Earthquake

Prepared by,

Sujith Velloor S

Lecturer

Civil Department

Engineering College

Tuwa

Outline1. Interior of earth

2. Convection currents cause the movement of plates

3. Tectonic Plate

4. Why do earthquakes occur?

5. Where do earthquakes occur.

6. Definitions

7. Seismic waves: forms

8. Measuring earthquakes

9. Classification of earthquake

10. Locating the shaking

11. Earthquake risk and prediction

12. Short-term predictions

13. Impacts of Earthquake Prediction

Interior of earth

1. Crust

2.Mantle

3. Core

Crust

It is lithosphere thinnest outer solid shell about(5-

40km)

There are 2 different type of crust

1.thin oceanic crust that underlines the ocean

basin

2.Thicker Continental crust that underline

continents

There are 2 different type of crust are made up of

different type of rock

Oceanic crust Basalt(3-4 mile)

Continental crust Granite (20-30 mile)

Mantle

It is Asthenosphere about

a thickness of 2900km

Mantle contain hot dense,

ultra basic igneous rocks in

plastic state

It has the property to flow

It has different

temperature at different

depths

Core

It is Barosphere Central part of earth

There are 2 different type

Inner Core(1290km)

Outer Core(2200km)

Temperature at the core is about 2500 degree

Celsius

Convection currents cause

the movement of plates

Convection Current Occur in mantle

because of high temperature & pressure

Gradient Between Core and Crust

It occur result in a circulation of earth mass,

Hot molten lava comes out & cold Rocks

goes into earth where it melt & become a

part of mantle

Potential Energy (PE) builds up

PE may be released as KE and the plates

move abruptly apart

This sudden release of energy is an

earthquake

Convection current of mantle causes

slide mantle on core This sliding of earth

mass is called Tectonic Plate

Tectonic Plate

Tectonic Plate

Why do earthquakes

occur? Fractures, faults

Energy released

and propagates in all

directions as seismic

waves causing

earthquakes

focusepicenter

The shaking of ground or Vibration

caused by slip or volcanic or magmatic

activity or sudden stress changes in

earth are called Earthquake

Where do earthquakes

occur:

1) Most earthquakes occur

along the edge of the oceanic and continental

plate

2) Along faults: normal, reverse,

transform

3) Between the Tectonic plate

4) Focus is the location for

earthquake origin

Definitions

Earthquake = Vibration of the Earth produced by the rapid release of energy

Seismic waves = Energy moving outward from the focus of an earthquake

Focus= location of initial slip on the fault; where the earthquake origins

Epicenter= spot on Earth’s surface directly above the focus

Seismic waves: forms

P-waves: (primary or first)

called compressional, or push-pull waves

Propagate parallel to the direction in which the wave is moving

Move through solids, liquids

Fastest moving – reach seismic station first

S-waves: (secondary)

Called shear waves

Propagate the movement perpendicular to the direction in which the wave is moving

Reach seismic station second

Longitudinal wave

P-waves

Sound waves

Transverse wave

S-waves

Light waves

Surface waves (Love waves & Rayleigh Waves).

1. Love Waves- Moves in Horizontal and

transverse plane- They are fastest waves than

Rayleigh waves-They Create Breaking

Rupture

2. Rayleigh Waves-Moves as oscillation-Waves are produced as when rock

thrown in pond-Waves are produced by intersection

of p and s waves

•b

•a

Which diagram shows a transverse wave and a longitudinal

wave?

an s-wave and a p-wave?

Measuring earthquakes

Seismometers:

instruments that

detect seismic

waves

Seismographs

Record intensity, height

and amplitude of seismic

waves

Locating the shaking

Measure time between P and S waves on

a seismogram

Need at least 3 seismographs

Locating the shaking

Earthquake size: two ways

to measure

1) Magnitude: Richter Scale

• Measures the energy released by fault movement

• related to the maximum amplitude of the S wave measured from the seismogram

• Logarithmic-scale; quantitative measure

• For each whole number there is a 31.5 times increase in energy

eg. an increase from 5 to 7 on the Richter scale = an increase in energy of 992 times!!

2) Intensity: Mercalli Scale:

What did you feel?

Assigns an intensity or rating to measure an earthquake at a particular location (qualitative)

I (not felt) to XII (buildings nearly destroyed)

Measures the destructive effect

Intensity is a function of:

Energy released by fault

Geology of the location

Surface substrate: can magnify shock waves e.g. Mexico City (1985) and San Francisco (1989)

Classification of

earthquake

Classification based on Location

1. Interplate earthquake:-boundary

layer(99%)

2. Intraplate earthquake:- Away from

boundary layer(1%)

Classification based on Focal Depth

1. Shallow earthquake:- <70km

2. Medium earthquake:- 70km-300km

3. Deep earthquake:- >300km

Classification based on Magnitude

1. Great-8 or above

2. Major-7-7.9

3.Strong-6-6.9

4. Moderate-5-5.9

5. Light-4-4.9

6. Minor-3-3.9

7.Very Minor-<3

Classification based on Epicentral

distance

1.Local Earthquake:- <1degree

2.Regional Earthquake:-1 to 10 degree

3.TeleSeimic Earthquake:- >10 degree

Frequency of Occurrence of Earthquakes

Descriptor Magnitude Average Annually

Great 8 and higher 1 ¹

Major 7 - 7.9 17 ²

Strong 6 - 6.9 134 ²

Moderate 5 - 5.9 1319 ²

Light 4 - 4.9 13,000

(estimated)

Minor 3 - 3.9 130,000

(estimated)

Very Minor 2 - 2.9 1,300,000

(estimated)

¹ Based on observations since 1900.

² Based on observations since 1990.

Earthquake damage

Ground Failure - constructions collapse

Fires - from broken gas and electrical lines

Landslides - EQ's triggered; occur in hilly/mountainous areas.

Liquefaction - water-saturated, unconsolidated materials flow

Tsunami (seismic sea waves; "tidal" waves) - can grow up to 65

m

Earthquake risk and prediction

Long-term methods

1) seismic hazard maps

2) probability analysis

based on:

- historical EQ records

- geologic EQ records

- slip-rate on active faults

- frequency and

magnitude of recent EQ's

Real-time 24 Hour

Forecast

Short-term predictionsPrecursor phenomena (<1 year to days)

1. Foreshocks: usually increase in magnitude

2. Ground deformation

3. Fluctuations in water well levels

4. Changes in local radio wave characteristics

5. Anomalous animal behavior???

Impacts of Earthquake Prediction

THANKING YOU