Earthquake hits NSW Hunter Region weeks after two similar events

ABC NEWS (Australia)

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.

Transcript

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.

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