How the movement of Earth's plates creates earthquakes worldwide
Plate tectonics is one of the greatest scientific discoveries of the 20th century. The Earth's surface is divided into about a dozen major lithospheric plates moving at speeds of 2-15 cm per year. Major plates: Pacific, North American, South American, Eurasian, African, Indo-Australian, and Antarctic plates. Plate boundaries come in three types: 1. Convergent boundaries (destructive): plates move toward each other. When oceanic meets continental plate, the denser oceanic plate subducts beneath, forming deep ocean trenches and volcanic arcs. The Japan Trench, Mariana Trench, and Peru-Chile Trench are examples. When two continental plates collide, massive mountain ranges form — the Himalayas are the product of India-Eurasia collision, still rising today. 2. Divergent boundaries (constructive): plates move apart, mantle material rises to form new crust. The Mid-Atlantic Ridge is the best example, widening at ~2.5 cm/year. Iceland sits directly on this ridge, explaining its frequent volcanism and seismicity. 3. Transform boundaries: plates slide past each other horizontally. The most famous is California's San Andreas Fault, where the Pacific Plate slides northwest relative to North America. Most earthquakes occur at plate boundaries. The world's most active seismic belt — the Circum-Pacific Belt (Ring of Fire) — is the boundary of the Pacific Plate.