Land is sinking at an alarming rate in some parts of the Bay Area, exposing shorelines to worse threats from sea level rise than was previously projected, a new study has found.  Several places along the San Francisco Bay — in San Rafael, Corte Madera, Foster City and Bay Farm Island next to the Oakland Airport — are sinking at a rate of more than 0.4 of an inch per year, the study from National Aeronautics and Space Administration found, based on satellite imagery. In those places, the sea level could rise by as much as 17 inches by 2050, more than double the regional average of 7.4 inches, compared to 2000 levels.