When rocks of the earth crust are suddenly disturbed , vibration are caused which spread in all direction from the place of disturbance. The passage of vibration through the rocks may induce a local and regional shaking in them and the shaking movement may last for various fraction of time is an earthquake.
Cause of Earthquake:-
- Tectonic earthquake:- It is broadly agreed that these are caused displacement of blocks of the rocks and according to H.F Reid theory any block on the earth that is under the influence of unequal forces withstand these force in initial stage by undergoes elastic deformation and the force get stored in the rocks as elastic strain till a limit but when the limit is exceed by operating forces. A fractures is caused at that stage in the block is a type of tectonic earthquake
- Non Tectonic Earthquake:- Due to volcanic eruption or collapse of ground.
Focus & Epicenter detail:- The origin of a particular earthquake is termed as Focus and the point or place on the surface vertically above the focus of an earthquake is termed as Epicenter
- P waves:- Primary waves ( Push and pull)
- S waves ;- Secondary waves
- L waves (Surface waves)
Intensity of Earthquake
- People do not feel any earth movement if the value = <3.4 (Richter Scale Equivalent)
- Most Building collapse if Value is = 6.2 -7.9
- Almost every thing is destroyed = >8.0
INDIAN SEISMIC CODES
- IS ; 1893 ( Part-1), 2002 : Criteria for Earthquake Resistant Design of structure ( V th Revision)
- IS: 13920, 1993 : Ductile Detailing of Reinforced Concrete Structures subjected to seismic forces
- IS : 13827, 1993 : Guidelines for Improving Earthquake Resistant of earthen Building.
- IS 13828, 1993 : Indian standard for Repair and seismic strengthening of Building.
- SP : 22 ( S&T), 1982: Explanatory handbook on codes for earthquake Engineering.
- Roofs of the building should be light weight type because earthquake is a function of mass so the building shall be light as possible
- Height of building in seismic zones IV and V only one storey
- Shape of building – For better earthquake resistant , the building should have a simple rectangular plan and be symmetrical as far as possible about both the areas.
- Walls :- when a longer wall is required , the wall should be strengthed by intermedite vertical buttresses.
- The width of the opening sholud not more than 1.20 m. and the sum of the width of opening in a wall should not exceed 33 % of total wall length
- Foundation;-The depth of foundation below existing ground level at least lie 400 mm. 2. The footing should be built by using stone, fired brick using cement or lime mortar. 3. the wall above foundation should be constructed using stone or burnt brick laid in cement