1640 Iran: Tabriz Earthquake

The largest earthquake ever recorded was the 1960 Valdivia earthquake in Chile, at magnitude 9.5. It generated a tsunami that traveled across the Pacific Ocean and caused damage as far away as Hawaii and Japan. The earthquake killed approximately 1,655 people and left 2 million homeless.

The deadliest earthquake in recorded history was the 1556 Shaanxi earthquake in China, estimated at magnitude 8.0-8.3, which killed approximately 830,000 people. Many casualties resulted from the collapse of yaodong (cave dwellings) carved into loess cliffs. The 2010 Haiti earthquake (M7.0, ~316,000 deaths) was the deadliest in modern times.

Pre-instrumental earthquake magnitudes are estimated from written accounts of damage, felt reports, geological evidence such as fault scarps and liquefaction features, and tsunami records. These methods provide approximate magnitudes with typical uncertainties of 0.3-0.5 magnitude units.

QuakeFYI's historical database covers earthquakes from approximately 2150 BC to the present, with over 5,700 significant events. Written records from ancient China, Greece, and the Middle East provide some of the earliest accounts. Instrumental recording began around 1900 with the first standardized seismographs.

An earthquake swarm is a sequence of many earthquakes occurring in a localized area over weeks to months without a clear mainshock. Unlike aftershock sequences where one large event is followed by smaller ones, swarms have no single dominant event. They are often associated with volcanic activity or fluid migration in the crust.