The findings will be published March 28 in Geochemistry, Geophysics, Geosystems, a journal of the American Geophysical Union.
"Our combined GPS and InSAR analysis clearly captured the movements over the last decade that neither GPS nor InSAR could sense alone" said Shimon Wdowinski, associate research professor of Marine Geology and Geophysics at the University of Miami.
In the new study, using the GPS instruments, Bock and his colleagues were able to take absolute readings of the city and its surrounding lagoons. And not only did they find the sinking, but they found that the area was tilting a bit, about a millimeter or two eastward per year. That means the western part where the city of Venice is is higher than the eastern sections. Prior satellite analyses didn't pick up on the tilt, Bock said, possibly because the scientists had been taking measurements using InSAR, which only provided the change elevation relative to other sites.
The relative nature of InSAR measurements might also explain why the new study detected Venice's subsidence, while other recent studies did not, Bock conjectured.
Venice's subsidence was recognized as a major issue decades ago, he noted, when scientists realized that pumping groundwater from beneath the city, combined with the ground's compaction from centuries of building, was causing the city to settle. But officials put a stop to the groundwater pumping, and subsequent studies in the 2000s indicated that the subsidence had stopped, he said.
"It's possible that it was stable in that decade, and started subsiding since then, but this is unlikely," Bock said. The current subsidence is due to natural causes, which probably have been affecting the area for a long time.
A significant part of those natural causes are plate tectonics. The Adriatic plate, which includes Venice, subducts beneath the Apennines Mountains and causes the city and its environs to drop sli
|Contact: Kate Ramsayer|
American Geophysical Union