A 6.3 earthquake off the Southern California coast early Friday morning had an unusual characteristic -- it didn't happen on a fault line like most earthquakes.
According to UC San Diego seismologist Dr. Debi Kilb, the type of oceanic quake that ruptured on Friday was extremely rare.
"This earthquake was different because it ruptured in a region that has no known fault line and where there aren't large earthquakes," Kilb said.
The quake was followed by 2 larger aftershocks. One was a 4.7 magnitude and the other was 3.5 magnitude.
Ron Eroen from the Catalina Harbor Patrol said the quake felt like a rolling motion that lasted some 25 seconds.
Kilb said overall, about 2,000 people felt the quake. It did not merit a tsunami warning because it was not large enough or near enough to the shore.
Kilb and her fellow seismologists are still looking into the elements surrounding the quake.
NBC 7 San Diego's Facebook followers reported feeling the quake in La Mesa, Poway, Ocean Beach and as far away as San Ysidro.
There were no early reports of damage or injuries.