5. “ringwoodite”

7. More complicated waves, too

8. Real life example At 23:24:50.6 GMT, on Nov. 22 2001, an earthquake occurred in Fiji (southwest Pacific) The P wave from this earthquake was recorded in Pasadena, CA at 23:36:50.7 GMT Therefore the observed travel time is 720.10 s The distance between the Fiji earthquake and the seismometer in Pasadena is 78.8o (8762 km). The theoretical (expected) travel time for a P wave at this distance is 721.25 s. Therefore the travel time residual is -1.15 seconds

10. Seismic stations from Fiji to the Tonga trench

11. Time residuals from Fiji across the Tonga trench

12. Inferred structure in one slice across the Tonga trench Fiji Tonga Pacific plate earthquakes  slower P waves faster P waves 

13. I Map of inferred structure 25 km down

14. 140 km down

15. Earthquakes used to do global tomography and where the seismic stations are

16. A few random tomographic slices

17. Comparison of different tomographic reconstructions