SAN FRANCISCO - The fourth small earthquake in six days rattled the San Francisco Bay area on Monday, but there were no reports of injuries or damage.

The temblor that struck at 10:07 a.m. had a preliminary magnitude of 2.6 and was centered about three miles northeast of Union City, according to the U.S. Geological Survey. It is considered a "microearthquake" by the USGS.

The quake occurred along the Hayward Fault, which runs underneath the eastern side of the San Francisco Bay and was the site of three other small earthquakes last week.

Two of those quakes had a magnitude of 3.7, and the other had a magnitude of 3.5.

Seismologists said the activity is not unusual for the area and does not necessarily mean the "Big One" will strike soon.