitude 7.2 earthquake. Thirty-nine seconds later, before the first quake's waves had even finished crossing the country, a second, larger shock hit almost the same spot: magnitude 7.5.

That ordering is the strange part. In a normal sequence the biggest shock comes first and everything after is an aftershock. Here it ran backwards. The USGS called it a doublet: two comparable mainshocks, not a quake and its echo.

I wanted to understand how that actually happens, so I wrote a long piece working from the physics out to the tectonics, why one rupture can light the fuse on the next through static and dynamic stress transfer, why this particular coastline (the Boconó–San Sebastián–El Pilar system) was primed to fail, why the tsunami warning was issued and then cancelled within the hour, and why northern Venezuela has done versions of this in 1812, 1900, 1967, and 1997. The 1812 event, it turns out, may itself have been a doublet.

Every figure is sourced to the primary literature (Kagan & Jackson on doublet statistics, King/Stein/Lin on Coulomb stress, the GPS and InSAR work on El Pilar creep), and I've tried to be careful about what's confirmed versus what's still preliminary this early after an event.

You've probably seen Nick Brandt's photos, the calcified bird and bat "statues" that went viral as a lake in Tanzania that turns living animals to stone. Brandt never actually claimed that, and the truth is more interesting than the myth.

Lake Natron is a hyperalkaline soda lake sitting in a closed basin in the Gregory Rift, fed by Ol Doinyo Lengai, the only volcano on Earth erupting sodium-carbonate (natrocarbonatite) lava in recorded history. No outflow, brutal evaporation, and that volcanic chemistry concentrate the water into essentially the same natron the ancient Egyptians used for mummification. Animals that die on the shore aren't petrified on contact; they're slowly desiccated and encrusted in soda over days and weeks. Same end result, completely different mechanism.