WILSON da SILVA and JOHN STAPLETON
Collapsed chimneys, cracks in walls and structural damage caused by an earthquake early yesterday have brought 36 claims to the GIO office in Lithgow.
The State Emergency Service said the only reports of damage came from the Lithgow district.
In Sydney, houses moved and windows shook but no damage was reported.
Mr Alf Davis, 79, of McCawley Street, Lithgow, was awakened by the collapse of his chimney on to part of his kitchen and living room.
Another resident, in nearby Montague Street, had bricks fall on to his driveway, smashing the windscreen of his car.
"My children started to yell when it started," said Mr Len Ashworth. "I have a very large and lazy dog, and last night he jumped a 1 1/2-metre-high fence and disappeared.
"People around here this morning were walking the streets as if on eggshells."
He said residents had reported six tremors between 1 am and 3 am, with smaller aftershocks continuing almost until sunrise.
Burglar alarms around the town went off, and a 500-megawatt generator at Wallerawang power station was stopped. It was repaired after nine hours. The Clarence colliery was evacuated for four hours.
In Katoomba, buildings shook and alarms were set off, but there were no reports of damage.
Dr Marion Leiba, a seismologist with the Bureau of Mineral Resources, said the pattern described by the quake on the seismograph at her home in Canberra"really looked spectacular".
The epicentre of the quake, which the seismograph recording showed lasted about eight minutes, was about six kilometres north-west of Lithgow.
It registered 4.3 on the Richter scale, making it the biggest on Australia's east coast this year.
The Bureau of Mineral Resources estimated the depth of the quake at three kilometres. This is unusually shallow, which accounts for the damage.
Nearly all the earthquakes in eastern Australia are caused by compression of the earth's crust as Australia moves north at six centimetres a year on the Indo-Australian plate.
Australia is near the centre of the plate. Most quake activity takes place on the edges, in New Zealand, New Guinea, and Indonesia.
Dr Leiba said: "The Lithgow quake is known as an intraplate earthquake, which means that it is caused by stresses inside the plate, which we suppose is related to what is happening at the margins, but we don't have a good enough theoretical model to know how."
She said Australia was "absolutely criss-crossed" by geological faults. There was no single fault, like the San Andreas Fault in America, which made it difficult to predict where the next earthquake would be.
In south-eastern Australia the earthquakes seem to be related to the Lachlan Fold Belt, which is an area of folded rock extending from central NSW to eastern Victoria. Lithgow lies at the eastern edge of the belt.
The last earthquake in Lithgow, which also registered 4.3 on the Richter scale, occured on February 13, 1985. It was directly underneath the town at about the same depth as yesterday's quake.