What two types of measurements do scientists use to describe the size of earthquakes?

Decoding the Shakes: How Scientists Talk About Earthquake Size

So, the ground starts rumbling. How do scientists actually describe how big an earthquake is? Turns out, they’ve got a couple of main ways to measure these earth-shaking events: magnitude and intensity. Think of it this way: magnitude tells you about the earthquake’s “power,” while intensity describes how it felt on the ground. They’re different sides of the same shaky coin.

Magnitude is all about the energy released right at the earthquake’s source, deep down where the fault slipped. Now, these scales aren’t linear; they’re logarithmic. What does that mean? Well, a jump of just one whole number on the scale means a huge leap in energy. Seriously, a magnitude 6.0 earthquake packs about 32 times more punch than a magnitude 5.0!

The Moment Magnitude Scale (Mw): Today’s Go-To

You might have heard of the Richter scale. It was a big deal back in the day, but it wasn’t perfect, especially for really massive quakes. That’s where the moment magnitude scale (Mw) comes in. It’s the gold standard now, used worldwide because it gives a much more accurate and consistent reading across the board, from small tremors to the big ones.

The moment magnitude is figured out by looking at a bunch of things: how much the fault slipped, how big an area was affected, and how much force it took to make it all happen. It’s a more sophisticated way of measuring, especially when you’re talking about the kind of earthquakes that can level cities.

Intensity: How Did It Feel?

Okay, magnitude tells you how much energy was released. But intensity? That’s all about what it felt like, and what it did on the surface. And here’s the thing: intensity isn’t a one-size-fits-all number. It changes depending on where you are, what the ground is like beneath your feet, and how far you are from the epicenter (that’s the point on the surface right above where the earthquake started). It’s about gauging the severity of the shaking based on what people experienced, what happened to buildings, and what the environment looked like afterward.

The Modified Mercalli Intensity Scale (MMI): Rating the Shaking

The most common way to measure intensity, especially here in the US, is the Modified Mercalli Intensity (MMI) scale. It’s been around since 1931, and it uses Roman numerals – I, II, III, all the way up to XII – to describe the shaking. I is so light you barely feel it; XII is catastrophic, total devastation.

The MMI scale is based on what people report seeing and feeling, and on assessments of the damage. Lower numbers are about personal experiences (“I felt a slight swaying”), while higher numbers are about structural damage (“Buildings collapsed”). Because it relies on observations, it’s super useful for figuring out the magnitude and location of earthquakes that happened way back when, even if we didn’t have fancy instruments to record them.

Magnitude vs. Intensity: The Nitty-Gritty

FeatureMagnitudeIntensityWhat it measuresThe total energy unleashed at the earthquake’s source.How strong the shaking felt and the damage it caused at a specific location.Scale typeA logarithmic scale – each whole number jump means way more energy.A qualitative scale based on observations – what people felt, what happened to buildings.Single value?Yep, one magnitude number describes the whole earthquake.Nope, the intensity changes depending on where you are.Modern ScaleMoment Magnitude (Mw) – the one scientists use today.Modified Mercalli Intensity (MMI) – how we rate the shaking’s effects.