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GPS geodesy: applications to geosciences

GPS geodesy: applications to geosciences. case overview. Puerto Rico-Virgin Islands microplate Soufriere Hills volcano, Montserrat Nicaragua forearc deformation New Madrid Seismic Zone. CASE 1. GPS results from Puerto Rico and the Virgin Islands: Constraints on microplate tectonics.

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GPS geodesy: applications to geosciences

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  1. GPS geodesy: applications to geosciences case overview Puerto Rico-Virgin Islands microplate Soufriere Hills volcano, Montserrat Nicaragua forearc deformation New Madrid Seismic Zone

  2. CASE 1 GPS results from Puerto Rico and the Virgin Islands: Constraints on microplate tectonics

  3. overview • general tectonics of Caribbean plate • model for northeastern Caribbean • Caribbean reference frame • microplate tectonics in northeastern Caribbean • deformation across Puerto Rico and the Virgin Islands

  4. What is societal interest in the research? SEISMIC HAZARD! Why is it important in Puerto Rico? probability of various ground motions in specified time USGS curves equate San Juan, Mayagüez with Seattle

  5. population density of Puerto Rico: 1,124 per square mile if US had same population density as Puerto Rico…. …population of US would be 3 billion

  6. circum-Caribbean seismicity (defines plate) Caribbean epicenters < 30 km depth from USGS

  7. Caribbean bathymetry BR: Beata Ridge; HE: Hess Escarpment NPDB: North Panama Deformed Belt; SCDB: South Caribbean deformed belt

  8. depth to slab NOAM subducts westward below Caribbean along Lesser Antilles http://www.ig.utexas.edu/research/projects/venez_margin/venez_margin.htm

  9. positions of the leading edge of Caribbean plate in the past… i.e. where subduction was http://www.ig.utexas.edu/research/projects/venez_margin/venez_margin.htm

  10. bathymetry “around the corner” note: Bahamas colliding with Hispaniola

  11. North American-Caribbean plate boundary MC: Mona Canyon AP: Anegada Passage MT: Muertos trough

  12. proposed microplates of the northeastern Caribbean from west to east: Gonave Hispaniola Puerto Rico-Virgin Islands (PRVI) (modified from Mann et al., 1995)

  13. bathymetry offshore Puerto Rico and Virgin Islands from: http://www.vangestel.com

  14. block-faulting west of St. Croix

  15. profiles across Puerto Rico from: http://www.vangestel.com

  16. models for Puerto Rico-Virgin Islands microplate ….Caribbean moves east relative to NOAM…. …left-lateral strike-slip along northern boundary

  17. ~40° CCW since Eocene; ~12° CCW since Miocene; 0 last 2 m.y.

  18. • seismicity mostly offshore supports rigidity of PRVI • thrust events along western MT and eastern PRT support rotation • little seismicity along AP provides no constraint • setting of western PRT isn’t clear

  19. GPS geodesy in northeastern Caribbean 1986 (NASA): 6 sites 1994 (NSF): 6 original sites plus new sites in Hispaniola, Puerto Rico and British Virgin Islands 1995 to present (NSF; NASA): expansion of network throughout • Hispaniola (Calais), • Puerto Rico, Virgin Islands (Jansma, Mattioli) occupations of subsets of sites done yearly since 1995

  20. definition of Caribbean reference frame …most of the islands sit on edges of the plate…

  21. interior of plate has lots of ocean, not much land …one spot in eastern Caribbean…Aves Island

  22. sites for Caribbean reference frame (stars) DeMets et al. (2000): AVES, SANA, ROJO, CRO1 plus transforms …currently, we use this plus BARB (unpublished)

  23. best fit NOAM-CARIB rate ~19 mm/yr ENE azimuth • twice as fast as NUVEL-1A • azimuth ~N70°E at PR

  24. problems with Caribbean reference frame: too few sites time series too short (noise significant) for key sites (AVES) potential that Caribbean is TWO plates and/or deforming potential improvements: additional sites in Honduras, Nicaragua, Lesser Antilles additional occupations (AVES for March--volunteers?)

  25. too few sites… Nicaragua

  26. can use BARB (already do) FSDO

  27. other sites in Lesser Antilles also may be on stable Caribbean… …. too early to tell

  28. only 2 occupations

  29. Caribbean deformation? (affects reference frame) two plates: western (SANA) and eastern (AVES) plates little seismicity in interior says no …some features suggest maybe we know that NOAM and SOAM are converging… “subduction” of Caribbean below Muertos Trough and South America

  30. GPS network in northeastern Caribbean

  31. potentially active faults on Puerto Rico

  32. data from continuous GPS sites (ITRF00) western Puerto Rico eastern Puerto Rico

  33. data from campaign GPS sites (ITRF00) western Puerto Rico eastern Virgin Islands

  34. do separate microplates exist?…yes clear difference between Hispaniola and Puerto Rico …extension of ~5 mm/yr across Mona rift • Hispaniola moves rapidly relative to Caribbean (slowly wrt NOAM) • PRVI moves slowly relative to Caribbean (rapidly wrt CARIB)

  35. does Puerto Rico rotate?…no • component of convergence across western Puerto Rico trench not compatible with rotation model… • similar azimuths of velocities throughout Puerto Rico not compatible with rotation about nearby vertical axis

  36. does Puerto Rico escape to east? have active faults? • island moves at ~85% of total CARIB plate rate wrt NOAM • Virgin Gorda has no motion wrt CARIB (no tectonic escape) • increasing velocities westward across PRVI (EW extension) • velocities for western PR sites are similar (faults?)

  37. The Dynamics of an Ongoing Andesitic Eruption: What we have learned from Surface Deformation at Soufriere Hills, Montserrat, BWI CASE 2

  38. eruption began in July 1995 as phreatic (steam) …became phreato-magmatic in October 1995 …explosions began in September 1996 initial GPS occupations began in August 1995 • L1 only receivers early • campaigns with dual frequency receivers began October 1995 • continuous GPS in summer 1996

  39. data from August 1995-October 1996 note large error bar on circle (L1 measurement)

  40. Tar River Valley - Looking ENE October 1995 English Crater 4 Ka Sector Collapse

  41. GPS analysis strategy • Campaign and continuous GPS geodesy done from 1995-2002 • Several CGPS sites destroyed over the years; current network is 6 sites - Choke Ring Antennae with UNAVCO radomes and FreeWave RF telemetry • Data processed in absolute point positioning mode with final JPL orbits, clocks, and earth orientation parameters - Time series in ITRF97 and the referenced to fixed CAR (DeMets et al., 2000) • GPS velocities are modeled assuming linear segments for each of three periods

  42. No Surface Flux Renewed Dome Growth Explosions -> <-Dome Growth Subsidence Again! -> <- Subsidence Inflation ->

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