August 2015 – QUEENSLAND – The area off the Cooloola Coast hit by multiple earthquakes since last Thursday has the highest level of seismic activity in Queensland but is still relatively inactive by world standards, a senior seismologist has said. Borumba Dam has been given a clean bill of health following the shakes. Geoscience Australia senior duty seismologist Dan Jaksa said eight earthquakes had been detected in Queensland since Thursday. Three of the quakes, which occurred about 120km east of Fraser Island, registered magnitude 5 or above. “Magnitude 5 is the strength of an atomic bomb test,” Mr. Jaksa told the ABC at the weekend. “Magnitude 5.7 is about 15 times bigger than a magnitude 5, so that’s 15 atomic blasts of energy.” An hour after Saturday’s magnitude 5.7 event, a magnitude 5.1 earthquake struck in the same spot north-east of Rainbow Beach.
Seqwater said yesterday although Borumba Dam was designed to easily withstand earthquakes much greater than magnitude 5.3, Thursday’s quake was considered large enough to undertake dam safety inspections at every Seqwater dam in the region. No damage was found but regular check will continue. Since Thursday there have been five more quakes between magnitude 2.8 and 3.9. Whether or not there will be more is impossible to predict but experts expect the aftershocks to ease off now. Mr. Jaksa said Geoscience Australia received more than 3000 reports in response to the three magnitude 5 events. “There are 400 or 500 earthquakes a year (in Australia), but they’re not near people or they’re in the (ocean),” he told the ABC. “Not all of them generate tsunamis and not all of them are near … but we analyze all of them and all the little ones too.”
Mr. Jaksa said Australia had seen a number of events where large earthquakes had happened in quick succession, the most famous being in Tennant Creek in 1988, when three earthquakes higher than magnitude-6 occurred within two hours. Seismologist Mike Turnbull confirmed that the magnitude 5.7 earthquake at 1.38pm on Saturday was an aftershock. “It’s happening 10km under the ground and if you get the rock breaking in a certain direction it will throw energy in that direction,” he said. He expects the aftershocks to ease off now. –Gympie Times