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GPS Geodesy as Windows on Earth New Discoveries
using GPS and other Geodetic Techniques Contribut
ions from Shelley Olds, Chuck Meertens and many
scientists UNAVCO, Boulder, CO
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Outline

• About Geodesy
• Plate Tectonics
• Global Positioning System (GPS)

• UNAVCO, Plate Boundary Observatory (PBO),
  EarthScope and You
• New Discoveries, Data and Science

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Once upon a time
The world was flat Then it was a sphere

• Eratosthenes (276 BC - 194 BC) measured the shade
  angle in wells in Alexandria Syene (Egypt)
• Earths circumference 252,000 strades (roughly
  46,000 km, 15 gt current measurement).

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Once upon a time

• The world was flat
• Then it was a sphere
• then it was a squished sphere
• then it had bumps!
• ... And its shape changes with time

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Geodesy

• Geodesy is the science of
• accurately measuring the Earths
• size, shape, orientation,
• gravitational field and
• the variations of these with time.

Traditional Geodetic Application Precise
positioning of points on the surface of the Earth
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A QUICK RECAP OF PLATE TECTONICS
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A quick Plate Tectonics recap
Crust
http//mediatheek.thinkquest.nl/ll125/images/stru
ct.jpg
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Types of Plate Boundaries

• Transform Divergent Convergent

(from USGS, 2005)
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Pre-plate tectonics Continental DriftGeologic
evidence
the plants and animals, the ice, the rocks match,
Alfred Wegner proposed Continental Drift in
1912 because.
and the climates and poles do not.
the shapes match,
http//volcano.und.edu/vwdocs/vwlessons/atg.html h
ttp//kids.earth.nasa.gov/archive/pangaea/evidence
.html
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GPS evidence for plate tectonics
GPS station positions are solidly attached to the
ground.
Q As the plates move, how will the position of
these stations change relative to one another?
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Space Geodesy

• Wegener's Dream
• "This direct measurement of continental drift
  must be left to the geodesists. I have no doubt
  that in the not too distant future we will be
  successful in making a precise measurement of the
  drift of North America relative to Europe."--
  Alfred Wegener, 1929

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Present Plate Motions from GPS
Measure motions over a few years Compare to
those over millions of years


Larson et al. 1997
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Moved from Simplified
Plate Boundaries Motions
(from http//en.wikipedia.org/wiki/Plate_tectonics
, 2008)
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to complex understanding

• Deep earthquakes reveal
• location of subducting lithosphere
• physical characteristics of the subducting
  material.

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ABOUT UNAVCO, EARTHSCOPE, US-ARRAY, SAFOD,
PLATE BOUNDARY OBSERVATORY
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UNAVCO

• NSF and NASA funded
• Non-profit
• Consortium
• Membership-governed
• Facilitates geoscience research and education
  using geodesy.

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UNAVCO-supported science

• Plate movement / Boundary zones
• Earthquakes / Transient deformation
• Volcanoes / active magmatic systems
• Glacial movements and isostatic adjustment /
  Hydrologic/seasonal changes / Atmospheric
  measurements
• LiDar, InSAR

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EarthScope Partners
EarthScope is funded by the National Science
Foundation and conducted in partnership with the
US Geological Survey.
EarthScope is being constructed, operated, and
maintained as a collaborative effort with UNAVCO,
IRIS, and Stanford University, with contributions
from NASA and several other national and
international organizations.
The data collected by EarthScopes three
observatories will help us to understand
processes that control earthquakes and volcanoes.
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US Transportable Array

• Includes 400 Transportable Seismometers
• Station occupies a site for 1½ - 2 years
• 10 years to leap-frog array across the US

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SAFOD
A borehole laboratory on the San Andreas fault
studying the physics of earthquake nucleation at
the depths where earthquakes begin
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Plate Boundary Observatory

• Continent-scale network of GPS, borehole, and
  laser strainmeters
• Focused on the extended plate boundary and
  extending into the continental interior
• Operated by UNAVCO

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UNAVCO PBO Instruments
GPS 1100 Continuous , gt2000 Campaign
75 Borehole Strainmeters and Seismometers
5 Laser Strainmeters
28 Shallow Borehole Tiltmeters
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ABOUT GPS
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Types of GPS Units

• Global Positioning System (GPS)

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High-precision systems for field surveying
Movable tripod with choke-ring antenna
Trimble 5700 geodetic receiver with flat antenna
Monument stability and centering and leveling the
antenna are critical !
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In Extreme Environments
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The Global Positioning System

• 31 satellites
• 20,200 km altitude
• 55 degrees inclination
• 12 hour orbital period
• 5 ground control stations
• Each satellite passes over a ground monitoring
  station every 12 hours

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Anatomy of a High-precision Permanent GPS Station

• GPS antenna inside of dome
• Monument solidly attached into the ground with
  braces.
• If the ground moves, the station moves.
• Solar panel for power
• Equipment enclosure
• GPS receiver
• Power/batteries
• Communications/ radio/ modem
• Data storage/ memory

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Instantaneous positioning with GPS

• Consumer grade accuracy of
• /- 10 m (30 ft) error (horizontal)
• /- 15 m (45 ft) error (vertical)

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High-precision GPS

• Current accuracies sub-cm.
• Use the carrier phase
• Dual-frequency receivers
• High-precision orbital information
• Good monuments
• Multiple stations
• Sophisticated processing software
• Collect lots of data

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Sources of Error

• Some GPS Error Sources
• Selective Availability
• Satellite orbits
• Satellite and receiver clock errors
• Atmospheric delays
• Ionosphere
• Troposphere
• Multi-path
• Human errors

The New Yorker, Roz Chast
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Atmospheric Delays

• Ionosphere (use dual frequency receivers)
• Troposphere (estimate troposphere)

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Multipath echoes

• Similar issue to ghost images on TV
• Causes inaccurate measurements
• If we were outside right now, what would cause
  potential multipath errors?

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SCIENCE RESEARCH USING GPS OTHER GEODETIC
TECHNOLOGIES

• GPS (Global Positioning System)
• InSAR (Interferometric Synthetic Aperture Radar
  from Space and aircraft)
• LiDAR (Terrestrial and Airborne Laser Scanning)
• Borehole and long-baseline strainmeters,
  seismometers, and tiltmeters

The Geodesists expanding toolbox
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Geodetic Applications

• Plate motion
• Earthquakes and slow slip
• Volcanic deformation
• Ice, water, air
• LiDar, InSAR

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Plate Motion
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Creeping Motion
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Geodetic Applications

• Plate motion
• Earthquakes and slow slip
• Volcanic deformation
• Ice, water, air
• LiDar, InSAR

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Seismic waves measured by GPS
High-rate GPS 4000 km away
Denali (Alaska) earthquake (2002)
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Transient motion associated with faults
Episodic Tremor and Slip
Parkfield Earthquake
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Episodic Tremor and Slip
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ETS Progression over days
Trem_movie_2008eq_time.mov

• http//www.pnsn.org/WEBICORDER/DEEPTREM/fall2006.h
  tml

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Propagation of Sumatra Earthquake

• http//www.seismology.harvard.edu/ishii/sumatra/i
  ndex.html Ishii 2005

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Geodetic Applications

• Plate motion
• Earthquakes and slow slip
• Volcanic deformation
• Ice, water, air
• LiDar, InSAR

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(No Transcript)
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GPS Station P697 on Mt. St. Helens
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Inflation Deflation
Inflation
Deflation
50 mm/yr
50 mm/yr
2000
2001
2000
2001
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Volcanic Deformation

• Volcanic
• Signals
• Sierra Negra,
• Galapagos

Time
Dennis Geist, U. Idaho
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Galapagos
InSAR and GPS Vectors Showing trapdoor faulting
event
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Yellowstone Ground Motions
Fig. 2. (A) Temporal variation of vertical ground
motions of labeled Yellowstone GPS stations
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W.-L. Chang et al., Science 318, 952 -956
(2007)
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Mt. Etna, Sicily

• gt 100 Synthetic Aperture Radar (SAR)
  interferograms from 47 dates during 1992-2000
• 14 cm range
• Timeline and activity
• 1991-1993 Flank eruption
• 1992-1993 Etna deflates as eruption subsides
• 1993-1995 Etna inflates, undergoes summit
  magmatic activity
• 1995-2000 Multiple inflation and deflation
  breathing episodes, accompanying repeated
  summit activity.

Based on time series inversion algorithms of
Lundgren et al. (J. Geophys. Res., 2001) and
Berardino et al. (IEEE, 2002).
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Geodetic Applications

• Plate motion
• Earthquakes and slow slip
• Volcanic deformation
• Ice, water, air
• LiDar, InSAR

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Crustal Loading from Glaciers

• Ice
• Viscous rebound from ancient glaciers
• Elastic response of present-day melting from
  global warming

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Isostatic Adjustment
(Sella and others, 2007)
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Weighing the ice sheets
Continuous GPS in the Arctic
Short-term elastic deformation of the ice load,
providing a measure of large-scale melting, and
hence contribution to sea-level rise Open
circles are the POLENET network installed for the
International Polar Year (IPY)
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Ground Water Effects
Southern San Joaquin Valley, California
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Ground Water Effects
P571 Bedrock in Sierra Nevada Foothills - Shows
secular uplift - Annual Cycle peaks in October
P056 Site in Sediments in San Joaquin Valley -
Shows rapid secular subsidence - Annual Cycle
peaks in March
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Hydrologic Loading

• Water
• Changing loads from
• Ocean tides,
• Wind-driven surges,
• Reservoir depletion
• Spring runoff
• Example
• The Salt Lake Basin
• - 3 cm vertical
• From spring runoff
• (U. Utah)

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Influence of the Atmosphere

• Air / Severe storm forecasting
• Changing loads from weather systems are an
  important source of noise
• Water Vapor,
• Atmospheric temperature,
• Pressure and electron density

Geodetic Monitoring of Natural Hazards Why Are
We Talking About the Atmosphere? John Braun
COSMIC/UCAR http//achaia.unavco.org/public/meeti
ngs/2008/scienceworkshop/viewabstract.asp?id2520
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Influence of the Atmosphere

• Atmospheric and Ionospheric Effects
• Precipitable Water Vapor (PWV) derived from GPS
  signal delays
• Assimilation of PW into weather models improves
  forecasting for storm intensity
• Total electron count (TEC) in Ionosphere

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Geodetic Applications

• Plate motion
• Earthquakes and slow slip
• Volcanic deformation
• Response to loading by ice, water, and air
• LiDar, InSAR

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New Orleans Flooding Subsidence
Dixon et al. (2006)
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GeoEarthScope

• LiDAR imagery
• InSAR imagery
• Geochronology

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Airborne Laser Swath Mapping (ALSM)
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LiDAR Image Unfiltered

• Landscape content

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LiDAR Image Filtered

• Landscape content

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(No Transcript)
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Terrestrial Laser Scanning (TLS) / Tripod LiDAR
Courtesy Gerald Bawden, USGS
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Parkfield 2004
Courtesy Gerald Bawden, USGS
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Parkfield bridge postseismic motionSeptember 04
to July 05
Pacific Plate
North American Plate
Courtesy Gerald Bawden, USGS
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Summary UNAVCO-Support Science

• Plate motion
• Earthquakes and slow slip
• Volcanic deformation
• Ice, water, air
• GPS, LiDar, InSAR

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Questions?

• Thank You