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?

   • 95 seconds
   • 60 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 84 km
   • About 50 km
   • About 210 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)?

   • Pick the station with the largest lag
   • Draw a circle of that radius around each station; they meet at the epicenter
   • Use the first station by itself
   • Average the three distances
6. 4.

   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 rock type changes at that depth
   • Waves keep one speed at each depth they reach
   • The core begins there
7. 5.

   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 13 km/s
   • About 7 km/s
8. 6.

   Earth cutaway with a shaded band. 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 1, at 60°
   • Station 3, at 150°
   • Stations 2 and 3
   • Station 2, at 120°
9. 7.

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

10. 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

11. 8.

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

    • About 2,921 km
    • About 2,171 km
    • About 750 km
    • About 5,180 km
12. 9.

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

    • About 5,180 km
    • About 6,401 km
    • About 3,480 km
    • About 2,259 km
13. 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 20%
    • About 12%
    • About 2%