Transcript Tracking Tectonic Plates

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…
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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:
HS3-NUVEL-1A
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)
Execute calculation
Results from Plate Motion Calculator:
Calculation results
plate velocity : 10.3 [cm/yr]
direction: 299.8 [deg. from North]
Plate Model: HS3-NUVEL-1A
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
Summit of Mauna Kea:
latitude 19.803° longitude -155.456°
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 10m
High Precision GPS
Location to
the level of
sub-centimeter
Access to GPS data:
http://sideshow.jpl.nasa.gov/mbh/series.html
ACU1
ADKS
ADRI
AGMT
AIS1
AJAC
ALBH
ALGO
ALIC
ALPP
ALRT
AMC2
AML5
AMMN
ANA1
ANKR
ANP1
ANTC
ANTO
AOA1
AOML
AREQ
ARL5
ARM1
ARM2
ARP3
ARTU
ASC1
ASHV
ASPA
ATL1
AUCK
AUS5
AVRY
AZCN
AZRY
AZU1
BAHR
BAIE
BAKE
BAKO
BAN2
BAR1
BARB
BARH
BARN
BAY1
BAY2
BAYR
BBDM
BBRY
BCWR
BEA5
BEMT
BEPK
BGIS
BIL1
BILI
BILL
BIS1
Summit of Mauna Kea:
latitude 19.803° longitude -155.456°
Motion data is given in
three components:
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.
N
63.74 mm / yr
W
35.16 mm / yr
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
GPS
Components
rate
azimuth
lat vel
long vel
GPS Resultant
velocity
azimuth
CHANGE
(GPS-model)
Δ vel
Δ az
EISL
Nazca
Easter Isl
-27.15
-109.38
33
106
-6.04
67.97
68.2
95
35.2
-11
ISPA
Nazca
Easter Isl
-27.12
-109.34
33
106
-5.19
67.54
67.7
94
34.7
-12
GALA
Nazca
Galapagos Isl
-0.74
-90.30
21
89
11.87
51.8
53.1
77
32.1
-12
GLPS
Nazca
Galapagos Isl
-0.74
-90.30
21
89
9.46
49.97
50.9
79
29.9
-10
ANTC
S Am
Andes
-37.34
-71.53
46
260
10.17
15.36
18.4
56
-27.6
-204
AREQ
S Am
Andes
-16.47
-71.49
48
261
2.58
-6.47
7.0
292
-41.0
31
BOGT
S Am
Andes
4.64
-74.08
45
261
14.81
0.7
14.8
3
-30.2
-258
CFAG
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
S Am
-15.95
-47.88
48
255
12.86
-3.7
13.4
344
-34.6
89
CHPI
S Am
S Am
-22.69
-44.99
48
254
12.08
-3.83
12.7
342
-35.3
88
CORD
S Am
S Am
-31.53
-64.47
47
259
12
0.48
12.0
2
-35.0
-257
FORT
S Am
S Am
-3.88
-38.43
48
253
12.94
-4.59
13.7
340
-34.3
87
KOU1
S Am
S Am
5.25
-52.81
46
255
11.84
-4.52
12.7
339
-33.3
84
KOUR
S Am
S Am
5.25
-52.81
46
255
13.21
-4.27
13.9
342
-32.1
87
LPGS
S Am
S Am
-34.91
-57.93
46
256
11.93
-1.31
12.0
354
-34.0
98
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
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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
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UNAVCO, Google Earth, EXCEL, etc.