A small earthquake has shaken parts of the Adelaide Hills early this morning, with reports as far afield as the city's outer southern suburbs.
According to Geoscience Australia's online earthquake tracker, the 2.2-magnitude tremor struck before sunrise, at 5:40am, with an epicentre near Mount Barker and Echunga.
There have so far been about 50 reports from people who felt the quake, which occurred at a depth of about 4 kilometres.
Most of the reports are from Echunga and surrounding towns within a 15-kilometre radius, including Stirling, Bridgewater, Aldgate and Hahndorf.
The biggest town to have felt the tremor was Mount Barker, which accounts for about a fifth of the reported detections.
But the tremor was also detected at Huntfield Heights in Adelaide's south about 25 kilometres away, as well as Wattle Park in the north-east.
Geoscience Australia senior seismologist Jonathan Bathgate said while there had been no reports of damage, the quake had been felt "quite widely through the community".
"Most people reported to us that they felt some shaking that lasted a couple of seconds — a bit of a rumble, people mistaking it for thunder or a truck passing by — but something that woke quite a few people up this morning," Dr Bathgate said.
"This area is relatively active, we do have earthquakes here quite frequently. Within 50 kilometres of the epicentre of this earthquake this morning, over the past 10 years there have been 24 other earthquakes recorded, so a couple of earthquakes a year on average."
For Kangarilla horse breeder Shane Farrell, it was a case of stirred but not shaken— he noticed the rattle, before drifting back to sleep.
"It wasn't dramatic, but I'm a very light sleeper," he said.
"I actually thought someone was shaking my bed or someone was trying to wake me up.
"My cat freaked out, actually … I opened my eyes and my cat was running around scared and went and hid.
"I thought it was an earthquake, but I wasn't 100 per cent sure, and then was told later on that it was."
The quake is not the first in the Adelaide Hills this year.
In March, there were magnitude 2.9 and 3.7 tremors near Mount Barker, as well as a magnitude-2.5 aftershock.
"The largest in that area was a magnitude-5.4 in 1954 which caused a lot of damage in Adelaide … [and] there is the potential in that area for relatively large earthquakes that can be damaging," Dr Bathgate said.
"The Australian continent is one of the fastest moving continents on the planet. We're moving north at about 7 centimetres every year, we're colliding with these tectonic plates.
"Some of that stress that is building up on those plate boundaries is transferred to within the plate, so we get these earthquakes that are generally smaller that occur along fault lines that we have within our tectonic plate."
