Perceptive Birds

[Gerard]

Last night, as many of you would know, Melbourne copped an earthquake of magnitude 5.3 and no less than 6 aftershocks measuring anywhere between 2.4 and 3.7 before 6:00am.

The most interesting thing was that the Hooded Parrots began going berserk in their cage about 15 seconds before the initial quake hit. I thought that they must have seen a mouse or a rat. Having seen no reason for their continuing panic, I was just about to tell them to settle down when I was nearly thrown out of the chair with the first thump I could feel and hear. During the worst of it the birds stopped flapping about and just gripped onto the side of the cage.

The initial quake of 5.3 would have lasted for approximately 60 seconds, but I could only feel and/or hear it for around 30 seconds. I could tell when it actually started and finished by the actions and attitudes of my Hooded Parrots. The good news was that the house hasn't suffered any damage...and just for the record, yes I did s%t myself as it was quite a jolt. It was the largest earthquake in Victoria for 109 years.

A similar incident occurred on a holiday to Bali in 1977. Approximately 2 minutes before a 7.2 magnitude quake hit, about 20 or so ducks all evacuated a large pond at the resort. They all did this in a very calm and orderly manner and just walked out of the pond in single file onto a mound that was 2 metres above the water level of the pond. I remember remarking to my father at the time, "Look at all the ducks".

It would seem that birds, like so many other animals, are far more attuned to these type of natural events than we are.

[avinet]

That's an interesting observation Gerard, and your birds would have picked up the initial tremors (or waves) from the earthquake before you could sense them.

An earthquake produces several types of tremors -
Longitudinal P-waves
Transverse S-waves
and Surface waves — both Rayleigh and Love waves

The P-wave is the quickest to propagate through the earth's crust, while the S and Surface waves are fairly similar in velocity. In general for a moderate earthquake such as the Victorian one last night, the ones we feel and the ones to cause damage are the Surface waves. As a general approximate rule the time difference between the arrival of the P-waves and the Surface waves in seconds, when multiplied by 8, will give the approximate distance to the epicentre. Given you estimated a 15 second period between the birds reacting and you feeling the quake yourself, the epicentre should have been around 120 kms from your home.

Your birds are obviously more sensitive to vibrations than you are

cheers,

Mike

[Gerard]

You are spot on Mike. The epicentre was located just east of Thorpdale which is located 97km ESE of where I live. Give or take a few seconds at either end of my time estimate and your calculation would be correct. This area of Gippsland has produced a number of tremors in the last few years, mostly in the 3 to 4.3 magnitude. Given that a magnitude 5 quake is 10 times stronger and releases 32 times more energy than a magnitude 4 quake (based on how the open-ended Richter Scale works) it was little wonder that we were given a good jolt.

Just goes to show that things can, and do, go bump in the night!

[Jack]

I know a few people from a Facebook site that said they had birds and eggs in the nest boxes that died because it was such a cold night and the parents didn't go back in the nest boxes after the earthquake.

How is an earthquake even 'made' here in Australia? Last time I read we weren't sitting on two plates.

[meandem]

We had a small tremor here about a fortnight ago, ours was at 9 o'clock at night. Thankfully all my birdies were asleep at the time!

I find it very interesting about what you had to say Gerard.

[avinet]

Jun 21, 2012 7:10:23 GMT 10 Jack said:

I know a few people from a Facebook site that said they had birds and eggs in the nest boxes that died because it was such a cold night and the parents didn't go back in the nest boxes after the earthquake.

How is an earthquake even 'made' here in Australia? Last time I read we weren't sitting on two plates.

The Australian Plate is moving roughly northwards at 70 mm a year, and as it moves stresses are formed in the crust - some parts of it slide over the mantle easier than other parts. These stresses eventually build up to the point where movement on a fault, causing an earthquake, is needed to relieve the stress. These intra-plate earthquakes are usually minor, although the strongest in Australia was a 7.3 near Murchison in WA.

This week's earthquake in Victoria is in a region that does have a history of quakes - Boolarra, about 30 kn south of Moe had a 5.0 quake in 2000, and back in 1969, two within 3 days that were 5.0 and 5.3.

A map showing earthquake risk for Australia is at www.ga.gov.au/image_cache/GA10950.pdf

cheers

Mike

[Jack]

Mike you're so wise

[anzac]

I have been through 2 earthquakes in Perth. I'm so old I remember the 1968 one that hit Meckering outside Perth) at 6.1. The 1979 one had many after shocks that rattled glassware off shelves, woke me up in the middle of the night with the bed shaking and toppled a crane near a building site near us and I remember watching that!

[anzac]

Sorry, the Meckering one was 6.8 and the 2nd one was at Cadoux in 1979 (180km outside Perth) and measured 6.1.

[Gerard]

I'm so old I remember the 1968 one that hit Meckering outside Perth) at 6.1.

Ssssshhhhhh Leanne...I'd like to think that we haven't reached our "Use By Date" yet...and just in case we have...for Christ's sake, don't tell anyone about it...lol.

[Aimie]

Birdies are so clever. I'm glad your house didn't suffer any damage Gerard.

I was only researching fault lines in Australia a month or so ago, there are a few of them. Someone had asked about earthquakes in Australia so i asked my best buddy Google about it ..... Scared me to see those ones that ANZAC had mentioned near Perth, hopefully they stay nice and calm while I live here.