EARTHQUAKE

Suchitra LaishramMSc.II yearPanjab University

OBJECTIVES List the different types of seismic waves, their

different properties and describe how seismologists can use them to learn about earthquakes and the Earth's interior.

Describe how to find an earthquake epicenter. Describe the different earthquake magnitude

scales and what the numbers for moment magnitude mean.

Describe how earthquakes are predicted and why the field of earthquake prediction has had little success.

WHAT ARE EARTHQUAKES?

The shaking or trembling caused by the sudden release of energy.

Usually associated with faulting or breaking of rocks.

STUDYING EARTHQUAKES

Seismology --The study of earthquakes and the waves they create.

 Seismologists --Scientists who study and measure earthquakes to learn more about them and to use them for geological discovery.

SEISMOGRAPHS

Modern day scientists use a instrument called a seismograph to record earthquakes.

Seismogram is a graph output by a seismograph.

This instrument records earthquakes using waves.

The larger the waves the larger the earthquake.

ELASTIC REBOUND THEORY Explains how energy is

stored in rocks Rocks bend until the

strength of the rock is exceeded.

Rupture occurs and the rocks quickly rebound to an undeformed shape.

Energy is released in waves that radiate outward from the fault.

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.

WHERE DO EARTHQUAKES OCCUR AND HOW OFTEN?

Abt 80% of all earthquakes occur in the circum-Pacific belt.

Most of these result from convergent margin activity. Abt 15% occur in the Mediterranean-Asiatic belt. Remaining 5% occur in the interiors of plates and on

spreading ridge centers.

SEISMIC WAVES Seismic waves are waves

of energy that travel through

the Earth's layers, and are a result of an earthquake.

Two types:Body waves -- Primary(p) waves and -- Secondary(s) waves

Surface waves -- Love waves and -- Rayleigh waves

BODY WAVES Primary waves (p) fastest waves. travel through solids, liquids, or gases. compressional wave, material movement is in the

same direction as wave movement. Secondary waves(s) slower than P waves. travel through solids only. shear waves - move material perpendicular to

wave movement.

SURFACE WAVE Two types Love waves-- are horizontally polarized shear waves existing only in the presence of a semi-infinite

medium overlain by an upper layer of finite thickness.

travel slightly faster than Rayleigh waves.

Rayleigh waves--travel as ripples with motions that are similar to those of waves on the surface of water

They are slower than body waves. In the layered medium (like the crust and upper

mantle) it depends on their frequency and wavelength.

TYPES OF EARTHQUAKES

 Tectonic Earthquakes --occur when rocks in the earth's crust break due to geological forces created by movement of tectonic plates.

Volcanic Earthquakes occur in conjunction with volcanic activity.

Explosive Earthquakes result from the explosion of nuclear and chemical devices.

Collapse Earthquakes are small earthquakes in underground caverns and mines.

CLASSIFICATION OF EARTHQUAKE

Earthquakes are usually classified on the following bases:

(a) Cause of origin;

(b) Depth of focus; and

(c) Intensity and magnitude of earthquake.

(A) CAUSE OF ORIGIN:

(i) Tectonic Earthquakes occur when the plates move

against one another. This movement can create stress that causes the Earth's exterior shell, the lithosphere, to shift or break.

(ii) Non-tectonic earthquakes. The non-tectonic earthquakes are mainly of

three types due to surface causes, volcanic causes and collapse of cavity roofs .

(B) DEPTH OF FOCUS(i) Surface-earthquakes : Surface-earthquakes are

those in which the depth of the focus is less than 10,000 metres.

(ii) Shallow-earthquakes : The earthquakes with the hypocentre at a depth of 10 to 50.

(iii) Intermediate-focus earthquakes : When the earth quake is originated at a depth of 50 to 300 Kms.

(iv) Deep-focus earthquakes : The deep-focus earthquakes or the plutonic earthquakes are those with hypocentres located at depths more than 300 kms. Majority of the deep focus earthquakes originate between 500 and 700 kms.

(C) INTENSITY AND MAGNITUDE OF EARTHQUAKES

Rossi-Forrel's Scale Mercalli Scale Richter Scale

(I) ROSSI-FORREL'S SCALE

The 1873 version of the Rossi–Forel scale had 10 intensity levels:

I. Microseismic tremorII. Extremely feeble tremor. III. Feeble tremor. IV. Slight tremorV. Moderate tremorVI. Strong tremorVII. Very strong tremor. VIII. Damaging tremorIX. Devastating tremor.X. Extremely high intensity tremor.

MERCALLI SCALE

Magnitude Richter scale measures

total amount of energy released by an earthquake; independent of intensity.

Amplitude of the largest wave produced by an event is corrected for distance and assigned a value on an open-ended logarithmic scale .

TYPES OF DAMAGE CAUSE BY EARTHQUAKE Physical Damage -- Landslides

-- Tsunamis -- Fires -- Mudslides -- Liquefaction

Structural Damage -- Buildings Collapse -- Roadways Collapse

Emotional Damage -- Deaths

CAN EARTHQUAKES BE PREDICTED?

With the present state of scientific knowledge, it is not possible to predict earthquakes and certainly not possible to specify in advance their exact date, time and location. 

However, a great deal of research is being conducted to develop reliable prediction methods such as

Unusual behavior of animal.Radon gas emission.Electro-magnetic variations, etc .

WORLD EARTHQUAKE PRONE AREA

EARTHQUAKE PRONE AREA IN INDIA

RECENT EARTHQUAKE LISTS

TO DO BEFORE ,DURING ,AFTER EARTHQUAKEBefore the Earthquake:-- Learn first aid,Be prepared to act.-- Stock up on emergency supplies.-- Arrange your work area for safety.

During an Earthquake:-- Remain calm as the quake occurs.-- Don't use elevators.-- Drop down; take cover under a desk or table and hold on.

After an Earthquake:--Remain calm and reassuring. -- ready to act without electricity or lights.-- If you must leave a building, use extreme caution-- Use telephones only to report a life-threatening

emergency.

HELPLINE GIVEN North and Central America UNESCO-HELP

Basins. Brazil National Water Agency Delegation. USACE Global and Climate Scientists Featured. PIANC USA Commissions. U.S. Geological Survey. U.S. Bureau of Reclamation and Sandia

National Upper Rio Grande Commissions.

THANK YOU