How earthquake waves reveal Earth's interior

Grade 9 Science Worksheet - Building Confidence

Circle the best answer.

1. 1.

   a first wave, then a second. Which wave reaches a seismograph first after an earthquake, by Ari's reading (USGS)?

   • The wave that crossed the inner core
   • The S wave
   • The P wave
   • Both at the same moment
2. 2.

   How does an S wave move rock as it passes, by Bo's reading (USGS)?

   • It shakes the rock sideways
   • It moves through the liquid outer core
   • It travels faster than the P wave
   • It squeezes and stretches rock along its path
3. 3.

   Note: model speeds P 6 km/s, S 3.5 km/s. At a station 84 km from a quake, P arrives after 14 s and S after 24 s (model speeds). What is the S-minus-P lag, by Jun's math?

   • 14 seconds
   • 24 seconds
   • 38 seconds
   • 10 seconds

4. Read this first

   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.

5. 4.

   Station X records an S-minus-P lag of 10 s, and station Y a lag of 50 s. Which station is closer to the quake, by Luz's reading?

   • Station Y, with the longer lag
   • Both are the same distance
   • It cannot be told from lags
   • Station X, with the shorter lag
6. 5.

   Three stations with circles around them. Why do seismologists use records from several stations to find a quake's epicenter, by Milo's reading (USGS)?

   • More stations make the waves travel faster
   • Each lag gives a distance, and arcs from several stations meet at one point
   • One station's lag gives the exact spot
   • Stations measure the quake's color

7. Use this

   Earth cutaway with a shaded band.

8. 6.

   What is the P-wave shadow zone, by Noah's reading (USGS)?

   • A band from 104° to 140° from a quake with no direct P waves
   • Where S waves arrive before P waves
   • The whole far side of Earth
   • A place where the ground goes dark
9. 7.

   Why are no direct S waves recorded beyond about 104° from a quake, by Pia's reading (USGS)?

   • S waves fade out after 104 km
   • S waves cross the core too fast to record
   • The solid inner core reflects them back
   • The liquid outer core stops S 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.

    In the USGS table, which listed layer is thickest, by Tala's reading?

    • The lower mantle, 2,171 km
    • The inner core, 1,221 km
    • The outer core, 2,259 km
    • The crust, 30 km
12. 9.

    Put the layers in order from the surface down, by Zee's reading (USGS).

    • Crust, mantle, outer core, inner core
    • Mantle, crust, inner core, outer core
    • Crust, outer core, mantle, inner core
    • Crust, mantle, inner core, outer core
13. 10.

    What is the Moho, by Esme's reading (USGS)?

    • A wave that circles Earth's surface
    • The crust-mantle boundary, where wave speed jumps up
    • A zone where waves come to a stop
    • The boundary between the liquid outer core and the inner core