Nambucca Heads earthquakes follow up

Yesterday, following the rare experience of a noticeable earthquake in our region, I provided a very rough map of the location of earthquakes in preceding 24hours to the one many people felt. I have since incorporated earthquakes since and for the week before. I've also increased the area we are looking at.

Mapping is all about enough data, and enough decent data. Collecting the data is essential and then looking at it so see whether it adds to the story helps us understand the world in which we live. Geoscience Australia provide an excellent online service to the public showing all the earthquake activity in our Country. Yesterday's post had enough data to demonstrate that there appears to be little relationship between inferred or known faults in the region and the location of earthquakes. More data since means more interesting features!

A comment from a reader asked about the trace of the Demon fault system (a system that is very evident even today despite it being apparently inactive for many millions of years). I have included a thick pale blue line that roughly approximates the Demon Fault system strike.

The map I have just updated implies that there is a fault system previously unknown. I have included a line that approximates the pattern of many quakes in area. What is interesting is that the apparent line of most quakes is perpendicular to the old Demon Fault. It is also interesting that the 'major' 4.2 quake is separate from the apparent line of quakes experienced in the last week or so. It is likely that the quakes in the Nambucca area are a parallel line of stress to the most frequent quake trend.

Either way, the map says more that I can so have a look and tell me what you think.

 *Update: At least three more quakes have been identified (one occurred since the above map) and another couple which was subsequently identified after cleaning out the background 'noise.

I also note that the quakes were almost entirely situated in a structural block known as the Nambucca Block. I guess another post will have to be done since the Nambucca Block provides insights into the way the New England Orogen has formed (Shaanan, Rosenbaum & Ranauld 2016).

Yes, I felt that Earthquake too

Earthquakes are a bit infrequent in our part of the world. So, when one is big enough to feel happens there is usually much excitement.

While in my home office a few hours ago (1.30pm this afternoon) I felt a strange sensation and the roof of my studio shook. About 1 minute later, my wife came up from the house and asked if I had felt something, because the house shook for a moment. So, onto trusty Geoscience Australia Earthquakes page I went. Sure enough a substantial (by our standards) quake hit somewhere under the ground near Urunga.

I've put together a quick map which shows all the mapped major faults in the area (noting that most of them are actually inferred). I have overlain the last 24hrs worth of quakes to see if there is a correlation. There appears to be very little if any. But that is unsurprising given most faults have probably been inactive for millions of years. But I suppose interesting anyway. Note that the data had not been double checked by Geoscience Australia when I put this together.*

*Since posting the above, the earthquake epicentre has been updated to near Nambucca Heads the hypocentre being approximately 10km below Nambucca Heads.

Eidsvold Earthquake 2015

I woke this morning to the news that a town to the west of Bundaberg had experienced a substantial earthquake. Well, substantial by Australian standards anyway. Geoscience Australia gives the intensity of 5.2 on the Richter scale. The quake occurred at about 2am local time (3am for those of us in the other eastern states coping with daylight saving).

The preliminary report from Geoscience Australia can be found here.

Seismograph from Eidsvold Station

It is in an interesting area because the area of the earthquake is in the northern part of the New England Orogen. This belt of squashed rocks extends from the Bundaberg area in a big arc all the way to Port Macquarie in the South. There are many faults in this area and some are still active, although they are generally small. An earthquake between Gunnedah and Tamworth in 2013 springs to mind.

The scale of the earthquake is quite large for Australia. Indeed the Newcastle earthquake was measured at 5.6. I've not done the maths but the new Eidsvold quake of 5.2 is about half the size of the Newcastle one (The Richter Scale is NOT linear).

Historically, the area is prone to small to medium sized earthquakes with Bundaberg being hit by a size 6.0 in 1918. This is nearly ten times more powerful than the most recent one though the 1918 quake occurred just off the coast.


Oh... and humour starts quickly:


https://twitter.com/iampatwilliams/status/567040767172952065/photo/1