Tracking Tectonic Plates Testing Plate Tectonics with Two

Tracking Tectonic Plates: Testing Plate Tectonics with Two Independent Methods Laurel Goodell Dept of Geosciences Princeton University

The theory of plate tectonics is supported by many lines of evidence… • • • Patterns of earthquake epicenters, depths, magnitudes, focal mechanisms. Topography of the ocean floor Age progression along certain volcanic island chains and symmetric aging of ocean rock with distance on either side of mid-ocean ridges. . Lack of ocean sediment at mid-ocean ridges and progressively increasing sediment thickness on either side of ridges Symmetric pattern of magnetism on either side of mid-ocean ridges. Locations and types of volcanism. Relative youth of ocean lithosphere compared to continental lithosphere. Composition of the oceanic lithosphere vs. composition of the continental lithosphere. Jigsaw puzzle-like fit of some continental shapes, fossils, rock types and rock ages across oceans Fossils of warm-climate organisms in areas now cold; fossils of cold-climate organisms in areas now warm. …and we might be hard-pressed to think of alternate explanations that could explain the same lines of evidence,

But isn’t it all circumstantial ? We can’t see the plates moving… or can we…. ? ?

Tracking Tectonic Plates: Testing Plate Tectonics with Two Independent Methods Method 1: Long-term average motions based on geologic data

Example of geologic data used to infer long-term rates and directions of plate motion

Data like these are used to develop various “Plate Motion Calculators, ” e. g. • http: //ofgs. ori. u-tokyo. ac. jp/~okino/platecalc_new. html

Application of Plate Motion Calculator : Summit of Mauna Kea: latitude 19. 803° longitude -155. 456°

Plate Motion Calculator (http: //ofgs. ori. u-tokyo. ac. jp/~okino/platecalc_new. html) This "Plate Motion Calculator" calculates the relative and absolute plate motion direction and speed at any point on the earth. The prototype of web-based plate motion calculator was developed by K. Tamaki. This calculator is a revised version by K. Okino using perl-CGI script. Method of Calculation: Select plate motion model, plate (or plates) and input latitude and longitude of the point, then press the "Execute calculation" button. Plate Model: HS 3 -NUVEL-1 A Moving Plate: Pacific Fixed Plate: n/a (not used in NNR models) Latitude[deg]: 19. 803 (North: positive, South : negative) Longitude[deg]: -155. 456 East: positive, West: negative) (see references below)

Results from Plate Motion Calculator: Calculation results plate velocity : 10. 3 [cm/yr] direction: 299. 8 [deg. from North] Plate Model: HS 3 -NUVEL-1 A Moving Plate: pa rotation rate: 1. 0613 [deg/my] Latitude of Euler pole: -61. 467 [deg. ] Longitude of Euler pole: 90. 326 [deg. ] Angular velocity: 1. 0613 [deg. /m. y. ] Latitude inputted: 19. 803 [deg. ] Longitude inputted: -155. 456 [deg. ]

Method 1: Long-term average plate motion vector 103 mm Summit of Mauna Kea: latitude 19. 803° longitude -155. 456° /yr

Tracking Tectonic Plates: Testing Plate Tectonics with Two Independent Methods Method 1: Long-term average motions based on geologic data Method 2: Near real-time motions from GPS data

Global Positioning System

Consumer GPS Units Accuracy of • +/- 10 m (30 ft) error (horizontal) • +/- 15 m (45 ft) error (vertical) Location to The level of about 10 m

High Precision GPS Location to the level of sub-centimeter

Access to GPS data: http: //sideshow. jpl. nasa. gov/mbh/series. html ACU 1 ADKS ADRI AGMT AIS 1 AJAC ALBH ALGO ALIC ALPP ALRT AMC 2 AML 5 AMMN ANA 1 ANKR ANP 1 ANTC ANTO AOA 1 AOML AREQ ARL 5 ARM 1 ARM 2 ARP 3 ARTU ASC 1 ASHV ASPA ATL 1 AUCK AUS 5 AVRY AZCN AZRY AZU 1 BAHR BAIE BAKO BAN 2 BAR 1 BARB BARH BARN BAY 1 BAY 2 BAYR BBDM BBRY BCWR BEA 5 BEMT BEPK BGIS BIL 1 BILI BILL BIS 1

Summit of Mauna Kea: latitude 19. 803° longitude -155. 456°

Motion data is given in three components: h Increase in latitude (positive slope) means the N-S component is to the north. Decrease in latitude (negative slope) would mean the N-S component is to the sorth. Increase in longitude (positive slope) means the E-W component is to the east. Decrease in latitude (negative slope) would mean the E-W component is to the west. Increase in height (positive slope) means the up-down component is up. Decrease in height (negative slope) would mean the up-down component is to the down. nort wes t Down (relatively s low)

N 63. 74 mm / yr W 72 35. 16 mm / yr . 79 m m / y r 61° 72. 79 mm/yr at an azimuth of 299°

Method 2: near real-time plate motion vector GPS Summit of Mauna Kea: latitude 19. 803° longitude -155. 456°

So, now we have plate motions for two different methods – but reference frames of the two methods are not the same. So… Investigate relative motions across plate boundaries, inferred by the two methods.

Nazca plate S. American plate

GPS Model Long Term latitude longitude rate azimuth lat vel long vel EISL Nazca Easter Isl -27. 15 -109. 38 33 106 -6. 04 ISPA Nazca Easter Isl -27. 12 -109. 34 33 106 GALA Nazca Galapagos Isl -0. 74 -90. 30 21 GLPS Nazca Galapagos Isl -0. 74 -90. 30 ANTC S Am Andes -37. 34 AREQ S Am Andes BOGT S Am CFAG GPS Resultant velocity azimuth 67. 97 68. 2 95 35. 2 -11 -5. 19 67. 54 67. 7 94 34. 7 -12 89 11. 87 51. 8 53. 1 77 32. 1 -12 21 89 9. 46 49. 97 50. 9 79 29. 9 -10 -71. 53 46 260 10. 17 15. 36 18. 4 56 -27. 6 -204 -16. 47 -71. 49 48 261 2. 58 -6. 47 7. 0 292 -41. 0 31 Andes 4. 64 -74. 08 45 261 14. 81 0. 7 14. 8 3 -30. 2 -258 S Am Andes -31. 60 -68. 23 47 260 11. 39 5. 84 12. 8 27 -34. 2 -233 CONZ S Am Andes -36. 84 -73. 03 46 261 20. 26 33. 17 38. 9 59 -7. 1 -202 COPO S Am Andes -27. 38 -70. 34 48 261 17. 86 14. 8 23. 2 40 -24. 8 -221 IQQE S Am Andes -20. 27 -70. 13 48 261 15. 93 26. 88 31. 2 59 -16. 8 -202 RIOP S Am Andes -1. 65 -78. 65 46 263 -0. 65 -3. 88 3. 9 260 -42. 1 -3 SANT S Am Andes -33. 15 -70. 67 47 260 16. 85 20. 57 26. 6 51 -20. 4 -209 UNSA S Am Andes -24. 73 -65. 41 48 259 11. 25 4. 86 12. 3 23 -35. 7 -236 BRAZ S Am -15. 95 -47. 88 48 255 12. 86 -3. 7 13. 4 344 -34. 6 89 CHPI S Am -22. 69 -44. 99 48 254 12. 08 -3. 83 12. 7 342 -35. 3 88 CORD S Am -31. 53 -64. 47 47 259 12 0. 48 12. 0 2 -35. 0 -257 FORT S Am -3. 88 -38. 43 48 253 12. 94 -4. 59 13. 7 340 -34. 3 87 KOU 1 S Am 5. 25 -52. 81 46 255 11. 84 -4. 52 12. 7 339 -33. 3 84 KOUR S Am 5. 25 -52. 81 46 255 13. 21 -4. 27 13. 9 342 -32. 1 87 LPGS S Am -34. 91 -57. 93 46 256 11. 93 -1. 31 12. 0 354 -34. 0 98 GPS Components CHANGE (GPS-model) Δ vel Δ az

21 47 Model: Converging at a rate of 68 to 80 mm/yr 47 47 33 47

51 GPS: 4 Converging at a rates of ~30 -50 mm/yr Picks up intra-plate deformation (S. American vectors quite varied, although still indicate convergence) 27 12 68 29

Many other projects possible, e. g. • Mid-Atlantic ridge • Crossing Pacific, Phillippine and Eurasion plates • Pacific/North American plate boundary

Lines of Evidence • Patterns of earthquake epicenters, depths, magnitudes, focal mechanisms. • Topography of the ocean floor • Age progression along certain volcanic island chains and symmetric aging of ocean rock with distance on either side of mid-ocean ridges. . • Lack of ocean sediment at mid-ocean ridges and progressively increasing sediment thickness on either side of ridges • Symmetric pattern of magnetism on either side of mid-ocean ridges. • Locations and types of volcanism. • Relative youth of ocean lithosphere compared to continental lithosphere. • Composition of the oceanic lithosphere vs. composition of the continental lithosphere. • Jigsaw puzzle-like fit of some continental shapes, fossils, rock types and rock ages across oceans • Fossils of warm-climate organisms in areas now cold; fossils of coldclimate organisms in areas now warm. • GPS (and VLBI) data.

Testing a theory • Case for plate tectonics is strengthened as both methods generally agree. • But over the time-span of GPS measurements, plates move at rates different than long-term model averages and thus rates must not be constant. • GPS rates for stations on the same plate are often similar, but not identical and sometimes quite different - indicating that internal deformation of plates does occur. • Some plate boundaries are “wider” than others.

Quantitative Skills • • Unit conversion Vector algebra Trigonometry Reading and interpreting graphs Geographic skills and spatial analysis, visualization Comparison and evaluation of numerical data Reference frames

Evolution of an Exercise acknowledgements: • W. Jason Morgan, Princeton Univ. Professor Emeritus Developed a version of this using VLBI data a decade ago. • Barb Tewksbury described a ““study your own tectonic plate” project at a workshop some years ago. • Using GPS Data to Study Crustal Deformation, Earthquakes, and Volcanism: A Workshop for College Faculty - at 2006 GSA Annual Meeting - similar workshop offered this year at 2008 meeting in Houston • UNAVCO, Google Earth, EXCEL, etc.