# Richter scale **URL:** \ **Category:** Factual Questions\ **Created:** [March 4, 2010, 3:57am UTC](https://boards.straightdope.com/t/richter-scale/531241 "2010-03-04T03:57:23Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Mangosteen](https://avatars.discourse-cdn.com/v4/letter/m/6a8cbe/32.png) [@Mangosteen](https://boards.straightdope.com/u/Mangosteen)\ **Post date:** [March 4, 2010, 3:57am UTC](https://boards.straightdope.com/t/richter-scale/531241/1 "2010-03-04T03:57:23Z")
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 _100_ _times_ stronger. > **[About Earthquakes in Hawaii | U.S. Geological Survey](https://www.usgs.gov/observatories/hawaiian-volcano-observatory/about-earthquakes-hawaii)** > > Thousands of earthquakes occur every year in the State of Hawaii. They are caused by eruptive processes within the active volcanoes or by deep structural adjustments due to the weight of the islands on Earth's underlying crust. ---
**Author:** ![Askance](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/askance/32/8281_2.png) [@Askance](https://boards.straightdope.com/u/Askance)\ **Post date:** [March 4, 2010, 4:04am UTC](https://boards.straightdope.com/t/richter-scale/531241/2 "2010-03-04T04:04:06Z")
The [Richter scale](http://en.wikipedia.org/wiki/Richter_magnitude_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 . ---
**Author:** ![Chipacabra](https://avatars.discourse-cdn.com/v4/letter/c/e19b73/32.png) [@Chipacabra](https://boards.straightdope.com/u/Chipacabra)\ **Post date:** [March 4, 2010, 5:02am UTC](https://boards.straightdope.com/t/richter-scale/531241/3 "2010-03-04T05:02:09Z")
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. ---
**Author:** ![Duckster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duckster/32/1244_2.png) [@Duckster](https://boards.straightdope.com/u/Duckster)\ **Post date:** [March 4, 2010, 5:28am UTC](https://boards.straightdope.com/t/richter-scale/531241/4 "2010-03-04T05:28:51Z")
> [@](#): > > The Richter magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. Adjustments are included for the variation in the distance between the various seismographs and the epicenter of the earthquakes. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions. For example, a magnitude 5.3 might be computed for a moderate earthquake, and a strong earthquake might be rated as magnitude 6.3. \*\*Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value. \*\* > > At first, the Richter Scale could be applied only to the records from instruments of identical manufacture. Now, instruments are carefully calibrated with respect to each other. Thus, magnitude can be computed from the record of any calibrated seismograph. (Bolding mine.) [http://earthquake.usgs.gov/learn/topics/richter.php](http://earthquake.usgs.gov/learn/topics/richter.php) ---
**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\ **Post date:** [March 4, 2010, 5:46am UTC](https://boards.straightdope.com/t/richter-scale/531241/5 "2010-03-04T05:46:41Z")
Note that these days, earthquakes are measured according to the [moment magnitude scale](http://en.wikipedia.org/wiki/Moment_magnitude_scale), not the Richter scale. Edit: It’s a little more complicated than that, but that is what they use for the big ones. ---
**Author:** ![Snarky\_Kong](https://avatars.discourse-cdn.com/v4/letter/s/a183cd/32.png) [@Snarky\_Kong](https://boards.straightdope.com/u/Snarky_Kong)\ **Post date:** [March 4, 2010, 5:46am UTC](https://boards.straightdope.com/t/richter-scale/531241/6 "2010-03-04T05:46:56Z")
> [@Askance](#): > > The [Richter scale](http://en.wikipedia.org/wiki/Richter_magnitude_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 . 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. ---
**Author:** ![Chief\_Pedant](https://avatars.discourse-cdn.com/v4/letter/c/a6a055/32.png) [@Chief\_Pedant](https://boards.straightdope.com/u/Chief_Pedant)\ **Post date:** [March 4, 2010, 11:34am UTC](https://boards.straightdope.com/t/richter-scale/531241/7 "2010-03-04T11:34:05Z")
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.