Exemplar for internal assessment resource Science for Achievement Standard 90942

The transfer of energy in an earthquake

When an earthquake occurs energy is transferred, from where the rocks break, and travels throughout the world. The bigger the quake the further from the epicentre the waves will travel. There are two types of earthquake wave, body and surface, generated during an earth quake. They carry energy away from the earthquake epicentre.

Body Waves:

Body waves and surface waves are the two types of seismic waves formed during great earthquakes. P waves and S waves are called body waves because they travel through the body of the Earth.

The p-wave:

Every earthquake creates P waves and S waves. P waves travel away from the focus of an earthquake where the rocks first fractured by compressing and expanding the rocks as they travel through solids, liquids and gases. P waves travel through all parts of the Earth. These waves are the fastest moving waves at 8kms-1. These waves produce the sound of an earthquake. So in the Christchurch earthquake it took about 5 seconds for the p-waves to hit Christchurch.

The s-wave: S-waves travel in a motion similar to a rope held tight at one end while the other end is lifted rapidly back and forth. S-waves only travel through solids and do not travel through the liquid outer core of the Earth. These waves move at 5kms-1.

© NZQA 2015 Exemplar for internal assessment resource Science for Achievement Standard 90942

Surface waves:

Body waves and surface waves are the two types of seismic waves formed during great earthquakes. When body waves reach the surface of the earth they interact to make surface waves. There are two main surface waves, the Rayleigh wave and the Love wave.

Rayleigh Waves

Rayleigh waves also move on the surface but are closer to how waves in the ocean move. Their movement is circular in motion as they move through the Earth but the circular motion is retrograde meaning the waves circle backward as they move forward. These waves are highly destructive and caused a lot of the damage in the Christchurch earthquake, especially the big buildings in the CDB area. . These waves move at 3kms-1.

Love Waves

Love waves move back and forth in the direction they are traveling. Take a slinky and lay it on a table and make waves that move through the slinky as you move it back and forth. This is similar to the action of Love waves. These waves are highly destructive and contributed to the liquefaction seen in Christchurch. These waves move at 4kms-1.

Earthquake waves are essential to take the massive amounts of energy away from where the energy is released.

© NZQA 2015