P-waves are the fastest followed by s-waves and then surface waves.
We use a seismograph to measure these waves. They are made with a pendulum with an attached pen and a drum of paper.
When the waves reach the seismograph the pen moves but the paper stays still.
They measure both horizontal and vertical movement.
Finding the epicenter
Three seismograph stations in the area of the quake are needed to find the epicenter.
Since p-waves are faster then s-waves, the p waves reach the seismograph first and then the s-waves.
We use the time between the p and s waves to determine how far the epicenter is from each station. If the distance from one station is 8km than we draw a circle with a 8km radius around that station. We do this for each station.
Where the circles intersect is where the epicenter is.
There are 4 layers of Earth. The inner core at the very center of the earth is a solid, and dense and made of mostly iron with traces of silicon, sulfur and oxygen. Its solid b/c of the pressure from the layers above..
The outer core is liquid and also mostly iron.
Next is Earths mantle. It’s the largest layer and is made of an upper and lower parts.
The upper mantle contains the crust. The crust and the mantle just below it is called the lithosphere, which is where the plates are located and move.
It ranges from 5-60km deep. The crust has more silicon and magnesium and less iron then the mantle.
H.W. pg 311 ques. 1-4 & pg 324 ques. 1-5, 8-14
People and Earthquakes
Seismologists study earthquakes.
The energy released from a quake is called the magnitude, and is measured on a Ricther scale. We use the lines on a seismograph, and apply them to the Ricther scale.
9.5 is the highest value on the scale. Every 1.0 increase on the scale is 32x the amount of energy released.
A quake of 2.0 is has 32x more energy than a 1.0 quake.
People and Earthquakes
Sometimes the vibrations from an earthquake can cause thick, wet soil to become very loose and it will almost act like a liquid. This is liquefaction and causes houses to collapse.
Tsunamis are giant , destructive waves of water that are caused mainly, by earthquakes that occur under water.
A sure sign that a tsunami is coming is the sudden rush of the shore water toward the sea.