A series of small earthquakes struck near the Salton Sea area overnight.

Nearly 20 micro-quakes — the strongest measuring magnitude 3.3, with others much smaller — struck the town of Niland near the eastern shore of the Salton Sea, according to the U.S. Geological Survey. A magnitude 3.6 quake was recorded near Salton City on the west side of the Salton Sea.

In September, a series of more than 200 small quakes hit the area. That prompted scientists to say for several days that there was an elevated risk for a big San Andreas fault earthquake. Many of the minor quakes were located under the sea itself.

The Salton Sea is one of California’s most seismically complex areas. It is located on a web of faults that scientists fear could one day wake up the nearby San Andreas from its long slumber.