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High-Rate GPS: Earthquakes, Ice Sheets, and Volcanoes

High-Rate GPS: Earthquakes, Ice Sheets, and Volcanoes. Kristine M. Larson University of Colorado. Outline. Low-Rate/High-Rate GPS Ice Sheets Earthquakes Volcanoes My Noise/Your Signal?. Plate Boundary Deformation. Global Plate Motions. ITRF2005 Altamimi et al., 2007.

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High-Rate GPS: Earthquakes, Ice Sheets, and Volcanoes

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  1. High-Rate GPS: Earthquakes, Ice Sheets, and Volcanoes Kristine M. Larson University of Colorado

  2. Outline • Low-Rate/High-Rate GPS • Ice Sheets • Earthquakes • Volcanoes • My Noise/Your Signal?

  3. Plate Boundary Deformation

  4. Global Plate Motions ITRF2005 Altamimi et al., 2007

  5. Episodic Slip Rogers and Dragert, 2003

  6. What about more geodetically challenging temporal behavior? • Ice sheet speeds, ~100 m/yr (1-2 cm/hr); are they linear? • Earthquakes, 1-30 cm/sec; large accelerations. • Volcanoes, 1-2 cm/hr; not linear, but low accelerations.

  7. Ice sheets Photo: Roger Braithwaite

  8. Ice sheet velocities in Greenland • Install poles; measure position. • Return following year; remeasure position; compute velocity. Thomas et al., 2000

  9. Geodetic Challenges • 1996: power and memory restrictions. • Tracking limited to 12 hours every 10-15 days. • Constellation limitations. • How long do we need to track?

  10. East North Vertical White noise (no smoothing) Loose random walk (smoothing) Tight random walk (more smoothing) Larson et al., Polar Geography, 2002

  11. Ice Sheet Velocity Variations Number of days where temperature was above freezing.

  12. Special session on Wednesday, G33B, G33C. Zwally et al., 2002.

  13. Earthquakes • Global plate velocities are based on ~10 million measurements per site. • Each Greenland (12-hr) ice sheet velocity is based on ~1000 GPS measurements. • For seismic applications, each position is based on 6-10 measurements. Denali, November 2002

  14. 12:00 UTC 05:00 UTC N N W E W E S S Geodetic Challenges • The constellation varies. A lot.

  15. Geodetic Challenges • Multipath (reflected signals) is important (and doesn’t difference out).

  16. Multipath looks the same from day to day

  17. How do you choose the shift time? If GPS orbital period is 1/2 sidereal day, shift time should be 1 sidereal day (or one day minus 236 seconds).

  18. Repeat Times: Vary by Satellite Choi et al., 2004

  19. Vary by Day of Year

  20. Vary within a Single Day Larson et al., JGR, 2007; Agnew and Larson, GPS Solutions 2007

  21. Does it Really Matter?

  22. Multipath @ Seismic Frequencies MKEA WSRT CRBT

  23. Seismograms East Miyazaki et al., 2004; Emore et al., BSSA, 2007.

  24. Advantages It’s an extra sensor. No clipping. Strong motion. No more double integrating acceleration. Displacement - static offsets Direct link between coseismic and postseismic. Summary: GPS Seismology

  25. Modelled Slip meters centimeters Miyazaki et al., GRL, 2004 Miyazaki and Larson, GRL, revised

  26. Larson, EPS, submitted

  27. m cm cm cm cm

  28. Volcanoes Photo: Jim Kauahikaua

  29. 55 cm extension 25 cm uplift Special session on Friday

  30. Pu`u `O`o AHUP KTPM PGF3 Sandwell et al., submitted to IEEE GRS

  31. Geodetic Challenges • Large signals, but over a much longer time. • But is multipath the biggest problem?

  32. Larson and Miklius, in preparation

  33. Concluding Remarks • High-rate GPS • presents many geodetic challenges… • but increases the number of geophysical applications of GPS & our impact on the AGU community. • What I have learned from high-rate GPS has improved my ability to model (and understand) errors in 24-hour averaged positions. • Multipath >> Seismology >> Multipath >> Soil Moisture.

  34. Multipath • The frequency of ground multipath is determined by the antenna height (and we know what that is). • The amplitude of ground multipath is determined by ground reflectance, which can be related to soil moisture content.

  35. 160 210 260 day of year Soil Moisture The data are free. Kurc and Small, 2004 PBO Site Marshall, CO Larson et al., GPS Solutions, 2007

  36. Acknowledgements • Co-authors • NSF & NASA • IGS & ITRF • UNAVCO, NEHRP, NGS, USGS, CORS, GEONET, NRCAN, SOPAC, CDDIS, IRIS, EUREF, SCIGN, GIPSY. • Fellowship from JSPS.

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