Submitted by : Jaideep kaur tiwana

Msc 2nd year

Submitted to : Prof. G.S. Gill

EARTHQUAKE: A Tragedy to life and property

• It is caused by the sudden release of slowly accumulating strain energy along a fault with in the earth’s crust.

• Areas of surface or underground fracturing that can experience earthquakes are known as FAULT ZONES.

The Focus and Epicenter of an Earthquake

•The point within Earth where faulting begins is the focus, or hypocenter

•The point directly above the focus on the surface is the epicenter

Classification of faults:

• Normal fault : a dip slip fault in which the block above the fault has moved downward relative to the block below.

• Reverse fault : a dip slip fault in which the upper block, above the fault plane, moves up and over the lower plane.

Strike slip faults• A left lateral strike slip fault : it is one on

which displacement of the far block is to the left when viewed from either side.

• A right lateral strike slip fault : it is one on which displacement of the far block is to the right when viewed from either side.

Earthquake locations around the world and their correlation to plate boundaries. Plate boundaries are outlined by red circles, which indicate past earthquake epicenters. Credit: McGraw Hill/Glencoe, 1st ed., pg. 143.

TECTONIC CAUSES

About 90% of the world's earthquakes and 81% of the world's largest earthquakes occur along the Ring of Fire.

The next most seismically active region (5–6% of earthquakes and 17% of the world's largest earthquakes) is the Alpide belt, which extends from Java to Sumatra through the Himalayas, the Mediterranean, and out into the Atlantic.

The Mid-Atlantic Ridge is the third most prominent earthquake belt.

WAVES PRODUCED DUE TO EARTHQUAKES:

Seismic wave behaviorP waves arrive first, then S waves, then L and RAverage speeds for all these waves is knownAfter an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.

Earthquakes generate seismic waves which can be detected with a sensitive instrument called a Seismograph.

Seismometers may be deployed at earth’s surface , in shallow vaults, in boreholes or under water.

The Richter magnitude of an earthquake is determined from the logarithm of the amplitude of waves. The original formula is: Richter magnitude ML = log 10A – log10 A0(δ)

The Richter magnitude scale (also LOCAL MAGNITUDE) assigns a magnitude number to quantify the energy released by an earthquake.

How is an Earthquake’s Epicenter Located?

Time-distance graph showing the average travel times for P- and S-waves. The farther away a seismograph is from the focus of an earthquake, the longer the interval between the arrivals of the P- and S- waves

Earth quake Effects and the Hazards they cause:

• Ground shaking • Surface faulting• Earthquake induced ground failure i.e.

landslides and liquefaction

• In coastal areas, earthquakes cause Tsunamis.

EARTHQUAKE DAMAGEEARTHQUAKE DAMAGE

•Landsides Landsides •Building damageBuilding damage

Liquefaction is a common phenomenon and is defined as the point where a water-saturated soil turns from a solid into a liquid due to loss of cohesion.

Liquefaction may occur several minutes after an earthquake. It can cause buildings to sink, underground tanks to float to the surface, and dams to collapse as once-solid sediment flows like water.

Earthquakes: TsunamisEarthquakes: Tsunamis An underwater earthquake with a magnitude of 8 or higher on the Richter scale can affect the earth’s oceans by causing a tsunami. Less commonly, tsunamis are also caused by submarine landslides or volcanic explosions.

This is because the earthquake generates a rolling wave out in the open water; however, as the waves approach shore, they start to “feel” the bottom of the sea floor. The waves slow down near the bottom, causing a huge wave to build up on top as the top is still moving at its original speed.

Types of zones in India:• ZONE 5: Very High damage risk zone. Kashmir, the

western and central himalayas, the North East Indian region and the Rann of Kutch fall in this zone.

• ZONE 4: High damage risk zone. The indo Gangetic basin and Delhi, Jammu and Kashmir , Faltan area (Maharashtra) is also in this zone.

• ZONE 3: Moderate Damage Risk zone.The Andaman and Nicobar Islands, parts of kashmir, Western Himalayas fall under this zone.

• ZONE 2: Low damage Risk zone. Southern parts and some Eastern coasts fall under this.

Major earthquakes in India:DATE PLACE MAGNITUDEDecember 26, 2004

off west coast northern Sumatra India

9.1

1869, Jan 10 Cocher Assam 7.5

1885, May 30 Sopar J&K 7

1897,June 12 Shillong Assam 8.7

1905,April 04 Kangra 7.8

2001,Jan 26 (Bhuj) Gujarat 7.7

2005,Oct 8 Muzzaffrabad in pakistan. (kashmir)

7.4

Can Earthquakes be Predicted?

Earthquake Prediction Programs•include laboratory and field studies of rocks before, during, and after earthquakes.•monitor activity along major faults•produce risk assessments

Earthquake Precursors •changes in elevation or tilting of land surface, fluctuations in groundwater levels, magnetic field, electrical resistance of the ground•Increase in rate of a seismic creep and slow movement along the fault.•Animal behavior: hibernating animals leaving their underground nests and seeking higher grounds.•Birds vacating the area•Deep water fish come closer to the surface.

Conclusion: No 100% accurate way to predict an earthquake . As more data is collected , predictions will get better.

On January 26, 2001, a magnitude 7.7 earthquake devastated the Kachchh region in the Gujarat India.

The two MISR images are pre- and post-earthquake scenes acquired on January 15 and January 31, 2001, respectively. 

Image courtesy NASA/GSFC/LaRC/JPL, MISR Team .