Earthquake

CONTENTS.

•Introduction.•Classification.

•Terminology.•Causes Of EARTHQUAKE.

•Effects Of EARTHQUAKE.

INTRODUCTION

• Earthquakes happens by shaking or displacement of ground.

• The momentary shocks occur on the earth are called as earthquakes.

• Technically it may be defined as: ”vibrations induced in the earth’s crust due to

internal / external causes that shake up a part of the crust , structures , living & non-living things existing on it”

The study of earthquake is required for :1) To make certain the factors that lead to

earthquake.2) To predict the occurrence of earthquake.3) To design and provide such structures that will

give protection against earthquake.

CLASSIFICATION OF EARTHQUAKE

5

DEPTH OF FOCUS

MAGNITUDE

CAUSE OF ORIGIN

DEPTH OF FOCUS

1 •SHALLOW EARTHQUAKES•Depth of focus lies up to 60 km below the surface

2 •INTERMEDIATE EARTHQUAKES•Originate between 60 & 300 km

3 •DEEP SEATED EARTHQUAKE•Originate between 300 & 700 km

MAGNITUDE

• Magnitude is a quantitative measure of the actual size of the earthquake.

• Measured with help of, RICHTER SCALE BODY WAVE MAGNITUDE SURFACE WAVE MAGNITUDE WAVE ENERGY MAGNITUDE

CAUSE OF ORIGIN

• TECTONIC EARTHQUAKES “Caused due to faulting or relative

displacement”

• NON-TECTONIC EARTHQUAKES “Caused due to volcanic eruptions, atomic

explosions or landslides”

Terminologies.

• Seismology:- The science which deals with study of Earthquakes in all their aspects is called Seismology.

Focus.

An earthquake is generally due to some disturbance of displacement in the rocks at some depth below the surface of the earth.

Epicenter

• The point or place on the surface vertically above the focus of a particular Earthquake is termed as epicenter.

Seismic waves.

• During each Earthquake Elastic waves are generated at the focus.

• These waves are called Seismic Waves.

Types Of Seismic Waves.

1. P-type Wave.2. S-type Wave.3. L-type Wave.

P-type Waves.

• These are called Primary Waves.• The particles vibrates in the direction of

propagation.

S-type Waves.

• These are also called Secondary waves.• The Particles vibrates at right angles to the

direction of propagation.

L-type Waves.

• These are also called long waves or Surface Waves.• They travel near the surface layer of the Earth.• These waves are recorded only after the arrival of P

and S waves.

Types Of L-type Waves.

• Rayleigh waves.• In which the displacement of the particles is

of a complex nature, partly being in the direction of propagation and partly at right angles to it.

• Love waves.• In which the displacement of the particles

practically horizontally that is in the direction of propagation.

Causes of earthquake

• The causes that lead to origin and propagation of shock waves through the ground during an earthquake may be non-tectonic or tectonic in character.

• Non-tectonic causes, vibrations induced due to volcanic eruptions.

• The volcanic eruptions may be of an explosive, blasting nature. Huge quantity of lava are thrown out suddenly under great pressure & with a big bang ,causing tremors all around.

The tectonic earthquake• The tectonic earthquakes are the most common & often the most

destructive events. Their exact cause of origin is yet not fully established.

• These are caused due to displacement of blocks along fractures called faults.

• The plane of rupture & displacement is called the fault plane & faulting respectively.

• Displacement is associated with a rebound or readjustment of curvature developed due to bending during stressing.

Elastic rebound theory• [1]preparatory process• [2]rupture phase• [3]post failure adjustment

1. Preparatory process

• The duration of the preparatory phase is to ultimately define the size of the actual earthquake.

• The number of foreshocks are often during this phase.

2. Rapture phase

• Main shock is the characteristic of this phase.• During these process rupture takes place

along the fault and all the stored energy is released as seismic waves.

3. Post failure adjustment

• The medium is restored to a state of equilibrium involving series of after shocks, which are simply manifestation of release of residual strain from the rocks.

Plate tectonics & earthquake• The concept of plate tectonics has been made in explaining

the origin of tectonic earthquake.• Already exhaustive data has been collected to show that

earthquake occur along the boundaries of plates moving apast each other.

• The deep focus & intermediate earthquake have a tendency to occur in few locations or nests only.

• The inner regions of plates are free from tectonic earthquake.

Reservoir associated earthquake

• A new class of earthquake associated with impounding of water in artificially created reservoirs have come to be recognized in itself.

• It is called Reservoir associated earthquake.

Cause.

• Sagging effect of the load.• Increased pore pressure.

Sagging effect of the load:-

• The rocks at the basin are to bear additional load due to impounded water, these adjust to the new loads by bending or sagging thereby initiating stress-redistribution in their regime.

Increased pore pressure.

• It is believed that when water is stored in a reservoir, the pore pressure in the basin rocks is increased considerably. Such an increase has an adverse effect on the shearing strength of the basin rocks, which may lead to their failure and slippage, and the associated increase in seismicity

Effect Of Earthquakes1. Shaking and Ground Rupture Shaking and ground rupture are the main

effects created by earthquakes, principally resulting in more or less severe damage to buildings and other rigid structures.

The severity of the local effects depends on the complex combination of the earthquake magnitude, the distance from the epicenter, and the local geological conditions, which may amplify or reduce wave propagation.

The ground-shaking is measured by ground acceleration.

Ground rupture is a visible breaking and displacement of the Earth’s surface along the trace of the fault, which may be of the order of several meters in the case of major earthquakes.

Ground rupture is a major risk for large engineering structures such as dams, bridges and nuclear power stations.

2. Landslides and avalanches Earthquakes, along with storms, volcanic activity,

coastal wave attack, and wildfires, can produce slope instability leading to landslides, a major geological hazard.

3. Fires Earthquakes can cause fires by damaging electrical

power or gas lines. In the event of water mains rupturing and loss of

pressure, it may also become difficult to stop the spread of a fire once it has started.

For example,more deapths in the 1906 San Francisco erthquake were caused by fire than by the earthquake itself.

4. Soil Liquefaction Soil liquefaction occurs when, because of the

shaking, water-saturated granular material such as sand temporarily loses its strength and transforms from a solid to a liquid.

Soil liquefaction may cause rigid structures, like buildings and bridges, to tilt or sink into the liquefied deposits.

5. Tsunami Tsunamis are long-wavelength, long-period

sea waves produced by the sudden or abrupt movement of large volumes of water.

Large waves produced by an earthquake or a minutes,

Tsunamis can also travel thousands of kilometers across open ocean and wreak destruction on far shores hours after the earthquakes that generated them.

Most destructive tsunamis are caused by earthquakes of magnitude 7.5 or more.

6. Floods A flood is an overflow of any amount of

water that reaches land. Floods occur usually when the volume of

water within a body of water , such as a river or lake , exceeds the total capacity of the formation, and as a result some of the water flows or sits outside of the normal perimeter of the body.

However, floods may be secondary effects of earthquakes, if dams are damaged.

7. Human impacts Earthquakes may lead to disease, lack of basic

necessities, loss of life, higher insurance premiums, general property damage, road and bridge damage.

Prepared By:

Hardik Kanuga

Harsh Contractor

Parth Joshi

Tushar Kaswala

THANK YOU