In an article in today’s New York Times, the “old” Richter scale of measuring earthquakes is said to be “seldom used”. But everyone in the article still refers to it, and I haven’t seen anything about it being replaced. I did a quick of the archives as well as a google search and came up empty.
Has the Richter scale been replaced? If so, with what? And why doesn’t anyone seem to know about it?
Cantrip, I could be wrong, but what I think the Times means is that the Richter scale has been recentered. Some earthquakes have recently been up- and down-graded. The exact numbers have escaped me, but the 1964 Good Friday quake in Alaska has been upgraded from its original measurement, and the 1906 quake in San Francisco has been downgraded from the original estimate. (It’s hard to peg that one because it occurred before the Richter scale came into being, I think.)
This is the britannica.com entry on the Richter Scale
So, it has been tweaked a little throughout the years. Sometimes you hear more about the Mercalli Scale of Intensity, which is reported in Roman numerals from I-XII (I think). It’s been around longer and has been adjusted also. It describes an earthquake’s force by the actual damage it inflicts and how people perceive firsthand.
If you go to http://quake.usgs.gov there is usually a link posted to each earthquake and you can fill out an online form describing how you felt the earthquake. That data is used to help them make out the Mercalli map for a quake.
Cantrip, the confusion stems partly from the fact that there are a few difference ways to measure the magnitude of an earthquake, and partly from the tendency for terms used by the popular media and general public to hang around after the scientists have moved on to something else.
The U.S. Geological Survey has a more extensive discussion of the different methods here. In a nutshell:
[ul]
[li]The method first developed by Charles Richter in the 1930’s (usually abbreviated M[sub]L[/sub]) applied only to california earthquakes within a 600-km radius of a particular type of seismographic instrument.[/li]
[li]Other seismologists adapted Richter’s technique to the more general cases of earthquakes everywhere. This adaptation produced two magnitude scales: m[sub]b[/sub], which measures the energy of body waves (seismic waves moving through the Earth’s interior), and M[sub]S[/sub], which measures the energy of surface waves (seismic waves moving through the uppermost layers of the earth’s surface). With a little tweaking to take regional variations into account, the calculated magnitudes m[sub]b[/sub] and M[sub]S[/sub] were roughly the same as Richter’s M[sub]L[/sub] measurements, so in practice folks tended to refer informally to any of these magnitude scales as “the Richter scale.”[/li]
[li]In the last 20-30 years, seismologists began to realize that the “Richter scale” (as determined by either m[sub]b[/sub] or M[sub]S[/sub]) was grossly underestimating the energy of very large earthquakes (generally M[sub]S[/sub] = 7.5 or higher). To compensate for this underestimation, a new magnitude scale - M[sub]W[/sub] - as developed that also takes into account the shear strength of the faulted rock, the area of the fault, and the average slip distance along the fault surface. This is a fundamentally different type of calculation than any of the Richter scale magnitudes (which are based on the amplitude of the seismic wave), so it’s not really appropriate to refer to M[sub]W[/sub] as being a measurement on the Richter scale… but since everyone is familiar with the term “Richter scale,” the media will continue to use this term.[/li][/ul]
While I was previewing this, I noticed BobT’s post. The Britannica item is basically correct, but the statement about no earthquake measuring above 9 is incorrect. The 1960 Chilean earthquake’s magnitude has been recalculated (using the M[sub]W[/sub] scale) as a magnitude 9.2.
The other scale BobT mentions - the Mercalli scale - is a measure of the relative intensity of an earthquake experience. It’s used these days mostly to judge the strength of past earthquakes from the historic record (prior to the 1930’s).
Thanks, all, esp. Fillet - that was a remarkably thorough and understandable answer.
According to the USGS the moment magnitude (MS) for the Chilean Quake was 9.5 and for the Alaskan tremor 9.2.
Thanks quasar - I think of those big mother earthquakes, get spooked and foul up my numbers. 
MW not MS. :rolleyes:
There’s also the Shindo (degree of shaking) scale used in Japan. It’s similar to the Mercalli scale, but a little more objective. It measures the degree of ground movement at a particular location on a scale from 1 (undetectable by humans) to 7 (probable complete destruction), with no decimals (although recently 5 and 6 were subdivided into “weak” and “strong” categories).
After a detectable earthquake (usually a daily occurance), a little map often comes up on TV covered with numbers showing how strong the shaking was at each point. This is usually followed by the location of the epicenter, depth of the epicenter, and the Richter measurement.
–sublight.