This jaw dropping quote from an unspecified GNS seismologist, is in an article in the New Zealand Herald by John Roughan. “Tell Christchurch whole story”
As a now ancient geologist I am somewhat gobsmacked that in over a hundred years of logging earthquakes up and down the Alpine Fault – there apparently has not been a sequence to equal the last nine months around Christchurch.
We really are in uncharted waters.
Warwick, your post, www.warwickhughes.com/blog/?p=850#comments, & comments on it tell an interesting story which should be followed up. Is there an update of the animation? Could this lead to an awaking of the Akaroa volcano? Could I suggest a seismic category? The rim of fire around the Australian plate (New Zealand, Vanuatu, PNG & Indonesia) must have some affect on Australia even if it is only humanitarian and political, although a really big volcanic eruption in Indonesia will affect our weather.
and for those who want to be educated on climate change and don’t want to wait for the $13 million ad campaign www.abc.net.au/unleashed/2761976.html
Warwick I’ll understand if you don’t publish this comment cos it is o/t
Warwick, further to my comment above this is interesting www.irishweatheronline.com/news/earthquakesvolcanos/2011-on-target-for-highest-number-of-recorded-earthquakes/20688.html (h/t to chiefio.wordpress.com/tips/ at 19 June 2011 at 10:32 pm Scarlet Pumpernickel)EM Smith (Chiefio) has regular posts in the category Earth Sciences which shows earthquakes around the world and volcanic action eg chiefio.wordpress.com/2011/06/13/volcano-action-warming-up/ (look at the Australia/New Zealand map about half way down the post- 38 earthquakes on the map)
keep strong
warwick , planetary angular separation ( PAS ) is the key to atmosiesmic activity around the solar system , PAS have possibly thousands of combinations as they form up in their
orbits around the sun , however , cycles can be identified from past repetive events ,
we see a ( 5 year 6 momth 2 week )( 11 year 1 month ) ( 22 year 2 month ) ( 49y 10m 3w )
& so forth brought about as Mercury’s 14 passes of Venus brings them to within 1.5 degs of starting point or azimuth .
Other planetary combinations activate cycles of their own & I guess you already know of them , the NZ Christchurch events coincided with a 2.3 year series brought on as Mars
aproaches Jupiter , what made this event stand out ?, both Jupiter & Mars were on their
perihelion aproach simultainiously, the next time they meet near those azimuths will be
on the 25th July 2022 . Ken .
Warrick,
The Alpine Fault is “active” but quiet at the same time. Most of the subsidiary faults in the system are also active but quiet. In NZ there is generally no middle ground on this except immediately after a substantial shake (as in Christchurch).
The elastic strain accumulates gradually with little or no slippage, then it lets go suddenly as a brittle failure when the stress field reaches a critical threshold. After the quake the stressfield goes through a readjustment process that contributes to lots of smaller quakes. Then as that process eases off the elastic strain begins to build again.
The return period for big eathquakes on the Alpine Fault is generally from about 250 to 400 years. We can tell this by dating landslides (14C), by dating periods of widespread fluvial sedimentation (sediment from landslides), and by dendrochronology.
The dendro approach is a particularly good one. You can look for areas where the canopy trees all seem to be the same age. Thats because they germinated at the same time on a landslide scar. Just core the trees and count the rings. So when you find dozens of the single-year tree stands all having the same age (within a year or two) then you are onto it. Then you find separate clusters every few hundred years. And thses have the same timing as sudden fluivial events the timing seems to be confirmed. Then you can carbon date the forests that were buried under landslide debris and get the same answers again. Then you can dig out the fault trace and date the organic materials trapped during each big earthquake and get the same answers.
Another way to date big earthqukes by dendrochronolgy is too look at trees that survived and earthquake but were damaged by it, e.g. branches busted off, root damage, change to the water table etc. What you do is look for evidence of disturbance, typically a period of several years of very slow growth that starts abruptly and diminishes gradually.
On the basis of the typical return period we are due for a big one on the Alpine Fault. The probability is of the order of around 1% to 2% per year at present, and growing gradually. We can expect the Apline Fault to give a surface movement of around 7 to 10 metres with a combination of uplift and translation. The magnitude is likely to be around 7.8 to 8.5 and the rupture length could be of the order of 200 km.