Thread: tsunami speed please explain

Hey Tonyz, I think you will find that the was wave recorded on the east coast early this morning

The actual shape (height and width) of tidal wave that strikes a coast depends on a bunch of factors one being the shape of the seafloor in between the initial earthquake centre. A tidal wave might only be 1m high but if its backed up by few km in width that's a lot of water the surge can quickly build up so that it penetrates a long way inland. That's why you should pay heed to tsunami warning and even if the wave looks small from the beach it still can pack a punch and an early "heading for the hills" is a good idea.

2004 earthquake, tidal wave hit east coast Sri Lanka and travelled 3 km inland, got photos to prove it.
The locals rushed to claim new land for themselves when the sea initially receded then the wave came, thousands drowned and hundreds were killed inland.
The east coast is very flat.

It also depends on what state the local tides were in. A 2m tidal wave at low tide would generally have considerably less impact than a 1m wave at the high tide peak. (Assuming more than 1m difference between the normal local max/min.)

I've experienced an offshore earthquake and tsunami in Bougainville, PNG, and in that there were some strange phenomena. On the east coast of the island, a tsunami of approx 1.5 metres hit, mainly passing under the native material houses (they've experienced them before) but taking out boats etc.nthat were underneath them. It did very little damage and there was no loss of life, mainly because it hit at about 2 a.m. However, on one of the rivers it came up like a tidal bore, then came back down again the same way. There were other phenomena associated with a large tailings bed.
On the west coast, the height was about 0.3m. there was no reported damage from the tsunami, but a 30' boat experienced a knock-down.
The shape of the sea bed and the landforms in particular areas can cause strange things to happen, including amplification. Heed the warnings.

It’s not only sea waves that are created, the actual blast was felt around the world. On a weather forum that I occasionally frequent hobbyists from US, UK, NZ, Europe and here were reporting aberrations in air pressure. I checked my graph and sure enough it was there too.

A06AF1ED-41D2-4B33-AB67-41DD69D90241.jpeg

Tsunami waves are something special. The maths behind them were a topic upon themselves that we studied in the "Geophysical fluid dynamics" module of my maths degree.

In deep ocean waters they can move at around 500-700 mph, though this shows down considerably as it gets shallower.

Originally Posted by apple8

It’s not only sea waves that are created, the actual blast was felt around the world. On a weather forum that I occasionally frequent hobbyists from US, UK, NZ, Europe and here were reporting aberrations in air pressure. I checked my graph and sure enough it was there too.

A06AF1ED-41D2-4B33-AB67-41DD69D90241.jpeg

The shockwave was clearly visible from space

I would suggest the major difference this time, was because it was a volcano erupting, not an earthquake; hence the whip cracking sound heard by many people.

Mick.

the more you read about this one, its starting to place all others way behind in pure power and force.

Having been born n bread in NZ I am totally in awe of earthquakes but this wernt no earthguake, with was an explosion the likes we havent seen before....
This old globe we sit upon is becoming very restless.

Originally Posted by Tonyz

the more you read about this one, its starting to place all others way behind in pure power and force.

Having been born n bread in NZ I am totally in awe of earthquakes but this wernt no earthguake, with was an explosion the likes we havent seen before....
This old globe we sit upon is becoming very restless.

Oh we have seen many more powerful that this one. The Krakatoa eruption sonic boom echoed right around the world 3 times. The way the atmosphere focusses the pressure waves if the wave goes far enough it to refocused back into a diabolical point on the other side of the globe. With Krakatoa the opposite side is somewhere off the coast of Peru. If there had been a ship/boat in the vicinity of that point it would have been smashed and sunk.

I'm looking FWD to the coming slightly cooler winter that we might get from it.

FWIW we have experienced earthquakes in California (SF 1989) and we were in Japan when the Kobe Earthquake hit in 1995. We were actually supposed to be in Kobe on the morning of the big one - the hotel we had booked was pancaked. We were still in Tokyo but we still felt it.

22Feb 2011 my dear dad parked in Oxford Tce Christchurch to see his accountant, walked in the front door, remembered some paperwork on front seat of car, crosses back over road opens passenger door and well all hell broke loose.
The CTV building fell apart in front of his eyes, missed his appointment and never saw his accountant again.

Where we lived in PNG when the earthquake (guria) occurred, the houses were specifically designed to be earthquake resistant, or were of native materials which were inherently resistant. These designs were effective, with building damage confined to minor damage to commercial buildings and one house that was damaged when a large boulder rolled down a hill. Lots of things were damaged by falling off shelves, etc.
As it occurred in the early hours of the morning, we did find out what many people wore (or didn't) to bed.

In Southern California (but also in lots of places in the USA) domestic buildings including multi storey apartment buildings are made of timber. The cladding is often coarse chipboard covered with chicken wire and stuccoed. The building we lived in most of time we were there was band new but shabbily made, 3 storey with ground level car parking underneath the building where you could see the 8 x 8" wooden pillars that supported the building. During earthquakes, of which there were many small ones (at least once a month) the whole building would sway back and forth no problems. I don't recall anyone leaving buildings when this happened - there was nowhere to go anyway as the dozens of buildings in our apparent complex were crammed in together with just access roads between them. Our nearest open space (a tennis court) was about 100 m away.

We had to keep an earthquake emergency backpack stocked and handy. We also had to have "The Talk" with our 5 year old who just started school that if there was a big earthquake it could take some time to come and get him. We were also eventually warned not to locate beds near windows as they could fall inwards during quakes. We only heard about this after a few months we were there and I kept meaning to move our bed and a few days later there was a bit of a shake about 2am and we slept right through it. No window failure but I moved it next day.

On morning there was a bang and the building shook, another earthquake we thought ho-hum but no it turns out to be a car that had slammed into the building. The driver was our idiot neighbour who was always entering the under ground garage at a ridiculous speed but that morning it had been raining and he lost control trying to make the curved entry into the carpark and had ploughed into one of the pillars.