Statistical analysis of site effects on Plate Boundary Observatory time series

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Statistical analysis of site effects on Plate
Boundary Observatory time series Chuck
Meertens Mike Jackson Adrian Borsa Steve
Fisher Dave Maggert
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Acknowledgements

• 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,
  Inc., IRIS, and Stanford University, with
  contributions from NASA and several other
  national and international organizations.
• The Plate Boundary Observatory is the geodetic
  component of EarthScope, installed and operated
  by UNAVCO and funded by the National Science
  Foundation.
• The UNAVCO Facility is supported by the National
  Science Foundation and NASA through a Cooperative
  Agreement.
• And many thanks to John Langbein, the IGS and its
  contributors for orbits, data, and this workshop!

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Talk Overview

• GPS Monumentation
• PBO GPS Analysis
• UNAVCO Data Center
• Time Series Analysis
• Annual Signals
• Comparisons with geology, monumentation

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What is the Plate Boundary Observatory?

• Focused, dense deployments of GPS and
  strainmeters
• 1100 continuous Global Positioning Systems around
  tectonic clusters
• 78 borehole strainmeters
• 5 long baseline strainmeters
• Portable GPS receivers
• Pool of 100 portable GPS receivers for temporary
  deployments to areas not sufficiently covered by
  continuous GPS
• Geo-EarthScope
• InSAR imagery covering the western US
• LIDAR imagery covering the northern and southern
  San Andreas Fault, Yellowstone Caldera, and
  faults in Cascadia and Alaska
• Geocronology

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Permanent GPS Stations
Deep-drilled braced monuments
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Shallow Monuments
Short-drilled braced monuments
Canadian Shallow Foundation Pillar
See Unavco Website for more information on
monumentation
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Sites screening
Excluded data from earthquake and magmatic sites
such as Mt. Saint Helens and Yellowstone (some
sites there also prone to snow problems!
20 mm
-8 cm Note Scale same on all plots in
this presentation
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Data Access - GPS

• UNAVCO Data Center
• GPS Data and Data Products (raw, RINEX, SNX,
  ascii)
• Browser Search and Retrieval
• Year/Day of Year ftp
• Daily, hourly, high-rate (1, 5 hz event download
  files)

• Okmok 4 GPS

1600 Permanent GPS Stations in archive. Data
freely available
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PBO GPS Processing Service
GPS Processing Service GYPSY Central Washington
U. GAMIT New Mexico Tech. Combination Solution
MIT Stable North American Reference Frame
(SNARF2.0) Service Now Available for non-PBO
stations for a fee Daily Time series and
periodic velocity solution products
Yellowstone (Magmatic - Rapid uplift!))
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Time Series Analysis
Time Series Analysis (a work in
progress) Starting Data Set 888 time series
from new PBO, existing PBO Nucleus, and 45 North
American reference sites. Currently 40 IGS
sites are included in the PBO Processing. Examine
d all time series and screened according to
length of series (800-1600 days) and general
quality (used only the best sites (fewest
gaps) Excluded volcanic and earthquake sites
that have large time-variable motions. 350
remaining sites analyzed using John Langbeins
Code Fit linear rate, annual, semi-annual terms.
No Spatial Filtering. - Examine only annual
magnitudes in this presentation Estimated white
and correlated noise (but have not analyzed
yet) Calculated QC parameters from TEQC as a
function of time Software available on John
Langbeins website Paper just out in JGR Noise
in GPS Displacement Measurements from Southern
California and Southern Nevada
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Annual Vertical - Stations with largest Signals
Largest Annual Vertical Signals gt4.5 mm)
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Ground Water Effects
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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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InSAR Reconnaisance
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Northern California
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Lake Shasta GPS/Lake Level Comparison

• Peak uplift late October when lake level is
  lowest (opposite of when water table typically is
  lowest)

• California Dept. of Water Resources water level
  data

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Sacramento
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Sacramento
Deep-drilled braced in sediments in valley again
peak of annual signal in March - in phase with
water table height
Shallow-drilled braced in bedrock in foothills.
As with other foothill sites around the Central
Valley peak annual signal in October
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Smallest Annual Vertical Signals
Smallest Annual Vertical Signals lt 0.5 mm
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Smallest Annual Signals
Lowest Annual Vertical Signal of each monument
class P562 Short-drilled braced (Annual Vertical
0.34 mm) RSTP Deep-drilled braced (Annual
Vertical 0.26 mm) Mojave Desert, Calif.
20 mm
P562
-8 cm
P562
RSTP
RSTP
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IGS Stations
There are 60 IGS sites in North America. 19 were
included in this study, most of which have
shallow monuments
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Site Geology
Deep-drilled sites in sediments have larger
annual signals than those in bedrock
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Annual Signal Compared to Monument Type
Deep-drilled and Short-drilled braced monument
sites typically have smaller annual signals than
shallow foundation sites (which are mostly in
bedrock)
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Discussion

• Annual Vertical Component Signal Analysis
• Largest signal in network (10.8 mm Central Valley
  of California). Annual signals at this site and
  others in the Valley are in phase with ground
  water pumping (peak vertical in late winter when
  water table is highest).
• Smallest ( 0.03 DDB - 0.10 mm SDB monuments in
  Mojave Desert)
• Annual signals can be spatially quite variable
  (e.g Southern Central Valley - depending on local
  pumping and aquifers).
• In the foothills surrounding the Central Valley
  the annual signal is in phase with runoff (peak
  vertical in fall when runoff low). Strong loading
  signal a Shasta lake also uplift trend indicative
  of drought
• From preliminary analysis of annual signals in
  range lt5 mm
• Deep-drilled braced monuments (DDB) in bedrock
  have lower annual signals than those in sediments
• Short-drilled braced (SDB) monuments (sites all
  in rock) have annual signals comparable to
  deep-drilled braced monuments (sites in bedrock
  or sediment). But DDB monuments show higher
  percentage at sub 0.5 mm amplitude
• Still need to analyze the noise characteristics
  further (white noise, power law, etc.)

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Recommendations

• Some Possible Recommendations for new
  Supersites
• Spatial filtering not possible without a number
  of sites at varying distances from station (need
  footprint.
• InSAR reconnaissance can be powerful tool for
  reconnaissance (but variables exist)
• Allow sufficient monumentation to make
  co-location vector ties, to monitor site
  stability, and accommodate sensor migration (e.g.
  new GNSS), but also plan for redundancy. We are
  working on this with JPL at Marshall, CO, test
  site.
• Cameras at sites !) (need accurate metadata)
• Change antennas and receivers at some sites from
  time to time. Sounds strange, but the bottom line
  is that if you see a change when you swap, then
  you do not understand all the contributions
  limiting accuracy. The target is a 1-mm reference
  frame. Precision is not enough.