Was It Boom, Blast or Bump in the Night?

Some called it an earthquake, others an explosion, still others a sonic boom, but no one seemed to know the source of the loud boom that resounded through parts of San Diego County on Tuesday night.

The only thing known for sure about the loud noise, which occurred about 8 p.m., was that it was not an earthquake, according to Caltech in Pasadena.

But earlier Tuesday, there was a little earthquake centered 28 miles southwest of Oceanside. The 1:03 a.m. temblor was one of hundreds of aftershocks there since a larger quake jolted an offshore fault in 1986, authorities said.

About the evening noise, the San Diego Police Department received “dozens and dozens” of calls from all parts of the city, Lt. Margaret Schaufelberger said. About 25 calls were received by the San Diego County Sheriff’s Department from a scattered area, including Lemon Grove, El Cajon and as far as Encinitas, a spokesman said.

Efforts were being made by both agencies to locate the source of the noise Tuesday night.

Tuesday morning’s quake measured 3.6 on the Richter scale, and officials reported no damage or injuries.

“A quake of that scale causes no damage, even if you’re right on top of it,” said Duncan Agnew, a geophysicist with the Scripps Institution of Oceanography in La Jolla.

A Caltech spokesman said that Tuesday’s tremor was an aftershock from an earthquake measuring 5.3 on the Richter scale that hit the area July 13, 1986, causing more than $700,000 damage.