Earthquake may simply expressed as a momentaryshock experienced by the earth at a particular locationand time.Earthquake may be technically defined as the vibrationsinduced in the earth’s crust due to internal or externalcauses that give a shock to a part of the crust and allthings existing on it
The study ofearthquakes is ofspecial significance tocivil engineer becauseit will help him predictthe occurrence ofearthquake and alsodesign and providesuch structures that willafford protection duringearthquake.
The greek word for earthquake isSeism and therefore the termseismic is associated withearthquakes.The science dealing with the studyof earthquakes is calledseismologyThe word seismic is used toqualify anything related toearthquake such as seismicintensity, seismic zoning, seismicwaves etc.
INTENSITY MAGNITUDEFOCUS ORHYPOCENTRE Intensity is a termThe point of origin used to measure the A term used to establishof an earthquake impact of the size of an earthquake,below the surface of earthquake. Intensity which is a measure of theearth. measures the amplitude of a seismic strength of shaking wave and is related to theEPICENTRE produced by the amount of energy earthquake at a releasedThe point on the certain location. during ansurface directly Intensity is earthquake. Magnitude isabove the focus determined from the total energy releasedwhere the vibrations effects on by an earthquake at itsare felt. focus. The Richter Scale people, human structures, and the is most famous to natural environment. measure the magnitude of Mercalli Scale was an earthquake. used to predict intensity.
Nowadays intensity of earthquakes are not measured.They have been replaced by magnitude. Top 5 Earthquakes by Magnitude. S. Date Place Magnitude No. 1 22 May 1960 Valdivia, Chile 9.5 2 27 March 1964 Alaska, USA 9.2 3 26 December Sumatra, Indonesia 9.1 2004 4 13 August 1862 Arica,Chile 9.0 5 26 January 1700 Cascadia, USA- 9.0 Canada
An earthquake may be caused by the following natural and artificial sources.NATURAL SOURCESTectonic Plates Movement 90%Faults in Rocks (Elastic Rebound Theory) 6%Volcanic Explosions 1%ARTIFICIAL SOURCESExplosion 1%Mine Collapse 1%Reservoir Failure 1%
SEISMIC WAVESThe energy released during earthquake travels to the earth in form of waves. The waves are called as P-Waves S-Waves L-Waves (Rayleigh Waves & Love Waves) P-Waves & S-Waves are called as body waves. L- Waves are also called as surface waves.
The seismic waves are very useful as followsThey were used to establish the internal structure of the earth.They are used to calculate the magnitude of earthquake. Richter Scale is based upon the amplitude of the seismic waves.They are also used to locate the epicentre of earthquakes.They are also used for groundwater and other explorations.
Isoseismal Lines – Hypothetical line passing through places of same earthquake intensity. They are also used to measure epicentre.Seismograph – An instrument used to record ground movements caused by earthquakes, explosions or other vibrations.Seismic Zone - A seismic zone is a region in which the rate of seismic activity remains fairly consistent. People often use the term “seismic zone” to talk about an area with an increased risk of seismic activity. Seismic hazard zones” is another term used.
The effects of earthquakes Loss of Life Building Collapse Ignition of Fire Ground Failure and Rupture Landslides and Avalanches Floods and Tidal Sources TsunamiChange in Soil and Rock Properties
WORLD SEISMIC ZONES or EARTHQUAKE HOTSPOTSBased on seismicity, the three most happening earthquake hotspots in the world are1. PACIFIC RING OF FIRE2. ALPIDE BELT3. MID ATLANTIC RIDGE
EARTHQUAKES IN INDIAThe major earthquakes in India are2004 Sumatra Earthquake (9.1)1934 Bihar Earthquake (8.7)1950 Assam (Shillong Plateau) Earthquake (8.7)1897 Assam (Tibetian Plateau) Earthquake (8.5)2005 Kashmir Earthquake (7.6)2001 Gujarat(Kutch) Earthquake (7.1)
EARTHQUAKES IN INDIA
EARTHQUAKE ZONES IN INDIAThere are five seismic zones named as I to V based on Modified MercalliScale (MM Scale) as details given below:Zone V: Covers the areas liable to seismic intensity IX and above on MMScale. This is the most severe seismic zone and is referred here as VeryHigh Damage Risk Zone.Zone IV: Gives the area liable to MM VIII. This, zone is second in severity tozone V. This is referred here as High Damage Risk Zone.Zone III: The associated intensity is MM VII. This is termed here asModerate Damage Risk Zone.Zone II: The probable intensity is MM VI. This zone is referred to as LowDamage Risk Zone.Zone I: Here the maximum intensity is estimated as MM V or less. This zoneis termed here as Very Low Damage Risk Zone.
EARTHQUAKE ZONES IN INDIAZone V: Kashmir, Punjab, the western and Central Himalayas, the North-East Indian region and the Rann of Kutch fall in this zone.Zone IV: Indo-Gangetic basin and the capital of the country(Delhi, Jammu)and Bihar fall in Zone 4.Zone III: The Andaman and Nicobar Islands, parts of Kashmir, WesternHimalayas, Western Ghats fall under this zoneZone II: Other parts of India namely Hyderabad, Lakshadweep, Orissa etc.Zone I : No
EARTHQUAKE ZONES IN INDIA Cities and Zones• Zone III :- Ahemdabad, Vadodara, Rajkot, Bhavnagar, Surat,Mumbai, Agra, Bhiwandi, Nashik, Kanpur Pune, Bhubneshwar, Cuttack, Asansol, Kochi, Kolkata, Varanasi, Bareilly, Lucknow, Indore, Jabalpur, Vijaywada, Dhanwad, Chennai, Coimbatore, Manglore, Kozhikode ,Trivandrum.• Zone IV :- Dehradun, New Delhi, Jamunanagar, Patna, Meerut, Jammu, Amristar,Jalandhar.• Zone V:- Guwahati and Srinagar.