Activity Locating an Earthquake Epicenter

Activity

LOCATING LOCATING AN EARTHQUAKE EARTHQUAKE EPICENTER

Try this activity to see how to plot the distace o! several seis"o#raph statios !ro" epiceters o! two earth$%a&es ad how to %se that data to iterpret where the earth$%a&e epiceters are located' Pro(le") How can fnding the distance o several seismograph stations rom an earthquake be used to fnd the epicenter?

______________________________________ __________________________ __________________________ ______________________  _________  Hypothesis) _________________________  ________________________  _____________________________________ __________________________ __________________________ __________________________ _____________________  ________  *aterials:  The S and P ave ave Time !"istance !"istance #raph$ a world map$ a drawing compass% compass% Proced%re) &% "etermine the di'erence between between the arrival times o the S and P waves rom the data table below%

(% )se the Time*"istance Time*"istance #raph to determine the distance in kilometers rom the earthquake earthquake to the seismograph station% +,ample: The di'erence in the arrival times in Paris or earthquake - is &( minutes% .n the chart/ the P and S wave wave curves are separated &( minutes verticall0 at &(/(12 &(/(12 km% 3% )sing the map scale and the distances distances to each earthquake earthquake as radii/ place place one end o a compass at each seismograph station location% )se the compass to draw a circle with the radius radius equal equal to the distance distance to the earthquake4s epicenter% 5% 6denti0 the epicenter ater drawing drawing at least three circles or each earthquake% earthquake% +ata ta(le)

7ocation o Seismograph 9& ;ew
9( Seattle

93 Bio de Caniero

95 Paris

ave 8rrival Times ave +arthquake 8 +arthquake -

"istance 9km 8

P S "i'

(:(5:21 P= &: &:&>:22 P= (:(:11 P= &: &:(5:52 P= __________ __________  

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P S "i'

(:(5:52 P= &:&5:3@ P= 3:32:22 P= &: &:&A:1( P= __________ __________  

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P S "i'

(:(>:22 P= &:(3:22 P= (:3:21 P= &:33:32 P= __________ __________  

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&2/122

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&(/(12

P S

(:32:&1 P= &:(5:21 P= &:3A:21 P=

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"i' 91 Tok0o

P S "i'

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__________   ____

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PROCEDURE: Locating an earthquake epicenter using a Time-Distance graph and S- & P- a!e arri!a" times 1.

Determine the lag time interval between the P-waves and S-waves using the seismogram arrival time data from the three seismic locations. Which seismic station is the closest to the earthquake epicenter?

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!o determine the distance from each seismic station to the epicenter" use the following steps# a. $%amine the seismogram data and appro%imate" in minutes&seconds" the time interval 'lag time( between the P-wave and the S-wave arrivals. 'to the nearest 1) sec(. b. *ocate the time scale on the !ime-Distance +raph along the left side. Place the edge of a piece of scratch paper along this scale. ,n the paper mark where the ero point is and the time lag obtained from the arrival time interval. c. Slide the paper to the right on the graph until the two markings fit between the P- and S-wave curves and is parallel to the time a%is. #$e precise% d. !he distance from the epicenter to the first location can be determined b reading the value on the horiontal a%is of distances directl below the edge of the scratch paper. e. /epeat the process for the other two locations and use these three distances to draw  three circles on a world map to triangulate the location of the earthquake

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S and P ave Time*"istance #raph