Investigation  3:  Seismic  Waves  

 

Table  of  Contents:    Folder  1:  Seismic  Waves  ............................................................................................................................  25  

Folder  2:  Locating  Earthquakes  .................................................................................................................  26  

Folder  3:  Exploring  Earth’s  Interior  ............................................................................................................  29  

Investigation  Summary  ..............................................................................................................................  32  

 

   

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Folder  1:  Seismic  Waves  

Instructions  

Step   Complete  

1. Click  on  the  radio  buttons  next  to  “Inv  3:  Seismic  Waves”  and  “Introduction”.  Double  click  on  “Introduction”  to  open  the  balloon.  Read  the  information.  Then  click  on  the  X  in  the  upper  right  hand  corner  of  the  balloon  to  close  it.  

 

2. Expand  “Folder  1:  Seismic  Waves”.  Open  the  “Description”  placemark  balloon.  Read  the  information  and  watch  the  animation.  Answer  the  questions  in  the  Observations  section.  You  will  need  to  refer  to  this  information  later.  

 

3. Use  your  observations  to  answer  the  Investigation  question.  You  can  look  back  on  the  notes  you  took  on  the  San  Francisco  earthquake  to  help.  

 

Observations  

What  are  seismic  waves?      

What  are  body  waves?      

What  are  surface  waves?      

What  are  S  waves?      

What  materials  S  waves  can  travel  through:      

What  are  P  waves?      

What  materials  P  waves  can  travel  through:      

What  are  rocks  composed  of?      

What  are  minerals  composed  of?      

What  is  elasticity?      

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 Interpretation  In the 1906 San Francisco Earthquake, which areas experienced seismic waves of the highest amplitude?

Claim:    

   

Evidence:  

 

 

 

Reasoning:      

 

 

 

 

 

Folder  2:  Locating  Earthquakes  

Instructions  

Step   Complete  

1. Expand  “Folder  2:  Locating  Earthquakes”  and  click  on  the  radio  button.  Each  red  dot  that  you  see  represents  an  actual  seismograph  station.    These  are  the  stations  record  the  seismic  waves  caused  by  earthquakes.    Use  the  zoom  and  rotate  tools  to  explore  the  overlay.    Are  the  stations  randomly  distributed?  Record  your  observations.  

 

2. Fly  to  your  town  and  find  the  station  nearest  to  you.  Click  on  it  to  see  its  name,  location,  and  status  (whether  it  is  active  or  inactive).  Use  your  ruler  tool  to  find  out  how  far  away  it  is.  Record  your  findings.    

 

3. Open  the  “2010  Chilean  Earthquake”  folder  and  “Description”  placemark  balloon.  Read  the  information  and  record  any  information  you  can  in  the  Observations  section.    Close  the  balloon.  

 

4. Open  the  “Chilean  Earthquake  Data”  folder  and  click  on  each  of  the  three  seismic  stations  shown.  These  are  just  a  few  of  hundreds  of  stations  that  recorded  the  large  Chilean  earthquake  of  2010.    Record  the  lag  time  at  each  station  in  the  table  in  the  Observations  section.    

 

5. Using  the  Ruler  tool,  measure  the  distance  from  the  earthquake  epicenter  to    

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each  of  the  three  stations.  Record  these  values  to  the  nearest  100  km  in  the  table.    Hint:  You  may  need  to  rotate  the  globe  before  completing  your  line  for  the  sites  farther  away.  

6. On  the  graph  paper  provided,  graph  the  distance  vs.  lag  time  for  the  three  stations.  You  should  have  three  points  on  your  graph.  Label  each  one  with  the  name  of  the  station.  Then  use  a  straight  edge  to  draw  a  line  connecting  the  three  dots.  Study  your  graph  and  record  your  findings.  

 

7. Fly  to  London,  UK.  Use  your  ruler  tool  to  measure  the  distance  from  London  to  the  Chilean  earthquake  epicenter.  Find  this  distance  on  the  x-­‐axis  of  your  graph.  Use  the  line  you  drew  to  predict  what  the  lag  time  would  have  been  for  a  seismograph  station  in  London,  UK.    Record  your  findings.    

 

8. Think  back  to  the  San  Francisco  earthquake  to  answer  the  interpretation  question.  Be  sure  to  use  complete  sentences.  

 

Observations  

How  many  seismograph  stations  are  there  worldwide  –  tens,  hundreds,  thousands,  or  tens  of  thousands?  

 

Are  the  stations  randomly  distributed?  If  not,  what  patterns  do  you  see?  

     

Which  seismograph  station  is  closest  to  your  town?  How  far  away  is  it?  

     

What  is  lag  time?        

2010  Chilean  Earthquake  Data  

Station   Lag  Time  (minutes)   Distance  (km)  

Paso  Flores,  Argentina      

Llaves,  New  Mexico      

Tiksi,  Russia      

   

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Graph  of  distance  vs.  lag  time  for  the  three  seismograph  stations.  

 

Is  the  relationship  between  lag  time  and  distance  relatively  constant?  

 

What  approximate  distance  does  each  minute  of  lag  time  represent?  

 

Distance  from  London,  UK  to  the  Chilean  earthquake  epicenter  (to  the  nearest  1000  km):  

 

What  lag  time  would  be  expected  at  a  seismograph  station  in  London  recording  the  Chilean  earthquake?  

 

Interpretation  What  could  affect  the  lag  time  between  the  arrival  of  S  and  P  waves,  other  than  distance  from  the  epicenter?    Do  you  think  the  computer  models  scientists  use  to  locate  earthquakes  consider  this?  

Claim:    

 

Evidence:  

 

 

Reasoning:    

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Folder  3:  Exploring  Earth’s  Interior  

Instructions  

Step   Complete  

1. Expand  “Folder  3:  Exploring  Earth’s  Interior”  and  click  on  the  radio  button.    Open  the  “Description”  placemark  and  read  the  information.  Then  close  the  balloon.  

 

 2. Study  the  diagram  above.    Record  your  observations.    

3. Mohorovicic  saw  that  the  speed  of  seismic  waves  increased  50  km  below  the  surface.  He  knew  that  seismic  waves  travel  faster  in  denser  material.  Therefore,  he  reasoned  that  Earth’s  upper  mantle  must  be  denser  than  the  crust.  Using  the  same  line  of  reasoning,  answer  the  interpretation  questions.  

 

4. Open  and  read  the  “Summary”  placemark  balloon.  Then  answer  the  questions    

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in  the  Investigation  Summary.  Be  sure  to  use  complete  sentences.  

Observations  

Name  Earth’s  five  major  layers.        

Which  layer  is  the  asthenosphere  part  of?        

What  is  the  lithosphere  made  of?        

What  happens  to  the  speed  of  seismic  waves  when  they  leave  the  lithosphere  and  enter  the  asthenosphere?  

     

What  happens  to  the  speed  of  seismic  waves  when  they  leave  the  asthenosphere  and  enter  the  lower  part  of  the  upper  mantle?  

     

What  happens  when  seismic  waves  move  from  the  upper  mantle  to  the  lower  mantle?  

     

What  happens  to  seismic  waves  when  they  enter  Earth’s  outer  core?  

     

Interpretation  How  dense  do  you  think  the  asthenosphere  is  compared  with  the  layers  above  and  below  it?        Claim:      Evidence:    

 

Reasoning:    

 

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Is  the  lower  mantle  more  or  less  dense  than  the  upper  mantle?    

Claim:      Evidence:    

 

 

Reasoning  

 

 

 

 

Is  the  outer  core  liquid  or  solid?    Claim:      Evidence:    

 

 

Reasoning:    

 

 

 

         

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Investigation  Summary  Why  are  seismic  waves  able  to  move  through  rock?  

 

 

 

 

 

What  is  the  most  destructive  type  of  seismic  wave?  

 

 

 

 

 

How  are  earthquake  hypocenters  located?  

 

 

 

 

 

What  can  studying  seismic  waves  tell  us  about  Earth?