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 P wave
   • The S wave
   • Both at the same moment
2. 2.

   P and S waves meeting a liquid layer. Which waves can travel through a liquid, by Kira's reading (USGS)?

   • Both P and S waves
   • P waves
   • Neither kind
   • S waves
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?

   • 10 seconds
   • 14 seconds
   • 24 seconds
   • 38 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 X, with the shorter lag
   • It cannot be told from lags
   • Station Y, with the longer lag
   • Both are the same distance
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)?

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

7. Use this

   Earth cutaway with a shaded band.

8. 6.

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

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

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

   • The liquid outer core stops S waves
   • S waves cross the core too fast to record
   • S waves fade out after 104 km
   • The solid inner core reflects them back
10. 8.

    What bends P waves and makes their shadow zone, by Ren's reading (USGS)?

    • Absorption by the oceans
    • Refraction at the liquid core
    • S waves blocking them
    • Reflection off the crust

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.

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

    • The crust, 30 km
    • The outer core, 2,259 km
    • The lower mantle, 2,171 km
    • The inner core, 1,221 km
13. 10.

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

    • Crust, mantle, outer core, inner core
    • Crust, outer core, mantle, inner core
    • Mantle, crust, inner core, outer core
    • Crust, mantle, inner core, outer core