The 1556 Shaanxi earthquake (Postal romanization: Shensi), known in Chinese colloquially by its regnal year as the Jiajing Great Earthquake "" (Jiājìng Dàdìzhèn) or officially by its epicenter as the Hua County Earthquake "" (Huàxiàn Dìzhèn), occurred in the early morning of 23 January 1556 in Huaxian, Shaanxi during the Ming dynasty. Most of the residents there lived in yaodongs—artificial caves in loess cliffs—which collapsed and buried alive those sleeping inside. Modern estimates put the direct deaths from the earthquake at over 100,000, while over 700,000 migrated away or died from famine and plagues, which summed up to a total loss of 830,000 people in Imperial records. It was the deadliest recorded earthquake in history, and in turn one of the deadliest natural disasters in Chinese history. Tectonic setting Huaxian lies within the Weihe Basin, one of the rift basins that form the southern and eastern boundaries of the Ordos Block. To the east the basin is continuous with the Shanxi Rift System. The Weihe basin formed during the Paleogene in response to northwest–southeast directed extension. Following a tectonically quiet period during the late Paleogene the rift basins became active again in the Neogene in response to NNW–SSE directed extension, activity that continues to the present. The basins in the Weihe-Shanxi Rift System are bounded by large normal faults, which have been responsible for large historical earthquakes. The Weihe Basin has an overall half-graben geometry, with the main controlling faults, such as the Huashan Fault and North Qinling Fault, forming the southern boundary. Earthquake The epicenter was in the Wei River Valley in Shaanxi Province, near Huaxian (now Huazhou District of Weinan), Weinan and Huayin. Huaxian was completely destroyed, killing more than half the residents of the city, with an estimated death toll in the hundreds of thousands. The situation in Weinan and Huayin was similar. In certain areas, crevices opened in the earth. Destruction and death were widespread, affecting places as far as from the epicenter. The earthquake also triggered landslides, which contributed to the massive death toll. The rupture occurred during the reign of the Jiajing Emperor of the Ming dynasty. Therefore, in the Chinese historical record, this earthquake is often referred to as the Jiajing Great Earthquake. Modern estimates, based on geological data, give the earthquake a magnitude of approximately 8 Mw on the moment magnitude scale and XI (catastrophic damage) on the Mercalli scale, though more