1556 Shaanxi earthquake

The 1556 Shaanxi earthquake was one of the deadliest natural disasters in Chinese history. It occurred in the early morning of 2 February 1556. This event happened during the Ming dynasty under the reign of the Jiajing Emperor. Because of this timing, Chinese historical records often call it the Jiajing Great Earthquake. The earthquake struck the Weihe River Valley in Shaanxi Province. It hit areas near Huaxian, Weinan, and Huayin.

The disaster was so massive that it affected more than 97 counties. These counties spanned several provinces, including Shaanxi, Shanxi, Henan, Gansu, Hebei, Shandong, Hubei, Hunan, Jiangsu, and Anhui. While buildings in distant cities like Beijing, Chengdu, and Shanghai only suffered slight damage, the local destruction was total.

To understand why the shaking was so violent, we must look at the local geology. The epicenter was located in the Weihe Basin. This basin is a rift basin that forms part of the boundary for the Ordos Block. Rift basins form when the Earth's crust pulls apart in a process called extension. The Weihe Basin formed during the Paleogene period. Later, during the Neogene period, the area became active again due to northwest-southeast directed extension. The basin is bounded by large normal faults. These are cracks in the Earth's crust where blocks of rock move downward. The main faults controlling the southern boundary include the Huashan Fault and the North Qinling Fault. The 1556 earthquake likely occurred because these large faults ruptured.

Scientists use different scales to measure the power of such an earthquake. Modern geological data suggests the earthquake had a magnitude of approximately 7.9 on the moment magnitude scale. Some earlier estimates placed it at 8.0. On the Mercalli scale, which measures the intensity of shaking and damage, it reached a level of XI. This level is classified as catastrophic damage. The maximum seismic intensity was recorded between XI and XII in Huaxian and Weinan. Throughout the rest of the basin, the intensity was at least VIII.

Following the initial rupture, the ground did not become still immediately. Aftershocks, which are smaller earthquakes that follow a larger one, continued several times a month for half a year.

The high death toll was caused by both the shaking and the local way of life. Millions of people in the Loess Plateau lived in yaodongs. These are artificial caves carved into cliffs made of loess, a fine, wind-blown soil. When the earthquake struck, these caves collapsed, burying the residents inside. The intense shaking also triggered massive landslides. In some counties, the loss of life was staggering, with as much as 60% of the population killed.

The direct deaths from the earthquake are estimated at roughly 100,000 people. However, the disaster caused a much larger loss of life through secondary effects. Famine and plagues followed the destruction. When adding those who died from hunger or disease to those who migrated away, the total reduction in the Imperial hukou registration was 830,000 people.

Historical records provide a window into the chaos of the event. The scholar Qin Keda lived through the earthquake and recorded his observations. He noted that at the start of a quake, people should not run outside immediately. He advised crouching down to wait, comparing it to how eggs might remain intact even if a nest collapses. The shaking was powerful enough to damage cultural treasures. It damaged the Forest of Stone steles, breaking 40 of the 114 Kaicheng Stone Classics. In the city of Xi'an, the shaking was so strong that it reduced the height of the Small Wild Goose Pagoda by three levels.

Geologists have studied the physical marks left on the landscape by this event. These marks are called fault scarps, which are steep slopes created by the movement of a fault. Studies between 1998 and 2017 suggest the earthquake produced scarps along the Huashan and Weinan faults. Some of these scarps were quite high. Near Huashan, the fault terrace contained artifacts from the Yangshao culture that were 4,000 years old. Different studies have provided different measurements for these scarps. One 1992 study and a 2010 study estimated the Weinan Fault scarps at 5 and 10 meters, respectively. Researchers are still working to confirm if these specific scarps were caused by this single earthquake or multiple events.

This disaster had a lasting impact on how people viewed the world. A Portuguese Dominican friar named Gaspar da Cruz visited Guangzhou later in 1556. He recorded his thoughts in his book, A Treatise of China, published in 1569. He viewed the earthquake as a possible punishment for sins. He also linked the event to the Great Comet of 1556, which he saw as a sign of calamity. Today, the 1556 Shaanxi earthquake remains a primary example of how tectonic activity in rift systems can reshape both the physical landscape and human history.