Appearantly the most powerful and largest earthquake ever recorded was a 9.4-9.6. The 1960 Valdivia earthquake. (according to what is available on the net)
While a 10+ seems rather impossible, according to Susan Hough it is theoretically possible;
''Seismologist Susan Hough has suggested that a magnitude 10 quake may represent a very approximate upper limit for what the Earth's tectonic zones are capable of, which would be the result of the largest known continuous belt of faults rupturing together (along the Pacific coast of the Americas).[34] A research at the Tohoku University in Japan found that a magnitude 10 earthquake was theoretically possible if a combined 3,000 kilometres (1,900 mi) of faults from the Japan Trench to the Kuril–Kamchatka Trench ruptured together and moved by 60 metres (200 ft) (or if a similar large-scale rupture occurred elsewhere). Such an earthquake would cause ground motions for up to an hour and trigger tsunamis for days, and if this kind of earthquake occurred, it would probably be a 1-in-10,000 year event.[35]''
(_Richter magnitude scale | Wikiwand)
While a 10+ seems rather impossible, according to Susan Hough it is theoretically possible;
''Seismologist Susan Hough has suggested that a magnitude 10 quake may represent a very approximate upper limit for what the Earth's tectonic zones are capable of, which would be the result of the largest known continuous belt of faults rupturing together (along the Pacific coast of the Americas).[34] A research at the Tohoku University in Japan found that a magnitude 10 earthquake was theoretically possible if a combined 3,000 kilometres (1,900 mi) of faults from the Japan Trench to the Kuril–Kamchatka Trench ruptured together and moved by 60 metres (200 ft) (or if a similar large-scale rupture occurred elsewhere). Such an earthquake would cause ground motions for up to an hour and trigger tsunamis for days, and if this kind of earthquake occurred, it would probably be a 1-in-10,000 year event.[35]''
(_Richter magnitude scale | Wikiwand)
