SCIGN
Combined Product Report
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April 20, 2004
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Last Updated Tuesday, April 20, 2004
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An overview of the SCIGN
array is discussed in Hudnut
et al., 2001. A list of
references to papers using SCIGN data is maintained on the SCIGN Web
site publication list. |
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This web page reports on
the combined SCIGN site velocity and time series results based on combination
of loosely constrained GPS site position estimates from the JPL and SIO SCIGN
analysis centers. The use of
these types of files allows the same reference frame and treatment of sites
to be applied to both analyses.
The products generated are GPS site velocities, parametric
representations of postseismic motions, and time series generated by daily
combination of these loosely constrained solutions. The JPL and SIO analysis centers generate similar products
and their results are available from their web sites. Links to these results are included
on the combined results web page and
below. The individual center results
are also included on the combined results web page converted to the same file
formats and reference system used for the combined results. |
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This report updates the June 2003 Report,
the March
2003 report, the Dec 2002
report and November 2003 Report
(linked as SCIGN_96_0309_Results.html) on the comparison and combination of the JPL and
SIO analyses of the SCIGN GPS data collected between Jan 1996 and 29 February
2004. As in previous reports we
include is this distribution, time series from the processing of SIO h-files
and JPL stacov files, and from the analyses carried out at each center. These time series directories replace
the ones available in previous reports.
All of the time series files have been brought to a common format for
both the velocity fields and the time series, and these files can be viewed
with the GAMIT/GLOBK Matlab toolkit distributed as GGMatlab. |
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The changes from the previous
report are: (1) Addition of newly
collected and analyzed results between Oct 2003 and Feb 2004. The release of this report was
delayed so that the postseismic deformation after this earthquake could
develop. (2) Potential position
changes for all antenna type and radome changes were included in this
analysis (most of these had been previously included but some in the North
America frame sites were missed). (See comments in scign.eq
file) (3) Section added to the
report showing the San Simeon/Cambria earthquake results. Tables have been added that give the
estimated coseismic displacements from the combined solution for the Hector
Mine and San Simeon/Cambria earthquakes. (4) The sites currently
being funded under the Unavco Western
US Existing Networks proposal are shown on the SCIGN sites figure. |
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The results for this report are linked to SCIGN_96_0402_Results.html. The full combined solution with SIO and JPL individual results are
available in SCIGN_96_0402.tar.Z
(Compressed 109 Mb, Uncompressed
352 Mb) The combined analysis only (velocity, logarithm and time series files)
are available in COM_96_0402.tar.Z
(Compressed 12 Mb, Uncompressed
49 Mb) |
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The combined SCIGN motion
model is realized in a multi-step analysis. The details of the analysis methods are discussed in the Analysis methods section. The details of the data sets used and
access to the data sets are discussed in the Basic
Data Sets section. |
Notes on Report.
(a) With this report, we
continue automatically generating the main web based results from the
analysis. The results are
linked to
SCIGN_96_0402_Results.html
Previous Reports: SCIGN_96_0309_Results.html.
(b) The data used in the
analysis is extended to the end of February 2004 but the procedures used remain
the same as reported in SCIGN_AC06_2003.html
(c) In this report, we
include the time series for the combined JPL and SIO results. We excluded the JPL results for Trimble
antennas because of inconsistencies between the SIO and JPL height estimates
for these sites.
The links below give files
and directories that remain the same for each release.
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File/Directory |
Description |
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Time series from the
combined daily analysis of the loose position files from JPL and SIO
results. File names are of the
form mb_NNNN_XXX.datY where NNNN is the four character code for the site, XXX
is the extent that indicates post-earthquake and/or jumps in the time series,
and Y is 1 for North, 2 for East and 3 for Height components. Time is in years. Time series are in
a North America (NOAM) fixed frame |
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Time series from the JPL
only analysis. |
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Time series from the JPL
web site series.html
with results ftp'd from sideshow.jpl.nasa.gov. The mb_xxxx files are in the tsview
format. The original files from
the JPL are also included in the directory. The time series have been transformed to a NOAM frame
using the ITRF-2000 NA Euler pole. |
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Similar to mpb_jpl but
from processing SIO H-files |
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Times series from SIO web
site obtained with ftp from ftp://garner.ucsd.edu/pub/timeseries
These files have been converted to the mb_xxxx files and the time series
limited to start in 1996 to match the JPL time series availability. The original SIO files are also
included in the directory. These
time series have been transformed to a NOAM fixed frame. |
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Simple file of longitudes
and latitudes of the California coast appropriate for use with Features
option in velview. |
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Simple file of longitudes
and latitudes of the California Faults appropriate for use with Features
option in velview |
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Simple file of longitudes
and latitudes of the California earthquakes since 1996 with magnitude >2
appropriate for use with Features option in velview (use the brown dots load,
Dbrown). Data obtained from the USGS NEIC |
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Earthquakes >3
magnitude since 1996 |
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Earthquakes >4
magnitude since 1996 |
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Simplified Hector surface
rupture |
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Simplified Landers surface
rupture |
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Word coastlines for use in
velview. |
Earthquake names:
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LA - Landers, NR -
Northridge, NA - After shocks of Northridge; HT - Hector mine; CA – San
Simeon/Cambria. The file scign.eq contains the GLOBK earthquake definitions and
site renames used in this analysis.
(Sites renamed to end in XPS are excluded from the forward Kalman
filter analysis but are included in the time series. These sites are often renamed by
earthquakes to names such as XHT). |
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The "data sets"
used in this analysis were: |
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The approach in the
analysis method was to treat the data from both groups in the same way using
the GLOBK software, which is designed to combined position estimates and
covariance matrices using a Kalman filter approach. |
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For the JPL stacov files
we changed the antennas heights at some sites to make them the same as the
heights in SOPAC site database.
For the Dorne Margolin antennas this change can be made exactly. For other antenna types we had to
assume that phase center model in the JPL analysis was the same as the SOPAC
analysis and that JPL had not applied horizontal position changes for these
antennas (such as the TRM14532.00 antenna at MATH) because in stacov files
only LC heights (and after April 2003, North and East offsets) are given in
the stacov files with no information about the models used for either the
antenna type or its characteristics at the L1 and L2 frequencies. |
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The random walk process
noise for each site with at least 70 measurements is deduced from the "Realistic Sigma"
model discussed under tsview in GGMatlab. The random walk process noise is set to yield the
realistic sigma for the velocity over the duration of measurements at a site. Sites with random walk process noise
<0.5 mm^2/yr are used in the SCIGN frame definition, sites with random
walk process noise <2.0 5 mm^2/yr have velocities estimated in globk. The remaining sites are used only in
the time series analysis. The
realistic sigma model used here is not unique; there are alternative methods
available (for example, the SOPAC Refined Model http://sopac.ucsd.edu/processing/refinedModelDoc.html. In the context of the combined
solutions, the model used has the advantage of being fast. The conversion to random walk process
noise is also somewhat ad hoc;
the random process noise is set to generate the realistic sigma over the
interval of data available. The
process noise values depend on the duration of the data. The full globk solution also
generates velocity sigmas larger than the process noise models would imply
and we believe the additional noise arises from the uncertainty in the frame
definition and the relative velocities of sites are better determined than the
sigmas imply. |
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In separate analyses, the
JPL and SOPAC files were combined with GLOBK to estimate the position and
velocities of the sites. After
the Hector mine earthquake (1999/10/16), we renamed all sites within 420km of
the epicenter (34.2752N -118.5962E) and estimated logarithmic time dependence
to the position after the earthquake. We also renamed sites that had
unexplained jumps. This
information is contained in the globk earthquake file scign.eq. We automatically added jumps when
antennas are changed from the injected Ashtech Choke ring antennas
(ASH700936E_C) to the milled choke ring antennas (ASH701945B_M). This change in antenna type causes
several millimeters of horizontal position change at some locations and does
not appear to be the same at all locations. Jumps were also added when ever there as a change in the
radome at a site and on any Trimble to Ashtech receiver and antenna change. For the full GLOBK
solution, we decimated the experiments and used values only once every seven
days. Because of missing days in
the JPL stacov files, there was little overlap in the selection of days. (Every seventh file was used). Also, because the velocity sigmas are
dominated by the process noise, there is little effect on the final sigmas of
the velocity estimates. |
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The SIO frame was realized
by rotating and translating the velocity field onto zero motion for the North
American sites and the Pacific plate motion velocities of the Pacific sites
given by the ITRF2000 North America/Pacific Euler pole. The RMS fit to this frame was 0.7
mm/yr in both North and East components. The JPL frame was realized by rotating and translating on
the SIO site velocities of site in California. |
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The combined time series
were generated by merging the daily h-files and stacov files, and rotating
and translating this daily merged file on the frame defined by the SCIGN
region frame sites. |
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The second analysis
adopted a reference frame based on the 219-sites from the above
analysis. Time series were
generated in this analysis by rotating and translating each daily combined
file on the reference frame.
Linear trends were fit to North, East and Height components from the
time series, and for sites affected by the Hector Mine earthquake,
logarithmic time variations after the earthquake |