slide on Earthquakes in Bangladesh.

1. EARTHQUAKES
Presented by:
Hasibul Hasan (334)
MD. Samsul Alam Dipu (349)
Prince Talukder (358)
1

2. Content
-Definition
-Locating the source of earthquake
-Seismic waves and types of SW
-Causes of Earthquakes
-Measuring of Earthquakes
-Type of Earthquake
-Effect of Earthquakes
-largest Earthquakes
-Earthquake in Bangladesh
-Earthquake Preventive Design
-Reference
2

3. Definition
-Vibration within earth materials are produced by the rapid release of energy is called
Earthquake
-A sudden movement of the Earth's lithosphere (its crust and upper mantle) is called
Earthquake. Earthquakes are caused by the release of built-up stress within rocks
along geologic faults or by the movement of magma in volcanic areas. They are usually followed
by aftershocks.
3

4. Locating the source of earthquake
■ Focus= location of initial slip on the fault; where the earthquake origins
A fault is a thin zone of crushed rock separating blocks of the earth's crust. .
■ Epicenter= spot on Earth’s surface directly above the focus
4

5. Causes of Earthquake
-Tectonic movements : The main cause is when tectonic plates ride one over the other,
causing orogeny (mountain building), and severe earthquakes.
- Volcanic eruption : When boiling lava tries to break through the surface of the earth, with
The increase of pressure of gases, certain movements are caused in earth crust. Thus VE
causes earthquake
-Earthquakes are caused by faulting, a sudden lateral or vertical movement of rock along a
rupture (break) surface.
-There are three main types of geological Fault that may cause an earthquake
*Normal,
* Reverse (thrust) and
* Strike-slip
5

6. Causes of Earthquake
Pictures :
6

7. Seismic waves and Types of SW
-Seismic waves originate at focus and travel outward in all direction.
- The energy released in an earthquake travels in waves
- There are mainly two types of seismic waves:
-Body waves ( again two types)= * Primary waves ( P waves )
*Secondary waves ( S waves )
- Surface waves ( L and R waves )
7

8. Primary waves
-Called P waves
-Compression waves- squeeze and stretch rock (Push and Pull)
-Can travel through any material- solid, liquids, and gases
-Travel the fastest ( 8 KM/sec)
-First wave to arrive at an Earthquake.
8

9. Secondary waves
-called S waves
-moves the ground up and down.
-Can travel only through solid material, not liquids or gases
-Travel a little more than half the speed of P waves ( 4.5 KM/sec)
-Cause building damages.
9

10. Surface waves
-Seismic waves that travel along Earth’s Surface ,and gives side to side or rolling
movement.
-When P and S waves reach the
surface, they make Surface
waves. That means travel
more slowly then P and S
wave.
-There are two types,
Love waves and Rayleigh waves
-Cause lots of
damage means more destructive.
10

11. Seismic wave properties
■ Velocity: function of the physical properties of the rock the wave is traveling through
– Velocity increases with rock density
– Velocity changes when passing from one material to another (increases/decreases)
– Liquids: S-waves do not get transmitted through liquid; P-waves slow down
■ Why is this important?
- If we know the velocity of the wave, we can infer
the type of rock it traveled through- that’s how we map
the interior of the Earth!!!
11

12. Measuring of Earthquakes
-Seismograph: Instrument used
to measure an Earthquake
-Seismogram: The paper
record of the Earthquake
data (shaking) is called a
seismogram
12

13. Earthquakes Magnitude
-Strength measured by the amount of released energy
-Earthquake is measured in Richter Scale
Measured the amplitude of earthquake waves on
Seismograph.
-Each increase in number represents
10x an increase in power.
-Example: a 4.0 is ten times stronger than a 3.0
13

14. Earthquakes Magnitude
-Earthquake magnitude is
measured in Richter Scale.
14

15. Types of Earthquake
-On the basis of depth there are three types of earthquake:
-On the basis of magnitude Earthquake are-
15
TYPES Depth of focus (KM)
1. Shallow Earthquake 60
2. Intermediate Earthquake 60-300
3. Deep Earthquake >300
TYPES MAGNITUDE
Great Earthquake M ≥ 8
Major/large Earthquake 7≥ M <8
Moderate Earthquake 5≥ M <7
Small Earthquake 3≥ M <5
Micro-Earthquake 1≥ M <3
Ultra Micro-Earthquake M <1

16. Effect of Earthquake
-Ground Shaking
-Damage to man made structure : constructions collapse
-Fires : from broken gas and electrical lines
-Flooding
-Tsunami : Giant wave created by undersea Earthquake, volcanic cruption.
Landslides :occur in hilly/mountainous areas.
16

17. Largest Earthquakes
17

18. Largest Earthquakes
18
Chile,California, Japan

19. Earthquake Zone Of Bangladesh
Bangladesh is Divided into three
Earthquake zone:
*Zone-1: High Risk
(Mymensingh, Sylhet,Rangpur etc)
*Zone-2: Moderate Risk
( Bogra, Dinajpur, Comilla etc)
*Zone-3: Low Risk
( Khulna, Jessor, Barisal etc)
19

20. Recent Earthquake in Bangladesh
Places Magnitude (on the Richter
scale)
Year
Chittagong 6.0 1997
Maheshkhali 5.2 1999
Rangamati 5.1 2003
Narail 4.2 2006
Mymensingh 5.1 27 July 2008
Dhaka 6.1 21 September 2009
Dhaka 7.5 11 August 2009
20

21. Earthquake Preventive Design
Structure that suggested for earthquake zone-
- Structure should be design according to BNBC
- 33% extra reinforcement provision to reduce the earthquake effect.
- Buildings can be constructed with L type Corner Column and T type inner column.
- 8’’ /12’’ column section with 5’’ to 8’’ brick wall thickness make the buildings
more tight.
21

22. Earthquake Preventive Design
For furthermore , the following general principles may be follow-
-Height of each floor should be 10’
- Foundation must be laid on hard soil
-Framed structure should be preferred.
22

23. References
- Physcial and Engineering Geology by S.K GARG
- A text book of Geology By PK Mukherjee
- Geology made simple by WH Mathewes
- https://en.wikipedia.org/wiki/Earthquake
- http://en.banglapedia.org/index.php?title=Earthquake
- http://www.observerbd.com/2016/01/05/129456.php
- https://www.eartheclipse.com/natural-disaster/causes-of-earthquakes.html
- https://www.soest.hawaii.edu/GG/ASK/earthquakes.html
- https://www.quora.com/What-causes-earthquakes
-https://en.wikipedia.org/wiki/Lists_of_earthquakes
23

24. THANK YOU
If you have any questions feel free to ask.
24