Following on Roger-I believe that Richter "saturates" on large magnitude earthquakes because it is based on movement at a certain distance using a certain instrument-so Richter will understimate magnitude in the 7 or higher range. Ms is surface wave magnitude (?), which can handle larger earthquakes. Mw is moment magnitude, which is the most accurate measure of energy released in the largest earthquakes. Someone correct me if I am wrong on any of this, but I have the right general idea....Chris