The magnitude 4.4 earthquake that struck near Westwood is the most significant shake in Southern California since a 5.5 earthquake hit Chino Hills in 2008, a
Robert Graves said there have been at least six aftershocks since the 6:25 a.m. earthquake. The largest so far has been a magnitude 2.7 earthquake that struck five miles northwest of Westwood.
Graves said there is always the small possibility that the 4.4 earthquake was only a prelude to an equal or stronger shake.
"Always the possibility that it's a foreshock," Graves said, adding that about 5% of earthquakes are followed by an equal or larger shake and that if it does happen, it would occur within the next several hours.
But Graves did say that "certainly we would expect more aftershocks."
Seismologists at the USGS have not yet determined exactly what fault this earthquake was on and Graves also said "we're continuing to analyze the data, but at this point, this seems to be what I would call a rather typical earthquake."
Monday's earthquake hit in the northern edge of the Santa Monica Mountains area, a general area responsible for the uplifting of the range over many thousands of years.
"The location is somewhat surprising. It's within the Santa Monica Mountains. We have not seen seismicity in it in recent times," said Caltech seismologist Egill Hauksson. "It has been dormant for quite some time."
In contrast, there are well known faults to the south of the Santa Monica mountains: the Hollywood and Santa Monica faults roughly along Hollywood and Santa Monica boulevards.
Graves said people reported feeling it within about 30 to 50 miles of the epicenter, Graves said.
Read more about Southern California earthquakes.