# 4.Measuring Earthquakes A. Seismometer - an INSTRUMENT that measures an earthquake.

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4.Measuring Earthquakes A. Seismometer - an INSTRUMENT that measures an earthquake

Know the difference!! 4.Measuring Earthquakes B. Seismograph - the RECORDED GRAPH made by a seismometer

1.) Find the time interval between the arrival of the first P wave and the first S wave at a given seismometer station. 2.) On the time-travel graph, find the equivalent time difference between the P and S wave curves. Match up the distance from the station to the epicenter. *Continued on Next Slide*

3.) Draw a circle from the given station city, with a radius of the distance from the epicenter. Do this for 3 seismograph stations. 4.) The epicenter is the intersection point of all 3 circles!

C.Magnitude - the amount of energy released during a quake. D.Richter - scale used to measure the size of the seismic waves. - An increase of 1 point on the Richter Scale means an increase of 10 times the magnitude of the quake. - Scientists no longer use this scale.

- MOMENT MAGNITUDE: a more scientific calculation of the magnitude of a quake based on the rocks and movement of the fault. - MODIFIDED MERCALLI: rates damage.

Remember, earthquakes have seismic waves that travel through the Earth. The liquid outer core causes P waves to refract, or bend, through the outer core. S waves cannot travel through liquids, so they get deflected to the sides. This results in the SHADOW ZONE…an area on Earth which receives no seismic waves from a given earthquake.

5.Earth’s Layers A.Crust - ocean crust is basalt - continental crust is granite - ocean crust is about 7 km thick - the continental crust is 7-75 km thick.

5.Earth’s Layers B. Mantle - Thick layer - Made up of peridotite, iron, and silicon

5.Earth’s Layers C. Core - Inner core and the outer core. - Both made of nickel and iron - The outer core is liquid.

6.Where do earthquakes occur? A. Most earthquakes occur along plate boundaries. B. Ring of Fire – around the Pacific Ocean

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