Re: [MLUG - DISCUSSION] looks like they finally have a shoot-to-kill order in N.O.

[Jonathan King <EMAIL:PROTECTED>]

On 9/1/05, Vern Green <EMAIL:PROTECTED> wrote:
> >
> It is a major fault, and a very active fault, just not as powerful as
> the west coast ones. 

It is a very weird fault.  It marks the boundary of what *could* have
been a major rift in the North American plate that happened way back
in the *Paleozoic* hundreds of years ago.  That rift failed, and the
continental plate is still in one piece.  But locally, something odd
is happening where we see movement very near the fault in the fault
zone, but not outside the fault zone.  This was just published, and it
is still very surprising.

> It is said that a magnitude 4 earthquake in St. Louis would cause
> millions perhaps billions in damage. A 4 is nothing in California
> anymore even though we do still have building damage if a building is
> on the epicenter.

M4 events *in* St. Louis would cause some damage, but you'd need a
bigger event than that to do billions in damage.  Boston, another
surprisingly earthquake prone area, gets M4 events every several
years, and although our code is no better than around here, it doesn't
cause billions in damage.  There are some unlucky liquour stores that
find out their shelves stink, but...
 
> Apparently in the 1800s there were some quakes that reached the
> magnitude of 8.

Best work I've seen suggests that the *shaking intensity* in the area
is what you would see if the quake had been on the west coast and had
been an M8 event.  But the energy radiated isn't nearly that much.

> If those happened in St. Louis today, the death toll
> and the damage would dwarf what they see in New Orleans right now.

I don't think the fault gets much closer to St. Louis than New Madrid.
 A replay of the 1811/1812 events would cuase a lot of damage, but I
don't think you could say "would dwarf".  Apparently thousands of
people are dead in N. O., and 80%+ of the city is completely flooded. 
That might not be a theoretical worst case for the continental US,
but, man, it must be close.  Evidently one of the worst worst cases
for natural disasters is a major earthquake in the vicinity of New
York City.  There is evidence that such events are very rare, but an
M6+ event near Manhattan pretty much ends that city as we know it. 
The "good" news is that you could wait thousands of years to see one.

> The Northridge quake out here in California was between a 6 and a 7, the
> Frisco quaker was nearly a 7. The last quake in turkey that claimed
> 17,000 lives was a 7.2.

And this is why you have to be careful.  The magnitude scale that is
calibrated to energy readiated is logarithmic.  The Northridge quake
was devastating, but it was "only" Mw=6.7.  That Turkish quake would
have had a moment magnitude about six times larger.  The quake in
Indonesia last December had an Mw of 9.3, which makes it within
shouting distance of the largest quake we thing to be possible on the
planet (which apparently are the very large Chile events and/or the
largest possible event in the Aleutian trench).
 
> So if an 8 ever hit in  St. Louis, I would predict little to be left
> standing in the St. Louis area and thousands would be dead. It is not
> a question of if it happens really, only a question of when.

No, it really is "if".  Mw=8 quakes *in* St. Louis would be a complete
surprise.  Mw=7.5 in New Madrid would not be, but the distance from
the epicenter would help a lot.  Destruction would be widespread and
lots of people would die, but it wouldn't necessarily end civilization
there as we know it.
 
jking

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