An earthquake knocked out power to roughly 2,500 homes in muswellbrook in NSW this morning. Hundreds of people reported feeling the quake that struck the Upper Hunter at 6am.
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00:00This morning, Geoscience Australia recorded a magnitude 4.5 earthquake just before 6 a.m.
00:09in Musselbrook.
00:10So the epicenter of the earthquake itself was around about 10 kilometers to the southwest
00:14of Musselbrook, and that was followed shortly after by a small aftershock of magnitude 2.5.
00:22In terms of the whole scale of things, how large is this and how deep was it in terms
00:28of its significance?
00:29Yeah, so a magnitude 4.5 earthquake, it's a moderate-sized earthquake, and this earthquake
00:37occurred very shallow in the Earth's crust, so probably at a depth of around 5 kilometers
00:43or possibly a little bit shallower than that.
00:46In the Australian context, we don't see earthquakes all that often, and a magnitude 4.5 earthquake
00:52can cause damage to vulnerable structures, such as unreinforced masonry buildings, which
00:58were potentially nearby in the town of Musselbrook.
01:01You say it doesn't happen in Australia very often, but this is the third one in three
01:05weeks, isn't it?
01:07That's right.
01:08So I guess what we're seeing in the Musselbrook region at the moment could be classified as
01:12what we say an earthquake swarm.
01:14So that's where we see a series of moderate-sized earthquakes of around about the same magnitude,
01:21and each of those earthquakes will have their own aftershock sequence, where we tend to
01:26see the aftershocks decaying over time.
01:29There is perhaps an elevated chance that we might see similar-sized earthquakes in the
01:34region relative to the normal baseline levels, but I guess our hope from now is that both
01:41the magnitude of these earthquakes will start to decrease as well as the frequency of the
01:48earthquakes will decrease over the coming weeks to months.
01:51What's the science?
01:52What's happening in the rocks underneath us?
01:56So that's a very difficult question to answer, but I guess in the broader context, the Australian
02:01crust is under stress from the broader plate tectonic forces.
02:07And so those stresses are building up over long periods of time, and that puts stress
02:12on the rocks in Australia, and over those long periods of time, there are zones of weakness
02:19that we know as fault lines that can break when that stress becomes too much.
02:24Now, I guess as we have observed in the area, there is a large amount of coal mining in
02:31the area.
02:32It's very difficult for us to determine whether the mining in the area has influenced the
02:39onset of these earthquakes or not, and that really requires a large baseline information
02:45in terms of the seismic monitoring in the area, which we really don't have, unfortunately.
02:49But we do know that earthquakes can in general occur anywhere across Australia.
02:55In terms of a pattern, if you like, is there analysis yet to see whether this is a pattern?
03:04It's very difficult to say.
03:05We really can't forecast the likelihood of these earthquakes continuing into the future.
03:11If we look at the historical pattern in the Greater Hunter Valley area, of course, we
03:17had the 1989 Newcastle earthquake, which is still one of Australia's most costly natural
03:24disasters and caused 13 fatalities as well.
03:29And then in the 1990s, we also saw another large earthquake near Ellalong in the Cessnock
03:34area.
03:35That was a magnitude 5.2 earthquake.
03:37So there is a history of moderate to large earthquakes in the area.
03:43And so perhaps what we're seeing at the moment is part of that longer term pattern of large
03:48earthquakes in the Hunter Valley region.