I know that a 7.0 quake is 10 times the intensity of a 6.0 quake. Does this mean that a 9.0 quake is 100 times stronger than a 7.0?

I was living in Hilo when the 7.2 quake hit the Big Island in Hawaii in 1975 and it shook us real good. I just can’t imagine what a 9.2 would be like if it were 100times stronger.

The Richter scale measures the seismic energy released by an earthquake, not the strength as perceived at ground level - that will vary a lot depending on many factors, such as how deep it was and what kind of rock you are on. But yes, a 9.0 releases 100x as much energy as a 7.0 .

It’s 10 times the amplitude per 1.0 increase on the richter scale, not 10 times the energy. The seismic energy scales with 3/2 power of the amplitude. So a 9.0 has 100x as much amplitude as a 7.0, but releases 1000x the energy.

Richter measures data at the ground surface, not seismic energy. The moment magnitude scale measures energy. They pretty much give exactly the same number up to around 8 (?, I dunno it’s been a while since I reviewed). The Richter scale levels out since shaking doesn’t really increase after a certain point. The duration and area affected will though, which is captured by the moment magnitude scale.

As noted above, the USGS currently uses the MMS scale, where the magnitude of an earthquake is a dimensionless number reflecting the energy released by the quake.

I think of it (simplistically) this way: The Richter scale measures how much the earth would jiggle a seismograph 100 KM from the epicenter (models are used to correct for the fact that in any given earthquake there isn’t a perfectly-placed seismograph). The MMS scale reflects how much energy was released. For middle ranges of quakes, the “bigness” of the earthquake on either scale is roughly the same for a given number.

In terms of energy, though, a 7.0 MMS quake releases 31.6 times as much energy as a 6.0 MMS quake. This might cause only a tenfold increase in jiggling at 100 KM, so the amplitude of a seismograph might vary tenfold, and on the Richter scale, you’ll hear people say 7.0 versus 6.0 is a tenfold “bigger” quake. This is not correct. Even on the Richter scale, it’s understood that to get that tenfold increase in seismograph jiggling, you may need 30x the energy. And of course how much seismograph jiggling you get 100 KM out is not a very accurate way to describe the actual energy of the quake itself because so many other factors are involved such as depth, direction, type of quake fault, rock type, and so on. That’s why USGS switched to the MMS scale. Another Richter-scale problem is that there’s only so much jiggling you can get with a seismograph, so there isn’t really such a thing as a “12” on the Richter scale; it’s really only useful for medium quakes.