to put this in perspective, and please, if you work for USGS or whatever, correct me if i am wrong: this is roughly the same magnitude of the 1994 Northridge earthquake in California.
i think i got the scale the wrong way around, the magnitudes reported now are only larger (than Richter) with smaller quakes compared to the Richter; it looks like 8.8ML ~= M8.8. Sorry, i looked at the chart the wrong way around.
Each incremental increase in magnitude is 10^1.5 in power. The difference between 1994 Northridge and this one is 2.1, so roughly 10^3 difference in power.
The Richter Scale is a logarithmic scale, based on shaking measurements (think of the old pencil-based seismograph!). Power. (10^1).
The Moment Magnitude Scale (the more modern/replacement of Richter Scale) is based on energy. Geological organisations reporting on an earthquake will usually show this as "M <number>" or "Mw <number>".
Richter works well for small-to-medium earthquakes, and it's not accurate for really large or distant earthquakes.
The energy released in an earthquake increases exponentially, not just linearly.
AFAIK, it was done that way to maintain rough congruence with historical seismic magnitude scales, which were more qualitative in nature. Modern seismic scale systems are significantly more scientific and quantitative but you can kind of retcon the historical systems if you set the exponential strength scale to 10^1.5 in the modern systems.
I'm actually not sure the Northridge earthquake was cited in the Richter scale, most references I see have it as about a 6.7, which based on the USGS catalog, was it's moment magnitude 6.7 Mw
i think i got the scale the wrong way around, the magnitudes reported now are only larger (than Richter) with smaller quakes compared to the Richter; it looks like 8.8ML ~= M8.8. Sorry, i looked at the chart the wrong way around.