Entry Quiz

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In the context of Natural hazards, define the key term "Magnitude".

Introduction

Learning outcomes:

To be able to:

understand the nature of seismicity and related hazards
know where and why seismic activity occurs
understand what is meant by ‘spatial distribution’, ‘magnitude and frequency’ in relation to seismic events.

Where are we on our specification?

Starter

Which types of boundaries do we usually associate with seismic activity?

Nature and distribution

Earthquake

focus - the point at which this pressure release occurs within the crust
● shallow focus (0–70 km deep): these tend to cause the greatest damage and account for 75 per cent of all the earthquake energy released
● intermediate focus (70–300 km deep)
● deep focus (300–700 km deep)
epicentre - the point immediately above that on the earth’s surface

Nature and distribution

The vast majority of earthquakes occur along plate boundaries

TASK 1:

Using a map of earthquakes from Hodder text book or https://slaveevo.com/goto/?ai=3156, add the main earthquake zones to the map below.

Describe the relationship between the location of earthquakes and plate boundaries.
Challenge: Why are these locations earthquake-prone?

TASK 2:

Using variety of sources, research and answer the following questions:

Describe how earthquakes can be measured.[6 marks]
Challenge: ‘Earthquakes cannot be predicted’. Evaluate this statement [6 marks]

Magnitude and frequency

The magnitude of earthquakes is measured in a variety of ways.

Richter scale
- logarithmic scale (1-10)
Moment magnitude scale (MMS)
- identifies energy release
- its scale is the same as that of Richter, that is, 1–10 [?]
Mercalli scale
- It measures the intensity of an event and its impact.
- It is a 12-point scale where Level 1 is approximate to 2 on the Richter scale.
- It goes up to Level XII (approximately 8.5 on Richter).

Magnitude and frequency

Seismic records enable earthquake frequency to be observed, but these records only date back to 1848 when an instrument capable of recording seismic waves was first developed. Before that we have to consult historical records as to the date and the effects of the identified event.