Bigger quake to come, says expert

A SEISMIC expert says the earthquake we had in April is a portent of things to come and that another "1954-style earthquake" is certain to hit the city.

A SEISMIC expert says the earthquake we had in April is a portent of things to come and that another "1954-style earthquake" is certain to hit the city.

Seismologist David Love from PIRSA says most of our quakes don't follow faultlines, so there's no point reaching for a map.

"The truth of the matter is that the earthquakes occur all over the place, regardless of where the faultlines are," he said.

"It's somewhat different from California, where you can see most of the earthquakes happen on major faultlines that they know are moving."

The South Australian earthquakes are "spread out far and wide", though there are "more on the hills than on the flats".

Dr Love said it was quite common for people to be able to hear and see an earthquake without feeling it. He said the earthquake compression waves were equivalent to sound waves. As the waves come up through the ground it is possible to hear low-frequency sound waves.

"It does sound like a rumbling as it comes and goes," he said.

"When you are closer it tends to be more a big boom sound, but what people actually hear is a probably a little subjective and probably depends on where they are and what they are doing."

People were jolted from their sleep when a magnitude 3.8 quake - the state's strongest in more than 20 years - struck just south of Mt Barker at 11.27pm on Friday. Its shockwaves were felt across the state.

It was the largest of four tremors that had struck close to Adelaide in the past 19 days, with three recorded near Kuitpo, including a 1.9 magnitude tremor on April 2.

Australian Seismological Centre director Kevin McCue said it was only "a matter of time" before SA experienced a repeat of the 5.5 magnitude quake of 1954 that caused $70 million damage across Adelaide.

"I think we probably haven't seen the worst yet, but the probability would be pretty small that it will happen in our lifetime," he said.

"But in places like Adelaide, very few buildings are designed to resist earthquakes.

"A 1954-style earthquake will happen at some stage in the future and Adelaide will be damaged. It's just a matter of time."

Mr McCue said SA experienced at least one magnitude 3.8 quake a year, and Adelaide faced the greatest risk of earthquake damage out of any major capital city due to its large number of volatile fault lines.

He said Friday's quake was a call to communities and authorities to be better prepared in the event of a more destructive tremor.

"This is the fourth relatively small earthquake in just a few weeks, which is unusual," he said.

"This earthquake was possibly up to a magnitude of even four and it's only the depth (of the quake) that saved you from damage.

"I think at the moment there is a high probability of an earthquake in this same area of the Adelaide metropolitan area.

"I think people like the state emergency services should be looking at their procedures again and what they need to be doing to respond to an earthquake.

"People who manage schools and hospitals ought to also be making sure they are not vulnerable."

However Mr Love said people should not be alarmed that Friday's seismic activity indicated something more sinister to come.

"We've got no way of predicting them and there hasn't been a particularly large number and nothing that should stand out," Mr Love said.

"There's always the chance of something bigger, but the probability of that really is quite low.

"If there are a lot of these in the next couple of months some people might get upset, but this is close enough to normal, except we don't usually have then down here, we usually see them up in the Flinders."

Mr Love said Friday's seismic activity was about 20km underground.

Police and emergency services were inundated with emergency calls from across the state as people near the epicentre reported the sound of an "explosion".

More than 500 calls were logged within hours of the quake hitting, with shockwaves felt up to 100km away and as far as Kangaroo Island, but by the light of day SES had reported no structural damage.

The AdelaideNow website was flooded with more than 1600 comments from people recounting their experiences.

Sharon Butler, 37, husband Scott, 42, and their three young children - Holly, 9, Thomas, 6, and Bethany, 5 - were asleep in their Wistow home when the quake struck.

"It sounded like a roar of thunder then there was a muffled bang and the house shook," Mrs Butler said. "I Googled it today and realised it was an earthquake; it was pretty exciting."

Mt Barker Natural Food Barn worker Patrick Buckley, 59, said he arrived at work yesterday to find stock on his shelves jumbled up and out of place, but hadn't been surprised by the quake.

"I've known that there was going to be some sort of activity so I've adjusted to it. Nostradamus predicted it," he said.

SA is among the state most susceptible to earthquakes and Adelaide, the Mt Lofty Ranges, the Flinders Ranges, the Eyre Peninsula and Mt Gambier are at most risk.

It is believed that normal tectonic-plate movement and pressure caused the quake.

Mr McCue said the Australian tectonic plate was moving north at 7cm a year, nudging with adjoining Eurasian and Pacific plates and increasing stress on this continent.

We have closed comments on this story for technical reasons. For more reader comments on the earthquake:
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Geoscience Australia seismologist David Jepsen told AdelaideNow the epicentre was somewhere near Mt Barker in the Adelaide Hills, but would have been felt strongest in multi-storey buildings in the CBD.

"It's located in a population centre, so expected to be felt quite widely," he said.

"If you're in a building of many floors, the shaking would be amplified, apartments or tall buildings in the city."

However, Mr Jepsen said it was unlikely there would be any aftershocks or major damage.

"Something of this size, it's highly unlikely there would be any damage."

Nor was there any risk of a tsunami, as the epicentre was not offshore and the quake not strong enough.

It is expected normal tectonic plate movement and pressure on the plates caused the quake, which is not geologically unusual.

There is at least one small earthquake near Adelaide each year, and Primary Industries and Resources SA recorded 20 quakes, ranging from 0.6 magnitude 6km north of Nuriootpa on March 2 to 5.1 on the Richter Scale south of the southern coast on April 5.

Adelaide's 1954 earthquake measured 5.4 on the Richter Scale and was several hundred times more powerful than last night's quake.

A Facebook group, "Earthquake in Adelaide", was set up minutes after the quake struck and had nearly 2000 fans within 30 minutes and more than 5200 fans by 11.30am today.

A Police spokesman said there had been about 250 calls to 000 and another 300 to the police asistance line.