Apart from safeguarding against human-induced hazards, how can cultural relics housed in museums withstand sudden natural disasters like earthquakes? On October 20, the 2024 International Symposium on Seismic Technology for Cultural Heritage took place at the Chengdu Museum. During the event, international experts and scholars presented the latest advancements in seismic protection of cultural relics. The reporter learned that Sichuan Province has been actively upgrading its antiseismic measures for cultural relics in recent years. Thanks to technological progress, these upgrades are now largely effective in keeping cultural relics stable and standing during earthquakes, preventing them from falling over.

Seismic Protection Starts with Museum Architecture

In 2008, the catastrophic "5.12" Wenchuan earthquake, a sudden and devastating event, led to significant destruction of immovable cultural relics, including the historic Erwang Temple in Dujiangyan. Despite the high-grade earthquake resistance measures in place at many museums, this earthquake still caused damage to over 2,700 pieces of cultural relics across various museum collections. What strategies can be effectively implemented to preemptively protect cultural relics from the irreversible damage caused by earthquakes?

"Following the '5.12' Wenchuan earthquake, the Chengdu Museum, which was undergoing architectural design, initiated the exploration of a unified earthquake resistance system for its structures, display cases, and the cultural relics themselves. This approach leverages new technologies and antiseismic methods to safeguard cultural relics," explained Ge Jiaqi, Director of the Key Scientific Research Base of Seismic Protection for Cultural Heritage, National Cultural Heritage Administration. The Chengdu Museum is the first one in China to adopt this model for design and construction, according to Ge Jiaqi.

Through a combination of model testing and extensive analysis of seismic hazards, researchers have concluded that the entire base isolation of museum buildings is essential to reduce the impact forces on cultural relics during seismic events. Therefore, during the excavation of the foundation for the Chengdu Museum, 361 seismic isolation rubber bearings were installed between the building's foundation and the superstructure, effectively reducing seismic energy input at its source. This base-isolation measure can ensure the safety of museum buildings even when the earthquake intensity reaches magnitude 8.

The Chengdu Museum is situated close to Chengdu Metro Line 2, with its nearest point being only 18 meters away from the subway tracks. Could the museum be affected by the vibrations during the operation of the subway? The research team thus conducted numerical simulations and field tests on the complex dynamic system comprising "subway train, track structure, tunnel, surrounding soil mass, base, and building structure" and identified targeted measures to dampen vibrations. Duan Yangbo, the deputy curator of the Chengdu Museum, introduced, "The subway construction team installed a floating slab on the subway adjacent to the Chengdu Museum, created a seismic isolation trench and a heavy building base plate, and designed a 33-meter-span cantilever structure on the north side of the museum. These measures effectively mitigate the threat of subway operation vibrations to cultural relics."

In recent years, an increasing number of museums have focused on the study of vibration sources prior to the construction of their buildings. The Protection and Restoration Center of Cultural Heritage at the Sichuan Museum has been consistently monitoring and evaluating the vibrations resulting from the construction of Chengdu Metro Line 13 and the museum's daily operations, among other sources. It has been determined that the vibrations related to construction activities within the museum building and during the museum's opening hours are the primary sources of vibration for the Sichuan Museum at present. This information serves as a basis for establishing guidelines for in-museum construction and for implementing seismic isolation measures during the exhibition of cultural relics.

Customized Seismic Protection for Cultural Relics

In addition to museum buildings, the cultural relics displayed within the museum must also be protected with isolation measures. To guarantee the utmost safety, multiple museums have meticulously tailored their seismic protection measures to provide customized solutions for significant cultural relics.

The reporter has learned that even if the museum building does not collapse during an earthquake, the cultural relics in the museum's exhibition halls and storerooms may fall due to violent shaking when impacted by seismic waves. "Traditional physical earthquake-proof measures for cultural relics include methods such as securing, fastening, and supporting. These methods are effective when used on cultural relics with a low risk of seismic damage and those made of materials with good structural integrity and load-bearing capabilities. However, for exceptionally large or heavy cultural relics, these conventional approaches are inadequate," noted Yu Jian, the deputy curator of the Sanxingdui Museum. Yu Jian explained that the new building of the Sanxingdui Museum was designed to withstand earthquakes up to a magnitude of 8 on the Chinese seismic intensity scale. However, during the assessment of the building's structural dynamic properties, it was observed that different exhibition halls and floors displayed varied response analyses to seismic activity. "We calculate the earthquake risk coefficient based on factors such as the floor position of the cultural relics, the form of the display cases, and the characteristics of the artifacts, and then implement appropriate earthquake-proof measures."

Among the many national treasure-level artifacts in the Sanxingdui Museum, taller bronze figures such as the Large Standing Man and irregular items like the Bronze Sacred Tree are among those with higher risks of seismic damage. The experimental results indicate that during an earthquake, the Bronze Sacred Tree will undergo considerable shaking, with a displacement surpassing 2.76 meters. The branches undergo significant deformation in this process, which poses a risk of collapse or breakage. In order to protect these national treasures, 26 earthquake-proof display cases have been custom-designed for the key cultural relics in the Sanxingdui Museum's new facility. Particularly, the display case for the Bronze Sacred Tree is six meters tall, four meters in diameter, and weighs up to seven tons. The key to the earthquake resistance of this display case is found at its base, which is equipped with seven earthquake-proof devices and six sliding mechanisms, collectively forming a unified earthquake-resistant platform. Experiments show that after isolation by the platform, the maximum displacement of the Bronze Sacred Tree is only 63.5 centimeters, and it remains largely in a translational state, significantly reducing the risk of shattering.

The Chengdu Museum has adopted a seismic isolation technique for its treasured Stone Rhinoceros, similar to the method used for the Bronze Sacred Tree. Equipped with the earthquake-proof device that absorbs seismic waves, the Stone Rhinoceros seems to be "suspended" during an earthquake, refusing to "rock" in unison with the ground, thereby preventing it from overturning. Furthermore, the Stone Rhinoceros's four feet are positioned in custom-made grooves and secured with bidirectional clamps to prevent slipping during seismic events.

As introduced, newly built museums in Sichuan have gradually started to adopt similar earthquake-proof technologies for cultural relics. Having implemented this technology, the Ya'an Museum and the Museum of the Ganzi Tibetan Autonomous Prefecture have reported no seismic damage to cultural relics during earthquakes exceeding magnitude six in recent years. In the Ma'erkang Zhibo Diaolou building cluster in Aba Prefecture, a stone diaolou that has tilted over two meters will also have its stability enhanced through methods such as vertical stayed cables and internal steel hoops.