NOTES of Earthquake , Earth Movements and Volcanoes
The Mountains that come into existence due
to folding are known as Fold Mountains. These mountains are by far the
widest spread mountains. They are formed by sediments getting deposited into geosynclines. They are usually found
along the edges continents because the thickest deposits of sedimentary rock
generally accumulate along the edges of continents.
Horst or Block Mountains Due to tension or compression, two parallel faults come into
existence and displacement of rock strata takes along both the fault planes and
a block of earth’s crust stands like a mountain and is known as Horst or a
Block Mountain. Sometimes, the land on the outer sides of the faults slides
down along a fault plane leaving the area in between at a higher level. This
portion is also known as Horst or Block Mountain. The slopes of horsts are very
steep and they usually don’t have peaks. Examples include the Sierra Nevada
Mountains in North America and the Harz Mountains in Germany.
When a block of land between two parallel faults subsides along a fault plane
leaving the adjoining areas at a higher level, the subsided part is known as
Rift Valley. These valleys have steep, wall-like slopes and the valley floors
are comparatively wider. Example is East African Rift Valley system, which
stretches from East Africa through Red Sea to Syria.
A tsunami is a series of water waves
caused by the displacement of a large volume of a body of
water, such as an ocean
or a large lake. They have a small amplitude
offshore, and a very long wavelength, which is why they generally pass unnoticed at
sea. They grow in height when they reach shallower water.
Homoseismal line is the line on the Earth's surface connecting points where the seismic wave arrives,
generated by an earthquake, at the same time.
Isoseismal Line is a line on a map joining points of equal
seismic intensity produced by an earthquake.
A seismic gap is a segment of an active
fault known to produce significant earthquakes
that has not slipped in an unusually long time when compared with other
segments along the same structure.
PLATE TECTONICS Tectonic plates move in
relation to one another. Earthquakes, volcanic activity, mountain-building,
trench formation occur along plate boundaries. The lateral movement of the
plates is typically at speeds of 0.65 to 8.50 centimeters per year. Tremendous
energies are unleashed resulting in tremors that transform Earth’s surface.
While all the plates appear to be moving at different relative speeds and
independently of each other, the whole jigsaw puzzle of plates is
interconnected. No single plate can move without affecting others, and the
activity of one can influence another
Whatever drives the movement, plate tectonic
activity takes place at the boundaries of these plates
Divergent boundaries: In such a boundary two plates are moving away from each other. An
example of this is the Mid-Atlantic Ridge, where magma rises from deep within
the Earth. This leads to an increase in volcanoes and earthquakes in the region
Convergent boundaries: They are also known as Destructive
Plate Boundaries. There are two main ways that two plates can converge. In
a collision boundary, the two plates push almost equally against each
other, buckling the material up in the middle. This leads to the formation of
mountain ranges, such as the Himalayas and the Alps. In geology, a nappe
is a large sheetlike body of rock
that has been moved more than 2 km to 5 km from its original
position. Nappes form during continental
plate collisions, when folds are sheared
so much that they fold back over on themselves and break apart. The resulting
structure is a large-scale recumbent fold.
subduction boundary, one plate slips beneath the other, leading to the
formation of a deep trench. The Mariana Trench in the Pacific Ocean, which at
11 km is the deepest point in the world's oceans, is an example where this is
Transform boundaries: These occur when two plates slip past each other. This slipping
however generally doesn't happen smoothly - because of friction the plates remain
in place for a while, building up a kind of stored potential energy from the
forces trying to move them, and then this energy is released suddenly when the
forces become too large. This sudden release of energy results in an
earthquake. A notable example of a transform boundary is the San Andreas fault