By Jem Anshaw
Since the Upper Hunter was rocked by a 4.7 magnitude earthquake on Friday, August 23, and a number of aftershocks since, there has been a lot of questions around the geological events raised by residents who have not experienced anything like it before.
The good news is that now more information will be available to earthquake scientists like Jonathan Griffin to help investigate what is happening.
“The main reason we’re in town is because we’ve been putting out some additional seismometers to potentially record any aftershocks of these earthquakes that occur,” he said at a recent information session held in Muswellbrook.
“We’ve got five new ones, two were put in about three weeks ago and we’ve put in three over the past couple of days, all within about 15 kilometres or so of Muswellbrook.
“They will give us more detailed picture, assuming there’s aftershocks, hopefully there’s no more big ones, but if there are we will catch those and get a better location on them than we do with our national network.”
One of the new sensors was close enough to the earthquake that occurred on Saturday, September 7 that it has provided Geoscience Australia with some data about the strength of the ground shake, which is uncommon in Australia as the sensors are not often close enough to the epicentre to capture that information.
Jonathan shared there were several questions put to the Geoscience Australia team at the information sessions mostly around how they record data, where and why earthquakes occur, and what to do in an earthquake.
They also found it interesting to be hearing firsthand everyone’s experiences when the earthquakes have occurred and what damage was caused.
Mine Blast or Earthquake?
With five new monitors in place within 15 kilometres of Muswellbrook, the question of how they differentiate between an earthquake or a shot being detonated at a local mining site was raised very quickly by locals.
Earthquake scientist Jonathan Griffin explained that they can look at the data to get a visual on what is causing the sensors to ping.
“With an earthquake, you’ve generally got two bits of rocks sliding past each other along a fault plane, one side gets a push, and the other side gets a pull, and we can see that in the waveforms that come through,” he explained.
“A mind blast is an explosion from a point, it kind of pushes out in all directions from that.”
If this data is ambiguous at all, they can then look at the time and day that it has occurred, mine sites don’t blast before dawn and very rarely on weekends.
Then, if all else fails, there is no shame in the team if they must pick up the phone and call any mining operations in the vicinity of an event to get an answer straight from the source.
