How earthquake waves reveal Earth's interior

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Model speeds

   Wave	Speed
   P	6 km/s
   S	3.5 km/s

2. 1.

   With model speeds P 6 km/s and S 3.5 km/s, how long is the S-minus-P lag at 210 km, by Bo's math?

   • 25 seconds
   • 35 seconds
   • 60 seconds
   • 95 seconds
3. 2.

   Three stations with circles around them. Three stations each find their distance to one quake. How is the epicenter found, by Jun's reading (USGS)?

   • Use the first station by itself
   • Average the three distances
   • Draw a circle of that radius around each station; they meet at the epicenter
   • Pick the station with the largest lag
4. 3.

   Going down past the Moho, earthquake waves suddenly speed up (USGS). What does this suggest, by Kira's reading?

   • The rock turns to liquid there
   • The core begins there
   • Waves keep one speed at each depth they reach
   • The rock type changes at that depth
5. 4.

   From mantle to core, wave speed drops about 30% (USGS). A model P wave at 10 km/s just above the core would travel about how fast just below, by Luz's math?

   • About 10 km/s, unchanged
   • About 7 km/s
   • About 3 km/s
   • About 13 km/s
6. 5.

   Why do earthquake wave paths curve inside Earth, by Milo's reading (USGS)?

   • Rock at different depths changes the waves' speed
   • Waves follow straight lines at one speed
   • The Moon's pull bends them
   • Earth's spin bends them

7. Use this

   Earth cutaway with a shaded band.

8. 6.

   Station 1 sits 60° from a quake, station 2 at 120° and station 3 at 150°. Which one sits in the P-wave shadow zone, by Noah's reading (USGS)?

   • Station 2, at 120°
   • Station 1, at 60°
   • Station 3, at 150°
   • Stations 2 and 3
9. 7.

   Of those stations at 60°, 120° and 150°, which records direct S waves, by Pia's reading (USGS)?

   • Station 3, at 150°
   • Station 1, at 60°
   • Stations 1 and 3
   • Station 2, at 120°
10. 8.

    Oldham identified Earth's core from earthquake records in 1906 (USGS). Which observation shows the outer core is liquid, by Ren's reading?

    • It transmits S waves faster than the mantle
    • Its waves arrive before the P waves
    • Its P waves speed up sharply
    • It does not transmit S waves, and P waves slow sharply

11. Data on the Earth's interior (USGS)

    Layer	Thickness
    crust	30 km
    upper mantle	720 km
    lower mantle	2,171 km
    outer core	2,259 km
    inner core	1,221 km

12. 9.

    Using the USGS thicknesses, how deep is the top of the outer core, by Tala's math?

    • About 750 km
    • About 2,921 km
    • About 2,171 km
    • About 5,180 km
13. 10.

    Using the USGS thicknesses, how deep is the top of the inner core, by Zee's math?

    • About 2,259 km
    • About 3,480 km
    • About 6,401 km
    • About 5,180 km