1/23/12 - Bellringer

►How might you measure an earthquake?

19.3 – Measuring and Locating Earthquakes

Magnitude

►Magnitude = a measure of energy produced by earthquake

►Amplitude = Height of wave►Richter Scale = numerical rating

system used to measure the magnitude of an earthquake

Richter Scale

►Numbers are determined by amplitude of largest seismic wave

►Each successive number represent an increase in amplitude of a factor of 10

►Example: Magnitude-8 is 10x larger than magnitude-7 Energy difference is even greater, = 32x

Richter scale

http://www.maelor-humanities.org.uk/GCSEhum/Resources/PP-photos/pp-KeyIss3/Richter.scale.jpg

Moment Magnitude Scale

►Rating scale that measures the energy released by an earthquake taking into account the size of the fault rupture, the amount of movement, and the rock’s stillness

►Comparison with Richter: New Madrid, MO 1812 - Richter scale 8.7 -- MMS 8.1 San Francisco, CA 1906 - Richter scale 8.3 -- MMS 7.7 Prince William, AK 1964 - Richter scale 8.4 -- MMS 9.2 Northridge, CA 1994 - Richter scale 6.4 -- MMS 6.7

Mercalli Scale

►Measures intensity of earthquake using Roman Numerals Worse damage = higher numeral

►Intensity = amount of damage caused by earthquake

http://www.state.il.us/IEMA/images/Mercalli.jpg

Intensity

►Depends on amplitude of surface waves

►Surface waves decrease in size with increase distance from focus Intensity decreases as well

Depth of Focus

►Shallow, Intermediate, Deep►Shallow = catastrophic with high

intensity Produce greater maximum intensity than

deep focus►Deep = smaller vibrations

Locating Earthquakes

►Seismogram and Travel-time Curve allow scientists to determine distance to epicenter

►Seismogram records time elapsed between arrival of waves

►Distance is determined by measuring separation of waves on seismogram and identifying the same separation on Travel-Time curve

Locating Earthquakes Cont.

►Multiple seismograms are needed because one just determines certain distance in any direction Circle is drawn around station with radius

equal to distance►Adding data from other stations

narrows area of focus 2 circles overlap @ 2 points 3 circles overlap @ 1 point = EPICENTER

Epicenter

http://wps.prenhall.com/wps/media/objects/3030/3102952/epicenter_tasa_shad.jpg

Seismic Belts

►Majority of Earthquakes occur along seismic belts that separate large regions of little or no seismic activity

►Most correspond closely with plate boundaries

►80% along Circum-Pacific Belt Subduction zone

http://upload.wikimedia.org/wikipedia/commons/thumb/0/09/Pacific_Ring_of_Fire.png/800px-Pacific_Ring_of_Fire.png

In-Class Assignment

►Get out a new sheet of paper!

►Mini Lab pg. 541

►Ignore #1►Turn in Traced Map with labeled

intensities, contour lines, and analysis question answers at the end of class