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?

   • 60 seconds
   • 95 seconds
   • 35 seconds
   • 25 seconds

3. Table, Model lag table, with columns Lag, Distance

   10 s, 84 km; 25 s, 210 km; 50 s, 420 km. Note: model speeds P 6 km/s, S 3.5 km/s.

4. 2.

   A station's lag is 50 s. Using the model lag table, about how far away is the quake, by Esme's reading?

   • About 210 km
   • About 84 km
   • About 50 km
   • About 420 km
5. 3.

   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)?

   • Draw a circle of that radius around each station; they meet at the epicenter
   • Use the first station by itself
   • Pick the station with the largest lag
   • Average the three distances
6. 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 3 km/s
   • About 7 km/s
   • About 13 km/s
7. 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
   • Earth's spin bends them
   • The Moon's pull bends them

8. Use this

   Earth cutaway with a shaded band.

9. 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 3, at 150°
   • Station 2, at 120°
   • Stations 2 and 3
   • Station 1, at 60°
10. 7.

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

    • Stations 1 and 3
    • Station 3, at 150°
    • Station 2, at 120°
    • Station 1, at 60°
11. 8.

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

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

12. 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

13. 9.

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

    • About 750 km
    • About 5,180 km
    • About 2,171 km
    • About 2,921 km
14. 10.

    A drill hole on the Kola Peninsula reached 12 km (USGS). About what share of the 6,401 km to Earth's center is that, by Ari's math?

    • About 0.2%
    • About 2%
    • About 20%
    • About 12%