To Find The Epicenter of an Earthquake Using the Difference in Time Between the P and the S Wave...

To Find The Epicenter of an Earthquake Using the Difference in Time

Between the P and the S Wave

Follow the Rainbow!

NSF Funded CUNY GK-12 Science NOW Project Copyright David Stolarz, January 22, 2010

NSF Funded CUNY GK-12 Science NOW Project

Using Scrap Paper

Finding the Epicenter of an Earthquake Using the Difference in

Time Between the P and the S Wave

The Completed Process

Finding the Epicenter of an Earthquake Using the Difference in Time Between the P and the S Wave


StationArrival Time of

P-WaveArrival Time of

the S-WaveP-S Wave Interval

Distance to the Epicenter

P-Wave Travel Time

Origin Time of Earthquake

A

B

C

Fill out the chart below using the three seismograms and the chart on Page 11 of the Earth Science Reference Tables.

Start Simple – Draw a Line Down From the P-Wave to the Time Scale







P-Wave Travel Time


A

B

C


Judge what time the P-wave starts







P-Wave Travel Time


A

B

C


08:16 17 18 19

A Quarter after 8 O’Clock! And No Seconds!

A zoom-in shows P-wave starting at approximately 08:16:00







P-Wave Travel Time


A 08:16:00

B

C


Put that value in the appropriate box







P-Wave Travel Time


A 08:16:00 08:21:00

B

C


Repeat the same process for the S-wave.







P-Wave Travel Time


A 08:16:00 08:21:00

B

C


08:21:00 (S-Wave Time)-08:16:00 (P-Wave Time)

Calculate the interval between the two wave arrivals at the seisomgraph







P-Wave Travel Time


A 08:16:00 08:21:00 00:05:00

B

C


08:21:00 (S-Wave Time)-08:16:00 (P-Wave Time) 00:05:00 (Time Difference) ( 0 Hours, 5 Minutes, 0 Seconds )

Enter that time in the appropriate box






P-Wave Travel Time


A 08:16:00 08:21:00 00:05:00

B

C

Go to page 11 of your Earth Science Reference Tables for the chart shown above






P-Wave Travel Time


A 08:16:00 08:21:00 00:05:00

B

C

Use the P-S Wave time interval to figure out the distance to the epicenter






P-Wave Travel Time


A 08:16:00 08:21:00 00:05:00

B

C

Scrap Paper

Place Marks at P-S Wave Interval Time and at 0.

Create a reference measurement using scrap paper and the P-S Wave value






P-Wave Travel Time


A 08:16:00 08:21:00 00:05:00

B

C

Scrap Paper

Scrap Paper

Slide paper up and over until thereference marksLine up with the P and S Lines.

Find the proper place where the reference marks match the P and S Lines.






P-Wave Travel Time


A 08:16:00 08:21:00 00:05:00

B

C

Scrap Paper

Lightly, make a reference mark in pencil on the reference table at this place on the P line.

For convenience, make a light pencil mark on the P line for use in the next step


Look straight down from the P line pencil mark and judge the epicenter distance.

.2 . 4 .6 .8


Lightly, make reference marks in pencil On the reference table at these two places .

Enter that value for the epicenter distance with proper units.


Look across at the y-axis to Judge the time value

00:06:4000:06:20

Trav

el T

ime

(min

utes

)


ERASE YOUR MARK!

Erase your pencil mark on the P-wave to keep your reference table clean


08:16:00 (P Arrival Time) 00:06:20 (P Travel Time)

Calculate what time the earthquake happened using the Arrival and travel times


08:16:00 (P Arrival Time)- 00:06:20 (P Travel Time)MINUS!

Obviously, the earthquake happened earlier than when its was felt miles away


Convert hours to minutes or minutes to seconds when necessary


Put the calculated time of earthquake in the proper box


Using Scrap Paper



Anything complex is easier when broken into smaller steps




Judge what time the P-wave starts and enter it in the box




Use the P-S Wave time interval to set reference marks for the sliding step


Using Scrap Paper



Create a reference measurement using scrap paper and the P-S Wave value


Using Scrap Paper





Using Scrap Paper



Look straight down from the P line pencil mark and judge the epicenter distance.


Using Scrap Paper



Look across at the y-axis to Judge the time value


Using Scrap Paper



Put the calculated time of earthquake in the proper box


Using Scrap Paper



Anything complex is easier when broken into smaller steps


Using Scrap Paper



Follow the same overall process for Station C




Judge what time the P-wave starts and enter it in the box




Use the P-S Wave time interval and the y axis of the reference table


Using Scrap Paper



Create a reference measurement using scrap paper and the P-S Wave time value


Using Scrap Paper





Using Scrap Paper



Calculate what time the earthquake happened using the Arrival and travel times


Using Scrap Paper



Calculate and place the time of earthquake in the proper box

$Z$Z

$Z

A

C

B

0 5000 km



7600

km

3600 km

All three arcs must pass through the earthquake epicenter, in this case, the San Andreas fault in California, USA.

Using scrap paper.

Use the Station info to locate the epicenter of the earthquake on a map



$Z$Z

$Z

A

C

B

0 5000 km

On the Station Map, Find Station A



$Z$Z

$Z

A

C

B

0 5000 km

Find Station B



$Z$Z

$Z

A

C

B

0 5000 km

Find Station C

$Z$Z

$Z

A

C

B

0 5000 km



Station

A

B

C

Use the Distance to Epicenter for each station


or


Station

A

B

C

$Z$Z

$Z

A

C

B

0 5000 km

Convert scientific notation for the distance to the epicenter for each station



$Z$Z

$Z

A

C

B

0 5000 km

Using the scale bar below as the reference, scribe a circle around the three points using a compass, string, or scrap paper.

3600

km

3600 km

Station

A

B

C

Scribe the arc for Station A using the map scale distance

$Z$Z

$Z

A

C

B

0 5000 km



The two circles cross at two points. A third circle is needed to confirm the earthquake epicenter.

5000 km

5000 km

Station

A

B

C

Scribe the arc for Station B using the map scale distance

$Z$Z

$Z

A

C

B

0 5000 km



7600

km

3600 km


Using scrap paper.

Station

A

B

C

If the distance is longer than the scale, use scrap paper to extend the scale.

$Z$Z

$Z

A

C

B

0 5000 km



7600

km

3600 km


Using scrap paper.

Where the three arcs cross is the epicenter – Circle it!

To Find The Epicenter of an Earthquake Using the Difference in Time Between the P and the S Wave...

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