On August 17th, 2015 we learned about

The difficulties in encapsulating an event like an earthquake

This morning, our household experienced the periphery of a 4.0-magnitude  earthquake. Which is to say that not one of us noticed anything until it was reported on the news. But a “4” is big, right? Or is it? Four of what, exactly? The logarithmic nature of the Richter Scale means that only the upper end of the scale really counts to most people, since that’s when environmental damage is more likely. The logarithmic scaling also leaves you with an artificial lack of granularity in the reporting of most earthquakes (you never hear about a 6.13563-magnitude quake), leaving the general public to hear what feels like a three-point system ranging from “ok” to “send help.”

Objectivity versus obfuscation

Part of the issue here is that Charles Richter based the system not on nuances of geology but on the way astronomers measure starlight. They liked the way logarithmic scales let you compress very large measurements into smaller units, and then just sort of overlaid that idea on a single seismograph in southern California. It also seemed more precise than previous tools, like the Mercalli Scale, which was based on subjective observations of things like swinging chandeliers or broken buildings. In that context, objective measurements, however limited, were a huge improvement.

The issues with the Richter Scale are tied more to how it’s used today. To make sense of it all, you not only have to know how a logarithmic scale works, but also that this particular scale doesn’t operate on base 10 like most people default to. So the difference between a 6.0 and a 7.0 quake isn’t a 10 fold increase in surface shaking, it’s actually a 32 fold increase.

What energy is being measured is worth noting as well. Newer calculations, like seismic moment measurements, include the size of the break at the earthquake’s fault, the distances moved, and the rigidity of the materials involved give you the total energy of the earthquake. The Richter Scale, in contrast, was only based on the amount of shaking that could be detected on the Earth’s surface in 1935. With all the other convolutions involved in the Richter Scale as a communications tool, you might want to give it credit for simplifying something about reporting earthquakes, but the resulting figures aren’t nearly as accurate as is now commonly possible with better monitoring, further reducing the system’s utility to the public.

Warning the public, but only about the wind

A stronger example of simplifying in the wrong way is the Saffir-Simpson hurricane wind scale. This scale gives us the standard class one through five hurricanes that you hear in weather reporting, and is often used as shorthand to give the public reference points for how serious a threat a storm may be (the Richter scale is off the hook on this one slightly since magnitudes aren’t reported as warnings in advance.) The problem is that the Saffir-Simpson scale only measures wind speed, which isn’t always the primary cause of damage in a hurricane. A class three storm can still be a bigger threat to safety than a class three storm if it brings more rain and flooding. The wind might be weaker, but everything else about the hurricane could potentially be worse.

Both of these tools can still serve a purpose, as they do measure key components of these natural disasters. They offer a way to describe slices of these complex events, and as a public communication tool, they’re missing, or obscuring, a lot. While hurricane classes aren’t on my mind too often, it would be great to be able to hear about earthquakes in the area without needing to break out a calculator to determine how much energy was involved, not that I actually think in joules too often. I admit that the alternative of hearing that this morning’s quake was 1.50802414 × 1010 calories is more likely to raise worries about my junk food consumption more than my house’s foundation.


My first grader asked: So how strong is a 6 earthquake? Is that really big? The most universally understandable figure seems to be that once you get to an 8.0-magnitude earthquake, tsunamis become a concern. As expected, such a tangible reference point, while thankfully outside our direct experience, seemed to make a bigger impression than just about any of the other concepts mentioned above.

 

Source: The Way We Measure Earthquakes Is Stupid by Sarah Zhang, Wired

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