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Earthquake Hazards Is an indirect cause of damage but can be wide-spread the abnormal behaviour of animals can also predict a
and produce some of the most devastating losses of life. earthquake, since it is thought that animals are more
Earthquake Severity and Magnitude Fissures may develop in certain soils during major quakes sensitive to minor changes in the physical properties of
due to Groundshaking but most fissures are shallow. the rock that is under stress and is about to break.
The power suddenly released in an earthquake produces Extreme dangers can include landslides and mudflows; This can include changes in temperature, sound, smell or
a terrifying experience, and is described in terms of its where burial alive is a real possibility. The vibration of an even the magnetic field.
magnitude and intensity. earthquake can cause sensitive soils to flow.
The Richter scale expresses the calculated energy Some soils liquefy as the soil grains collapse altogether, Physical Indicators:
released by the earthquake. and water is released from microscopic pores. Changes in groundwater levels - water levels in the wells
It is based on a logarithmic scale with which each whole Structures build on sensitive soils will collapse and sink. fall as the rock dilutes.
number on the scale represents a tenfold increase in the Quake induced landslides in China during 1920 killed Microseismic activity- the release of strain as
seismic wave trace amplitude. 100,000 people. microcracks open.
The Mercalli Intensity Scale employs observation of Seismic velocity changes- anomalies in the velocity of P
earthquakes effects on man-made structures . Tsunamis: and S waves.
The Mercalli Scale is expressed by roman numerals. These are ocean waves that are produced by Radon gas emission- gas liberated from the rock under
Example- I-II is barely noticeable and XI is total earthquakes, volcanic eruptions or major landslides. They the seismic activity.
damage, waves can be seen on service. can sweep ashore, causing damage at points thousands Animal behavioural changes- animals are more
of kilometres from the earthquake epicentre. sensitive to changes than humans.
Dangers from Earthquakes: Similar waves can also be produced within
Earthquakes seldom produce sufficient warning to permit enclosed/restricted bodies of water which as lakes and Equipment Used:
evacuation or relocation. reservoirs. Seismic arrays.
The major problem is the fact that they cannot be Damage can be severe where the waves move forward up Tiltmeters.
predicted, and the greatest dangers come from the the shoreline or overtop dams, allowing downstream areas Creepmeters.
interactions between the earthquake and man-made to be inundated. Borehole strain gauges.
structures. Valdes, Alaska 81 lives were lost in 1964 as a result of Laser measuring devices.
Crushed from a falling building, burned in fires that burst the tsunami produced by an earthquake.
from ruptured pipes or fuel tanks, swept away or getting Preparation:
buried are a few dangers that are associated with Predicting the Unpredictable: The best method is to have an effective hazard
earthquakes. Before the Kobe earthquake in 1995 there were flashes of reduction programme rather than attempting to control
red and blue light in the sky, which have been explained the earthquake.
Earthquakes Damage: as light emitted from silica crystals as they began to 1. Education- the population are given earthquake
They can cause damage in four different ways: fracture. This is called fractoluminescence and it is drills and personal protection plans that are
1. Groundshaking. uncertain whether this phenomenon can be used to predict important to prevent any serious injury and
earthquakes. outline what to do before, during and after an
2. Surface rupture. Anomalies have shown that P Waves velocities first fell,
3. Ground failure event.
and then immediately rose before each major episode and
4. Tsunamis. that the duration of the anomaly was directly linked to the 2. Zoning- mapping out the areas of high hazard
magnitude of the earthquake that followed. risk, but if it is impossible to not build here they
Groundshaking: will design buildings which can withstand the
This is the most severe cause of damage. Public When under stress, the water saturated rocks sometimes effects of an earthquake.
buildings that are unable to be evacuated quickly such as increases in volume just before they fracture. This is 3. Building- tends to be strengthened with
schools, hospitals and churches may collapse during this thought to be due t the opening of microcracks which triangular bracings so that they can flex
event and cause massive loss of life. results in an increase in rock porosity, which brings a laterally rather than vertically. You can also place
The collapse of Veterans Hospital in Sylmar, reduction in the density of the rock. stiff rubber bearings into the foundations to
California in 1971 that killed 45 people. Water will slowly migrate into the new cracks and so the isolate the structure from the lateral ground
overall water pressure within the rock is reduced. This motion. Oil-filled isolators can also be used to
Surface Rupture: has the effect of temporarily reducing P Wave velocities dampen any vertical movement. There can also
This is the horizontal or vertical displacement of the from miner earthquakes until more water seeps in. The be computerized weights on the roof which can
ground surface along a narrow fault zone. length of time this takes seems to indicate the magnitude absorb and dampen the vibrations of the
It may affect a smaller area than Groundshaking but it of the impending earthquake, which occurs shortly after earthquake by moving with the ground-
severely damage structure located adjacent to faults. the pore-water pressure, is restored. motion.
The damage from surface rupture was severe in the The dilatation-fluid diffusion modal explains some of the
California earthquake of 1971 mentioned above. other physical phenomenon which has been recorded prior
to an earthquake.