In-depth analysis of "Peak Burst": What does the active Indian Ocean plate mean?

The safety of people all over the world is protected by science and technology.

Written by Dong Hanwen (Institute of Geology, Chinese Academy of Geological Sciences)

At the beginning of the film "Peak Blast", a news report said: "The Indian Ocean plate has been in a state of obvious activity recently, causing disasters of varying degrees in many countries around the world." These disasters are geological disasters caused by plate movement: earthquake disasters and secondary geological disasters such as landslides, mudslides, and subsidence. The story in the film takes place in this context.

Figure 1. Source: Trailer of Peak Explosion

01 Why does the active Indian Ocean plate cause earthquakes in surrounding countries?

Research shows that earthquakes are not randomly distributed, but in regular belts, which we call seismic belts in geology. Seismologists monitor earthquakes around the world and the results show that most of the world's earthquakes develop along the boundaries of lithospheric plates, and some occur in active fault zones within the continents, mainly in the Pacific Rim Seismic Belt, the Mediterranean-Indonesian Seismic Belt, the Ocean Ridge Seismic Belt and the Intracontinental Deformation Belt.

The Circum-Pacific seismic belt is located at the junction of the Pacific Plate, the Eurasian Plate, the Indian Plate, the Antarctic Plate and the American Plate. The crustal movement is very active and it is the world's largest seismic activity belt. This seismic belt concentrates 80% of the world's earthquakes and is the main occurrence area of ​​most catastrophic earthquakes and global earthquakes above magnitude 8.

The Mediterranean-Indonesian seismic belt is the junction of the Eurasian Plate, the Indian Plate and the African Plate. The crust is relatively active and concentrates 15% of the world's earthquakes. The earthquake mentioned in the movie is in the area where this seismic belt has a strong impact (the southeast edge of the Qinghai-Tibet Plateau, see the picture below).

Figure 2. Active tectonic divisions and major earthquakes in the Qinghai-Tibet Plateau (after Deng Qidong et al., 2014)

The ocean ridge seismic belt is distributed along the axis of the global ocean ridges. All of them are shallow-source earthquakes with generally small magnitudes.

Intracontinental deformation zones refer to plate collision impact zones (fault zones) and rift zones (such as the East African rift seismic zone), which are some relatively small seismic zones distributed around the world. They are the result of intracontinental deformation under the influence of plate tectonics.

02 Why do so many geological disasters occur in succession in the same place? The above-mentioned seismic belts are earthquake-prone areas. Geological disasters will occur repeatedly in these areas. For example, at 14:28 on May 12, 2008, the unexpected 5.12 Wenchuan earthquake occurred near Yingxiu Town, Wenchuan County, Sichuan Province, my country, with a magnitude of 8.0MS (MS is the surface wave magnitude, which is the magnitude of an earthquake measured by the amplitude of a shallow source earthquake of about 20 seconds). The area destroyed exceeded 100,000 square kilometers, and the casualties were very serious. It is the most influential earthquake since the founding of the People's Republic of China. At 23:36 on July 14, 2021, an earthquake occurred again in Wenchuan County, Aba Prefecture, Sichuan (30.97 degrees north latitude, 103.37 degrees east longitude), with a magnitude of 4.8 and a focal depth of 15 kilometers.

Coincidentally, let's look at Tangshan, Hebei Province in our country. On July 28, 1976, Beijing time, a magnitude 7.8 Tangshan earthquake occurred in Tangshan and Fengnan (118.2° east longitude, 39.6° north latitude), with a focal depth of 23 kilometers. After a lapse of 44 years, at 6:38 on July 12, 2020, a magnitude 5.1 earthquake occurred in Tangshan (39.78° north latitude, 118.44° east longitude), with a focal depth of 10 kilometers. Hebei, Tianjin, Beijing, Liaoning and other places all felt the earthquake.

This is not only the case in China, but also around the world. For example, Haiti, which suffered a 7.2 magnitude earthquake last month (August 14), had experienced a 7.0 magnitude earthquake in 2010. Haiti is an island country located in the northern Caribbean Sea, at the junction of the Caribbean Plate and the North American Plate. It is also part of the Pacific Rim seismic belt and is an earthquake-prone area.

03 What about the series of geological disasters such as landslides and ground subsidence in the film?

These geological disasters in the film are called secondary disasters of earthquakes in geology, that is, geological disasters that are not directly caused by seismic waves, but are caused by other external factors after the earthquake.

In fact, in addition to landslides and subsidence, earthquakes can also trigger many other geological disasters, such as collapse, ground fissures, and sand liquefaction.

Figure 3. The sinkhole in the film (Source: Trailer of Peaky Blinders)

The small county town in Guizhou in "Peak Explosion" is located on the southeast edge of the Qinghai-Tibet Plateau. It is strongly affected by the collision of the Eurasian Plate and the Indian Plate. The local area is a typical karst landform area with a large number of caves. Therefore, it is very easy to cause local ground subsidence under the influence of earthquakes (Figure 3), and there is the possibility of secondary landslides. Therefore, both the trapped people and the rescuers are in great danger and may be swallowed up by secondary landslides at any time. The huge amount of loose rock and soil produced by collapse and landslides may cause mudslides, and the further development of ground fissures may lead to collapse and landslides. The collapse and sliding bodies block the river to form a barrier lake, causing disasters to the upstream and downstream. The unstable broken mountains and collapse and sliding accumulation bodies are in danger of collapse and sliding again, etc. So when an earthquake occurs, the rescuers do not only save the trapped people at the moment, but also find ways to prevent secondary disasters from causing greater casualties. The methods such as quickly evacuating the masses and blasting the mountains to clear the square in the film are all to minimize the secondary damage caused by secondary disasters.

04 Since the distribution of earthquakes is regular, why don't people living near earthquake zones move to other places? This is an interesting question. Every time an earthquake occurs, people will ask similar questions. This may be because the public is not very clear about the factors that affect the size of earthquake disasters. Generally speaking, the size of an earthquake disaster is closely related to its magnitude, intensity, location and time of the earthquake, the earthquake resistance of buildings, and people's awareness of earthquake prevention and disaster reduction.

(1) Magnitude and intensity

Magnitude is the level of energy released by an earthquake. The greater the magnitude of an earthquake, the greater the energy released, and the greater the possible disaster. Generally speaking, for every increase in the magnitude of an earthquake, the earthquake energy increases by about 31.6 times. According to the investigation and estimation of the earthquake cycle, the brewing period of a magnitude 8 earthquake generally takes at least 200-300 years, and a magnitude 7 earthquake also takes nearly 200 years to complete the energy accumulation.

Intensity refers to the impact and degree of damage caused to the ground and various buildings after an earthquake occurs. Intensity is different from magnitude. Magnitude reflects the size of the earthquake itself and is only related to the amount of energy released by the earthquake; intensity, on the other hand, reflects the consequences of an earthquake. After an earthquake, the intensity in different locations is different. In fact, the maximum intensity range of an earthquake is limited. Taking the 5.12 Wenchuan earthquake as an example, the area with an intensity of more than 10 degrees is a narrow strip, and there are only a few smaller areas above 11 degrees. Casualties are mainly concentrated in areas within 10 degrees, and casualties in the range of less than or equal to 9 degrees decrease successively.

(2) Location (city or uninhabited area) and time (day or night)

If an earthquake occurs in an uninhabited mountain, desert or seabed, no matter how large the magnitude is, it will not cause casualties or losses. This was the case with the 7.5 magnitude earthquake that occurred in northern Tibet on November 8, 1997. On the contrary, if an earthquake occurs in a densely populated, economically developed, and socially wealthy area, especially in a large city, it may cause a huge disaster. Therefore, the site selection, construction, management and planning of a city should avoid active faults and geological disaster sites.

Generally speaking, if a destructive earthquake occurs at night, the casualties may be greater than those during the day, up to 3 to 5 times on average. One of the reasons for the heavy casualties in the Tangshan earthquake was that the earthquake occurred at 3:42 in the middle of the night, when most people were still asleep indoors. If this earthquake had occurred during the day, the number of casualties would have been much smaller. Many people believe that major earthquakes often occur at night, but this is actually an illusion. Statistics show that the probability of a destructive earthquake occurring during the day and at night is about the same, and there is no significant difference between the two.

(3) Earthquake resistance of buildings

The collapse and severe damage of buildings during earthquakes is one of the most important direct causes of casualties and property losses. The quality and earthquake resistance of buildings directly affect the extent of the disaster, so it is necessary to make good earthquake-resistant fortification of buildings.

(4) People’s awareness of earthquake prevention and disaster reduction

Conducting earthquake and earthquake science education before an earthquake to prevent and relieve disasters, and conducting disaster relief drills in a planned manner can improve the quality and skills of the entire population in earthquake prevention and disaster reduction. Previous earthquake events have shown that self-rescue and mutual rescue are the most important and effective ways to save lives after an earthquake. After being trained, the self-rescue and mutual rescue of the masses will greatly increase the success rate of rescue.

In short, people will certainly carry out urban planning and construction based on local geological conditions in advance, but there are many factors that determine the size of earthquake disasters. In addition to site selection, there is still a lot that can be done for disaster prevention and mitigation.

05 What are the current technical means of disaster prevention and reduction? my country has a vast territory and complex geological conditions. Earthquakes, floods, landslides, mudslides and other natural disasters occur frequently. The 2008 Wenchuan earthquake caused great damage to people's lives and property. In recent decades, huge economic losses have been caused by natural disasters every year. Natural disasters have become an important factor affecting my country's economic development and social security.

In order to effectively promote disaster prevention and reduction, countries around the world generally attach importance to the research and development and application of scientific and technological means. The main approach is to build laboratories and basic databases, increase scientific research investment, use space information technology, and build a disaster monitoring and early warning technology system.

Spatial information technology, whose full name is remote sensing geospatial information technology (or "3S" technology), includes remote sensing technology (RS), geographic information technology (GIS) and global positioning system (GPS). It is a modern information technology that combines space technology, sensor technology, satellite positioning with computer technology and communication technology to collect, process, analyze, manage, disseminate and apply spatial information.

For example, in the film, there is a scene where early warning of landslides is given so that rescue workers have time to make judgments and develop rescue measures. This is done with the help of high-precision satellite data and three-dimensional computer simulation to predict what may happen to the landslide, thus providing a reliable basis for decision makers.

Spatial information technology represented by 3S has provided effective technical support in disaster prevention and mitigation of natural disasters such as earthquakes, floods, landslides, and mudslides, especially playing an important role in rapid response, emergency relief, and post-disaster reconstruction.

The safety of the people of the world is protected by scientific research and technology. At present, many universities in my country (such as Wuhan University, China University of Geosciences, etc.) have opened majors related to spatial information technology, set up courses such as geographic information systems, remote sensing and geographic information science, surveying and mapping, geological engineering, and disaster geography, and have trained a large number of outstanding talents over the years. In addition, there are many scientific research institutes in China engaged in related work, including the Ministry of Emergency Management and its directly affiliated units, the China Earthquake Administration, the National Safety Production Emergency Rescue Center, the Ministry of Natural Resources and its directly affiliated units (such as the China Geological Survey, the National Basic Geographic Information Center and the Chinese Academy of Surveying and Mapping, etc.), the key laboratories of the Chinese Academy of Sciences (such as the key laboratories of mountain hazards and surface processes, etc.) and universities directly under the Ministry of Education (such as China University of Geosciences, Chengdu University of Technology, etc.).

In today's world dominated by knowledge economy and information technology, vigorously strengthening the application of science and technology in disaster prevention and mitigation is the only way forward in the field of disaster prevention and mitigation in the future.

Natural disasters are ruthless, but people are kind. Thank you to the rescue workers for their hard work!

May everyone in the world be safe and sound~