Mar 24, 2025
Thousands of earthquakes occur daily worldwide, but most are too weak to be felt. Sensitive seismometers record around 500,000 tremors annually, with only about 100,000 noticeable and just a few hundred causing significant damage.
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Most earthquakes occur within the Earth’s crust, but some originate deep underground. The deepest earthquake ever recorded happened 750 km below the surface in the Bonin Islands, Japan—far deeper than where scientists once believed quakes could form.
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Some powerful earthquakes have shifted landmasses dramatically. The 2010 Chile earthquake moved the city of Concepción by 3 metres, while the 2004 Indian Ocean earthquake slightly altered the Earth’s rotation, shortening the day by microseconds.
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Heavy rainfall, melting glaciers, and large reservoirs can induce seismic activity. The weight of water alters pressure on fault lines, occasionally leading to earthquakes. This has been observed near major dams, such as the Koyna Dam in India.
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Around 90% of the world's earthquakes occur along the Pacific Ring of Fire, a horseshoe-shaped zone stretching around the Pacific Ocean. This area is also home to 75% of the planet’s active volcanoes, making it one of the most geologically active regions.
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Over 1,800 years ago, Chinese scientist Zhang Heng created the first known seismoscope. This ancient device could detect distant earthquakes using a system of weighted balls and dragon-shaped sensors, proving ancient knowledge of seismic activity.
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Many animals, including dogs, cats, and birds, have shown unusual behaviour before earthquakes strike. Scientists believe they may detect underground vibrations or changes in air pressure, though this phenomenon is still being studied.
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Earth isn’t the only place that experiences seismic activity. 'Moonquakes' have been recorded by seismometers left by Apollo astronauts. These tremors, caused by gravitational forces and thermal expansion, can last much longer than earthquakes on Earth.
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The strongest earthquake on record struck Chile in 1960, registering a magnitude of 9.5. Known as the Valdivia Earthquake, it triggered massive tsunamis and aftershocks that lasted for months, affecting coastal areas as far away as Japan and Hawaii.
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Certain human activities, such as mining, fracking, and reservoir-induced seismicity, have been linked to earthquakes. Injecting wastewater into deep wells can destabilise fault lines, as seen in parts of the United States where induced quakes have increased.
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