Science 7: Unit E: Planet Earth Topic 5 - Earthquakes

What is an Earthquake again? Earthquake – trembling or vibration of the ground. They are caused by a sudden release of energy that has slowly been building up in the Earth’s crust. This energy is in the form of seismic waves. Earthquake – trembling or vibration of the ground. They are caused by a sudden release of energy that has slowly been building up in the Earth’s crust. This energy is in the form of seismic waves. Seismic Wave – Energy waves that travel outwards from the source of an earthquake. Seismic Wave – Energy waves that travel outwards from the source of an earthquake. Seismologist – Scientist that studies earthquakes and tries to predict when and where an earthquake will arrive. Seismologist – Scientist that studies earthquakes and tries to predict when and where an earthquake will arrive.

How do scientists measure earthquakes? Seismologists use technology to measure earthquakes. Seismologists use technology to measure earthquakes. Seismograph – device attached to bedrock which detects and measures the vibrations of an earthquake. It is made up of a pen which can move and a rotating drum. As the pen moves along the rotating drum, it makes a jagged line. Seismograph – device attached to bedrock which detects and measures the vibrations of an earthquake. It is made up of a pen which can move and a rotating drum. As the pen moves along the rotating drum, it makes a jagged line. Seismogram - Seismogram - the graph reading produced by a seismograph machine.

The Richter Scale Is the scale used to measure how strong an earthquake is. It starts at 0 and can go as high as necessary. Is the scale used to measure how strong an earthquake is. It starts at 0 and can go as high as necessary. A jump on the Richter Scale of a single number means a difference in energy and force of 30X. So an earthquake that measures an 8 on the Richter Scale is times stronger than a 5- point earthquake. A jump on the Richter Scale of a single number means a difference in energy and force of 30X. So an earthquake that measures an 8 on the Richter Scale is times stronger than a 5- point earthquake. The most powerful earthquake in history was in 1556 in China. It was ~9.0 on the Richter Scale. An estimated 850’000 to 1 million people died. The most powerful earthquake in history was in 1556 in China. It was ~9.0 on the Richter Scale. An estimated 850’000 to 1 million people died.

Where exactly does an earthquake occur? Almost always near a tectonic plate boundary. Almost always near a tectonic plate boundary. Focus – The actual source of the earthquake’s seismic waves. Focus – The actual source of the earthquake’s seismic waves. Epicentre – The location on the surface of the Earth DIRECTLY ABOVE the focus. Epicentre – The location on the surface of the Earth DIRECTLY ABOVE the focus. The epicentre is where the earthquake feels strongest and the damage is greatest. The epicentre is where the earthquake feels strongest and the damage is greatest.

Type of Seismic Waves 3 Kinds of seismic waves occur during an earthquake: 3 Kinds of seismic waves occur during an earthquake: I. Primary (P) Waves – first waves released, fast moving. They can pass through solids, liquids, and gases. They are the weakest of the waves. I. Primary (P) Waves – first waves released, fast moving. They can pass through solids, liquids, and gases. They are the weakest of the waves. II. Secondary (S) Waves – Travel more slowly, and can only pass through solids. II. Secondary (S) Waves – Travel more slowly, and can only pass through solids. III. Surface Waves – Slowest, but most powerful of the waves. These are the waves that destroy buildings. III. Surface Waves – Slowest, but most powerful of the waves. These are the waves that destroy buildings.

How the different waves help us. Because P Waves can travel through liquids, if an earthquake occurs anywhere on Earth, the P Waves will be detected everywhere. Because P Waves can travel through liquids, if an earthquake occurs anywhere on Earth, the P Waves will be detected everywhere. S Waves can’t travel through liquids so if an earthquake occurs in Australia, we wouldn’t register the S Waves because they can’t travel through the mantle or outer core. S Waves can’t travel through liquids so if an earthquake occurs in Australia, we wouldn’t register the S Waves because they can’t travel through the mantle or outer core. Shadow Zone – the area of the Earth that does not receive either P or S waves. (P Waves are bent straight across the Earth by the Outer Core) Shadow Zone – the area of the Earth that does not receive either P or S waves. (P Waves are bent straight across the Earth by the Outer Core)

Faults Fault – a visible crack in the crust caused by the stresses of two plates pushing or pulling. Fault – a visible crack in the crust caused by the stresses of two plates pushing or pulling. Earthquakes tend to occur on or near fault-lines. Earthquakes tend to occur on or near fault-lines.

Types of Faultlines Normal Fault – Caused by tension force from two diverging plates. Earthquakes are shallow and involve rock moving downward. Normal Fault – Caused by tension force from two diverging plates. Earthquakes are shallow and involve rock moving downward. Reverse Fault – Caused by compression force from two converging plates. Earthquakes are deep in the crust. Areas with reverse faults are known as subduction zones. Reverse Fault – Caused by compression force from two converging plates. Earthquakes are deep in the crust. Areas with reverse faults are known as subduction zones. Transform Fault – Caused by shear force from two shearing plates. Transform Fault – Caused by shear force from two shearing plates.

Other Consequences of Earthquakes Tsunami Tsunami Avalanche Avalanche Rock slide/mudslide Rock slide/mudslide Liquefaction – the softening of rock into sand/quicksand. Usually occurs with sedimentary rock. Liquefaction – the softening of rock into sand/quicksand. Usually occurs with sedimentary rock.

What should you do in the event of an Earthquake? Remain as calm as possible. Remain as calm as possible. Find room under a hard surface such as a desk or table. Find room under a hard surface such as a desk or table. Crouch down, covering your head with your hands (see Fig on p. 395). Crouch down, covering your head with your hands (see Fig on p. 395). Evacuate the building only when you are told to do so. Evacuate the building only when you are told to do so. Leave quickly as aftershocks almost always follow an earthquake. Leave quickly as aftershocks almost always follow an earthquake.