Saturday November 6, 1999
TWO earthquakes, each releasing about half the seismic energy of the Hiroshima atomic bomb, occurred off the coast of Newcastle in May.
And an even larger quake occurred last year off Nelson Bay, according to seismology data.
The first quake, measuring 2.4 on the Richter scale, occurred seven kilometres underground on May 3 at 2.58pm.
A second quake, slightly stronger at 2.6 on the Richter scale, occurred nearby two days later at 9.51am.
But a bigger earthquake, felt at Shoal Bay and Corlette, registered 3 on the Richter scale when it struck off Nelson Bay shortly after 8pm on March 28 last year.
The quake's epicentre was located 20km offshore from the town, about 50km east of Newcastle.
All up there have been at least 36 recorded earthquakes in south-east Australia alone between January and June this year.
The earthquake information has been recorded by the Seismology Research Centre (SRC), a division of instrumentation and data acquisition company Mindata, based at the La Trobe University Research and Development Park in Victoria. The SRC says for each unit of an earthquake's magnitude there is a ten-fold increase in ground displacement.
It says because larger earthquakes last longer than small earthquakes, there is about a thirty-fold increase in seismic energy released for each unit increase in magnitude.
An earthquake measuring 1 on the Richter scale releases a similar amount of seismic energy as a typical quarry blast.
But an earthquake measuring 5 releases about the same seismic energy as a 10,000 tonne equivalent nuclear blast, such as that used at Hiroshima.
The major Newcastle earthquake of December 28, 1989, measured 5.6, claimed 13 lives, injured more then 160 and left a damage bill of about $4billion.