Measuring Earthquakes NCES: 6.E.6.2 & 6.E.6.4 Kim Lachler Updated 10/14

Measuring Earthquakes Seismogram Instrument used to measure the strength and location of earthquakes Seismograph The paper that comes out of a seismogram showing the waves.

Measuring Earthquakes Focus The point inside the earth where movement along a fault first occurs and energy is released Epicenter The point on the earth’s surface located directly above the focus Focus

Types of waves Primary (P waves) cause rock to move back and forth in the same direction Go to http://www.britannica.com/EBchecked/topic/532925/seismic-wave

Types of waves Secondary (S waves) cause rock to vibrate at right angles to the direction the waves are moving Go to http://www.britannica.com/EBchecked/topic/532925/seismic-wave

Types of waves Love (L waves/surface) slowest, largest, most destructive waves Go to http://www.britannica.com/EBchecked/topic/532925/seismic-wave

Wave timing By reading several different seismograms in different locations the location of the focus/epicenter can be determined. This is done by looking at what time the P-S waves arrive times and triangulating.

Scales Richter scale Based on the seismic graph using logarithms to calculate It is objective, calculating the amount of energy released Not easy to understand

Scales - Richter A reading of 5 indicates a disturbance with ground motion 10 times as large as a reading of 4. The energy released increases by a factor of 30 for every unit increase on the Richter scale. The strongest quake since 1900 was on May 22, 1960 in Chile. It scored a 9.5 on the Richter scale.

Scales Mercalii Scale It is subjective and varies from location from the epicenter Easy to understand

Scales- Mercalii I Felt by very few people; barely noticeable. II Felt by a few people, especially on upper floors. III Noticeable indoors, especially on upper floors, but may not be recognized as an earthquake. IV Felt by many indoors, few outdoors. May feel like heavy truck passing by. V Felt by almost everyone, some people awakened. Small objects moved. trees and poles may shake. VI Felt by everyone. Difficult to stand. Some heavy furniture moved, some plaster falls. Chimneys may be slightly damaged. VII Slight to moderate damage in well built, ordinary structures. Considerable damage to poorly built structures. Some walls may fall. VIII Little damage in specially built structures. Considerable damage to ordinary buildings, severe damage to poorly built structures. Some walls collapse. IX Considerable damage to specially built structures, buildings shifted off foundations. Ground cracked noticeably. Wholesale destruction. Landslides. X Most masonry and frame structures and their foundations destroyed. Ground badly cracked. Landslides. Wholesale destruction. XI Total damage. Few, if any, structures standing. Bridges destroyed. Wide cracks in ground. Waves seen on ground. XII Total damage. Waves seen on ground. Objects thrown up into air.

Bibliography Holt, Rinehart & Winston, North Carolina, Holt, Rinehart & Winston, Orlando, Fl, 2005 USGS, earthquakes http://earthquake.usgs.gov/learn/glossary/?term=earthquake accessed 10/04/10 Earthquakes, http://earthsci.org/education/teacher/basicgeol/earthq/earthq.html#Earthquakes accessed 10/04/10 Ammon, J., Charles, Seismic waves & Earth’s interior http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/waves_and_interior.html accessed 10/7/10 The university of Liverpool, The scales for measuring earthquakes, http://www.matter.org.uk/schools/content/seismology/richterscale.html accessed 10/7/10 How stuff works, How does a seismograph work? What is the Richter scale?, http://science.howstuffworks.com/environmental/earth/geophysics/question142.htm accessed 10/7/10 MichiganTech, Modified Mercalli Intensity Scale, http://www.geo.mtu.edu/UPSeis/Mercalli.html, accessed 10/7/10 ABC, Earthquake, http://cse.ssl.berkeley.edu/lessons/indiv/davis/inprogress/QuakesEng3.html accessed 10/7/10