There is another magnitude scale used, which is more "direct" than the familiar Richter Scale - It's called "Modified Mercalli Intensity Scale" and is abbreviated MM
This scale is more aimed to the general public and describes the extent of damage and how the event felt to people, where as the Richter Scale is a mathematical [Logarithmic] scale of magnitude and intensity.
The MM scale uses Roman Numerals to match a scenario list. "I" being the lowest [equal to magnitude 1.0 Richter Scale], and "XII" being the highest [equal to higher than 7.0 Richter Scale].
There's also the "Moment Magnitude" Scale, which is used that is a combination of 3 types of measurements that Richter Scale uses [ML or Magnitude Local, mb or body-wave magnitude, and MS or surface wave magnitude].
Richter Scale intensity is a Logarithm that increases 10 fold [10 log] per full unit.
This means that a 5.0 event has 10 fold the power released than a 4.0 event.
Another example is a magnitude 6.7 releases over 900 times [30 times 30] the energy of a 4.7 earthquake. Inversly, it takes about 900 magnitude 4.7 quakes to equal the energy released in one magnitude 6.7 quake.
A magnitude -1.0 releases 900 times less energy than a magnitude 1.0
Check out the USGS's website for more information.
I read about that fatality in the USGS seismic report on that quake. I feel bad for that person's family.
I just can't believe that there was only one fatality, and minimal injury. That is so fortunate!! Out here in So. California, there's typically more casualties, even resulting from a lower magnitude [this is mostly due to the type of fault and the way the energy releases on it].
My Sister lives in Bellevue and my Brother-in-law [her husband] works for Boeing, and was at work when it hit [the big Boeing field / plant at ??? city, can't recall the name off hand].
Washington State had began Seismic Retrofitting and started to adopt some earthquake procedures / protocols, after our Northridge quake of 1994. This event was a major lesson for California, Oregon and Washington.
One good thing is that Washington now has the ideas of Northridge to use for basics, plus this recent event to use for a kind of "Beta Test".
I hope not to sound morbid, but that's the way seismic engineering advances. Each event teaches more and more to all aspects of the field - from the geologists, to the seismologists, to the structural engineers and architects, to the construction worker.
So, you got to see the Mt. St Helens event kind of close [closer than I did]. I'll tell you one thing, with the threat of Volcanoes, Tornadoes and Hurricanes as a function of nature, I'll take the earthquakes anytime!! At least with an earthquake, one can somewhat get away from it's destruction! Can't do that with the other stuff
When there's one of the early morning earthquakes [the ones that wake a person up at 3:30 AM], we just go outside - away from the house and from danger of falling 12 KV primaries, or exploding gas lines - and just ride the thing out. After the big aftershocks hit, go in the house, check for structural damage, then contact family.
Fortunatly, we do not have any fault lines near us that would put us in the epicentral area of something big, but when the big ones from remote areas come through here, they shake things well!
I can usually feel the P waves that lead the path about 5 to 10 seconds before the S waves come and combine together, causing precursed event [shaking begins].
It's kind of funny; My Wife can't sleep if there's a small noise coming from somewhere - like a TV set on in another room - Whereas I could sleep through a bombing attack!
When an earthquake occurs, I spring awake at the first hint of traveling P waves [almost when the fault snapped!]. My Wife just sleeps right through them! When they get intense enough to cause trouble [more like if they continue building up], then I'll force her out of bed and get her in the yard [where she usually complains that I have woke her for no reason - still groggy!!]
So much for this message.