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SEISMOGRAPH
THE SCIENCE WHICH STUDIES
EARTHQUAKES IN DETAIL IS
KNOWN AS SEISMOLOGY.
SEISMOGRAPH
AN INSTRUMENTSWHICH
MEASURES THE INTENSITY OF
EARTHQUAKES IS KNOWN AS
SEISMOGRAPH.
EARTHQUAKE
A VIBRATION OR SHAKING OF THE CRUST MAY BE
CALLED AS EARTHQUAKE. IMPORTANT CAUSES OF
EARTHQUAKE ARE
1] FOLDS
2] FAULTS
3] LANDSLIDES
FAULTS
Fault, in geology, is a fracture
in the Earth's crust along
which a section of the crust
has been displaced relative to
another section, in response
to forces of tension or
compression as a result of
tectonic movement. This
movement may be in a
vertical or horizontal
direction, or a combination of
the two. The fracture may
range from centimeters to
hundreds of kilometers long,
such as the San Andreas
Fault in California. The
movements at fault lines may
be sudden if generated in a
severe earthquake.
FOLDS
A single fold is a hinge defined by the maximum curvature of the beds.
The hinge line joins the points of maximum bending along a bed. The
axial surface, or plane, passes through the hinges of successive beds,
while the axis of the fold is any line on the bed which is parallel to the
hinge line. When the axis is inclined to the horizontal, the fold is said
to plunge. Axial surfaces are vertical in upright folds, while surfaces
dip at varying angles and are sub horizontal in recumbent folds. In the
latter, the upper limb may become detached and thrust one over the
lower to form a structure known as a nappe, which is common in the
Alps.
LANDSLIDES
Landslide, is a descent of a mass of earth and rock down a
mountain slope. Landslides may occur when water from rain and
melting snow sinks through the earth on top of a slope, seeps
through cracks and pore spaces in underlying sandstone, and
encounters a bed of shale inclined towards the valley. The water
collects along the upper surface of the shale, which it softens to
form slippery clay. If the support is sufficiently weakened, a mass
of earth and rock slides down along the well-lubricated bedding
of shale.
EARTHQUAKE WAVES
AT THE TIME OF EARTHQUAKES THREE
TYPES OF WAVES ARE PRODUCED
1] PRIMARY WAVES.
2] SECONDARY WAVES.
3] LONG WAVES.