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Gallery 3

# Earthquake Lab

Perform experiments and challenge yourself as you explore the phenomena of earthquakes and their effects.

## How it works

Experiment with the exhibits to see how an earthquake affects buildings and the ground.

## Things to try or ask around the exhibit

• Have you ever felt an earth tremor or an earthquake?
• Can you build a structure that resists an earthquake shaking? Compare with a friend.
• Try hard and soft ground. Do they work differently?
• What shapes work best when constructing?
• Compare the movement of the platform on the screen to the movement of your structure using an accelerometer. Are they the same?
• What's the last earthquake that you can remember hearing about in the news?

## Background

Earthquake Lab uses a ‘shake table’. This is a pneumatically powered platform that shakes from side to side, simulating one way earthquakes affect the ground. Shake tables are very important in the study of earthquakes and in earthquake engineering.

By building models of structures, or even using full-sized buildings, we can simulate the effects of different types of earthquakes on man-made structures. Test objects are fixed to the platform as if it were the ground they would be built on and then shaken, often until they fall apart. Video recording, accelerometers, transducers and other devices are used to observe and record the effects of an earthquake on the structure.

Unlike moment magnitude which measures the energy released in an earthquake, we use the modified Mercalli Intensity Scale to measure how much an earthquake damages buildings. It works on a scale from 1 to 12 (or I to XII). The lower numbers of the Mercalli scale represent how the earthquake was felt by humans, while higher numbers of the scale are based on observed structural damage in buildings (usually VIII or above on the scale). If an earthquake of magnitude 5.6 hits a deserted area, the Mercalli reading would be low, because it's an unpopulated area. However, if the epicentre of the 5.6 magnitude earthquake hits heavily populated areas (such as Sydney), then the Mercalli reading would be high, because of building destruction.

If the period of vibration of the ground during an earthquake matches the period of vibration of a building, a resonance effect is created, much like a person pushing a swing higher and higher by pushing at ‘the right time’. The resonance effect increases the likelihood of a building being damaged in an earthquake. Depending on soil structures and other factors, a single storey building usually has a period of 0.1 seconds, a two storey 0.2 seconds and so on. This can be generalised to an N storey building having a period of 0.1 * N seconds.

## Finding the science in your world

Since 1994, all buildings in Australia, including domestic buildings, are required to be designed and constructed to resist earthquakes. An earthquake Loading Code (AS1170.4) has been published by Standards Australia to assist engineers and architects to design and construct buildings to resist earthquakes without collapsing, though they may well suffer damage in the process.