Saturday's magnitude 4.1 aftershock near Rowland Heights suggests the cluster of earthquakes triggered by the 5.1 temblor Friday is moving northeast.
The 2:32 p.m. earthquake occurred about three miles northeast of Friday night's large earthquake. Other aftershocks hit within 2.5 miles of the epicenter of the La Habra quake.
"There could be additional earthquakes to the northeast," said Caltech seismologist Egill Hauksson.
But he noted scientists can't predict where earthquakes will go.
"We just have to watch what happens," Hauksson said.
If the earthquakes do move to the northeast, they could shift from the Puente Hills thrust fault system toward the Whittier fault.
There is precedent for earthquake aftershocks jumping faults. The Whittier Narrows earthquake, a magnitude 5.9, struck on the Puente Hills thrust fault system on Oct. 1, 1987. Three days later, a magnitude 5.6 aftershock hit on a different fault, Hauksson said.
That aftershock killed one person, twisted several chimneys and broke windows. Damage was reported in Whittier, Pico Rivera, Los Angeles and Alhambra.