1. 10.2 L OCATING AND MEASURING

2. H OW DO WE MEASURE EARTHQUAKES ? The instrument used to detect and measure the waves produced by earthquakes is called seismographs. Can detect movement hundreds or even thousands of Km’s away. There are more 10,000 around the world. Data is recorded on a seismogram (record sheet)

3. H OW DO WE MEASURE EARTHQUAKES Types of seismographs: Some record in a side to side fashion Some in an up and down fashion Modern stations usually have three (up/down, side to side represented in north/south and side to side represented in east/west)

4. H OW DO WE MEASURE EARTHQUAKES How it works: A drum is slowly turned by a clock. There is a heavy weight w/a pen attached. If the bedrock is disturbed then the drum moves. The pen does not move. If the drum is steady then it will produce a straight line. If the drum is in motion then the pen will produce a zigzag.

5. H OW DO WE MEASURE EARTHQUAKES Interpreting the Seismographic data: P waves travel faster than S waves. The initial zigzag that reaches a station is the P wave. The second wave that reaches the station is the S wave. By using a time travel chart one can determine the distance from the epicenter a station may be.

7. L OCATING THE E PICENTER By drawing three circles on the map and pinpointing where they intersect, one can determine the epicenter of an earthquake.

9. M EASURING M AGNITUDE Magnitude – The measure of the E released in an earthquake. Richter Scale – Created by Charles R. Richter Each whole number increase represents 31 fold increase in E release. Ex. A 6 on the Richter scale has 31x’s more E release than a 5 and 10x’s as large. Not good for measuring large earthquakes. Moment Magnitude – indicates total E released by an earthquake.