25-08-2017, 09:32 PM
EARTHQUAKE WAVES
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INTRODUCTION
In sports, the best offense is sometimes a good defense. And that's how most engineers approach earthquake hazards, too. Natural hazards like earthquake, cyclones and floods become natural disasters because unsafe building construction continue in the country in spite of national building code and Indian standards on hazards safety as these are neither mandatory nor are enforced strictly. Existing town and country planning acts, master plan and area development rules and building regulations do not adequately incorporate safety requirements against natural hazards.
WHAT IS EARTHQUAKE?
The earthquake is the sudden release of some stored energies in the earth’s crust and upper mantle that causes sudden shaking in part of earth’s crust. One of the most interesting aspects of monitoring the earthquake is a problem placed deep into earth’s crust itself. When the large rock masses are subjected to mechanical pressures acting over long periods of time stresses go on accumulating in them until finally a stage is reached when rocks are strained to the breaking point. Due to there is rupturing of rock masses and give rise to fault. The scrapping together of two rough surfaces during this enforced moment of rock masses against each other sets up vibrations, which is called as earthquake.
EFFECTS OF EARTHQUAKE:
1) The most masonry and wooden buildings become distracted and big cracks are seen on the earth.
2) The communication system is totally distracted due damages to the roads, railways, bridges etc.
3) New water falls and streams are created on account of the disturbance of the underground water bodies.
4) Rivers adopt new courses; this provides new agriculturally useful lands.
5) In some places topography of the land is changed which facilitates easy transportation.
6) The dams across the rivers are damaged causing lot of destruction on the downstream side.
7) Underground water level is also affected such as lakes and swamps are created at many places.
8) Earthquake-induced ground failure has been observed in the form of ground rupture along the fault zone, landslides, settlement and soil liquefaction.
TYPES OF EARTHQUAKE WAVES:
Earthquake waves originate at a point many kilometers deep below the earth crust, this point is known as focus. The point on the earth surface vertically above the focus is called as epicenter. The main area of earthquake surrounds this point. The first type of earthquake waves that originate from focus are known as longitudinal or ‘P’ waves. Their speed ranges from 5.4 to 13.8 km/sec. The other type of waves, which vibrate at right angles to the direction of propagation of ‘P’ waves are called as Transverse or ‘S’, waves. Their speed ranges from 3.2 to 7.2km/sec.