All About Earthquakes for Dummies

Some faults in the San Andreas Complex

Our staff have all been trained to be sort of purists about information. In other words, we prefer that if you want to pass along information – be it instructional, educational, whatever – that the information be as free as possible of error. In other words, we don't like misinformation, especially when that misinformation concerns the foundation of the content. The reason we're saying this today is because of the post "Earthquakes" a Brit "science writer" by the name of Chris Woodford published at his website, ExplainThatStuff.com.

Woodford's post is a couple  thousand words long, and we suspect that he got a lot of it right, mostly boilerplate about earthquake preparedness and a discussion of why anchorpersons who say a quake registered six "on the Richter Scale" are full of hooey. But we're not here to pick nits about the difference between the Mercalli scale and moment magnitude or the definition of microseismic events (which Chris calls "micro earthquakes"). No, we're here to beat the guy about the head and neck for the section he titled "What causes earthquakes?"
According to Woodford,

"You might think Earth is a giant lump of rock, but you'd be wrong—it's more like a freshly boiled egg: there's a hot, molten core bubbling away inside a surprisingly thin outer crust. The countries we live in feel like they're safely anchored on solid rocky foundations, but really they're fixed to enormous rocky slabs called tectonic plates that can slide around on the molten rock beneath. Imagine living your life on an eggshell!"

Here's a guy who claims to have spent twenty-five years "explaining science and technology," yet he subscribes to the notion that, except for a "surprisingly thin outer crust," the entire planet is "molten." Guess he's never talked to a geologist...

Well, Chris, you're wrong. The Earth's structure is fairly simple; consisting of crust, mantle, and inner and outer cores, but only the outer core is "molten"; the rest is solid. According to our back-of-the-envelope calculation, only about 15 percent of the earth (the outer core) is liquid.

Woodford also compounds another misconception when he says that,

"Some of the most violent earthquakes happen around the edges of tectonic plates in the Pacific Ocean, forming an intense area of activity known as the Ring of Fire (so-called because there are many active volcanoes there too)."

That will come as a surprise to people in Haiti, Iran, central China, and even Los Angeles (which isn't particularly near any active volcanoes). Chris also conflates fault blocks with tectonic plates, "explaining" that,

"...every once in a while two grinding plates will suddenly jolt into a new position. The energy released by this movement creates an earthquake."

No, Chris, the "jolt" is on a much smaller feature, a geologic fault. If the entire plate were to suddenly shift, there'd be hell to pay over a continent-sized area. Fortunately for people in the interior of a plate, movement at the plate edges is distributed across a large network of much smaller "cracks."

We imagine there's more, but that's as far as we got before we ran out of time. That's enough, however, to name Woodford our Dumbass of the Day for today.

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SI - EARTHQUAKES