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