Tremors continue to rattle NSW Mid North Coast

Most of the tremors have been felt around the Macksville area, although the magnitude-4.2 quake struck offshore.

Tremors, the largest of which was a magnitude-4.2 quake, are continuing to rattle the Mid North coast of NSW, with authorities wondering if a big one may be on its way.

More than 40 tremors have hit the area since Friday of last week, with five felt since the larger quake occurred on Wednesday afternoon.

Geosciences Australia says the magnitude-4.2 quake, which struck at a depth of 10km offshore north of Nambucca Heads, may have been felt up to 76 kilometres away and was strong enough to cause damage up to 6km away.

What to do if a quake hits

Local Emergency Operations controller, Superintendent Paul Fehon said, in a major quake, people should take cover, hold onto something and stay where they are.

"The thing with an earthquake is there's nothing to tell you that it is coming and then we do have to consider the secondary phase of an earthquake which could be a tsunami," he said.

"It's been a couple of weeks now of feeling tremors and we just take the advice from Geoscience Australia.

"They're the experts who can tell us what possibly is happening in regards to the tectonic plates out there. Fortunately the tremors have been minor and there's been no reports of any damage."

Tremors or earthquakes?

Geoscience Australia senior seismologist Phillip Cummins said the most recent quakes shook an area around Valla.

He said they were on the land, in the continental crust and not offshore.

"They can all be described as earthquakes no matter how small they are," Professor Cummins said.

"I should point out that the ones we locate have to be big enough to be recorded at several stations. But there are actually many more smaller quakes occurring."

Whole lotta shakin' goin' on

Sometimes a pattern of foreshocks could build up to bigger ones, or sometimes Professor Cummins said there would be "possibly hundreds of them and they'll just eventually die out".

He said scientists don't really know what makes the smaller earthquakes cluster in time and space.

"We're still in the dark about that," Professor Cummins said.

"We really can't say why the earth chose this particular time and this particular place to increase the seismic activity.

"They're still a bit mysterious."