Tsunami warning: Auckland facing multiple menace

Apr 7, 2013 | Posted by: roboblogger | Full story: The New Zealand Herald

As one of the world's most tsunami-threatened countries, New Zealand faces the triple menace of distant-source tsunami, regional tsunami and local-source tsunami.

Comments
1 - 6 of 6 Comments Last updated May 26, 2013

“Geologist [I'm Climate Change]”

Since: Mar 07

Nuneaton

#1 Apr 8, 2013
This one is interesting but have run out of time to comment on it in this session,(will be back later).

Have a nice day: Ag

“Educating Utus”

Since: Aug 10

Wanganui, New Zealand

#2 Apr 8, 2013
Is it possible to channel the tsunamis into South Auckland?

“Educating Utus”

Since: Aug 10

Wanganui, New Zealand

#3 Apr 8, 2013
And Flaxmere?

“Geologist [I'm Climate Change]”

Since: Mar 07

Nuneaton

#4 Apr 10, 2013
Nice article.

Finally got back to it.

Interesting bit to watch on Tonga-Kermadec-NZ arc is the seismic gap bit S. of the Kermadec islands and N. of the "Brothers" submarine volcano. This one is in the latest stage of recompression with all the volcanoes in this unnamed segment apparently dormant for a long (~50 years) timespan so far, and the seismicity both in the forearc & also descending plate, lower than the actively recompressing Kermadec segment to N. and the NZ segment to S.

The date of the Kermadec arc tsunami is currently unknown but is likely several centuries ago, it has a faster recompression rate than NZ.
The date of the NZ segment tsunami is well known at around 1460AD giving the Hao Whenua legendary Maori earthquake and tsunami. The event appears in NZ to have relaxed the crust @ least to the backarc basin main central rift and appears to have had an ESE or E. vector which means that magma arriving from further N. in the backarc rift arrives @ the arc graben (such as happened @ Tarawera when gas rich basalt erupted through the Tarawera domes without hitting the Okataina magma chamber sited in the arc proper. A further bit of great interest is that the forearc segment @ christchurch has had a lot of the NZ forearc dumped on it when the crust @ Hikurangi relaxed, and this is now compressing (created a bit of a mess last year).

Another bit of great interest for NZ is the southern NZ range which was responsible for a giant tsunami in the early Holocene. This range is in the latest stage of recompression and the transform fault in range core is becoming increasingly tight. Magma imported in deep crustal fractures from this range appears to get squeezed out along the transform fault core in pods to emerge at M. Egmont in a backarc basin @ Taranaki, as a result of the North island NZ segment relaxing rather faster creating a decompressed bit NE of the range. Next crustal relaxation time is a good guess and is likely in the last 1/3 to 1/5 add on time of the currently elapsed ~8000 year timespan.

The other fun & games bit for NZ is the Hunter ridge backarc basin forming the SE. margin of the Fiji plateau. This one is a huge backarc basin which is bordered by the megathrust+backthrust zygomorphs (double arcs) of the New Hebrides, Vanuatu, and santa Cruz {these fun for OZ & currently seismically active & recompressing}. The REAL hunter ridge starts @ Hunter island and extends in a curl through Ceva-I-Ra atoll and ends @ SE. Fiji, which is mostly a rifted backarc sector of the N. Tonga arc.
The Hunter ridge is important as a result of its backarc volcanoes (in particular Tavenui) which drained magma from the Hunter ridge backarc basin rift fracture set @ erupted sporadically throughout prehistory via 14C dating. This backarc basin is in the latest stage of recompression, is VERY seismically quiet, and all of its volcanoes except for Matthew & Hunter in the Junction box with the New Hebrides are dormant (or not even characterised as recent yet).
The last crustal relaxation event for the bulk of the Hunter ridge backarc basin appears to have been late Pleistocene (~10000-12000 Bp), and has a convergence rate of ~6.5 to 7cm/yr NNE via N. movement of the australasian plate. The runout when this backarc basin magathrust goes "pop" will likely be in the 500m bracket with slow plate crawl (about 400m) lasting over a day and a first break tsunami height of around 85m (ouch) with a long wavetrain of diminishing height with time as the fast bounce evolves to slow crawl.
Backarc basins ar problematic as their runout distance is not set (they can be as short as an arc (~15m) or run out to the backarc backfault with runout for the Hunter ridge in that case being close to 1Km (may last a week). The last event (late pleistocene) appears to have been particularly large.

Have a nice day: Ag

“Geologist [I'm Climate Change]”

Since: Mar 07

Nuneaton

#5 Apr 10, 2013
Torqueing Heads wrote:
Is it possible to channel the tsunamis into South Auckland?
See article for main sources of the "Bloody great big" type.

Also note that the events in the article (1868 peru & N. Chile) and 1960 (Central Chile) as in 2010 were all short runout arc events with a tsunami height approximating the forearc runout distance.

The Patagonia arc is a backarc basin (~3.5cm convergence rate).
The Altiplano arc is also a backarc basin. the N. part of which has recompressed & relaxed, and the S. part is still recompressing @ is in the latest stage with all the volcanoes quiet.
The La Rioja range between them is a range with a VERY long recurrence interval time and appears to have relaxed in the early Holocene.
The Peru range (NW. of the volcanoes) is another classical range and appears to be in a later stage of recompression.
Ecuador & Colombia are arcs with a backarc cordillera range with huge runouts, giant tsunami and a long recompression interval time (it fortunately points to Japan).
Central America points to NZ and last gave a 10m+ teletsunami in NZ ~950AD immediately after the original Mayan apocalypse of ~820AD or thereabouts and its quake destroyed surviving occupied buildings in the mountain city strongholds (never rebuilt).
Mexico also points toward NZ. The main mexican volcanic zone arc (a backarc basin) appears to have a BC date for its last main tsunami @ or before Olmec occupation times.

All of those may also affect Auckland in a big way if runouts are above those of a classical arc (10-15m @ source).

One other main teletsunami source for NZ was an event in ~550AD which was tracked down to 535AD when 2 small asteroids landed in the S.part of the gulf of Carpentaria (OZ) and the seismic shock broke the megathrusts in the lesser Sunda, Banda, Sanghie, Halmahera, S.Philippines, Irian Jaya, Papua, New Britain and Bougainville arcs. The resulting teletsunami from the latter 2 arcs reached 10m+ at NZ and all the affected arcs & ranges ran out to the backfault (along with a dark ages dust veil effect).
That last one is difficult to repeat, but at least the asteroids will be seen coming (the local tsunami created by the small craters was rather small).

That should do the job.

Have a nice day: Ag
bellpawt

New Zealand

#6 May 26, 2013
re: Tsunami going into South Auckland; Yes ! Down the Tamaki estuary towards Mt Wellington and Otahuhu...Theres another arm of the Tamaki estuary which heads towards the new subdivisions of Dannemora et al If the tsunami comes in from the north the tsunami can approach through the Manukau Harbour also ... A move on Papakura in south can then be made by the tsunami rolling over Manurewa from the west and the north-east .. Takanini, Ardmore and Drury will also be inundated . New Lynn will go, too Devonport and many other Northern suburbs .. I can see no reason why, with some element of surprise the tsunami can't claim 350,000 lives in Auckland, can you ?

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