EARTHQUAKES
(PART SEVEN)
The New Madrid Seismic Zone, stretching from east
central
Their largest concern for
this area is the disastrous effects of Earthquake
Soil Liquefaction that will occur during a large quake. Liquefaction is
transformation of loosely packed, saturated sand and/or silt into a fluid mass.
Liquefaction is a temporary quicksand condition. The NMSZ, which includes parts
of
Liquefaction
is induced seismically by earthquake tremors that generate the pressures needed
to separate grains of sand saturated with water, resulting in a viscous fluid
mixture of water and suspended sand grains like that of a “cement slurry when
freshly poured.” The only way that loose sand can have any strength is if the
grains touch each other, supporting each other’s weight and any burdens coming
from above, the sides, or below. Liquefaction disables grains from touching one
another.
Thus,
liquefaction is not a random geologic occurrence! The probability of its
occurrence increases with the co-existence of the following three variables:
1.
Young loose sand/soil, such as found in alluvial deposits—that is, sediment
deposited by flowing water, as in a riverbed, flood plain, or delta.
2. A
shallow ground water table (less than 50 feet).
3. The
presence of active seismic faults.
These
three variables exist in the New Madrid Fault Zone in the alluvial
The
ubiquitous evidence of old and repetitive liquefactions throughout the New
Madrid Seismic Zone strongly suggests that liquefaction will be a very big
problem if it detonates some zinger earthquakes like it did in 1811-1812.
Examples of old liquefaction include sand blow explosion craters, earthquake
ponds, channel blowouts, simple sand boils, compound sand boils, sand dikes,
sand sills, lateral spread sags, sunk lands, and earthquake lakes.
The
ground failure that resulted from liquefaction during the New Madrid earthquakes
of 1811 and 1812 was severe. We’re talking about vertical displacement of 3 to
6 feet and lateral displacement up to 33 feet. A recurrence of that type of
event would have severe consequences for structures.
Seismically-induced
liquefaction effects can be severe. The New Madrid Seismic Zone has demonstrated
severe liquefaction effects in the past when it was relatively uninhabited. An
earthquake in the zone today would likely cause liquefaction to recur as the
three variables—alluvium, high water table, and seismicity—remain present
today, as in the past. The population centers near the NMSZ are at risk for the
effects of liquefaction.
Last week Gene, W5SXV,
brought up the subject of the Richter Scale, so let’s look at some interesting
figures that Charles Richter developed in 1935 and are still used to this day to
measure earthquakes strength.
The Richter scale is open
ended and logarithmic which means there are no upper and lower limits to the
scale, and that every time the magnitude goes up by one unit, the amount of
energy this represents increase thirty times.
The following are measurements of the Richter scale and the equivalent amount of
TNT each represents:
RICHTER
TNT ENERGY
1.
1.0
6 ounces
2.
1.5
2 pounds
3.
2.0
13 pounds
4.
2.5
63
pounds
5.
3.0
397 pounds
6.
3.5
1000 pounds
7.
4.0
6
Tons, equal to a small atomic bomb.
8.
4.5
32
Tons
9.
5.0
199 Tons
10.
5.5
500 Tons
11.
6.0
6270 Tons
12.
6.5
31,550 Tons
13.
7.0
199,000
Tons
14.
7.5
1,000,000 Tons
15.
8.0
6,270,000 Tons
As you can see from these
figures, earthquakes can produce and unleash a tremendous amount of energy that
will produce waves of destruction in there paths.
There are now heavily
populated areas in the New Madrid Fault Zone where studies show that the ground
will fall away during a large earthquake changing elevations drastically. During
the earthquakes of 1811 and 1812, Lake St. Francis, which is in the wildlife
management area 600, located 15 miles southeast of
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FEMA:
New Madrid earthquake preparedness is agency priority
Preparing for a catastrophic earthquake along
the New Madrid fault is a priority, FEMA officials said before a congressional
field hearing on government readiness to handle natural disasters, and the ''New
Madrid Seismic Zone is at the top of the list,''
one section chief of the Federal Emergency Management Agency, said.
''It's our primary objective.''
There is ''significant concerns'' for the
potential of a catastrophic earthquake equal in magnitude to those that struck
parts of the
FEMA has been sharply criticized for its
handling of the aftermath of Hurricane Katrina, and they would not say whether
the Katrina criticism had prompted the agency's interest in the 50-mile-wide New
Madrid fault zone, centered near the southeast
A strong earthquake could disrupt the flow of
commodities by underground pipeline, rail, barge and highway; halt the flow of
food exports, fuel oil and coal outside the region; and block routes for
emergency services.
A House subcommittee which oversees FEMA and
emergency management, traveled to
After
that trip, that committee said they are leaning toward introducing legislation
that would separate FEMA from the Homeland Security Department. That's in
response to criticisms that FEMA's traditional role of dealing in natural
disasters has gotten lost in Homeland Security's emphasis on fighting terrorism.
''Response was slow and key decisions were made late,'' and ''We can't afford to
get it wrong again. Business as usual doesn't work in a catastrophic disaster.''