What are the Moment Magnitude Scale equivalents to the Richter Scale?
There are no direct equivalents. MMS is designed so that the numbers roughly correspond to the Richter scale, so your best bet is that MMS would be the same as Richter. But they actually measure different things, so they may come out different for any given earthquake. For instance, see http://quake.ualr.edu/public/moment.htm . Two of the quakes measure higher on Richter – the other two are higher on MMS. But all the numbers you’re looking at are small, and they’re often closer for smaller quakes. Richter measurements are based on vertical displacements on a particular type of seismometer at a standard distance of 600 km, and were really only intended for use in one particular study in California. While there is no theoretical upper limit to the scale, it turns out that the type of measurement it uses doesn’t work well for earthquakes over about magnitude 8. MMS also takes the area of earthquake into account, which Ri
