To say an earthquake measures 5.0 (or whatever) on the Richter Scale is incorrect (I just found out, while researching a cypher ability for The Strange RPG). The Richter Scale was retired in 1970! Now its the Moment Magnitude Scale, and you'd just say that an earthquake has a magnitude of 5 (or whatever).
Apparently, a magnitude 32 quake was detected once. Not on Earth though; it was a *starquake* detected on December 27, 2004 from the ultracompact stellar corpse (magnetar) SGR 1806-20. The quake, which occurred 50,000 light years from Earth, released gamma rays equivalent to 1036 kW in intensity. Had it occurred within a distance of 10 light years from Earth, the quake would have possibly triggered a mass extinction