M E A S U R I N G M AG N I T U D E

TECTONIC LANDSCAPES

SPECIFICATION DETAIL

• 3.1d The measurement of earthquake magnitude (the Mercalli and Richter scales).

• Diagrams showing the characteristics of focus and epicentre.

LEARNING OBJETIVES

• Know the differences between the Mercalli (intensity) and Richter (magnitude) scales.

• Explain how earthquakes occur with reference to the epicentre and focus of earthquakes.

DEFINITIONS

• Watch Seismograph: Here

• Mercalli scale: (intensity)Uses seismic scale to measure the intensity of an earthquake. It is used to measure the effects of an earthquake.

• Richter scale: (magnitude)A logarithmic scale used to express the total amount of energy released by an earthquake(It is a base 10 logrimithic scale: e.g. 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0, )assign a single number to quantify the energy released during an earthquake.

The Richter scale can be used to measure the magnitude (power) of a tremor using an instrument called a seismograph.

HOW ARE EARTHQUAKES MEASURED?

It is a logarithmic scale which means that a size ‘6’ earthquake on the Richter scale is 10 times larger than a size ‘5’ and 100 times larger than a size ‘4’.

HOW DOES A SEISMOGRAPH WORK?

The Mercalli scale rates an earthquake's magnitude based on observations of the damage it causes on a scale of 1 to 12.

THE MERCALLI SCALE

Items shake from shelves:

scale 5

Buildings collapse: scale 10

Intensity

(Mercalli)

Observations (Mercalli)

Richter Scale Magnitude (approx.

comparison)

I No effect 1 to 2

II Noticed only by sensitive people 2 to 3

III Resembles vibrations caused by heavy traffic 3 to 4

IV Felt by people walking; rocking of free standing objects 4

V Sleepers awakened; bells ring 4 to 5

VI Trees sway, some damage from falling objects 5 to 6

VII General alarm, cracking of walls 6

VIII Chimneys fall and some damage to building 6 to 7

IX Ground crack, houses begin to collapse, pipes break 7

X Ground badly cracked, many buildings destroyed. Some landslides

7 to 8

XI Few buildings remain standing, bridges destroyed. 8

XII Total destruction; objects thrown in air, shaking and distortion of ground

8 or greater

TASK: SORTING

• Using the following statements, sort them into which best describes the scales.

• Here

Intensity

(Mercalli)

Observations (Mercalli)

Richter Scale Magnitude (approx.

comparison)

I No effect 1 to 2

II Noticed only by sensitive people 2 to 3

III Resembles vibrations caused by heavy traffic 3 to 4

IV Felt by people walking; rocking of free standing objects 4

V Sleepers awakened; bells ring 4 to 5

VI Trees sway, some damage from falling objects 5 to 6

VII General alarm, cracking of walls 6

VIII Chimneys fall and some damage to building 6 to 7

IX Ground crack, houses begin to collapse, pipes break 7

X Ground badly cracked, many buildings destroyed. Some landslides

7 to 8

XI Few buildings remain standing, bridges destroyed. 8

XII Total destruction; objects thrown in air, shaking and distortion of ground

8 or greater

TASK: WATCH THESE CLIPS

• Tachoma, Japan earthquake: Here• Chilean earthquake: Here• Kashima, Japan earthquake: Here• Tokyo, Japan earthquake: Here• Maryland, USA earthquake: Here

Which scale was the most easy to use? Why?

EXAM PRACTISE

• Describe 2 differences between the Mercalli and Richter scale. (2 marks)

One difference is …………

A second difference is that……………

LEARNING OBJETIVES

• Know the differences between the Mercalli (intensity) and Richter (magnitude) scales.

• Explain how earthquakes occur with reference to the epicentre and focus of earthquakes.

EPICENTRE

• Epicentre on google earth: here• Interactive : Here

EPICENTRE AND FOCUS

EXAM QUESTION

• Outline a difference between the focus and epicentre of an earthquake. (2marks)

LEARNING OBJETIVES

• Know the differences between the Mercalli (intensity) and Richter (magnitude) scales.

• Explain how earthquakes occur with reference to the epicentre and focus of earthquakes.