Earthquakes

EARTH QUAKES Source: Kobe I EERI - Slide #43

Earthquakes are a natural phenomena, like drought, flood and Cyclones.

Earthquakes in simple terms is a sudden trembling or shaking movement of the earth surface.

Larger earthquakes usually preceded by tremors and some violent shocks and followed by smaller earthquakes of diminishing size called aftershocks.

What are Earthquakes? A sudden release of energy accumulated in deformed rocks causing the ground to tremble or shake. - Causes rupturing or brittle failure of crustal rocks. - Energy is released. - Movement of fault blocks takes place along a fault plane. Source: www.earth.leeds.ac.uk/dynamicearth

INSI DE E AR TH

Layers of the Earth By analyzing the seismograms from many earthquakes, scientists have discovered that three main levels or shells exist within the Earth: CRUST

Source: www.thetech.org

MANTLE The region just below the crust and extending all the way down to the Earth's core is called the mantle. The mantle, a dense, hot layer of semi-solid rock approximately 2,900 km thick.

The Earth's outermost surface is called the crust. The crust is relatively light and brittle. Most earthquakes occur within the crust. Scientists believe that below the lithosphere is a relatively narrow, mobile zone in the mantle called the asthenosphere (from asthenes, Greek for weak). CORE Beneath the mantle is the Earth's core. The Earth's core consists of a fluid outer core and a solid inner core.

Local conv ecti ve current s in the mantl e

Maj or Tectoni c pl ates on the Ear th’ s surf ace

Types of

inter pl ate boundari es

Types of Faults

Basic Term inology

Ar ri val of sei smic wave at a sit e

SEISMIC WAVES Sei smi c waves ar e of tw o types - Body wav es - Sur face waves Body waves consist of Primary waves (P-waves) and Secondary waves (S-waves) Surface waves consist of Love waves and Rayleigh waves

Types of Waves

MAGNITUDE

Magnitude is a quantitative measure of the actual size of the earthquake. Its obtained from the seismogram and accounts for the dependence of the wave form amplitude on epicentral distance Increase in magnitude by 1.0 implies 10 times higher waveform amplitude and about 31 times higher energy released. For instance, energy released in a M7.7 earthquake is about 1000 times that released in a M5.7 earthquake.

INTENSITY

Intensity is a qualitative measure of the actual shaking at a location during an earthquake and it is assigned in Roman Capital Letters There are many intensity scales. Two commonly used ones are 1) Modified Mercalli Intensity (MMI) Scale. 2) MSK Scale Both scales are quite similar and range from I(less perceptive) to XII (most severe) The intensity scales are based on three features of shaking - perception by people and animals - performance of buildings - changes to surroundings

Basic Difference : Magnitude versus Intensity

Reducing illumination with distance from an electric bulb

Schematic of early Seismograph

Some typical accelerograms

Indian Subcontinent: among the world’s most disaster prone areas 65% of land vulnerable to Earthquakes 8% of land vulnerable to Cyclones 5% of land vulnerable to Floods > 1 million houses damaged annually + human,

PAST EARTHQUAKES IN INDIA

Seismic Zone Map of India: Year-1962

Seismic Zone Map of India: -1966

Seismic Zone Map of India: -1970

Seismic Zone Map of India: About 65 percent -2002

of the land area of India is liable to seismic hazard damage (about 26% under MSK Intensity VII, 18% under VIII and 12% under IX and higher).

Seismic Map of Bihar

Earthquakes in Bihar         

04 June 1764 23 Aug 1833 23 May 1866 7.0 23 May 1866 5.5 30 Sept 1868 07 Oct 1920 15 Jan 1934 11 Jan 1962 6.0 21 Aug 1988 6.8

Bihar WB Brd Nepal Brd Nepal Brd

6.0 7.7

Jharkhand Bihar Brd Hazaribagh Bihar –UP Brd Indo – Nepal Brd Indo – Nepal Brd Bihar Nepal Brd

5.7 5.5 8.0

hould social development increase vulnerability?

ncontrolled/unplanned development

ajor cities in hazardous zones –Srinagar, Guwahati & all NE capitals are in zone V –Jammu, Delhi, Patna, Jalandhar in IV –Mumbai, Chennai,Calcutta, Ahmedabad, Trivandrum, Coimbatore, Kochi,Kozhikode in III

ajority of buildings wherein do not conform.

azard

te effects

ulnerability

isk

Ear thquake

Ri sk

= Probability of ground motion = Soil properties, topography presence of Reservoirs (RIS), Mines (MIS) = Building types, Age

= Hazard x Site effects x Vulnerab

Earthquake Don’t Kill People but Buildings Do

VULNERABILITY • 1819 Gujarat [Kutch] 8.0 (2000 deaths) • 2001 Gujarat [Bhuj] 6.9 (13805 deaths) • Increased vulnerability in two centuries

How Architectural Features Affect Buildings During Earthquakes

The normal learning from other’s experiences….

Normal Long Term Human Response to Earthquakes (Key, 1988)

The Himalayas… among the most seismic regions on earth.. •1833 Bihar 8.7 •1897 Assam 8.7 •1900 CoimbatorePalghat •1905 Kangra HP •1934 Bihar – Nepal 8.3 •1950 Assam 8.6 •1991 Uttarkashi 6.6 •1988 Bihar-Nepal 6.8 •1999 Chamoli 6.8 •Can we Bhuj learn from others •2001 6.7

experiences?

•And our own? •

The fight against damage, destruction and death from earthquake Continues….

Let’s make a safer world

Thank You