Physics of a tsunami

With my parents still in New Zealand and on the coast in Greymouth (in the direct line for any tsunami emanating from the Honshu earthquake) I was reading around the speed of Tsunamis with some personal interest. However, I didn’t have to, since the Pacific Tsunami Warning Center [sic] has all the predicted “hit” times for the arrival of the wave or, more often, waves.

SEA LEVEL READINGS CONFIRM THAT A TSUNAMI HAS BEEN GENERATED WHICH COULD CAUSE WIDESPREAD DAMAGE. AUTHORITIES SHOULD TAKE APPROPRIATE ACTION IN RESPONSE TO THIS THREAT. THIS CENTER WILL CONTINUE TO MONITOR SEA LEVEL DATA TO DETERMINE THE EXTENT AND SEVERITY OF THE THREAT.

ESTIMATED INITIAL TSUNAMI WAVE ARRIVAL TIMES AT FORECAST POINTS WITHIN THE WARNING AND WATCH AREAS ARE GIVEN BELOW. ACTUAL ARRIVAL TIMES MAY DIFFER AND THE INITIAL WAVE MAY NOT BE THE LARGEST. A TSUNAMI IS A SERIES OF WAVES AND THE TIME BETWEEN SUCCESSIVE WAVES CAN BE FIVE MINUTES TO ONE HOUR.

Apologies for the SHOUTING, but this is obviously a rather important message.
UPDATE HERE and again HERE

And there is NZ on the list, with a predicted arrival time of 1930 GMT this evening. That’s 2130 SA time and 0830 tomorrow local time: over 12 hours after the earthquake hit. And that gives you an idea of how massive the scale of this is, because tsunami waves can top 900kph.

The wave speed is the square root of the product of the gravity constant (g) and water depth.

Tsunamis are normally produced by an earthquake or displacement of the seafloor due to plate shifts, etc. This produces a very large wave very rapidly, which then possesses significant energy.

The energy is distributed through the depth of the water initially, as it is displaced, but because of gravity and friction with the seabed, tends to decrease with increasing depth after a short while.
In deep water, the frictional affect on the wave speed is negligible near the surface. The more shallow the water (for instance as it approaches shore), the greater the affect of friction in slowing the mass of water above the seabed; most of the energy of the wave is transferred to the seabed, a small portion is lost to the atmosphere and in heating of the water.

Therefore, the more shallow the water, the slower the wave speed.

And with the Pacific generally being rather deep, the waves are travelling rather fast.

Thankfully, given the distances involved, that still gives my parents significant time to ensure their safety. Sadly, others nearer the epicentre, or without access to this information will probably not be so lucky.

Quotes from Christchurch

The Christchurch earthquake and its aftermath have been undeniably tragic. Boston.com’s always impressive The Big Picture has probably the best collection of photos of the devastation, but they’ve been justifiably beamed around the world so many times that you’ve probably seen a lot of them already.

My Mum and Dad are touring New Zealand at the moment and were due to visit Christchurch next week.  Obviously, they have had to change their plans and we’re all hoping that their flight from Christchurch airport via Sydney and Jo’burg to Cape Town in a couple of weeks time will still be able to go ahead.

This has obviously been an emotional time for those involved. However, that doesn’t mean – no matter how unreal the situation seems – that you can just make stuff up to describe it.

Firstly, I’m looking at you, 63-year-old teacher’s assistant Kevin Fitzgerald and your

I thought the devil was coming up out of the earth.

quote. Is that really what you thought, Kevin? Because it sounds a bit lunatic ninja to me. Look, I appreciate that it must have been a harrowing experience, but was that really your first thought as your “building undulated menacingly” (love that image)?
Not that there had been, perhaps, an earthquake (one of over 5,000 in the Christchurch area since September), but that a mythical nasty bloke was on his way up from the home of the DA?
And then – once the dust had actually and metaphorically settled – you stood by that thought and told the entire world about it.

Seriously, even in the extremely unlikely event that I had thought that the devil was coming up out of the earth, once I had worked out that there had been an earthquake in this earthquake zone known for its earthquakes and a reporter shoved a microphone under my nose, I’d probably have chosen not to mention it. My quote would probably have been more along the lines of:

I thought it was a really big earthquake.

It might be a lie (it might not) but at least I wouldn’t look as silly as you do now.

And in that vein, Kevin, thank the good lord above (not for the devastating earthquake, the horrendous damage to livelihoods, the needless loss of loved ones and scenes of utter desperation, obviously) but thank him anyway, Mr Fitzgerald, for South African clergyman and Christchurch resident Dr Tienie Bekker. For Dr Bekker and his good lady wife were put on this earth to make your “devil coming up out of the earth” quote seem entirely reasonable.

As Dr Bekker told SAPA:

We were lucky that we could buy food as we were on the outskirts. Many have had to be helped. Drinking water is minimal in quite a few areas. A lot of people are without power.

Which all seems entirely reasonable. But then he describes the actual moment the earthquake hit and that’s where things get a bit odd:

I was just out on my way to an appointment after midday, had just finished lunch, when I felt this wave. My house started moving up and down. My wife compared the experience to a tumble dryer on a roller-coaster.

Wait. What? She compared it to what, Tienie?

My wife compared the experience to a tumble dryer on a roller-coaster.

Right. So she did.

Where to begin? I guess the obvious place would be how does she know?
Is there some weird sub division of roller-coaster fanatics which gets off on taking household appliances on rides?
Is Mrs Bekker one of these people?

And even if there was and she is, how does the seatbelt fit? Surely there is some significant danger in large consumer durables not being properly anchored when traversing several hundred metres of track replete with terrifying bends and gravity-defying loops.
Presumably there is a optimum size for these things. A simple kettle or iron would likely fall out almost immediately, while a mid-size appliance such as microwave might lend itself to being correctly and safely strapped into the seat.
But a tumble dryer is a large item and my fear would be that its uneven weight distribution together with its dimensions would probably prevent it from being adequately affiliated with the carriage of the ride in question.

Where would one plug it in? Because, if we presume that Mrs Bekker’s description is suggesting that a tumble dryer on a roller-coaster moves somehow more violently than any other item on a roller-coaster, then we must surely assume that it is switched on.
I have never seen a roller-coaster with plug points and that fact has never bothered me before because I had also never seen the need for them.

All that has changed.

In addition, does Mrs Bekker’s description merely refer to the motion of the said appliance on the roller-coaster? Or is there heat involved too? Did things suddenly get noticeably warmer as the quake hit? Because that’s part of tumble drying as well.
As is the ubiquitous lint filter. So are we looking at just movement, movement and heat or movement, heat and a mysterious purple-grey felt covering everything in Dr and Mrs B’s house?

I’m not aware of these things, because I don’t live in an earthquake zone – but neither do a lot of other people and they also need enlightening, Mrs Bekker. Should we just expect to feel a bit giddy with a slight sense of elation after an earthquake has hit or should we expect to feel hot and a bit fuzzy?

And could her description help in designing better quake-proof buildings? After all, their house is still standing, they are unharmed. Should all houses in earthquake zones come with a height restriction, a long queue and the need to be accompanied by a large alternative to a washing line?

Because if that is how the Bekkers survived – think how many other lives could be saved.

Did the earth move for you in 2005?

The chatter in Gauteng is (possibly) all about last night’s Gauteng earthquake/tremor which, it turns out, wasn’t in Gauteng at all. It measured 2.8 on the Richter scale and twitter was instantly ablaze with the thought that the Daily Star’s prophecy might actually have come true, although of course a quick look at this page would tell you that Southern Africa is actually hit fairly regularly by small earthquakes.

There’s no way of actually predicting where or when an earthquake might strike. If there was – like there is with volcanoes – then evacuations could take place and the number of casualties would be drastically reduced. Obviously there are areas which are at higher risk than others, but you’ll find that SA is pretty safe in this regard.

Which makes Chris van der Walt’s prediction that:

an enormous earthquake is going to hit the Rand (Greater Johannesburg area) very soon…

somewhat bizarre. Even more so when you hear the details of this enormous earthquake:

The earth opened up like a massive chasm with buildings toppling over. It stretched from the east and south of Johannesburg and came together in the city centre. From there it continued to the West Rand.

Yikes. And who told Chris that all this was going to happen?
Well, that would be the Holy Spirit. Yep – a voice from upstairs.

But look, it’s not all bad news. Chris points out that you might get away in time (but terms and conditions apply):

Again I say what the Lord said: “An enormous earthquake is going to hit the Rand (greater Johannesburg area) soon and it is unavoidable. It is going to be disastrous. I will protect My children who listen and take them away in time.” 

Which to me seem to be a bit of a threat to sign up to christianity or die a horrible death in Johannesburg in late 2005.
Chris continues:

In me there is no doubt about the genuineness of this word of God and it will also be proved the day when the earthquake occurs.

Which, of course it never did: casting some doubt on the “genuineness” of the big man upstairs.

All in all, I feel hugely let down by this god thing again. Just like when he topped those 5 kids last February. Instead of saving people in Haiti, where a real earthquake really happened and killed about a quarter of a million people, he’s wasting everyone’s time by talking to Chris in Gauteng and making a mountain out of a minedump.

Chris says:

God does not say these things as a merciless, cruel God. On the contrary, He gives this word to warn people unto repentance, irrelevant of their culture or religion. 

I don’t see it that way. I see a god who is going to kill many thousands of people by a non-existent earthquake tearing open a massive chasm through the city, complete with toppling buildings. And the only people who are going to be saved are, conveniently, those in his religion.

Which all sounds pretty merciless and cruel to me.

Call off the World Cup!

…and evacuate the country!

Because, after much seismic activity around the globe this year, it seems that an expert has predicted the country is almost certain to be hit by a major natural disaster. 

And it could strike during this summer’s footie tournament!!!!!!

Yes, expert Dr Chris Hartnady thinks SA is about to be hit by an earthquake. And he has singled out Durban and Cape Town as the areas most likely to be hit.

As the Daily Star points out

That’s bad news for England’s stars, who are set to face Algeria in Cape Town June 18.

 And the 3 million people that live here as well, right? Right?

Dr Hartnady believes the tectonic plates of the Earth’s crust are active on a fault line that could pose a major threat to South Africa.
He said: “A major earthquake disaster in the region is inevitable because wide areas of southern Africa are affected by the slow, southward spread of the East African rift system.
It is not a question of if, but when. The consequences would be so expensive in terms of mortality and economic cost that the risk of being ill-prepared is unacceptably high.”

Personally, I think Dr Hartnady is talking out of the African rift system between his butt cheeks, but it is obviously a concern: an earthquake would cause untold damage to beautiful Cape Town.

Still, on the up side, it might tidy Durban up a bit.

Quake it up baby now

Apologies if you have just experienced that minor tsunami off the Atlantic Seaboard. I was just doing some sit-ups and I sneezed. I do hope Camps Bay and its infamous residents are all ok.

Of course, this happens to the best of us. Take Deepak Chopra who was meditating on Shiva mantra and accidentally caused a 7.2 magnitude earthquake on Sunday afternoon. Seriously:

Had a powerful meditation just now – caused an earthquake in Southern California. 

As Dan Evon writes, saying sorry is the least Chopra could do:

The earthquake Sunday destroyed homes, schools, and left thousands of people without electricity. If Chopra is responsible for the earthquake, he owes the world a little more than an apology.

As I mentioned above, Chopra is not the only one bearing this awesome responsibility: just this evening, I wasn’t meditating and absolutely nothing happened.

Phew.