Topic 5: Earthquakes
Do we live in an Earthquake area? Where in Canada do earthquakes happen?
To study earthquakes scientists use seismographs. They measure the earth’s movement They read the seismograms They have to be attached to bedrock In order to feel the Vibrations that Result from an Earthquake
Before they had the technology they used other devices to study earthquakes This urn has eight dragon heads attached to it with little balls inside their mouths. When there is earthquake movement the balls will shake. Whatever toads mouth the ball falls into is the direction of the Earthquake.
Animals are also thought to predict earthquakes. Bees Deep-sea fish Rabbits
Use a method of measurement called the Richter Scale. Starts at zero and can go as high as necessary. The amount of energy released increases the number on the scale. A 7 is 30 times STRONGER than a 6. And 900 times stronger than a 5.
Greater the number doesn’t mean the greatest surface destruction. That depends upon the depth of the Earthquake, the surface geology, the design of the building and the population.
Mercalli Scale- Measure the intensity, measures the destructiveness
Earthquake Waves Episodes of ground-shaking movement in an earthquake are caused by Seismic Waves
They travel from the source of the earthquake. The aftershocks are actually smaller earthquakes, that will often cause damage to buildings. In 1995, Kobe, Japan
Types of Earthquake Waves P Waves = fastest and can pass through solids, liquids and gases S Waves = slower and can pass only through solids Surface Waves = slowest, but their rolling motion do the most damage
P waves travel right through the centre of the Earth S waves do not go through the core, so the core must be liquid.
Locating an Earthquake P waves travel faster than S waves so you can determine the location of an earthquake by the interval between P and S waves (just like thunder and lightening) Focus- where it begins, where the primary and secondary waves come from Epicenter- the surface location directly above the focus The farther apart the waves are, the farther away the Earthquake is.
Earthquake Zones Since 1990 there have been 4600 (greater than 3.0) earthquakes in Canada, USA, and Mexico.
Types of Rock Movement in Earthquakes Rock in the Earth is always under pressure, which can cause the rock to bend and stretch. When the pressure is to great, the rock breaks suddenly and creates a fault.
Movement along a fault can spread more than a kilometer in a second. Fault zones exist where tectonic plates meet.
Three Types of Faults Normal Fault Tension is the force that is causes the stretching. The rock above the fault moves downward.
Reverse Fault Compression is the force that can squeeze rock, which is from the movement of the plates. The rock above the fault is forced up and over the rock below the fault.
Strike-Slip or Transform Fault Shear is the force that causes slipping. In places where plates are moving sideways past each other. The rock along the edges has many bumps in it so the get caught on each other and will twist and be strained.
Preparing for Earthquakes People in earthquake zones prepare for them. They will often attach the furniture to the walls so it won’t shift or fall over. They store heavier items near the floor. How Earthquake safe is your home? http://www.eq-iq.org.nz/quakehouse/accessible.asp
Buildings and road are built differently in earthquake areas. Rigid structures break during quakes because they have very little flexibility. Buildings made out of steel, wood and reinforced concrete can bend a little bit without breaking.
Other Effects of Earthquakes They can happen under the sea, causes Tsunamis. Can cause great damage when the travel across oceans and break on the shore.
In 1985 outside of Mexico City the sandy base on which the city was built turned quickly into quicksand from shock waves causing massive damage.