Stop press: Paul R. Whitaker sent me this e-mail to
comment on the text above:
How is New York prone to rare earthquakes. Getting the facts straight.
This is for you to enjoy. I have spent a lot of time on this. No, not to
criticize, but to help you. Though not a Geologist or a Seismologist, I
have read and researched these areas a lot.
I find your site interesting and well put together. Should you want to
post this, feel free. But hey - give me a credit for writing this. Which
In advance, sorry about it being rather long. I had no idea it would
turn out this long.
No matter. Good to get some feedback on any inaccuracies -- just goes
to show the old truth that even, in principle, reliable sources can/will
have something wrong.
You may not know this, but Africa did NOT collide with North America. We
use to be all one continent called Pangea.
True. Although I'm no geologist ;^), I can't fathom why the
source mentioned a collision. And why I copied it...
Due to the "Blanket effect" (When too much heat gathers under very large
land masses); the continent ripped apart at what is now the Mid-Atlantic
Ridge. It is still doing so. The Atlantic is getting 2 inches wider a
year. This is why Africa(Mali area) fits into the US east coast from
Boston down to the Carolinas. Also why the soil is almost exactly the
same. Surtsey, Iceland and other islands are on the top of this. Africa
is still heading north though, pushing the Alps, the Caucusus and the
mountains through Turkey and the middle east upwards. Hence the
earthquakes that are so violent in Turkey and the ceaseless eruptions of
Etna in Italy.
Don't believe me? Check any atlas that shows ocean depths and you will
see that big crack running down the middle of the Atlantic. National
Geographic's atlas is a great reference.
Hum, I've been awake on my geography lessons all those years
Great. Does this mean I have pushed you back to square one? No. Here
are the geological forces behind potential New York quakes:
400 million years ago, the Western Hemisphere snaps away from Europe and
Africa (making a very loud noise) and forms a 10,000 mile swamp. This
swamp becomes the Atlantic Ocean. The Americas begin to slide westward
and the fishing dramatically improves in Spain.
I've got the figure of approx. 200 million years ago -- in the
Mesozoic Era -- for that?
Geologically, you cannot push something the size of North America
without "a little resistance." You have also got the Pacific Ocean on
the other side and it doesn't want to give up any of its territory. The
Pacific is huge now, it use to be twice that size.
North and South America begin getting mid-plate fractures which causes
uplift. The two best example of this are: (a) The Appalachians that
stretch from Georgia to the Gulf of St. Lawrence and (b) the uplifting
in Brazil that stretches from Paraguay east to Belo Horizonte.
Pay attention for a second, this gets complicated:
The Canadian shield is the oldest rock on the planet. The oldest part of
it is in the in the area of the Northwest Territories in Canada. Way up
near where the Mackenzie delta empties into the Beaufort sea. On a map
you can see a wierd "Bird Shaped" lake. That is called Great Slave Lake.
This rock turns out to be over 1,000,000,000 years old. (For the
Americans, that's a billion for the English - its a lot, but not a
billion. I know I am Canadian, but we call it a billion too.) Because of
the makeup of this rock, it is very solid, very heavy and very thick.
So, along comes this Mid-Atlantic ridge split. Like a teenage brat, it
thinks it's going to move the Americas west without any problem. The
Canadian Shield looks at it with a certain amount of distaste and
probably thought "yeah sure." The Hemispheres start to move.
For Human beings, patience is a virtue. For geology, it's a must.
With the resistance from the Canadian Shield and the Pacific Ocean
plate, North and South America have areas that are far more willing to
slide along than other areas.
What happens? Faults begin to open. One of the best, and earliest,
examples is the fault in eastern Ontario known as "Mazinaw Rock" or "Bon
Echo Provincial Park." This geological formation is two miles in length
of a "Vertical Thrust Fault." The east side went up 350 feet and the
West side went down 350 feet. Solid Granite rock being pushed around
like it was peanut butter. Even five advances of ice that were two miles
thick have had little erosional effect on this structure. This is only a
small part of a fault system that goes from James Bay (That wierd
looking part of Hudson Bay at the top middle of Canada), down through
eastern Ontario, into New York state (Creating the Adirondacks) then
near Albany, NY; it abruptly bends east then south down through the
Hudson Valley. Hey, now you know why the Hudson river is so darn
straight, it's following an old fault line.
That fault line comes out at the west side of Manhattan. Why there?
Because Manhattan is a SOLID chunk of Granite.
Or gneiss and schist.
That is why the subways are so shallow in New York City.
Not to mention the ease of construction (a relative term), also in
the mostly deep-bedrock southern reaches of Manhattan. Although
tunneling rock is, all in all, cheaper as a method (especially if
the rock is solid enough to not require extensive supporting), the
operating costs and vertical movement of passengers are more
favourable in a shallow-dug system. But there are long stretches
of tunnels dug into rock, for example encompassing almost 20 per cent
of the old IRT line(s), (including the second longest double-track
tunnel cut in rock in the US), also incorporating one of the widest
concrete tunnel arches in the world.
The fault got shattered during the last couple of Ice ages. Ice is
really heavy and it pushed the land on the north side way down, it is
now pushing back up. Hence, the frequent small quakes in Quebec. It too
created a fault system. Right on top of the Bon Echo fault. This fault
(another straight line for quite some time) created the St. Lawrence
river valley (another essentially straight river.) This fault continues
right under the middle of Lake Ontario (Causing Toronto to have certain
"Earthquake building codes" for buildings over 30 floors.(No, they are
not made out of snow and ice.))The fault bends southwest near Hamilton,
ON. From hear it heads under Lake Erie where it enters Ohio just west of
Cleveland. Then down through Ohio to near Memphis, TN. Other small
faults fracture out from this and these are the culprits that caused all
those 19th century quakes near Memphis, that caused a lot of people to
turn to religion suddenly.
This whole system is the one that "Can" cause earthquakes in New York,
Boston, Memphis, Cleveland, Buffalo, Washington DC, Philadelphia, etc..
However, the thing moves "Very slowly" compared to the San Andreas in
California. This means that its "frequency of events" (earthquakes)
happen hundreds of years apart. But because they are "Vertical thrust
faults" the quakes can have more of a "First shock" that can do some
real damage. Bear in mind, most of New York is built on solid granite.
Sure, it will move during the first shock of a quake. But it will move
like a chunk of concrete: Back and forth a couple of times. What causes
most of the problems during a quake is when you get crappy soils. The
quake force rolls in and the area starts moving like a waterbed or a
large thing of Jello. That is where you get real damage. The best
examples of this are: The Marina district in San Francisco and the
Mexico City quake. (Hey, let's build a city in an earthquake zone on an
old lake bed. Let us also put it in a steep sided valley near the base
of one of the nastiest volcanoes in the world. Then let us fill it
with 19 million people. Geologically, Mexico City is one of the WORST
places in the world for a city. A close second would be Tokyo.)
This could be a problem in areas of: Boston, Brooklyn, Washington DC,
Newark. However, Manhattan would likely only feel a couple of
vibrational shocks then settle down.
The question indeed is how strong the couple of vibra shocks are.
Although the island is largely solid stone (and enables much of the
buildings and structures to be founded on it) that still doesn't remove
the risk of damaging buildings and services on top of that bedrock that
transmits the waves. Not to mention places like Battery Park City...
The bedrock in Manhattan reduces much of the effect of any earthquake,
but the lack of respective building codes and the antiquity of the
below-ground services causes trouble also in the northern parts of the
island (not least with walls cracking up there due to a quake a
thousand kilometers to the south...). After all, as evidenced by the
numerous quakes in the east coast, it's not quite like here in Finland,
where there is also solid bedrock but no fault lines or quakes. The
bedrock helps a lot, but doesn't make a "once-in-a-thousand-year" quake
I hope you enjoyed this "Essay of mine".
Yes, we did. Thanks. :^)