Within two hours, scientists upgraded Sunday night's earthquake from magnitude 3.7 to a 4.2, more accurately locating its epicenter in the Santa Monica Mountains and determining that it occurred at a depth of 3 to 4 kilometers.
After initially calculating that the temblor was probably an aftershock of the 4.4 magnitude March 17 quake, seismologist Lucy Jones of the U.S. Geological Service said that further analysis of Sunday night's quake showed that it was not located in the same zone as other aftershocks, and was thus probably a separate event.
Like the March event and a magnitude 2.5 quake in Beverly Hills, she added, Sunday night's quake occurred in the Santa Monica Mountains -- near but not on the Santa Monica-Hollywood fault.
As of 9:45 p.m., Jones had not heard any reports of damage. She said that thus far there had been two small aftershocks, noting that "there's always the possibility we could get more."
The earthquake was the third above magnitude 4 in the last three months, she said.