Seismologists believe that some of the earthquakes occurring in various regions of our planet are caused by human activity. In contrast to seismic shocks caused by the movement of tectonic plates, induced earthquakes occur due to:
- human development of mineral resources in quarries and mines;
- extraction of oil, geothermal energy and gas from deep layers of the earth’s crust;
- creation of dams and artificial lakes, changes in river channels;
- conducting underground nuclear tests, etc.
Thus, in Oklahoma, where oil is intensively produced, the number of earthquakes with a magnitude of 3.0 has increased from 2 to 800 over the past 30 years.
What earthquakes are caused by human activity
Can human activity affect the intensity and frequency of earthquakes? Researchers respond that it can, but not significantly. Some activities can trigger an earthquake by changing the weight and stress on tectonic plates or by influencing friction processes in the fault zone. But there is no evidence that humans could have caused earthquakes with a magnitude greater than 5.3. Strong and destructive seismic tremors, such as the earthquake in Turkey and Syria in February 2023, are natural phenomena that cannot be affected.
The frequency of the strongest earthquakes has been relatively constant since written records. Since 1900, about 18 earthquakes with a magnitude of 7.0 or higher occur every year. There is no evidence over the past hundred years to suggest that the frequency of strong, destructive earthquakes tends to increase. The increase in the number of weak tremors may be due to both anthropogenic human activity and the use of advanced measuring instruments of a new earthquake monitoring system.
The danger of induced earthquakes
Induced earthquakes occur near the Earth’s surface, in contrast to natural seismic activity associated with the movement of lithospheric plates. Their strength is relatively small, and they are of a local nature. The main causes for this are related to digging and drilling. Oil companies often pump water into a well. Under its pressure, oil is released to the surface. Water injected to a depth of several hundred and even thousands of meters can affect the intensity of friction between tectonic plates, causing landslides and weak seismic tremors.
The strongest induced earthquake with a magnitude of 5.3 occurred in 1962 at the military plant in Commerce City, Colorado. A well was drilled here for the disposal of toxic waste with a depth of 4 km. In 4 years, more than 620 million liters of liquid were dumped into it, which caused a series of small tremors. A year later, a local 5.3 magnitude earthquake struck the region and caused almost 1 million dollars in damage to Denver’s industrial areas.
Another example of induced earthquakes is the accumulation of large amounts of water at Hoover Dam, which occurred in 1930 and caused a series of several hundred weak tremors. That is why Chinese seismologists express concern about the condition of the concrete Three Gorges Dam and consider it earthquake-prone. It is the largest construction in the world, weighs more than 65 million tons and poses risks of induced earthquake. If the retaining wall is damaged by seismic tremors, water could flood the valley where millions of people live.
How to reduce risks
Due to the damage that induced earthquakes can cause, it becomes relevant to establish rules aimed at limiting activities in earthquake-prone regions of the planet. If drilling operations are carried out in areas with high seismic risk, it will be impossible to forecast earthquakes and determine their true cause. Therefore, it is important to protect regions with increased seismic hazard from the additional risk of earthquakes that can take the lives of many thousands of people.
Special programs aimed at economic development and environmental conservation have already been developed in the United States (California, Texas, Oklahoma, Ohio) and Canada. They include modeling and assessment of general seismic risks, as well as the occurrence of induced earthquakes. In Europe, such rules have not yet been adopted and are under development.