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

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

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

   • 38 seconds
   • 24 seconds
   • 14 seconds
   • 10 seconds
4. 4.

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

5. Read this first

   Use this

   Earth cutaway with a shaded band.

6. 5.

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

   • A place where the ground goes dark
   • The whole far side of Earth
   • A band from 104° to 140° from a quake with no direct P waves
   • Where S waves arrive before P waves
7. 6.

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

   • The solid inner core reflects them back
   • S waves fade out after 104 km
   • S waves cross the core too fast to record
   • The liquid outer core stops S waves
8. 7.

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

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

9. 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

10. 8.

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

    • The crust, 30 km
    • The lower mantle, 2,171 km
    • The inner core, 1,221 km
    • The outer core, 2,259 km
11. 9.

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

    • Crust, mantle, outer core, inner core
    • Crust, mantle, inner core, outer core
    • Crust, outer core, mantle, inner core
    • Mantle, crust, inner core, outer core
12. 10.

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

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