Earthquake 01

1. CE 2201
Engineering Geology & Geomorphology
Shubhagata Roy
DEPARTMENT OF CIVIL AND ENVIRONMENTAL
ENGINEERING
FAREAST INTERNATIONAL UNIVERSITY

2. What is Earthquake
An earthquake is an unpredictable event in
which masses of rock shift below Earth's
surface, releasing enormous amounts of energy
and sending out shock waves that sometimes
cause the ground to shake dramatically.
 Energy released radiates in all directions
from its source, the focus.
 Energy propagates in the form of seismic
waves.
 Sensitive instruments around the world
record the event.

3. The Release of Energy

4. The Focus & the Epicenter
The point within
Earth where faulting
begins is the focus,
or hypocenter.
The point directly
above the focus on
the surface is the
epicenter.

5. Plate Boundaries

6. Faults

7. Faults

8. Plate Tectonics Theory
 Earth is divided into sections called Tectonic
plates that float on the fluid-like interior of the
Earth.
 Earthquakes are usually caused by sudden
movement of earth plates.
Rupture of rocks along a fault
 Faults are localized areas of weakness in the
surface of the Earth, sometimes the plate
boundary itself.

9. Tectonic Forces
 The interior of the Earth is dynamic – it cools
down and thus provides energy for
convective currents in the outer core and in
the asthenosphere.
 Additional energy comes from radioactive
decay...

10.  Plate Tectonics theory is very young (1960-
ies)
 It provides answers to the most fundamental
questions in seismology:
 Why earthquakes occur?
 Why are earthquake epicenters not uniformly
distributed around the globe?
 At what depths are their focal?

11. Plates
 The earth’s surface is broken into ~ 20 rigid
plates.
 All plates contain oceanic crust; some also
have continental.
 All plates move on convecting mantle “at the
rate fingernails grow.”
 Plates interact at their edges causing
volcanoes and earthquakes.

12. Plates
 The “Plates” of Plate Tectonics are fragments
of lithosphere.
 Lithosphere, the outermost layer of Earth,
consists of…
 The crust and
 The uppermost mantle
 Lithosphere is strong and rigid.
 Lithosphere moves over the asthenosphere
which is…
 Weaker
 Softer

13. Plate tectonics yields a unified explanation of:
 Earth’s major surface processes
 The distribution of earthquakes
 The distribution of volcanoes
 The origin of continents and ocean basins
 The past distributions of plants and animals
 The mechanism of orogenesis (mountain
building)
 The driving engine of the rock cycle

14. Plate Motion
 All plates move relative to one other.
 Motion is very slow (on a human time scale)*
- 1 to 15 cm/yr.
 Motion is continuous.
 Motion averages 5 cm (2 inches) per year.
“as fast as your fingernails grow”.
*On a geologic time scale plate motion is extremely
rapid

15. Earth’s Major Plates
Seven major lithospheric plates-
 Pacific (largest)
 Eurasian
 African
 North American
 Antarctic
 South American
 Australian

16. Earth’s Minor Plates
Many minor plates and “micro plates”
 Juan de Fuca
 Philippine
 Arabian
 Caribbean
 Cocos
 Nazca
 Scotia
 Some plates have been destroyed (Farallon
plate)

17. Earth’s Plates

18. Plate Boundaries
 Plates are rigid.
 When they interact, plate interiors remain
intact.
 Plate boundaries, however, are modified by
deformation-
 Faulting
 Folding
 Thickening / Thinning
 Melting
 Plate boundaries are the locations of large-
scale geologic phenomenon-
 Volcanoes
 Earthquakes
 Mountain chains

19. Plate Boundaries

20. Identifying Plate Boundaries
 Plate boundaries are marked by earthquake
foci (centers).
 Plate interiors are comparatively earthquake
free.

21. Plate Boundaries