San Francisco is sinking
SAN FRANCISCO - San Francisco is one of several major cities in the United States that's sinking, according to new research.
Researchers from Columbia University found that San Francisco is in a so-called "fast-sinking" zone.
While some large cities are being affected by the over-pumping of groundwater, San Francisco is sinking due to the compaction of filled-in land at spots including Treasure Island, the city's eastern bayshore.
The authors found that parts of the city subsided around 5 millimeters a year. On average, San Francisco sank a millimeter annually, Los Angeles 0.7 millimeters per year and San Diego 1.1 millimeters per year. Houston led all major U.S. cities, with about 20 millimeters of sinking annually.
Leonard Ohenhen, postdoctoral researcher at the Columbia Climate School’s Lamont-Doherty Earth Observatory, told KTVU on Monday that building codes need to account for the settlement.
"A lot of buildings are created with building codes where the total allowable settlement for a building for a 20-foot foundation is about 25 millimeters for the lifetime of the building," he said. "So if you have ongoing sinking in an area that is 5 millimeters per year, you already double that allowable settlement, which can cause structural problems to the building. "
Rising oceans can also contribute to the problem.
Experts say seas are rising an average of 4 millimeters a year as the land is sinking, increasing the likelihood of coastal flooding.