Earthquakes faults Earthquakes occur when rock masses in the Earth’s crust move suddenly along ruptures called faults. The rock movement may occur vertically, horizontally or in combination. Earthquakes and Volcanoes

Focus Focus – The location on a fault where the greatest amount of movement is. It is far underground. Epicenter Epicenter- the point on the surface directly above the focus

Energy waves Energy travels outward from the focus in waves. intensity Richter Scale The intensity of an earthquake can be expressed on the Richter Scale.

Earthquake Waves Types of Earthquake Waves S Wave An “S Wave” (“shear” or “secondary”) causes material to move up and down as it goes through.

A “P Wave (or “Primary” or “Pressure” wave) consists of compressions which move straight through a material. p & s waves animations

P waves S waves P waves can travel through solids, liquids and gases. S waves can travel only through solids.

Seismometer Earthquake waves are detected on a Seismometer.

seismograph Seismometers produce a seismograph

Pfaster farther away the greater the difference in arrival time P waves travel faster than S waves. The farther away from the epicenter, the greater the difference in arrival time of P and S waves.

distance from the epicenter time interval between arrival of P and S waves. This graph lets a person calculate the distance from the epicenter, knowing the time interval between arrival of P and S waves.

An earthquake occurred on June 23, 1946 and these were recorded times of P and S wave arrivals at different stations.

For example, the P/S time interval in Saskatoon was 0 h, 2 min and 37 seconds

1400 km 2 minutes and 37 seconds would correspond to about 1400 km.

A circle with a 1400 km radius could be drawn on a map with Saskatoon in the middle. The epicenter would be somewhere on this circle km Saskatoon

circles overlap epicenter The procedure could be repeated for all the other stations. The point where all 5 circles overlap would be the epicenter of the earthquake.

intercept epicentre Eg. All 3 circles intercept at this point, so this would be the location of the epicentre circles In a different example, circles were drawn around 3 seismic stations.

High Risk Zones for Earthquakes: 1. They are located near a plate boundary. 2. There is a history of earthquakes in the region. 3. There are numerous active faults. The West Coast of North America has had many earthquakes.

More Information on Earthquakes from National Geographic

Volcanoes magma surface A volcano is formed when magma makes its way to the surface.

Three types of Volcanoes liquid very large The lava is quite liquid and flows down the sides. These volcanoes are very large but not very steep. An example is Hawaiian volcanoes like Kilauea

form mainly from explosive eruptions of lava. Blown violently into the air, the erupting lava breaks apart into fragments called cinders. The fallen cinders form a cone around the volcano's central vent.

such as Mount St. Helens, build from both explosive and slow flowing eruptions. Layers of tephra alternating with layers of viscous lava flows create steep-sided, often symmetrical cones that we think of as the classic volcano shape.

Effects of Volcanoes Earthquakes Not all volcanoes have all these effects. Earthquakes always occur when a volcano erupts

More Information on Volcanoes from National Geographic