Clarendon-Linden Fault System
The Clarendon-Linden Fault System is either a complex system of
long faults with associated shorter branches and parallel segments,
or a region of many short faults aligned north–south from the
Lake Ontario shore southward to Allegany County, NY. Some studies
have indicated that the system may extend under Lake Ontario to
close to the Canadian shore. The area you are standing in at the
cache site is where the fault slipped and part of the land raised
up while part sank.
Perhaps our most famous earthquake is the quake that occurred on
August 12th, 1929. This quake, near Attica NY occurred on the
Clarendon-Linden Fault system with a Richter scale rating of 5.6.
Damage included heavy structural damage to several brick buildings,
around 250 chimneys were toppled, almost every monument in a local
cemetery were thrown down, several wells to the west of the town
went dry and a crack formed in the railroad embankment near the
Exchange St. Station. The damage was severe enough to earn a rating
of VIII on the Modified Mercalli Scale.
What is a Fault?
In geology, a fault or fault line is a planar fracture in rock in
which the rock on one side of the fracture has moved with respect
to the rock on the other side. Large faults within the Earth's
crust are the result of differential or shear motion and active
fault zones are the causal locations of most earthquakes.
Earthquakes are caused by energy release during rapid slippage
along a fault. A fault that runs along the boundary between two
tectonic plates is called a transform fault.
Since faults do not usually consist of a single, clean fracture,
the term fault zone is used when referring to the zone of complex
deformation that is associated with the fault plane. The two sides
of a non-vertical fault are called the hanging wall and footwall.
By definition, the hanging wall occurs above the fault and the
footwall occurs below the fault. This terminology comes from
mining. When working a sloping ore body the miner stood with the
footwall under his feet and with the hanging wall hanging above
him.
Types of Faults
Faults can be categorized into three groups based on the sense of
slip. A fault where the relative movement (or slip) on the fault
plane is approximately vertical is known as a dip-slip fault. Where
the slip is approximately horizontal, the fault is known as a
transcurrent or strike-slip fault. An oblique-slip fault has
components of both strike-slip and dip-slip.
For all naming distinctions, it is the orientation of the net dip
and sense of slip of the fault which must be considered, not the
present-day orientation, which may have been altered by local or
regional folding or tilting.
Dip-Slip faults can also be broken down into two categories,
"Reverse" and "normal". In a reverse fault, the hanging wall moves
downwards compared to the footwall, in a normal fault, the hanging
wall moves upwards as compared to the footwall.
Strike-Slip faults where the footwall moves to the left as compared
to the hanging wall are known as "Sinistral" faults, while faults
with movement to the right are known as "Dextral" faults.
Earthquake measurement
Richter Scale
The Richter Scale is used to rate the magnitude of an earthquake --
the amount of energy it released. This is calculated using
information gathered by a seismograph. The Richter Scale is
logarithmic, meaning that whole-number jumps indicate a tenfold
increase. In this case, the increase is in wave amplitude. That is,
the wave amplitude in a level 6 earthquake is 10 times greater than
in a level 5 earthquake, and the amplitude increases 100 times
between a level 7 earthquake and a level 9 earthquake. The amount
of energy released increases 31.7 times between whole number
values.
The largest earthquake on record registered an 9.5 on the currently
used Richter Scale, though there have certainly been stronger
quakes in Earth's history. The majority of earthquakes register
less than 3 on the Richter Scale. These tremors, which aren't
usually felt by humans, are called microquakes. Generally, you
won't see much damage from earthquakes that rate below 4 on the
Richter Scale. Major earthquakes generally register at 7 or
above.
Mercalli Scale
Mercalli ratings, which are given as Roman numerals, are based on
largely subjective interpretations. A low intensity earthquake, one
in which only some people feel the vibration and there is no
significant property damage, is rated as a II. The highest rating,
a XII, is applied only to earthquakes in which structures are
destroyed, the ground is cracked and other natural disasters, such
as landslides or Tsunamis, are initiated.
The following is an abbreviated description of the 12 levels of
Modified Mercalli intensity.
I. Not felt except by a very few under especially favorable
conditions.
II. Felt only by a few persons at rest, especially on upper
floors of buildings.
III. Felt quite noticeably by persons indoors, especially on
upper floors of buildings. Many people do not recognize it as an
earthquake. Standing motor cars may rock slightly. Vibrations
similar to the passing of a truck. Duration estimated.
IV. Felt indoors by many, outdoors by few during the day. At
night, some awakened. Dishes, windows, doors disturbed; walls make
cracking sound. Sensation like heavy truck striking building.
Standing motor cars rocked noticeably.
V. Felt by nearly everyone; many awakened. Some dishes,
windows broken. Unstable objects overturned. Pendulum clocks may
stop.
VI. Felt by all, many frightened. Some heavy furniture
moved; a few instances of fallen plaster. Damage slight.
VII. Damage negligible in buildings of good design and
construction; slight to moderate in well-built ordinary structures;
considerable damage in poorly built or badly designed structures;
some chimneys broken.
VIII. Damage slight in specially designed structures;
considerable damage in ordinary substantial buildings with partial
collapse. Damage great in poorly built structures. Fall of
chimneys, factory stacks, columns, monuments, walls. Heavy
furniture overturned.
IX. Damage considerable in specially designed structures;
well-designed frame structures thrown out of plumb. Damage great in
substantial buildings, with partial collapse. Buildings shifted off
foundations.
X. Some well-built wooden structures destroyed; most masonry
and frame structures destroyed with foundations. Rails bent.
XI. Few, if any (masonry) structures remain standing.
Bridges destroyed. Rails bent greatly.
XII. Damage total. Lines of sight and level are distorted.
Objects thrown into the air.
Sources include Wikipedia, MCEER-UB Earthquake Engineering
website, Science direct website, USGS website and the paper "A
seismological study of two Attica, New York earthquakes" by Robert
B. Herrmann
Logging requirements
To log the cache, post a photo of yourself, or your group with your
GPS at the cache site OR a photo of your GPS with the raised
portion of the lad in the background from the second site. You must
also email me the following information.
1. This section of land used to be flat, which section of
land raised, and which sank? General direction of land forms will
be accepted.
2.The fault motion has a component of right lateral strike slip and
one of reverse faulting. With this in mind, which side is the
hanging wall, and which one is the foot wall?
3.Visit N 43 01.292 W 078 08.000. Email me the elevation of
BOTH the posted coords & the second set. Also, what is the
difference in elevation?
3. Research another NY earthquake and email me the following
information, Location, date, time and Ricther and Mercalli Scale
ratings.
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