Terrawatch: cities that change the shape of the planet

The weight of buildings in dense urban areas can lead to subsidence, with effects particularly marked by the coast

It's well known that ice sheets are heavy enough to bend the underlying rocks, but what about cities? Are some cities capable of reshaping the bit of planet they sit on?

By 2050 around 70% of Earth's population are projected to live in cities. This set Tom Parsons, a geophysicist with the United States Geological Survey, to wondering if the associated redistribution of mass into concentrated urban areas is capable of causing subsidence. Using the San Francisco Bay region (7.75 million people) as a case study, Parsons estimated the weight of all the buildings and their contents to be around 1.6 trillion kg - comparable to the weight of water behind a dam. Taking into account the underlying geology of San Francisco, Parsons modelled the pressure that the city exerts and showed that San Francisco's buildings are responsible for between 5 and 80mm of subsidence. The findings are reported in the journal AGU Advances.