Thread by @celestelabedz

I just learned on the @USGS earthquake history page that the largest recorded quake on May 20th was a M7.2 in 1990 in South Sudan. Event page: earthquake.usgs.gov/earthquakes/ev…

Africa isn't the first to most minds when thinking of quake-prone areas, but it does get some! Short thread:

Here's a map of quakes with M>6.0 since 1980 in the @USGS catalog. As you might guess, most large quakes (~130 of the ~150 shown) occur on the major tectonic plate boundaries surrounding the continent.

The quakes that are actually on the continent tend to follow the East African Rift system, which is like an almost-plate-boundary that's slowly pulling apart the Nubian Plate and the Somalian Plate (minor plates that sometimes get lumped into one African Plate). @USGS diagram:

These two minor plates have been pulling apart for ~25 million years, causing the crust between them to get stretched, thinned, and faulted up. With another few 10s of millions of years, motion like this can completely split the continental lithosphere, forming a new ocean basin.

That pulling and stretching makes rift systems like this one prone to quakes and volcanoes. The residents of what is now South Sudan (still part of Sudan at the time) felt the power of this rift 30 years ago today, when the M7.2 earthquake hit.

The M7.2 was one of many quakes there in 1990. Four days later, there were two major aftershocks (M6.5 & M7.1), two months later a M6.6, & countless smaller quakes as well. This also occurred when residents were fighting a famine and in the midst of the Second Sudanese Civil War.

If you'd like to explore the biggest quakes on a date, use the @USGS quake history page here to search all years of a date: earthquake.usgs.gov/learn/today/

Or the @IRIS_EPO "Birthquake" tool to find the biggest events on one particular day (like your birthday!): iris.edu/app/birthquake/