Woooaaahh earthquake 2016-11-14

Forums › Off topic › Woooaaahh earthquake 2016-11-14

1 | ... | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32

2476 posts

Uber Geek

Lifetime subscriber

#1673969 19-Nov-2016 09:18

frednz:

I don't think all that many Lower Hutt residents have studied the tsunami evacuation zones map and some panicked unnecessarily and evacuated from "safe" properties.

There is so much fear and confusion in Lower Hutt about this. Even some people on the hills left for higher hills. The are so many people ignorant of the difference between a tsunami on an open coastline and in an enclosed bay.

If a tsunami enters Wellington harbour through the heads or even through Rongotai, it will dissipate quite rapidly because the width of the harbour is much wider than the width of the entrance(s). In fact, the wave will spread around the entire perimeter of the harbour. The harbour perimeter from the Wellington CBD to Eastbourne is over 22km. The entrance through the heads is less than 2km wide. That means the wave energy at landfall be 90% dissipated by at least 90%, i.e. at any point around the harbour the wave energy will average less than 10% of the any point in the original wave entering the harbour. That''s mainly why the disastrous 1906 San Francisco earthquake only produced a 10cm wave in that very large harbour.

The worst case is if resonance occurs, where the frequency of the wave reflections matches that of the harbour then the waves will be amplified just like water sloshing around in a bathtub. That's why so many pools in Hamilton lost a lot of water because resonance amplified the wave height.

Tsunami in Bays

[Edit to correct spelling - I don't know why I don't notice typing mistakes until after I post]

tdgeek

29746 posts

Uber Geek

Trusted

Lifetime subscriber

#1673970 19-Nov-2016 09:22

Could current towers (cellular, radio, TV) be upgraded to send non internet (as thats down ) AMFM radio via a local internet feed?

This way we can have normal radio, internet radio if the internet is up, and local internet radio to smartphones if the wider internet is cut, including cut backhaul to cell towers? Just another option to widen the ease and coverage of accessing radio when things go belly up

tdgeek

29746 posts

Uber Geek

Trusted

Lifetime subscriber

#1673971 19-Nov-2016 09:26

Hammerer:

frednz:

I don't think all that many Lower Hutt residents have studied the tsunami evacuation zones map and some panicked unnecessarily and evacuated from "safe" properties.

There is so much fear and confusion in Lower Hutt about this. Even some people on the hills left for higher hills. The are so many people ignorant of the difference between a tsunami on an open coastline and in an enclosed bay.

If a tsunami enters Wellington harbour through the heads or even through Rongotai, it will dissipate quite rapidly because the width of the harbour is much wider than the width of the entrance(s). In fact, the wave will spread around the entire perimeter of the harbour. The harbour perimeter from the Wellington CBD to Eastbourne is over 22km. The entrance through the heads is less than 2km wide. That means the wave energy at landfall be 90% dissipated by at least 90%, i.e. at any point around the harbour the wave energy will average less than 10% of the any point in the original wave entering the harbour. That''s mainly why the disastrous 1906 San Francisco earthquake only produced a 10cm wave in that very large harbour.

The worst case is if resonance occurs, where the frequency of the wave reflections matches that of the harbour then the waves will be amplified just like water sloshing around in a bathtub. That's why so many pools in Hamilton lost a lot of water because resonance amplified the wave height.

Tsunami in Bays

[Edit to correct spelling - I don't know why I don't notice typing mistakes until after I post]

Another tsunami in a bay. What we got in ChCh was small, but the bay factor caused this

http://www.stuff.co.nz/national/nz-earthquake/86443298/little-pigeon-bay-cottage-smashed-by-tsunami-waves

Hammerer

2476 posts

Uber Geek

Lifetime subscriber

#1673974 19-Nov-2016 09:32

That is entirely expected in Little Pigeon Bay.

Little Pigeon Bay has no heads and actually narrows down its length so it is not comparable with Wellington Harbour. In this case there is no mouth or widening of the bay to force the wave to spread out. So it works more like open coastline but the narrowing bay with a rising floor also forces the water higher.

[Edited to correct name and format]

tdgeek

29746 posts

Uber Geek

Trusted

Lifetime subscriber

#1673977 19-Nov-2016 09:37

Hammerer:

That is entirely expect in Pigeon Bay. Pigeon bay has no heads and actually narrows down its length so it is not comparable with Wellington Harbour. In this case there is no mouth or widening of the bay to force the wave to spread out. So it works more like open coastline but the narrowing bay with a rising floor also forces the water higher.

Yes, I wasn't comparing to your post directly, just to show what can happen which is opposite to Wellington, but would apply to sales inlets in the Wellington, Sounds, areas. I should have clarified.

geoffwnz

1587 posts

Uber Geek

ID Verified

#1673987 19-Nov-2016 10:09

I think one of the main issues with most people not understanding tsunami is that the only point of reference for waves that they have are surf waves. A completely different thing.

Tsunami tends to be a mass of displaced water that has to go somewhere. Things like the Indonesia quake and tsunami, wasn't it something like several km of seabed lifted 100m? That's a considerable mass of displaced water.

MotorDrive Rallying

Geektastic

17943 posts

Uber Geek

Trusted

Lifetime subscriber

#1674267 19-Nov-2016 18:11

Looks like the government is indeed listening to our conversations...!

Sharesies

Trade NZ and US shares and funds with Sharesies (affiliate link).

tdgeek

29746 posts

Uber Geek

Trusted

Lifetime subscriber

#1674298 19-Nov-2016 19:42

geoffwnz:

I think one of the main issues with most people not understanding tsunami is that the only point of reference for waves that they have are surf waves. A completely different thing.

Tsunami tends to be a mass of displaced water that has to go somewhere. Things like the Indonesia quake and tsunami, wasn't it something like several km of seabed lifted 100m? That's a considerable mass of displaced water.

Wasn't a 100m. More like 10m, which in itself is huge

tdgeek

29746 posts

Uber Geek

Trusted

Lifetime subscriber

#1674299 19-Nov-2016 19:44

Geektastic:

Looks like the government is indeed listening to our conversations...!

Very good, but what about those with no cellphone, its flat or its down?

enozkeeg

84 posts

Master Geek

#1674300 19-Nov-2016 19:45

Geektastic:

Looks like the government is indeed listening to our conversations...!

NZHerald

It doesn't matter if your cellphone is on or not...

I didn't know our KGB had the ability to turn on my phone...

geoffwnz

1587 posts

Uber Geek

ID Verified

#1674301 19-Nov-2016 19:46

tdgeek:

geoffwnz:

I think one of the main issues with most people not understanding tsunami is that the only point of reference for waves that they have are surf waves. A completely different thing.

Tsunami tends to be a mass of displaced water that has to go somewhere. Things like the Indonesia quake and tsunami, wasn't it something like several km of seabed lifted 100m? That's a considerable mass of displaced water.

Wasn't a 100m. More like 10m, which in itself is huge

Ah yep. But yes, over the area it moved, a huge volume/mass of water that decides it needs to be elsewhere urgently.

MotorDrive Rallying

tdgeek

29746 posts

Uber Geek

Trusted

Lifetime subscriber

#1674309 19-Nov-2016 20:19

geoffwnz:

tdgeek:

geoffwnz:

I think one of the main issues with most people not understanding tsunami is that the only point of reference for waves that they have are surf waves. A completely different thing.

Tsunami tends to be a mass of displaced water that has to go somewhere. Things like the Indonesia quake and tsunami, wasn't it something like several km of seabed lifted 100m? That's a considerable mass of displaced water.

Wasn't a 100m. More like 10m, which in itself is huge

Ah yep. But yes, over the area it moved, a huge volume/mass of water that decides it needs to be elsewhere urgently.

I've watched that tsunami over and over and it still astounds me.

Geektastic

17943 posts

Uber Geek

Trusted

Lifetime subscriber

#1674313 19-Nov-2016 20:46

tdgeek:
Geektastic:

Looks like the government is indeed listening to our conversations...!

Very good, but what about those with no cellphone, its flat or its down?

What happens if your radio is flat or the tower is down?
What happens if your carrier pigeon is eaten?

It's not either or its another channel.

frednz

1467 posts

Uber Geek
Inactive user

#1674316 19-Nov-2016 20:58

Hammerer:

frednz:

I don't think all that many Lower Hutt residents have studied the tsunami evacuation zones map and some panicked unnecessarily and evacuated from "safe" properties.

There is so much fear and confusion in Lower Hutt about this. Even some people on the hills left for higher hills. The are so many people ignorant of the difference between a tsunami on an open coastline and in an enclosed bay.

If a tsunami enters Wellington harbour through the heads or even through Rongotai, it will dissipate quite rapidly because the width of the harbour is much wider than the width of the entrance(s). In fact, the wave will spread around the entire perimeter of the harbour. The harbour perimeter from the Wellington CBD to Eastbourne is over 22km. The entrance through the heads is less than 2km wide. That means the wave energy at landfall be 90% dissipated by at least 90%, i.e. at any point around the harbour the wave energy will average less than 10% of the any point in the original wave entering the harbour. That''s mainly why the disastrous 1906 San Francisco earthquake only produced a 10cm wave in that very large harbour.

The worst case is if resonance occurs, where the frequency of the wave reflections matches that of the harbour then the waves will be amplified just like water sloshing around in a bathtub. That's why so many pools in Hamilton lost a lot of water because resonance amplified the wave height.

Tsunami in Bays

[Edit to correct spelling - I don't know why I don't notice typing mistakes until after I post]

Thanks very much for this information. Do you think that, based on your observations (which I think make a lot of sense), the tsunami evacuation zones shown on the map for Lower Hutt are a "bit" conservative? I suppose you can't blame people for evacuating if they were within the tsunami zones shown on the map. And I suppose you can't blame people for sounding the sirens if they were taking the tsunami evacuation map seriously. After all, people are just trying to do their best.

Even though we were in a house several kilometres north of the zones on the map, some of our neighbours decided to evacuate when the sirens were going at about 3am. We decided to stay put because I just couldn't imagine a massive wall of water being able to travel 10km north up the valley from Wellington Harbour! But I suspect that many of those who evacuated had never seen a tsunami evacuation map and evacuated solely because a very loud siren wailed on nearby for 40 minutes or so. And I don't suppose you can blame them for that!

It's interesting to ponder what would have happened if a tsunami had been able to travel even 3km north up the valley. Wouldn't this mean that large areas of coastal Wellington would by then have been completely under water?

An explanation of how the tsunami zones are expected to be interpreted can be seen here.

Wazza69

69 posts

Master Geek

ID Verified

#1674331 19-Nov-2016 21:47

How have people approached putting together their emegency kit? Have you gone for one of the pre-mad kits or gone around and bought it all from different shops? Any recommendations appreciated. We have just returned to Wellington from the UK after 15 years to a 7.6 quake!

Thanks

1 | ... | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32