High-Rate GPS Applications for Seismology: What Next?

1. High-Rate GPS Applications for Seismology: What Next? Kristine M. Larson Department of Aerospace Engineering Sciences University of Colorado Kristine.Larson@colorado.edu http://spot.colorado.edu/~kristine

2. Outline • GPS - a short history • High-Rate GPS • GPS-Seismology results • Denali, November 2002 • Tokachi-Oki (Hokkaido), September 2003 • Technology improvements • Implications for PBO

3. Campaign-style GPS 8 hour averages of 5 minute observations. “short” baselines 7 GPS satellites

4. Continuous GPS Global positions; 12-15 satellites; solutions 1/wk 24 hr avg of 5 min observations

5. Continuous GPS Larson and Freymueller, 1995; Larson et al., 1997

6. Currently 28 satellites; 5 min observations - 24 hour avg positions

7. Why (part 1) ?

8. Why (part 2)? Tracking network before and now

9. Volcano Monitoring 15 minute (filtered) averages of 5 minute observations Kilauea Volcano Larson et al. (2001).

10. Greenland Ice Sheet Swiss Camp Zwally et al., 2002, Science

11. Full constellation; observations 10 hours every 10 days; Remove assumption that the receiver doesn’t move. days

12. Seasonal variations related to melt-water at the ice-rock interface. days

13. But now data outages matter … hours Larson et al., 2002

14. GPS Seismology - 30 s time (seconds) Hector Mines Nikolaidis et al., 2001 (JGR).

15. Using existing instrumentation: how well can GPS measure seismic waves? • Data from geodetic quality receivers (dual-frequency). • Prefer geodetic quality monuments. • Data available by anonymous ftp.

16. IGS Network Continuous; data freely available by ftp; geodetic standards.

17. CORS Network Continuous; data freely available by ftp; some geodetic standards

18. Why are GPS sites running at 1-Hz? • NASA: low Earth orbit science missions. • NGS: surveyors. • Coast Guard (NGS): low precision navigation. • FAA WAAS (wide area augmentation system): high precision real-time navigation.

19. Sites running at 1 Hz -IGS

20. Sites running at 1 Hz - CORS

21. Sample at 30 sec. Edit data. Decimate to 5 min. Orbits are held fixed. Estimate one position per day. Sample at 1 Hz Edit data. No decimation. Orbits are held fixed. Estimate one position per second. Traditional GPS 1 Hz GPS The same software (JPL-GIPSY) is used to analyze the data.

22. 24-28 satellites are viewed for 24 hours Geometry of the satellites affects position minimally. 6-8 satellites will be viewed within 1 hour. Geometry of the satellites in the sky determines the precision. Traditional GPS 1 Hz GPS

23. Relative ground motions [i.e. to a site held fixed] Displacementestimated Insensitive to small ground motions, but no upper limit… Inertial local reference frame ground motions Accelerationmeasured Sensitive to small ground velocities or large accelerations Seismology 1 Hz GPS

24. 24 hours of GPS Data Fairbanks Southern California

25. Original Denali GPS Network

26. Denali Fault earthquake • 1 Hz GPS FAIR • Strong motion 8022 • High-pass filtered to remove baseline drift. • Fix co-seismic offset [Eberhart-Phillips et al., 2003]

27. 1 Hz GPS at FAIR

28. FAIR BREW

29. Surface Wave Observations

30. GPS Surface Waves

31. Can GPS do the vertical? Yes, but not as well as the horizontals.

32. What next - from a science perspective? • Source processes • Modeling the surface waves • Triggering studies

33. Denali 1 Hz GPS Strong motion Eberhart-Phillips et al., 2003 (Science)

34. Denali Seismic Instrumentation

35. Denali Seismic Instrumentation

36. Denali Seismic Instrumentation

37. Preliminary Results

41. Triggering

44. Gomberg et al., 2004 (Nature)

45. 2003 September 25 Tokachi-Oki (Hokkaido) Earthquake

46. Strong Motion Network Harvard Mw 8.3

47. Strong Motion Network GPS Network

48. Coseismic Displacements: traditional GPS Kato

49. Inversion for Rupture Koketsu et al.

50. GPS-static offsets Strong motion