Earthquake Hazard: Introduction

This earthquake, saw over 150,000 houses destroyed or burned, 320,000 residents made homeless and 6,336 citizens killed. More details: Phoenix Kobe

The Earth's lithosphere is considered to comprise about a dozen major rigid plates with numerous mini-plates between. It is along the boundaries between these plates that most geological deformation occurs. Many large scale geomorphological features such as mountain ranges and volcanoes occur at plate boundaries as do most of the world's earthquakes. An earthquake is an abrupt movement of the Earth, caused by the sudden release of strain that has accumulated over a long time.

The majority of large earthquakes each year occur either in the subduction zones of the circum-Pacific region or along major fault lines that extend between the Mediterranean and China. If an earthquake occurs in a populated area, it may cause many deaths and injuries as well as property damage. Two of the most recent and famous large magnitude earthquakes both occurred in regions adjoining the Pacific Ocean, in Chile (1960) and Alaska (1964).
Two measures of earthquakes are the energy released or magnitude (often referred to on the Richter Scale) and the degree of ground shaking or intensity (measured from surface damage by the Modified Mercalli Scale).

Recent earthquakes, such as the 1995 Kobe, Japan (see Phoenix Kobe), and 1999 Taiwan earthquakes demonstrate the earthquake hazard faced by many nations of the world, and the great costs or losses that communities suffer.

Generally speaking, earthquakes cannot be predicted with certainty and therefore, reducing the losses is very much reliant on pre-planning to cope with the hazard impact. Losses, both tangible and intangible, can be reduced through proper hazard mitigation planning, to ensure that building safety standards are in place, that there is land zonation and restrictions on land development in earthquake prone regions, and that opportunities for secondary hazards (e.g. fires and floods) are minimised.

Scientists have for many years now been working on developing methods to predict the occurrence of earthquakes. However progress is slow - earthquake prediction is a science that requires considerable research effort and longterm event monitoring.

Learning Outcomes

On completing this module you should be able to appreciate what is likely to happen during earthquakes of differing magnitude and why earthquakes happen. You should also have a basic understanding of the response of materials to earthquakes, enabling you to communicate effectively with scientists, engineers and planners on matters of earthquake hazard mitigation and development of disaster response programmes.

In this module you will learn about:

1. What is an earthquake?

2. How can we locate the origin of an earthquake?

3. Where and why do earthquakes occur?

4. How are earthquakes measured?

5. What are the possible impacts of an earthquake?

6. To what extent can earthquakes be predicted?

7. How can we mitigate and prevent earthquake hazards?

Some examples of historic earthquake events are given, together with a reference list which covers the Edgecumbe earthquake sequence of March 2, 1987 located near the town of Edgecumbe in the Bay of Plenty. This is one of the best documented earthquakes in New Zealand.