Two earthquakes struck the South Bay Thursday morning (Jan. 7), the U.S. Geological Survey is reporting. Centered east-northeast of Milpitas, the first had a preliminary magnitude reading of 4.1 and struck at 10:09, the second -- a 1.6 -- followed at 10:22 a.m. The temblors were felt in Palo Alto as well.
Both followed another, 2.8 magnitude quake that occurred Wednesday night in the same area, near the intersection of the Calaveras and Hayward faultlines, David Oppenheimer of the Geological Survey told KCBS radio.
He cautioned residents not to fear that the quakes are foreshocks of a larger temblor.
"Not every magnitude 4 earthquake is followed by a magnitude 8 earthquake," Oppenheimer said.
Thursday's first earthquake had a depth of 5.6 miles. It was centered about 6 miles east-northeast of Milpitas and 11 miles north-northeast of San Jose City Hall.
The second had a depth of 0.2 miles and was centered in the same location as the first.
The Geological Survey maintains a map of recent quakes on its website.