test test

1
GSA Cordilleran/Rocky Mtn. Section 2008
About GPS, UNAVCO, and EarthScope Science and
Research Helmut Mayer, Susan Eriksson (UNAVCO,
Boulder, CO) Corné Kreemer (University of Nevada
Reno)
2
Overview

• About UNAVCO and EarthScope
• Global Positioning System (GPS) Basics
• (Satellites, Timing, Trilateration, Precision
  and Accuracy)
• Equipment and Survey Techniques
• Applications of GPS
• Plate motions
• Reference frames
• Earthquakes
• Transient Deformation
• Volcanic Deformation
• Isostatic Rebound (Greenland, Midwest/Canada)
• Glacier Flow
• Interferometric Synthetic Aperture Radar (InSAR)
• Light Detection and Ranging (LiDAR)

3
What is UNAVCO

• NSF and NASA funded
• Membership-governed
• Non-profit
• Consortium
• Supports and promotes Earth science by advancing
  high-precision techniques for the measurement and
  understanding of deformation of the Earth

4
Education and Outreach

• Mission
• Promote a broader understanding of Earth science
  through the scientific methods, data, and results
  of the unique suite of scientific research of
  UNAVCO's community
• Foster collaboration between the scientific and
  educational communities
• Faculty-in-Residence Program
• Increase the number and diversity of students to
  strengthen and sustain the next generation of
  Earth scientists.
• Provide
• Short courses and professional development
  courses
• Visualization and map tools
• High-level data products
• Undergraduate research internships
• Summer jobs for college students

5
Data for Educators
http//www.unavco.org/edu_outreach/data.html
6
EarthScope

• 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.
• Guidance is provided by the research and
  educational communities

7
EarthScope
Research goal Explore the structure and dynamics
of the North American Continent Education goal
Provide opportunities for all ages to participate
in a national scientific experiment.
Circles GPS Triangles Seismometers
8
EarthScope Science Goals

• Explore the Structure and Dynamics of the
• North American Continent
• Structure and evolution of the continent and deep
  Earth
• Earthquake processes and seismic hazards
• Magmatic processes and volcanic hazards
• Active deformation and tectonics
• Continental geodynamics
• Fluids in the crust
• Exploration and discovery
• Requires an Interdisciplinary Approach

9
SAFOD

• A borehole laboratory on the San Andreas fault
  studying the physics of earthquake nucleation at
  the depths where earthquakes begin.
• Drilling, Sampling, Downhole Measurements Have
  Been Carried Out Within the San Andreas Fault
  Zone
• Established Access to the San Andreas Fault at
  Seismogenic Depth
• Lateral drilling this past summer to recover
  cores from the fault zone

10
USArray

• A continent-spanning deployment of seismometers
  for imaging the deep interior of the North
  American continent.

11
Transportable Array
12
Plate Boundary Observatory

• Part of the EarthScope project
• Installing gt800 continuously operating
  high-precision GPS stations, borehole and laser
  strainmeters, and tiltmeters
• Manage gt 200 pre-existing GPS stations (PBO
  Nucleus)
• Western U.S. and Alaska
• Study the strain resulting from plate motion
  across active boundary zone between the Pacific
  and North American Plates in the western United
  States and Alaska.

13
PBO Instruments
1100 Continuous GPS
103 Borehole Strainmeters and Seismometers
5 Laser Strainmeters
28 Shallow Borehole Tiltmeters
13
14
GPS Stations
15
The Global Positioning System

• 24 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

16
The GPS Signal

• GPS signal tells a receiver the satellite clock
  time
• GPS receiver compares clock times receiver -
  satellite, hence time of flight, hence range,
  hence receiver position
• GPS signal driven by atomic clock on each
  satellite
• Clock frequency 10.23 MHz
• Two carrier signals (sinusoidal) are coherent
• L1 154 x 10.23 MHz wavelength 19.0 cm
• L2 120 x 10.23 MHz wavelength 24.4 cm
• Bits (1 and -1) encoded on the carrier tell the
  time
• C/A code on L1 - satellite time (C1)
• Precise P code on L1 and L2 - satellite time (P1
  and P2)
• Navigation Message - satellite position,
  satellite clock bias, etc.

17
What is being measured?
GPS Satelliteclock, Ts
Transmitted signal of known code (either C/A or
P code)
Received signal, driven by satellite clock Ts
Antenna
Model signal, driven by receiver clock T
GPS Receiverclock Tr
Pc(Tr-Ts) Pseudorange

• GPS is actually a timing system
• Receiver firmware correlates received signal with
  replica model
• Observed time delay c is pseudorange (a biased
  range)

18
Positioning

• Trilateration

Need 3 satellite signals to locate the receiver
in 3D space 4th satellite used for time accuracy
Calculate position within sub-centimeter
19
Consumer GPS Units

• Accuracy of
• /- 10 m (30 ft) error (horizontal)
• /- 15 m (45 ft) error (vertical)

20
GPS Positioning Methodsand Typical Precision

• Pseudorange positioning
• hand-held GPS, few-meter
• hand-held GPS receiving differential corrections,
  1-meter
• differential pseudorange with carrier
  smoothing, 10-cm
• limited by multipath errors
• Dual-frequency carrier phase positioning
• hand-held GPS using RTK base station, 1-cm
  relative
• geodetic GPS (global), 2-3 mm horizontal, 7-mm
  vertical
• geodetic GPS (regional), 1-2 mm horizontal, 3-5
  mm vertical
• (Blewitt, 2002)

21
What makes it high-precision

• High precision sub-cm level
• Use better internal clocks
• Use the carrier phase to determine the distance
• Dual-frequency receivers
• Good monuments
• Multiple stations
• Sophisticated processing software
• Collect lots of data

22
GPS Error Sources

• Some GPS Error Sources and ways to deal with
  them
• Selective Availability (off at the moment)
• Satellite orbits (use precise orbits)
• Satellite and receiver clock errors (double
  difference
• Atmospheric delays
• Ionosphere (use dual frequency receivers)
• Troposphere (estimate troposphere)
• Multi-path (careful site selection, antenna,
  receiver mitigation research on-going)
• Anti-spoofing (use AS capable receivers L2C in
  future)
• Human errors (training, fixed monuments)

23
Atmospheric Delays

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

24
Multipath echoes

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

25
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

26
Campaign Surveying
Trimble 5700/RT Campaign System
27
Kinematic Surveying
Kinematic surveying with a GPS base station and a
GPS rover, in this case mounted on the survey
sled of the Glacier Roughness Sensor (GRS) to
measure microtopography on the Greenland Inland
Ice
Base Station
Rover
MICROTOP Expedition 1997, Jakobshavns Isbræ,
West Greenland (Herzfeld and Mayer, 1999)
28
GPS Applications

• Plate Motions
• Continental Drift to Plate Tectonics
• Reference Frames
• Plate Boundaries
• Earthquakes
• Transient Deformation
• Volcanic Deformation
• Isostatic Rebound
• Hydrologic Loading
• Glacier Flow

29
Earth Science moving from kinematics to
dynamics . from the
descriptive to the numerical
from components to integration
Science
30
Geologic evidence for Continental Drift
the plants and animals, the ice, the rocks match,
Alfred Wegener 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
31
Seafloor Spreading and Plate Tectonics
added evidence from magnetic stripes, age of the
sea floor, bathymetry, earthquakes
led to the theory of seafloor spreading and plate
tectonics in the 1960s (Hess, Dietz, Vine,
Matthews, Wilson, Cox, Atwater, )
http//volcano.und.edu/vwdocs/vwlessons/atg.html h
ttp//www.unavco.org - Education and Outreach
Maps
32
Plate Tectonics
PLATE BOUNDARIES GENERALLY BUT NOT FULLY KNOWN
In most places we know general plate boundary
geometry from geology, topography, and
earthquakes Ideal plate boundaries very narrow
Many real plate boundaries - especially
continental - are deformation zones up to 1000
km wide, with motion spread beyond nominal
boundary

Gordon Stein, 1992
In some places Indian Ocean. Mediterranean, NW
Asia, etc. were still trying to figure out plate
geometry
33
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
• In the 1970s and 80s space geodetic techniques
  such as VLBI verified plate tectonics and showed
  that current plate motions are very close to
  those estimated from geologic and earthquake
  evidence (NUVEL). Subsequently GPS techniques
  have refined tectonic models, mapped out
  microplates and quantified plate boundary
  deformation and have shown that motions in the
  plate boundary are anything but linear or
  constant in time.

34
Present Plate Motions from GPS
Measure motions over a few years Compare to
those over millions of years
35
Reference Frames

• International Terrestrial
  Reference Frame 2000 (ITRF)
• Standard North American
  Reference Frame (SNARF)
• - UNAVCO SNARF Working Group,
  Geoff Blewitt, Chair
• Will provide an improved reference frame that
  accurately defines the precise coordinates and
  time evolution of a set of stations representing
  "stable North America.

ITRF 2000 Velocities (left) compared to a
N.America-fixed Reference frame (WUSA, SAO, right)
36
Global Plate Motions and Boundary Zones
Observed GPS Velocities plus Earthquake Slip
Directions
Plate Tectonic Model with Deformable Boundaries
Model Velocities and Plate Boundary Strain
GSRM Model of Kreemer and Holt
5170 geodetic velocities from 86 different
studies
37
Global Strain Rate Map
Kreemer et al. (2003)
38
Geodetic Strain Rates Great Basin
?
GeodeticStrain Ratesin Great Basin

Source C. Kreemer, Nevada Geodetic Laboratory,
UNR.
39
Intracontinental Deformation - Asia
Kreemer et al. (2003)
40
GPS Applications

• Plate Motions
• Continental Drift to Plate Tectonics
• Reference Frames
• Plate Boundaries
• Earthquakes
• Transient Deformation
• Volcanic Deformation
• Isostatic Rebound
• Hydrologic Loading
• Glacier Flow

41
Denali Earthquake
3 November 2002

• Long, complex rupture
• Magnitude 7.9, shallow strike-slip
• SE directivity
• Large Love waves

USGS fact sheet
42
Denali GPS Seismograms
43
Seismometer vs. high-rate GPS Measurements

• Seismometer
• Broadband and strong motion instruments
• Direct measurement in inertial reference frame
• Measure acceleration or velocity ? integrate for
  displacement
• Can saturate or clip distorted
  amplitude/phase
• Very sensitive even to remote earthquakes

• High-rate GPS
• Receiver measures distance between receiver and
  multiple satellites
• Estimate position/displacement in terrestrial
  reference frame
• No integration required
• No upper limit to amplitude
• Sensitive only to larger or near vicinity
  earthquakes

44
Seismic Cycle Subduction Zone
Interseismic Strain Accumulation
Coseismic Strain Release
45
Sumatra Earthquake, 26 Dec. 2004
Vigny et al. (2006)
46
Global Deformation Sumatra EQ
Kreemer et al, 2006
47
Tsunami Warning ?

• Rapid displacement
• Data confirm that it arrives mostly with body
  waves
• Can be resolved using 15-minutes after the quake
• Accuracy 7 mm
• Can be used to estimate earthquake slip model

Blewitt et al, 2006
48
Rupture Propagation
Vigny et al. (2006)
49
Postseismic Deformation
Plag et al, 2005
Heki et al, 1996
50
Postseismic Deformation
2005 M8.7 Nias Earthquake
Kreemer et al, 2006
51
GPS Applications

• Plate Motions
• Continental Drift to Plate Tectonics
• Reference Frames
• Plate Boundaries
• Earthquakes
• Transient Deformation
• Volcanic Deformation
• Isostatic Rebound
• Hydrologic Loading
• Glacier Flow

52
Episodic Tremor and Slip Along the Northern
Cascadia Margin
Changes in daily positions calculated from
continuous GPS data reveal long-term trends that
indicate crustal movement.
Time series of daily positions of UCLU and CHWK
wrt DRAO (Penticton) for 1999-2001 (Herb Dragert,
Geol. Survey of Canada)
53
Seismic Records of Tremor Activity
54
Correlation of Tremor Slip in the Victoria Area
Updated from Rogers Dragert, Science, 2003

• Blue dots show GPS east component at Victoria
• Bottom graph shows total of hrs with tremor
  activity in a 10-day window
• The shaded bars show predicted time windows for
  ETS

55
Conceptual Model of ETS on the Cascadia
Subduction Zone
Both offshore and at greater depths (gt50km), the
two plates converge steadily at 4 cm/yr, the
geological average rate.
Across the shallower interface, the plates are
locked for centuries, rupturing only at times of
great thrust earthquakes.
View from East
At depths of 25 to 45 km, plates resist motion
temporarily for 14 months and then slip a few
centimetres over periods of 1 to 2 weeks,
accompanied by distinct seismic tremors.
View from South
56
GPS Applications

• Plate Motions
• Continental Drift to Plate Tectonics
• Reference Frames
• Plate Boundaries
• Earthquakes
• Transient Deformation
• Volcanic Deformation
• Isostatic Rebound
• Hydrologic Loading
• Glacier Flow

57
Volcanic Deformation

• Volcanic
• Signals
• (Sierra Negra
• Galapagos,
• Dennis Geist)

Time
58
GPS Applications

• Plate Motions
• Continental Drift to Plate Tectonics
• Reference Frames
• Plate Boundaries
• Earthquakes
• Transient Deformation
• Volcanic Deformation
• Isostatic Rebound
• Hydrologic Loading
• Glacier Flow

59
GPS SITES DEMONSTRATE POST-GLACIAL REBOUND
GPS sees motion today due to ancient ice
sheet Canada rises US sinks
Sella et al., 2007
(from Seth Stein)
60
Continuous GPS in the Arctic open circles are
stations in the new IPY POLENET (G-NET) network.
Isostatic Rebound
61
POLENET GPS system overview
62
GPS Applications

• Plate Motions
• Continental Drift to Plate Tectonics
• Reference Frames
• Plate Boundaries
• Earthquakes
• Transient Deformation
• Volcanic Deformation
• Isostatic Rebound
• Hydrologic Loading
• Glacier Flow

63
Hydrologic Loading

• Hydrologic
• (non-tectonic
• Signals)
• Example from
• The Salt Lake Basin
• - 3 cm vertical
• From spring runoff
• (U. Utah)

64
GPS Applications

• Plate Motions
• Continental Drift to Plate Tectonics
• Reference Frames
• Plate Boundaries
• Earthquakes
• Transient Deformation
• Volcanic Deformation
• Isostatic Rebound
• Hydrologic Loading
• Glacier Flow

65
Glacier flow Jakobshavns Isbræ, Greenland
66
Glacier flow Jakobshavns Isbræ, Greenland
Network surveying on the ice
67
Glacier flow Jakobshavns Isbræ, Greenland
68
GPS is used to study many topics

• UNAVCO-supported science includes
• Plate tectonics
• Boundary zones
• Earthquakes and tectonics
• Volcanoes and active magmatic systems
• Glacial movements and isostatic adjustment
• Delta subsidence and precision mapping

69
GPS science is used worldwide
70
InSAR
71
5.6 cm
8.4 cm
2.8 cm
0 cm
72
The earthquake cycle coseismic deformation
2003 6.6 Bam earthquake
1999 M7.1 Hector Mine earthquake
Jonsson et al., BSSA 2002
Fialko et al., Nature, 2006 Prittchard, Physics
Today 2006
73
LiDAR
74
Airborne LiDAR
Digital Elevation Models (DEMs) generated from
GeoES NoCal LiDAR data Full Feature and Bare
Earth
75
Flathead Lake, MT
Courtesy W. Carter R. Shrestha
76
GeoES Northern California LiDAR
ENTIRE SAN ANDREAS HAS NOW BEEN IMAGED WITH HIGH
RESOLUTION AIRBORNE LIDAR!

• Data acquired Spring 2007
• Significant community involvement
• NoCal dataset complements B4 LiDAR dataset
  covering southern San Andreas
• Additional GeoEarthScope LiDAR acquisition
  projects planned for 2008
• Southern/eastern California
• Yellowstone, Teton, Wasatch
• Pacific northwest
• Alaska

77
ALSM and InSAR
Comparisons of Techniques for measuring surfaces
and detecting changes in surfaces
GPS InSAR ALSM TLS
Sample Density 1 site/10 km2 10,000 pixels/ km2 1-10 hits/ m2 1000 hits/ m2
Position Precision 1-20 mm 2-3 m 5-15 cm 0.6-5 cm
Change Detection 1 mm 1-2 cm 10 cm 1 cm
Scale Global 100 km 10-100 Km 1 km
Ball park numbers for typical applications
78
GeoEarthScope

• Includes acquisition of aerial and satellite
  imagery and geochronology.
• Part of the EarthScope Facility project funded by
  NSF (MREFC).
• Managed at UNAVCO.
• Assist with EarthScope instrument siting.
• Examine strain field at different
  temporal/spatial scales than geodetic seismic
  instrumentation.
• Data will be freely available.
• For updates and links to data products
  www.unavco.org/geoearthscope