NEWBURYPORT — Calls flooded area police departments late yesterday afternoon telling police of a “loud bang” that one caller likened to the noise of a structure collapsing.

But police and firefighters deployed in Rowley, West Newbury, Newbury and Byfield found themselves roaming the neighborhood streets with no indications of the source of the noise.

That’s because the rumble came from below the earth’s surface.

“It looks like Amesbury Middle School’s seismograph had a spike,” local weather observer and Triton Regional teacher Ray Whitley said as he logged onto the school’s Web site to take a look. “There was definitely some activity.”

And the U.S. Geological Survey Web site confirmed it: A 1.8 magnitude earthquake rumbled through the area at 4:35 p.m.

“We are sitting on the Clinton-Newbury fault line; it runs right through here,” Whitley said. “We do have activity here. There are no plate edges, but we do get frequent tremors in the ones or twos but no fives.”

The Clinton-Newbury fault line trends east to west to northeasterly at its northeast end near Newbury.   In Massachusetts, the fault zone is approximately 97 miles long.  

The fault zone curves southwestward to Clinton and Worcester, and then southward into the state of Connecticut.

Gail Regis, a teacher at Amesbury Middle School who got the seismograph for the school through a grant, said before confirmation from the web site she wasn’t sure if the spike was due to an earthquake or just a loud plow that went by. Amesbury police, however, did not receive any calls about a loud noise.

Regis has the seismograph in her classroom as part of Amesbury Educational Foundation’s Innovative Grant for 2006-07. Regis received $10,000 to put toward starting The Boston College Educational Seismology Project at the school.

Newbury and West Newbury police said they also got a large influx of calls but could not find the source.

Whitley said the last large earthquake to have rocked this area was in 1755 when, according to history, the quake caused all the church bells in Boston to ring.

“The fault lines runs right through Byfield,” Whitley said. “Even if Weston doesn’t have anything yet, it doesn’t mean it didn’t happen.”