The seaquakes have been picked up by seismograph stations in the region.

Richter scale ratings are determined soon after an earthquake, once scientists can compare the data from different seismograph stations.

The collapse registered recorded seismic waves in magnitude 3.9 to 4.0, by seismograph stations of the University of Utah.

A dense network of seismograph stations installed around the epicentre detected only six small aftershocks all within six weeks of the main shock.

It was noted that there were no tremors reported at seismograph stations and an earthquake could be ruled out as the cause of the break.

Seismic waves from the "coal mine bump" (collapse) were reported as magnitude 3.9 to 4.0 by seismograph stations in Utah and Nevada.

P waves are pressure waves that travel faster than other waves through the earth to arrive at seismograph stations first hence the name "Primary".

These waves arrive at seismograph stations after the faster moving P waves during an earthquake and displace the ground perpendicular to the direction of propagation.

Scientists detect more minor earthquakes than ever before, it says, but only because more seismograph stations have been placed around the world.

To record the microquakes, the observatory has set up six seismograph stations around the Moodus area.