The continental drift hypothesis, which came into being in the early 1920s, holds that there is no need to shrink when strata fold. When the mainland moves, if it is resisted, the leading edge will fold, just like when a ship sails on water, it will produce waves at the bow.
In the 1960s, some people put forward the hypothesis of seafloor spreading, arguing that the paleomagnetic field and age data are symmetrically distributed due to the continuous renewal and expansion of the seafloor.
When the expanding oceanic crust reaches the edge of the volcano, the mantle subducted under the continental crust gradually melts away, so it is impossible to find the ancient oceanic crust. In 1970s, on the basis of continental drift theory and submarine spreading theory, plate tectonics theory came into being.
Plate tectonics emphasizes that the global lithosphere is not a whole, but consists of six plates: Asia-Europe, Africa, America, Pacific Ocean, Indian Ocean and Antarctica.
These plates are on the asthenosphere at the top of the mantle and drift with the convection of the mantle.
The crust inside the plate is relatively stable, and the boundary of the plate is a zone with more crustal activity. The fundamental cause of plate tectonic activity is the interaction of several huge rock layers.
Because earthquakes are one of the manifestations of plate tectonic activities, the interaction between plates is also the basic reason for earthquakes. In addition, earthquakes are almost always distributed at plate boundaries.