The earthquake near Shaanxi, China on the morning of January 23, 1556 was the deadliest earthquake on record and the third deadliest natural disaster ever. An estimated 830,000 people were killed as the earthquake destroyed an 840 km or 520 mile wide area. More than 97 counties in the provinces of Shaanxi, Anhui, Gansu, Hebei, Henan, Hunan, Jiangsu and Shanxi with some counties losing up to sixty percent of their population.
The epicenter was in the Wei River Valley in the Shaanxi province near the cities of Huaxian, Huayan and Weinan. Huaxian was hit hardest with every single building and home destroyed killing more than half its residents which lead to some references of the disaster as the Great Huaxian Earthquake. It is also referred to as the Jiajing Great Earthquake because it occurred during the reign Jiajing Emperor of the Ming Dynasty.
The Wei River Valley Basin is a major fault line where four tectonic systems intersect. The Cathaysian, Latitudinal direction, Longxi and Qilu-Qin-ling systems all meet making the area vulnerable for a major earhtquake. The magnitude of the 1556 earthquake is estimated between 7.9 and 8.6 on the Richter scale. Areas as far away as 500 km or 310 miles from the epicenter were affected. Crevices as deep as 20 meters or 66 feet were opened in ground by the quake.
One contributing factor to the high death tolls was millions of people living in man-made Loess caves. Much of the population in the Gansu, Shaanxi and Shanxi provinces lived in earth shelters called yaodongs in artificial caves made in the high cliffs of the Loess Plateau. The earthquake caused many of the caves to collapse and landslides destroyed many more.