New York Skyline can start to be very different if the metropolis continues to flow
Gary Hershorn / Getty Images
More than two dozen of the largest cities In the United States, which could affect thousands of buildings and millions of people.
The problem was reported beforeespecially in coastal areas. But using satellite technology, which sends radar signals to the surface of the earth and measures the time necessary for them to bounce back, scientists have found that it affects 25 of the largest cities in the country.
“By comparing several images taken in the time of the same area, we can detect tiny vertical ground movements, a few millimeters per year,” explains the team member Manoochehr Shirzaei to Virginia Tech. “It's like taking a period of high resolution of the earth surface and watching how it goes up or flowing over time.”
Fort Worth, Houston and Dallas presented the highest rates of subsidence in all large cities, exceeding 4 millimeters per year, on average. For New York, Chicago, Houston, Columbus, Seattle and Denver, the average collapse was greater than 2 millimeters per year.
“Houston – The city to flow the fastest in the 28 most populous American cities – at 42% of its area of land stable faster than 5 mm per year, and 12% stretch more quickly than 10 mm per year”, according to the researchers.
They say that most of the subsidence is caused by the extraction of groundwater, however, in certain cities, such as New York, Philadelphia and Washington DC, the sinking is mainly caused by an “ISOSTATIC GLACIAN”.
“During the last ice age, these areas were covered with massive glacial caps. The pure weight of the ice pushed downwards on the crust of the earth, like sitting on a memory foam mattress, ”explains Shirzaei. When the ice melt thousands of years ago, the pressure got up and the ground started to bounce slowly, he said.
“But this rebound is not uniform,” said Shirzaei. “In some regions, such as the American East Coast and the Midwest, the earth still flows rather than the climb, because they are close to the foreground, an area that had been pushed by the weight of the ice near and collapses now.”
In Seattle, Portland and San Francisco, plates tectonics is probably to blame for sagging.
“We have to start treating sagging as the slow disaster that is,” says Shirzaei. Scientists have also found that certain cities sink at different rhythms in different places, or sink into certain places and rise in others. “This unequal movement creates an angular distortion and stress, potentially leading to cracks in walls and foundations, ill -aligned windows and doors, or worse, a structural failure,” explains Shirzaei.
Jesse Kearse At the University of Kyoto, Japan, used similar satellite data to show that Many New Zealand cities are also calm. “A key challenge that remains for the geophysical community is how to attribute the trends observed to specific causes, whether anthropogenic or natural geological processes,” he says.
