Earthquakes Seismology

Earthquakes — sudden shaking caused by tectonic plate movement, volcanic activity, or other geological processes — occur at a rate of approximately 500,000 per year (1,000+ strong enough to be felt). The Richter Scale (logarithmic, each step = 10x ground motion) was replaced by the moment magnitude scale (Mw) for modern measurements. The most powerful earthquake recorded: the 1960 Valdivia earthquake (Chile, Mw 9.5) — generating tsunamis that reached Japan, 17,000 km away. The 2011 Tōhoku earthquake and tsunami (Japan, Mw 9.0-9.1) killed 15,897 people, caused the Fukushima nuclear disaster, and permanently shifted Japan's axis by 17 cm. The 2010 Haiti earthquake (Mw 7.0) killed 160,000-316,000 people — the same magnitude earthquake in Japan or California would kill hundreds (earthquake death tolls are primarily determined by building quality and emergency response). USGS monitors seismicity globally; major faults (San Andreas, Cascadia, North Anatolian) are under intense scientific observation.