velh.cmm4
velh.largeerr.cmm4
velh.nontect.cmm4
velh.reject.cmm4
contain horizontal velocities for those sites for which such velocities could be estimated. The first file provides these for sites that we believe are reliable. The next three files are: (1) sites for which the errors are very large; (2) sites for which the motion is real but probably affected by nontectonic sources (geothermal areas and a large reservoir); (3) sites which we believe are otherwise unreliable.
The format of these files is:
Column 1: Site name and type. The names are 4-character codes; the type is
either _GPS (continuous or survey-mode GPS), _EDM (US Geological
Survey trilateration) or _VLB (fixed or mobile VLBI). If a point
was used by more than one technique, the name will appear more than
once; for example, site PINY was observed both by mobile VLBI and by
survey-mode GPS, and REDH served first as a trilateration point and
than as a point for survey-mode GPS.
Column 2: Site latitude.
Column 3: Site longitude, positive for East.
Column 4: East velocity (in a local East-North-Up framework), relative to the
North American plate, in mm/yr.
Column 5: Standard error of the East velocity.
Column 6: North velocity (in a local East-North-Up framework), relative to the
North American plate, in mm/yr.
Column 7: Standard error of the North velocity.
Column 8: Correlation between the East and North velocities.
Column 9: Number of epochs used in estimate. For most of the time covered,
GPS data were combined into monthly files; after large earthquakes, a
smaller temporal spacing was used. (See the file epochplot.pdf).
The number of epochs is therefore not equivalent to the number of
days of occupation, but should give a useful sense of how many data
went into the final velocity estimate. For the EDM and VLBI data,
the number of epochs corresponds more closely to the number of
occupations.
Column 10: The time span, in years, from the first to the last epoch.
Column 11: The average of the epoch times.
After column 11, there may be additional entries to indicate ties between
sites. These ties are assigned a letter I if the tie was "hard", forcing the
velocities at tied sites to be identical, or a letter s if the tie was "soft",
allowing some variation. For example,
CHAF_GPS 34.3006 -119.3310 -29.13 0.36 28.23 0.32 0.020 5 8.6 1991.5 I034
SOLI_GPS 34.2983 -119.3427 -29.13 0.36 28.24 0.32 0.020 12 16.2 1993.6 I034
means that these two nearby sites have been forced to have the same horizontal
velocity, and
REDH_EDM 35.6050 -120.2606 -22.16 0.47 26.04 0.40 0.096 56 19.0 1980.6 s055
REDH_GPS 35.6050 -120.2606 -23.23 0.40 26.11 0.38 -0.008 15 11.5 1995.2 s055
that these two sites, which are the same mark observed with different methods
(largely used over different times) have been constrained to have similar
velocities. These ties have been used both to tie the VLBI and GPS reference
frames, and to set the rigid-body rotation for the trilateration networks.
velu.cmm4
velu.largeerr.cmm4
velu.nontect.cmm4
velu.reject.cmm4
contain vertical velocities for those sites for which such velocities could be estimated. The first file provides these for sites that we believe are reliable. The next three files are: (1) sites for which the errors are very large; (2) sites for which the motion is real but probably affected by nontectonic sources (geothermal areas and a large reservoir); (3) sites which we believe are otherwise unreliable.
The format of these files is:
Column 1: Site name and type. The names are 4-character codes; the type is
either _GPS (continuous or survey-mode GPS), or _VLB (fixed or mobile
VLBI); vertical velocities cannot be reliably estimated from the
trilateration data. If a point was used by more than one technique,
the name will appear more than once; for example, site PINY was
observed both by mobile VLBI and by survey-mode GPS.
Column 2: Site latitude.
Column 3: Site longitude, positive for East.
Column 4: Vertical velocity (in a local East-North-Up framework), in mm/yr,
positive up. Because of possible systematic errors, the zero level
should not be assumed to be zero velocity relative to the geoid, the
ellipsoid, or sea level.
Column 5: Standard error of the vertical velocity.
Column 6: Correlation between the East and vertical velocities.
Column 7: Correlation between the North and vertical velocities.
Column 8: Number of epochs used in estimate. For most of the time covered,
GPS data were combined into monthly files; after large earthquakes, a
smaller temporal spacing was used. (See the file epochplot.pdf).
The number of epochs is therefore not equivalent to the number of
days of occupation, but should give a useful sense of how many data
went into the final velocity estimate. For the EDM and VLBI data,
the number of epochs corresponds more closely to the number of
occupations.
Column 9: The time span, in years, from the first to the last epoch.
Column 10: The average of the epoch times.
contains estimates of offsets of sites at the times of large earthquakes.
The format of the file is:
Column 1: Site name (4 character code). All offsets are from GPS data. Note
that there are sites included that are not in the velocity file:
in these cases there was enough data to estimate an offset, but not
a velocity.
Column 2: Site latitude.
Column 3: Site longitude, positive for East.
Column 4: Time of the offset, in decimal years. The correspondence between
times and earthquakes is:
1992.3200 1992/04/23 04:50 33.960 -116.317 6.1 Joshua Tree
1992.4918 1992/06/28 11:57 34.200 -116.437 7.3 Landers
& 1992/06/28 15:05 34.203 -116.827 6.3 Big Bear (combined)
1994.0466 1994/01/17 12:30 34.213 -118.537 6.7 Northridge
1994.1300 1994/02/25 12:59 34.357 -118.480 4.0 aftershock
1999.7918 1999/10/16 09:46 34.594 -116.271 7.1 Hector Mine
2003.9808 2003/12/22 19:15 35.709 -121.104 6.5 San Simeon
Column 5: East offset, in mm.
Column 6: Standard error of the East offset.
Column 7: North offset, in mm.
Column 8: Standard error of the North offset.
Column 9: Vertical offset, in mm, positive up.
Column 10: Standard error of the vertical offset.
Column 11: Correlation between the East and North offsets.
contains estimates of postseismic motions of sites after large earthquakes. All postseismic motions are modeled as
u(t) = D*log(1+t/10)
where D is the amplitude, the log function is the common logarithm, and t is the time in days from the time of the earthquake.
The format of the file is:
Column 1: Site name (4 character code). All estimates are from GPS data. Note
that there are sites included that are not in the velocity or
offset files: in these cases there was enough data to estimate
postseismic motions only.
Column 2: Site latitude.
Column 3: Site longitude, positive for East.
Column 4: Time of the earthquake, in decimal years. The correspondence between
times and earthquakes is:
1992.4918 1992/06/28 11:57 34.200 -116.437 7.3 Landers &
1992/06/28 15:05 34.203 -116.827 6.3 Big Bear (combined)
1994.0466 1994/01/17 12:30 34.213 -118.537 6.7 Northridge
1999.7918 1999/10/16 09:46 34.594 -116.271 7.1 Hector Mine
2003.9808 2003/12/22 19:15 35.709 -121.104 6.5 San Simeon
Column 5: East amplitude, in mm.
Column 6: Standard error of the East amplitude.
Column 7: North amplitude, in mm.
Column 8: Standard error of the North amplitude.
Column 9: Vertical amplitude, in mm, positive up.
Column 10: Standard error of the vertical amplitude.
Column 11: Correlation between the East and North amplitudes.
contains coordinates and a brief description of the sites.
The format of the file is:
Column 1: Site name (4 character code).
Column 2: Site latitude.
Column 3: Site longitude, positive for East.
Column 4: The elevation above the ellipsoid, in meters.
The remainder of each line gives some station information. If this is ALL CAPS it is either the stamping of the monument, or else (if it contains underscore characters) the PBO designation for a continuous GPS site. Lowercase information is either a description of an unstamped monument, or the name of a continuous GPS or VLBI site; note that mobile VLBI sites have convntional monuments.
Examples:
Monuments
LACU 34.494410 -119.713897 1164.83 divot in shank of broken-off mark
REFU 34.534795 -120.052095 757.09 REFU 1993
Continuous GPS
BILL 33.578243 -117.064601 470.05 BILL_SCGN_CS1997
ROCH 33.611024 -116.609772 1393.74 Pinemeadow
Fixed VLBI
HAYS 42.623297 -71.488161 116.69 Haystack 37-m radiotelescope
gives the residual timeseries for each site, after the quantities estimated above (velocities, offsets, and postseismic signals) have been removed.
The format of the file is:
Column 1: Site name; all timeseries are from GPS data.
Column 2: Time of value.
Column 3: East residual displacement, in mm.
Column 4: Standard eror of the East displacement. Very large values indicate
either very poor data, or that this component was downweighted for this
epoch.
Column 5: North residual displacement, in mm.
Column 6: Standard eror of the North displacement. Very large values indicate
either very poor data, or that this component was downweighted for this
epoch.
Column 7: Vertical residual displacement, in mm; positive up.
Column 8: Standard eror of the vertical displacement. Very large values indicate
either very poor data, or that this component was downweighted for this
epoch.
Column 9: Correlation between the East and North displacements.
Column 10: Correlation between the East and vertical displacements.
Column 11: Correlation between the North and vertical displacements.