12.540 Principles of the Global Positioning System Lecture 23

1. 12.540 Principles of the Global Positioning SystemLecture 23 Prof. Thomas Herring Room 54-611; 253-5941 tah@mit.edu http://geoweb.mit.edu/~tah/12.540 12.540 Lec 2312.540 Lec 23

2. OVERVIEW • Final lectures: Application areas and GPS results • Analysis of contemporary motions in the Tien Shan region of central Asia. • Start to look at the Earthscope program: NSF/USGS/NASA program to study the dynamics of the Western United States and Alaska 12.540 Lec 23

3. Central Asia Analysis • Network • Development of network • Transition from “pins” with tripods to IVTRAN fixed-heights monuments • Continuous stations • Analysis methods • Pre-continuous station analysis • Merger with global GPS analyses • Motion relative to Eurasia • Methods of used to realize a Eurasia fixed frame • Vertical motions • Vertical motions as a function of existing topographic heights 12.540 Lec 23

4. Network • Development of Network • First measurements made in July 1992; just after start of International GPS Service (IGS). Since then measurements each year and often multiple campaigns per year. • The current network has over 1000 sites, many of them being recovery marks for the main stations (typically 3 per location) • Network extends from Kyrgyzstan to the Kazakh Platform • In 1995, the first continuously operating stations installed. Currently, 9 continuous sites with 2 IGS sites (POL2, SELE) • Results available on web at:http://www-gpsg.mit.edu/~tah/cont98g/cont98.html(Pages include time-series, phase residuals, atmospheric delay estimates) 12.540 Lec 23

5. Central Asia Study Area Kazakhstan Kyrgyzstan 12.540 Lec 23

6. Regional view of network Zoom Eurasia Fixed Frame realized using ITRF2000 50% confidence ellipses shown 12.540 Lec 23

7. Monument evolution • Original monuments were mainly steel pins in bedrock which required tripod setups • Starting in 1995: IVTRAN designed fixed-heights were installed. Simplified setup. Three recovery marks installed for each original monument. • After 1995, measurements made on the recovery marks rather than original marks. • With the original marks and fixed height marks, for many stations two independent velocity estimates (results shown later) 12.540 Lec 23

8. Analysis methods • Prior to 1995; selected IGS from Europe, Asia and Australia included in the analysis of regional data • After 1995 when POL2 became an IGS site and was routinely included in the IGS analysis; only local sites included in the MIT analysis • Using GAMIT/GLOBK; regional analyses are included in the Scripps Institution of Oceanography IGS (SOPAC) analysis including orbit improvement (more important in early data). ftp://garner.ucsd.edu/pub/hfiles • Campaigns are combined with SOPAC h-files for velocity field and repeatability analyses. 12.540 Lec 23

9. Analysis Method • Types of analyses performed with combined files: • Velocity field analysis. Multiple types • Global: Global selection of sites along with regional sites. Eurasian frame then defined using the ITRF2000 Eurasian rotation pole. • Eurasian: Only sites from Eurasia included. Eurasian frame defined to minimize velocities of stable Eurasian sites • In both analyses: Option to force velocities at nearby sites (<0.5 km separation) to be the same (some exceptions) • Repeatability analysis: • Each campaign is rotated/translated to best align as a function of time with positions and velocities from one of the velocity analyses. 12.540 Lec 23

10. IVTRAN Monuments Rod length 355 mm Monument components Installed monument (SST antennas used in Central Asia 12.540 Lec 23

11. Statistical analysis • Since the network contains both continuous sites and campaign sites, we include statistical process noise in the velocity analyses to account for temporal correlations in the time series. • Each site has random walk process noise (2 mm)2/yr • Without process noise, velocities of continuous sites would have sigmas of < 0.1 mm/yr; with process noise sigmas are between 0.6 and 1.0 mm/yr e.g. 12.540 Lec 23

12. Frame Realization • Realization of Eurasian frame; Two methods used • ITRF2000: Used global distribution of sites(52) on many plates to rotate/translate frame onto ITRF2000. ITRF2000 Eurasia pole used to rotate to Eurasia fixed frame • Fit to ITRF2000 (52-sites): • Horizontal RMS 0.8 mm/yr; √c2/f 1.2 • Vertical RMS 1.8 mm/yr; √c2/f 2.4 • Eurasia only: Used 14 sites on stable Eurasia to define frame • Fit to Eurasian sites only(14-sites) • Horizontal RMS 0.5 mm/yr; √c2/f 0.8 • Vertical RMS 1.8 mm/yr; √c2/f 2.3 • Notice c2 is <1 for Eurasia but >1 for global; sigmas depend on size of region considered. 12.540 Lec 23

13. ITRF2000 Residuals Horizontal RMS 0.8 mm/yr 52-sites 12.540 Lec 23

14. Eurasia only residuals Horizontal RMS0.5 mm/yr 14 sites Postglacial rebound model at NYAL, ONSA 12.540 Lec 23

15. Differences between co-located sites • Of the approximately 400 sites with high-quality velocity estimates, 104 sites are collated between old and new monument styles. • Comparison: 12.540 Lec 23

16. Collocated velocity estimates Zoom 50% confidence intervals Differences are consistent with sigmas 12.540 Lec 23

17. Motion in Eurasia Frame Motion from difference analyses Best Estimates:Site East North mm/yr mm/yrPOL2 0.5±0.6 3.0±0.6SELE 0.9±0.8 3.7±0.8 AZOK 1.2±0.9 1.1±0.9CHUM -0.3±1.0 0.4±1.0 12.540 Lec 23

18. Complete Velocity Field Zoom Field dominated by North-South compression Also East-West extension to East 12.540 Lec 23

19. Conclusions • North of the Tienshan the motion of sites relative to Eurasian appears to be less than 1 mm/yr • Within the Kyrgz Tienshan ~13 mm/yr North converge • East west extension across the range front of ~3 mm/yr • Height rate range of ~4 mm/yr • Median RMS scatter of position estimates 1.4-1.8 mm horizontal and 4.6 mm height. • Consistent statistics are obtained with random walk process noise of (2 mm)2/yr. 12.540 Lec 23

20. What is Earthscope • Earthscope is Major Research Equipment (MRE) project in the National Science Foundation (NSF) with contributions from NASA and other government agencies • A major component of this project is the Plate Boundary Observatory (PBO) which uses the Global Positioning System (GPS) to study in detail deformation of the Earth on time scales from seconds to decades. • Plans for interferometric synthetic aperture radar (InSAR) measurements (NASA) • Project is a major application of space based systems to study the Earth (www.earthscope.org). 12.540 Lec 23

21. Components of Earthscope • The MRE portion of Earthscope is $240M over the next 5-years (started late 2003). • There are three major components: • USArray: Moving array of 400 seismic stations that work their way across the US; 120 new permanent stations • SAFOD: San Andreas Fault Observatory at Depth. Project to drill into the San Andreas fault near Parkfield California. • PBO: Plate boundary Observatory; 875 continuously operating GPS receivers and 175 bole-hole strainmeters over the Western United states 12.540 Lec 23

22. USArray Each black dot represents a seismic station deployment over the next five years. 12.540 Lec 23

23. SAFOD Idea is to drill into the San Andrea fault in an area with repeating earthquakes and observe the processes that occur during, before and after earthquakes 12.540 Lec 23

24. PBO 12.540 Lec 23

25. Strainmeter deployment Instruments measure local horizontal strain on three gauges (dl/l). Measurements are converted to east and north strain components Elaborate installation process. PBO is installing a large number of these instruments 12.540 Lec 23

26. Specific results from Earthscope • Transient behavior in Earth Deformations (this and next lecture) • Postseismic: Deformation after recent California earthquakes and relating post-seismic rates to pre-seismic values • Effects of water • Concerns with Earthscope 12.540 Lec 23

27. Examples of Geophysical Signals 12.540 Lec 23

28. Velocity evolution through the seismic cycle Weak Lower Crust Modeled changes in velocities through the earthquake cycle. Times are shown for early, middle and late in cycle Strong lower crust Weak Mantle With strong lower crust less variation during cycle. 12.540 Lec 23 From Hetland and Hager, Relationship of geodetic velocities to velocities in the mantle,GLR, 31, L17604, doi:10.1029/2004GL020691, 2004

29. Hector Mine Co- and Post-seismic displacements Vectors show coseismic offsets and postseismic displacements after 7-years Postseimic estimated with two different methods. 12.540 Lec 23

30. Time series for site LDES 178 mm Coseismic offsets 57 mm 12.540 Lec 23

31. Time series with coseismic offset removed Accumulated postseismic 28 mm 13 mm 12.540 Lec 23

32. Time series 60-day averaging 31 mm postseismic 12.540 Lec 23

33. Analysis of postseismic signals One method of analysis for signals is principle component analysis Number of components related to number of processes acting during postseismic period 12.540 Lec 23

34. Large scale postseismic deformation Examine North component of motion (averaged 60-days) Figure from Andy Freed and Roland Burgmann 12.540 Lec 23

35. San Simeon Earthquake 12/22/2003 Magnitude 6.5 earthquake Co-seismic displacement shown 12.540 Lec 23

36. Motion after earthquake: PBO stations installed to measure postseismic motion 12.540 Lec 23

37. Time series of North motion of sites near San Simeon Grey lines show motion expected for this part of California 12.540 Lec 23

38. Parkfield earthquake (9/28/2004) Magnitude 6 (latitude) 9 months after San Simeon, the Parkfield Earthquake Again showing long term transient after event 12.540 Lec 23

39. Longitude Motion after Parkfield 12.540 Lec 23

40. Full North/East Time series for Parkfield site Pre-EarthquakeNorth 19.1±0.1 mm/yrEast -15.2±0.3 mm/yr 2006-2007 VelocitiesNorth 10.5±0.3 mm/yrEast -10.0±0.5 mm/yr 12.540 Lec 23

41. Summary • Results from different regions of the world (Tien Shan and Earthscope). • Steady state deformation showing strain accumulation • Non-steady motions. So far postseismic deformation. Next class look at other types of non-steady motion. 12.540 Lec 23