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How does “not a matter of if, but when” = June-July 2010

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Jane of the Jungle
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« on: April 24, 2010, 07:22:13 AM »

It would be interesting to know if Dr Chris Hartnady definitely predicted
Earthquakes during this specific time, or was it the Daily Star and others who came to this conclusion Roll Eyes
London, Apr.11 ( ANI ). A top South African earthquake expert predicted recently that South Africa is ‘almost certain to be hit by a major earthquake. It’s not a matter of if, but when’. The Daily Express quoted Dr Chris Hartnady of the Umvoto Africa CSIR Satellite centre as saying that the coastal harbour cities of Durban and Cape Town are the areas most likely to be hit by an earthquake because of the rapid spread of the East African Rift fault-lines.
Despite considerable research efforts by seismologists, scientifically reproducible predictions cannot yet be made to a specific day or month.However, for well-understood faults seismic hazard assessment maps can estimate the probability that an earthquake of a given size will affect a given location over a certain number of years.

Defollyant Iconoclast
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In solidarity with rwenzori: Κοπρος φανεται

« Reply #1 on: April 24, 2010, 10:19:43 AM »

I have it on good authority that Dr Chris Hartnady’s prognostications are not taken very seriously by South African geologists and geophysicist because he’s been predicting this sort of disaster for many years now without any actual hits.  Seismologists in any case don’t generally give such tight timeframes for expected events because there are so many influencing factors.  At most, a seismologist would say something like, “Based on historical observations and a knowledge of the geological forces, such-and-such area can expect at least one magnitude 7 or greater event in the next 100 years.”

Moreover, his argument concerning the African Rift Valley doesn’t stand up to scrutiny.  Malawi and northern Moçambique are hugely more at risk of experiencing serious earthquakes than SA because that’s where the geological action is happening.  Essentially, Africa is in the process of being ripped into two pieces along the Rift Valley from north to south by tectonic forces ― a bit like tearing a sheet of paper ― and the tearing point is presently far to the north of SA.  It will be a few million years before it migrates far enough south to cause problems in Durban.  You can read more about it here and here.

« Last Edit: April 24, 2010, 10:34:16 AM by Mefiante, Reason: More is less... » Logged
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« Reply #2 on: May 04, 2010, 15:36:24 PM »

The seams where tectonic plates meet can be of two kinds:

Divergent boundaries are seams where tectonic plates are pulling away from each other.   These usually occur on the seabed, but can also occur on continents, as is the case with the African Rift Valley.

Subduction zones are seams where tectonic plates "collide".   The one plate is then forced below the other.   An example of this is the Worcester fault.   Such a "collision" would usually happen at about the rate that a human finger nail grows.

Whereas both types of tectonic boundary can be unstable and prone to earthquakes, they are in a sense opposites in that the one respresents an area of tension and the other an area of compression in the earth's crust.   The 1969 earthquakes in the Western Cape were caused by such compression.

Quote from:  Geoscience
A geological fault, the Worcester fault, is the most significant feature defining the geology of the Breede River. Across this fault a total movement of up to 6km has occurred and the fault system is still active (as the 6.3 Richter Tulbagh earthquake of 1969 testifies).


Had Dr. Hartnady forecast an earthquake near Cape Town due to the Worcester fault, it would make some sense, but I find the prediction of such an earthquake in relation to the African Rift Valley rather incredible.
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« Reply #3 on: May 04, 2010, 15:51:06 PM »

south africa, and pretty much the rest of africa;s, fault lines are timid at best.  we havent had geothermal activity here in yonks.  and what earthquakes we get, is a minor rumble.
i think, the reason why haiti and chille got the boot end of things, is cause they are situation in an area where there are oodles of geological happenings.  with the one plate turning this way, another the other way, this one subducting, that doing this.  its a pretty busy place.
and, if i may offer my meagre opinion, (since i know sweet blue buggerall how this works), i can only assume, that if pressure builds one spot, and its released, it creates tension elsewhere. 
eg:  the haiti earthquake releases tension, which puts extra pressure on the two plates that meet on the chilli coastline.  eventually the pressure is released there.  i think its ciclical.  and ongoing.
i have no idea if the happenings of those earthquakes could have caused,  by effect, the volcano, and the turkey quakes.  i think nobody can truly guess the scope of how these things stick together, and how one movement of the crust, impacts on the crust accross the world, and on the mantle, which is what the entire crust floats on.  i think if we did know, we might just have to change our underwear.
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