CE 2201Engineering Geology & Geomorphology

Shubhagata Roy

DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

FAREAST INTERNATIONAL UNIVERSITY

EARTHQUAKE

INTRODUCTION TO EARTHQUAKE

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.

INTRODUCTION TO EARTHQUAKE

The Release of Energy

INTRODUCTION TO EARTHQUAKE

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.

WHERE DO EARTHQUAKES OCCUR

Plate Boundaries

WHERE DO EARTHQUAKES OCCUR

Faults

WHERE DO EARTHQUAKES OCCUR

Faults

CAUSES OF EARTHQUAKE

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.

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...

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?

PLATE TECTONICS

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.

PLATE TECTONICS

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

PLATE TECTONICS

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

PLATE TECTONICS

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

PLATE TECTONICS

Earth’s Major Plates

Seven major lithospheric plates- Pacific (largest) Eurasian African North American Antarctic South American Australian

PLATE TECTONICS

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)

PLATE TECTONICS

PLATE TECTONICSEarth’s Plates

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

PLATE TECTONICS

Plate BoundariesPLATE TECTONICS

Identifying Plate Boundaries

Plate boundaries are marked by earthquake foci (centers).

Plate interiors are comparatively earthquake free.

PLATE TECTONICS

Plate BoundariesPLATE TECTONICS