The city with its 13 million inhabitants and 220 years of history, the capital of Iran, drops by about 25 cm annually. This conclusion was published in the scientific journal Nature.
Tehran is located at the foot of the Elbrus Range, near (almost 100 km) from the Caspian Sea, and stretches for almost 50 km from west to east along the mountain slope. The altitude is on average 1.2 km above sea level, but there are areas where it reaches 2 km .
According to the latest satellite data - Tehran, subsides at an alarming rate of about 25 cm per year. The most densely populated megapolis in Western Asia was under threat of large-scale destruction due to possible geophysical cataclysms.
Scientists from the German Research Center for Geophysical Research GFZ in Potsdam have analyzed, based on satellite data, the extent of subsidence in the Tehran region from 2003 to 2017. The modern InSAR methodology was used, interferometric radar with synthesized aperture, widely used in geodesy for remote sensing. Such technology is used for geophysical monitoring of earthquakes, volcanoes and landslides, as well as in the design of structures and analysis of sedimentation and structural stability.
The team of researchers has discovered three different areas in which the earth is lowered by more than 25 cm per year over the period 2015-2017.
The drawdown map also shows safe areas where minimum deviations from stable levels have been identified. However, the data on the regions located in close proximity to Tehran International Airport - a dangerous subsidence of 5 cm per year has been recorded.
It should be noted that the subsidence of cities and agricultural lands occurs all over the world. Studies show that the main reason for "land abandonment" is human activity. Population growth leads to a sharp increase in the extraction of groundwater and other mineral resources. For example, some areas of Jakarta, the capital of Indonesia, are shrinking by 20 cm per year, while land in the San Joaquin Valley in California is sinking by 60 cm per year.
An alarming analysis of the geophysical situation in the area of Tehran suggests that the subsidence of the Iranian capital is going at an alarming rate, which is one of the highest in the world at the moment. The main threat to life and infrastructure of the city comes from 10% of the densely populated areas of Tehran in the south-west.
"Walking through these areas, we see uneven street surfaces, shifted curbs, cracks in the walls and even bent buildings, some of which have already had to be demolished," the researchers from GFZ say.
Huge cracks, several kilometers in length and up to four meters in width and depth, have already appeared on the ground southeast of Tehran, some of which threaten to overturn power lines and damage the railroad tracks. The Varamin Valley subsides by 25 cm a year, making agricultural land unviable, as water quickly flows through the cracks in the ground and crops dry up.
They continue to grow, and the growth of underground cracks sometimes causes sudden failures. Thus, A. Beitollahi, head of engineering seismology at the Tehran Construction Research Center, knows a peasant who fell into a 6-meter crack. Such agricultural lands become unviable because the cracks release irrigation water from the surface and leave the plantings dry. 120 km of railway, 2300 km of roads, 21 bridges, 30 km of oil pipeline, 200 km of gas pipeline, 70 km of high-voltage power lines and more than 250 000 buildings are in the danger zone.
Of course, the Iranian authorities are informed of a serious threat and the government is trying to confront the impending disaster. About 100 thousand illegal water wells have already been shut down all over the country in recent years, but according to various estimates at least 30 thousand unauthorized water wells will continue to operate in Tehran itself and its environs. Uncontrolled water production leads to the depletion of underground horizons and, as a result, catastrophic subsidence of land.
The decline, which has already occurred, can be irreversible, say impartial studies. Now researchers have found that the land can not rise back even after the rains, that is, something happened with the porosity and structural characteristics of the rocks. By the way, this loss can also lead to sudden flooding - something that scientists at the University of New South Wales in Sydney, Australia, have "delighted" the Iranians.
Do not forget that Iran is a nuclear country, it has its own reactors and nuclear centers for non-military use. Now the number of operating centrifuges is 19 000, and there are more than 10 tons of low-enriched uranium.