Thread: Tsunami Warning

Originally Posted by Quiggers

Local radio is having a field day here, right now!

Time to go surfing!

GQ

If everybody had an ocean
Across Byron Bay.
Then everybodyd be surfin
Like LRA
Youd seem em wearing their baggies
Huarachi sandals too
A bushy bushy blonde hairdo
Surfin Byron Bay

Youd catch em surfin at Tweed Heads
On the border line
Santa cruz and trestle
Australias narabine
All over manhattan
And down doheny way
Everybodys gone surfin
Surfin Byron Bay.

Well all be planning that route
Were gonna take real soon
Were waxing down our surfboards
We cant wait for june
Well all be gone for the tsunami
Were on surfari to stay
Tell the teacher were surfin
Surfin Byron Bay.

Haggerties and swamies
Pacific palisades
San anofree and sunset
Redondo beach l.a
All over la jolla
At Byron Bay

Everybodys gone surfin
Surfin Byron Bay

Everybodys gone surfin
Surfin Byron Bay

Everybodys gone surfin
Surfin Byron Bay

Originally Posted by Quiggers

Local radio is having a field day here, right now!

Byron Bay to Ballina - and some residents have rung in saying they're on the way to higher ground etc.....

sounds like a major beatup......

Time to go surfing!

GQ

I don't think you can describe it as a beatup. From the detection of the earthquake by remote seismographs, and the calculation of the position of the earthquake showing that it is in an area of ocean (and hence could generate a tsunami), there is only a few hours before the tsunami will reach the Australian coast. If a warning is to be much use, it is best given at this stage, rather than wait for ocean tide gauges to report whether a far-field wave has been generated.

The NSW coast IS vulnerable to tsunamis, although the location of dangerous earthquakes is more likely to be south of NZ than in Melanesia for a variety of reasons. In this case it appears (although the warning for NSW is still current) it seems that the tsunami will be insignificant at this distance. The problem is that the generation of a tsunami is not dependent just on the earthquake magnitude, but on the depth of the focus, and the depth, slope and material of the sea bottom, plus the propagation of a tsunami is very dependent on the sea floor topography and nearby coastlines, plus, in the far field, the depth and shape of the thermocline.

John

My apologies, John.

The paranoid loonies around here, predicting 100 foot waves etc, I find funny - too much smokin the grassy stuff, some of them, but not me...

Having looked at the map earlier today, and understanding how waves travel, I would have thought the that wave energy, (given its source of origination) would dissipate as it 'hits' the east coast and islands further north (and there's a lot of north, north of here)...

to get us here at Ballina we'd need the SE travelling submarine wave to bounce off something 'out there', but Lord Howe isn't big enough and the wave energy should dissipate by the time it gets to South America.... if it hasn't already done so passing thru Vanuatu etc....

I hear Bondi Beach has also been evacuated...

...be good if it hits Cheviot Beach, may stir up and land the body of a former Prime Minister....

cheers, GQ

Originally Posted by Quiggers

My apologies, John.

The paranoid loonies around here, predicting 100 foot waves etc, I find funny - too much smokin the grassy stuff, some of them, but not me...

Having looked at the map earlier today, and understanding how waves travel, I would have thought the that wave energy, (given its source of origination) would dissipate as it 'hits' the east coast and islands further north (and there's a lot of north, north of here)...

to get us here at Ballina we'd need the SE travelling submarine wave to bounce off something 'out there', but Lord Howe isn't big enough and the wave energy should dissipate by the time it gets to South America.... if it hasn't already done so passing thru Vanuatu etc....

I hear Bondi Beach has also been evacuated...

...be good if it hits Cheviot Beach, may stir up and land the body of a former Prime Minister....

cheers, GQ

The dangerous wave is not submarine - it is a surface wave, and looking at a map after you have prompted me shows that the great circle from the Solomons is more or less tangential to the NSW coast - but the wave would be refracted by the shallowing water depth to bend towards the coast more, and there could also be rather unpredictable changes in direction due variations in the vertical temperature gradient in the water. Rather than looking at "rays" from the epicenter (and remember we don't know too accurately where that is anyway) it is best to think of wavefronts moving outward - and these will not remain circular, but will get distorted by the effects mentioned.

But it was inevitable that given the necessity of issuing a warning, some people would go overboard - it is one of the problems with tsunami warnings.

John

Entirely fair and accurate comment John.

I was just thinking that by refraction, dissipation would occur.

By submarine I meant the shock wave that runs at about 700mph just below the surface, which is unctuous, until it hits a deflective object, like a beach or a reef or whatever. Then there's a problem!

At 1245 today, no signs of a probo here...(insert smiley face with a snorkel!)

GQ

Numpty's Missus - Redcliffe is pretty safe - any wave would break as it entered the bay and dissipate on all the sandbanks (I've run aground on most of them).

Quiggers - The surface wave travels fast and is unnoticeable in deep water, but as the water shallows it steepens, gets higher, and eventually breaks. The particle motion in this type of wave is circular, and the longer the wavelength (and these are long) the bigger the circle - and when the bottom of the circle touches the seafloor it drags back and the surface water piles up and breaks, giving the flow of water ashore that you saw on television. If there is a sudden change to shallow water like at the entrance to Moreton Bay, it breaks there, and the ensuing flow would barely reach the inner parts of the bay. Could be a problem on the seaward side of Bribie, Moreton, Stradbroke though, not to mention Fraser.

John

6 years ago when still employed by Telstra, I was in discussion with the CSIRO (Dr. Andrew Forbes, http://www.marine.csiro.au/media/04releases/23jan04.htm ) about using out of service submarine communications cables in the Indian Ocean for the detection of nuclear weapons testing, ocean temps, earthquakes, and possible tsunamis. See http://www.csiro.au/files/mediarelea...sNuclearIn.htm

The problem was that we needed to store soem no longer needed cable in the cable depots in Manila and Singapore - and someone would have to pay for the storage (which isn't cheap). Telstra was willing to cover their share of the costs but agreement from the other cable owners wasn't forthcoming (the cable ownership is shared).

Then a few years ago we had the devastating New Year tsunami in Asia - all those countries whose administrations who were reluctant to pay some money were the ones worst hit by the tsunami.

This technique is already in use in the Pacific by the Japanese Earthquake Research Institute http://www.eri.u-tokyo.ac.jp/ and by the US at Woods Hole Oceanographic Institute http://www.whoi.edu/ - both organisations with which I had corresponded.

Ron

Just like road blackspots not being fixed until people are killed, Usually many people.