But going back to earthquakes, they occur for the same reason as that of sea floor spreading: the moving of plates several km. underneath the earth

Now that's why the most catastrophic earthquakes also occurs in the Pacific side of Asia & the Americas such as: in Cal., Central Am., Peru, Japan, INDONESIA, & etc

Conversely, that's the reason why we never hear of earthquakes in New York (or the east coast U.S.), or the Brazilian Atlantic coast

As for the Himalayan ranges, the same concept applies whereby the Australian [oceanic] plate keeps colliding with the Indian [continental] plate

Therefore, Mt. Everest & the rest of the Himalayan ranges (as well as the mountains of America & Asia Pacific), are slowly but continuosly rising thru time

Also, that's the reason why massive earthquakes hits India & the Himalayan region every now & then