Why do earthquakes occur?

Earthquakes are measured on a Richter scale calibrated from 1-9. This scale was created by seismologists* Charles Richter and Beno Guttenberg. An earthquake with a magnitude of 1 is the mildest while that of magnitude 9 is  the strongest. Tremors are felt when an earthquake measures 3 or greater on this scale.

*Seismologist is one who studies the earth.

How can houses be protected against earthquakes?

• Load bearing walls can be strengthened using steel reinforcements along with continuous horizontal ties at  roof, lintel and plinth level.

• All parts of a building must be continuously bonded.

• While large windows may look attractive, they and any other kind of openings weaken the structure.  There should be no openings at the corners.

• Foundation should be at a uniform depth and constructions on loose soil must be avoided.

• In Black cotton soils of more than 2 meters depth, raft foundations must be laid.

• Buildings like institutions, hospitals and schools must be provided with base isolation. The technique of base isolation consists of providing bearings in between two plinth beams so that vibrations from ground are not fully transferred to  the structure .

• Toughened glass or wired glass which can  break  into fine pieces without causing any danger must be used for windows. Steel frame door shutters must be used instead of natural timbers.

• Double-heighted stilted structures must be avoided as they tend to twist during earthquakes.  All junctions should be secured with the help of steel to impart extra strength to walls.

• 'Architectural Acrobatics' ie. irregular shapes of buildings must be avoided. The building morphology or shape must be kept simple like squares or rectangles as they are more stable.

• Cantilevers in the building should be avoided as they should not be more than a metre in depth.

• Main Switch in the building is a must, so as to cut off electrical supply to building at the time of an earth quake. Also circuit breakers must be installed as most fires are due to short-circuits.

• Doors especially in bathrooms should open towards the outer side. Although, this takes up extra space, they are easier to open in times of emergency.

• Materials like PVC which produce poisonous fumes during fire must be avoided. 

• Airconditioning ducts should be installed using materials like aluminum foil and glass wood wool instead of cotton wool and gunny bags.

What are the safety measures builders should follow?

• Buildings should be designed for wind forces and seismic forces as per IS 1893-1984, IS 4326-1993, IS 13827-1993, IS 13828-1993 codes. 

• The foundation for the columns as well as load bearing walls should be carried down to firm soil and to the same level instead of footings at different levels based on the soil.

• Normally length of buildings should not be more than three times their width.

• Parapet walls, Heavy cornices, Long cantilevers of beams and slabs should be avoided as these cause greater vibrations and tend to sway buildings when earth quakes.

What should you do if an earthquake occurs?

• Although earthquakes still cannot be predicted quake locations can be identified and their area can be measured accurately.

• Stocking up of emergency supplies can aid in comfort and safety during and after an earthquake. People who live in areas prone to quakes should store enough supplies to last for at least 72 hours. Emergency supplies should include food, water, portable radio, flashlight, batteries, and first-aid supplies.

What are the Major Earthquakes in India ?

Earthquakes in India

Ground Shaking - Shaking of the ground caused by the passage of seismic waves near the epicenter of the earthquake is responsible for the collapse of most structures. The intensity of ground shaking depends on distance from the epicenter and on the type of bedrock underlying the area.

• In general, loose unconsolidated sediment is subject to more intense shaking than solid bedrock.

• Damage to structures from shaking depends on the type of construction. Concrete and masonry structures, being brittle, are more susceptible to damage than wood and steel structures, which are more flexible.