ORIGIN AND OCCURRENCE OF EARTHQUAKE Flashcards
(also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting
from a sudden release of energy in the Earth’s lithosphere that creates seismic waves.
EARTHQUAKE
place of origin of the earthquake in the interior of the earth.
FOCUS/HYPOCENTER
place on the earth’s surface, which lies exactly above the center of the
earthquake.
EPICENTER
the point which is diametrically opposite to the epicenter
ANTI CENTRE
The enormous energy released from the focus at the same time of the
earthquake is transmitted in directions in the form of waves.
SEISMIC WAVES
- An imaginary line joining the points of same intensity of the earthquake is called
an.
ISOSEISMAL
An imaginary line which joins the points at which the earthquake waves have
arrived at the earth’s surface
COSEISMAL
The imaginary line which joins the center and the epicenter
SEISMIC VERTICAL
– a fracture in rocks that make up the earth’s crust.
FAULT
is caused by a sudden slip on a fault.
The tectonic plates are always slowly
moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the
friction, there is an earthquake that releases energy in waves that travel through the earth’s crust and
cause the shaking that we feel.
ORIGIN OF EARTHQUAKE
the generally accepted scientific theory that considers the Earth’s lithosphere to
comprise a number of large tectonic plates which have been slowly moving since about 3.4 billion
years ago.
PLATE TECTONICS
TYPES OF FAULT
- NORMAL FAULTS occur mainly in areas where the crust is being extended such as a
divergent boundary. - REVERSE FAULTS occur in areas where the crust is being shortened such as at a convergent
boundary. - STRIKE-SLIP FAULTS are steep structures where the two sides of the fault slip horizontally
past each other; transform boundaries are a particular type of strike-slip fault.
CLASSIFICATION AND CAUSES OF EARTHQUAKES
- TECTONIC EARTHQUAKES
exclusively due to internal causes, i.e. due to disturbances or adjustments of geological
formations taking place in the earth’s interior.
- NON-TECTONIC EARTHQUAKES
are generally due to external or surficial causes. (Of course, earthquakes which occur due to
volcanic eruptions are also termed as non-tectonic earthquakes).
NON-TECTONIC EARTHQUAKES
- Due to huge waterfalls
- Due to avalanches:
- Due to meteorites:
- Due to the occurrence of sudden and major landslides:
- Due to volcanic eruption:
- Due to tsunamis:
- Due to manmade explosions:
- Minor tremors
Factors affecting the intensity of earthquake
- Distance from the epicenter.
- Compactness of the underlying ground.
- Types of construction.
- Magnitude of earthquake.
- Duration of the earthquake.
- Depth of the focus.
variously called primary waves, push-pull waves, preliminary waves, longitudinal waves,
Compressional waves, etc. These are the fastest among the seismic waves. They travel as fast as 8 to
13 km per second. Therefore, when an earthquake occurs, these are the first waves to reach any
seismic station and hence the first to be recorded. The P waves resemble sound waves because these
too are compressional or longitudinal waves in nature.
P WAVES
These are also called shear waves, secondary waves, transverse waves, etc. Compared to P. waves,
these are relatively slow. They travel at the rate of 5 to 7 km per second. For this reason, these waves
are always recorded after P waves in a seismic station.
S WAVES
These are called long waves or surface waves. These are the slowest among the seismic waves.
Therefore, these are the last to be recorded in the seismic station at the time of occurrence of the
Earthquake. They travel at the rate of 4 to 5 km per second. These are called surface waves because
their journey is confined to the surface of the earth only. They are complex in nature and are said to
be of two kinds, namely, Rayleigh waves and Love waves
L WAVES
