Land under U.S. largest cities sinks: research

NEW YORK, May 8 (Xinhua) -- The land underneath the largest cities in the United States is sinking, a phenomenon threatening buildings, roads and rail lines, but that sinking, known as subsidence, is not happening in the same way in each place, or even the same way across one city, according to new research.

Researchers mapped out how land is moving vertically across the 28 most populous U.S. cities and found all the cities were compressing like a deflated air mattress. Twenty-five of them are dropping across two-thirds of their land. About 34 million people, about 10 percent of the U.S. population, live in the subsiding areas, according to the study published on Thursday in Nature Cities.