SAN FRANCISCO, Dec. 16 (UPI) -- Pennsylvania scientists say the danger of earthquakes in the San Francisco Bay area is greater than generally thought.
Penn State University geoscientists wanted an explanation for different slip rates on the San Andreas fault north and south of the Golden Gate Bridge that would help explain how Mount Tamalpais, northeast of San Francisco in Marin County, came to rise above the bay.
The researchers hypothesized that a fault running diagonally from the northern Hayward fault to the San Andreas fault in Marin County could transfer the necessary motion to the San Andreas and might explain high topography around Mount Tamalpais.
However, proving a thrust fault's existence turns out to be a difficult task.
Thrust faults occur when one piece of terrain rides up over another forming a characteristic uplift pattern with one side gradually sloping up and the other more precipitous. Blind thrust faults terminate below the Earth's surface and are therefore often missed.
Such a blind thrust fault, as it would be termed, are dangerous, Dr. Kevin P. Furlong, a Penn State geoscientist, said recently. He noted that a blind thrust fault caused the 1994 Northridge earthquake.
