On the west side of the Pacific Ocean, the easternmost part of Asia, lies a long and slender island arc. On the east coast of the Pacific Ocean and the westernmost part of the Americas, stands the magnificent Andes Mountains. They span from the cold zone to the equatorial tropics, span many countries with very different cultural characteristics, and become a unique and magnificent beauty along the Pacific Coast. People generally refer to this island arc-coastal mountain range area as the "Rim Pacific Structural Belt." But in different research contexts, this structural belt also has different names. For example, earthquake researchers call it the "Pacific Rim Seismic Belt"-because it is a high-density area for earthquake development; people who study volcanoes call it the "Ring of Fire". Needless to say, the volcanoes on this annular structural belt are also quite famous.
Frequent development of volcanoes and earthquakes not only make people curious about the formation of the Pacific Rim structural belt, but also give people an urgent desire to understand it in order to better cope with geological disasters. Modern plate tectonics tells us that the Pacific plate moves eastward towards the American plate and westward towards the Eurasian plate. Due to the high density of the oceanic plate, when the Pacific plate encounters the continental plates on both sides, it will subduction under the continental plates and penetrate deeply into the earth. Areas where plates rub against each other form long V-shaped depressions and deep trenches.
The Pacific Plate meets the Eurasian Plate on the west side. It bends downward very severely during subduction, and has relatively little contact and friction with the upper Eurasian Plate. Therefore, the Pacific plate experiences little resistance and has a high subduction speed. During high-speed subduction, only a part of the plate material can quickly react with water to form magma under high temperature and high pressure conditions. These magma erupts not far from the trench to form volcanoes, thus creating a series of volcanic island arcs. As the plate material that continues to subduction reaches deeper and farther, a large amount of magma is formed. After this magma upsurges, a smaller "mid-ocean ridge"(essentially an spreading zone) is formed behind the island arc, farther away from the trench. This small oceanic crust expansion causes the crust behind the island arc to become an oceanic crust, which in turn sinks into a back-arc basin. Today's Sea of Japan is a typical back-arc basin, in which there is an oceanic crust spreading zone very similar to the mid-ocean ridge.
The Pacific Plate hit the American Plate on the east side and was difficult to bend downward during subduction, but stuck closely to the upper plate. Therefore, the subduction of the Pacific plate is subject to high resistance and low speed. This kind of subduction is extremely prone to major earthquakes. Under slow subduction, most of the plate material forms magma not far from the subduction zone, and a large amount of magma surges upward directly through the continent in front, forming a magnificent linear mountain system on the land. Since there is no material going deep into the extreme depths, back-arc basins will not be formed. So there are no island arcs on the east coast of the Pacific, only tall mountains along the subduction zone.
So why do different subduction patterns appear on both sides of the Pacific? There may be multiple reasons. Some people think it is related to the tectonic movement of the continental plate above. For example, the formation and evolution of the giant rift system in the East Asian continent and the westward movement of the Philippine Sea plate have all contributed to the expansion of the back-arc basin on the western side of the Pacific Ocean. Others believe that it is related to the age of subducting plates on both sides of the Pacific plate. For example, the western Pacific ocean floor was formed in the Jurassic period and is older than the eastern ocean floor. The older oceanic plate gradually becomes heavier after long-term cooling, and the gravitational pull-down effect becomes stronger, causing the underlying plate to tilt steeply and bend more severely.
As long as the Pacific Ocean is still subducting towards the continents on both sides, the development of the Rim Pacific tectonic belt will not stop. The driving force for the continuous advancement of the Pacific plate comes from the mid-ocean ridge of the Pacific. The hot mantle rises from here and flows to both sides to become the driving force for the asthenosphere in the lower part of the plate. The Pacific plate floating on the asthenosphere continues to expand to both sides driven by the lower driving force. If one day, the thermal driving force of the Mid-Pacific Ridge stops, or the entire Mid-Ocean Ridge subverts into the trench, the history of the development of the "Ring of Fire" will have to be put to an end.