earthquakes(1)

 Geological consideration for choosing sites of building in seismic areas.

Damages to structure because of earthquake can be reduced or even prevented by properly siting the structure with respect to geological conditions & by suitably designing them.

1)    Building should be founded on hard bed rock. Building situated on river alluvium , steep slopes always suffer more in an earthquake. These situations should be avoided.

2)    Simple rigid structure stands up well against vibration. All parts of a building should therefore well tied together so that the whole structure react to vibration as a unit. Foundation also must be so designed that the whole structure vibrates as a single unit. For large building raft type foundation are advisable. Building with irregular shapes & tall structure should be avoided.

3)     If the period of vibration of a structure is the same as that of the foundation rock it will collapse because of resonance. Therefore the types of building on each type of rock must be so chosen as to avoid resonance.

4)    Provision has to be made in the design of structure to guard against acceleration produced by earthquake. Areas like the Indian peninsula it is common practice to adopt a factor as low as possible for economic point of view.

Geological Effects :-                                                                                                                                      1) Minor faulting takes place.                                                                                                     

  2) Course of river may change.

3) Waterfall may create.                                                                                                       

 4) Groundwater level may rise or down in well.                                                

  5] Some of well may dry.                                                                                                         

6) Landslides may takes place.                                                                             

  7] Tsunami, [great tidal waves] are generate which often do greater damage on   coast.

Earthquake in regions of dams :- An earthquake is a 100 % geological phenomenon & any connection  both dam & earthquake has to be proved on the basis of geological evidence , but no geological evidence has been produced to show a dam has caused an earthquake.

Hence as no cause & effect relationship has been established between dam & earthquake & there is no justification for maintaining that dam cause earthquake.Koyana earthquake 1967.