SCEC Crustal Motion Map Table Formats

Velocities

The velocity_file gives the estimated velocities at the sites. Some sample lines are

 PINY_VLB 33.6092 -116.4588 -17.96  16.66 0.91 1.00 -0.070 83.83 90.11  6.3  21
 PINY_GPS 33.6092 -116.4588 -15.37  17.91 0.95 0.92 -0.074 86.47 92.44  6.0   7 >04
 PINY_GLA 33.6092 -116.4588 -14.90  18.91 0.95 0.99 -0.061 92.87 01.17  8.3  10
 PIN2_GPS 33.6121 -116.4576 -16.84  19.16 1.11 1.08 -0.047 90.24 92.44  2.2  22 >04
 PIN2_GLA 33.6121 -116.4576 -14.80  19.25 0.80 0.83 -0.068 92.54 01.81  9.3 137
 PIN3_GPS 33.6122 -116.4580 -14.43  18.48 1.00 1.04 -0.069 92.20 98.49  6.3   7
  code     lat      long     Ve      Vn  Se    Sn    Ren  start  end   dur nep tie/comm

code

the station code. This starts with a 4-character station code or name, referring to a specific monument or permanent site; the last first letter after the underscore shows the type of data. G for GPS, E for EDM (Geodolite), V for VLBI. The last two letters usually complete the data type, but are modified if we allow a different velocity after an earthquake. In the example above For example PINY is a monument occupied by both VLBI and GPS, and from the GPS we estimate two velocities: _GPS before the Landers earthquake, and _GLA after it. The site PIN3 has only a _GPS suffix because we estimate only a single velocity, even though all the data are from after the earthquake. NOTE that even if a station was surveyed only after an earthquake, its suffix is _GPS even though its velocity represents the post-seismic field; such cases can be identified by the start and end times.

lat

the geographical latitude, in degrees.

long

the east longitude, in degrees.

Ve

the east velocity, in mm/yr, relative to the North American plate.

Vn

the north velocity, in mm/yr, relative to the North American plate.

Se

the standard error (standard deviation) of the east velocity, in mm/yr.

Sn

the standard error of the north velocity, in mm/yr.

Ren

the correlation between the east and north velocities (0 uncorrelated, 1 fully correlated).

start

the date of the first data used, in decimal years CE, with the first two digits removed. This date was derived from the monthly combination, and so may misstate the actual time of the data by up to 2 weeks.

end

the date of the last data used.

dur

the time span between start and end, in years, as an indicator of the length of data used.

nep

the number of epochs used. For VLBI this is the number of days of observations; for GPS and EDM observations over closely-spaced times have been counted as a single epoch.

tie/comm

indicates, if a < followed by a number, a tie between two sites; these ties are numbered (somewhat arbitrarily) and flagged with a >. In the example above, PINY_GPS and PIN2_GPS have been tied together: their velocities are linked, though with a difference allowed. These sites are within 500 m of each other, and the longer span of pre-Landers data at PINY improves the solution. Most of the ties are between GPS and EDM sites, to constrain the translation and rotation of the EDM network.

If the line ends with a ?, this means that there is some question about the reliability of the velocity, such as might be caused by a monument in an unstable setting; see the list_of_possible_problem_sites. An F in this column denotes the sites (all GPS) used to constrain the reference frame to North America (some of these sites have tie numbers, which point to VLBI ties not included in the table).

      The sites are ordered according to a "geographical sort" which will (in general) place nearby monuments close together in the list.

      Any line NOT starting with a space is a comment line.

Coseismic Offsets

The list_of_coseismic_offsets describes the step offsets associated with earthquakes; note that sites amy be included in this list for which we have not estimated a velocity. Some sample lines are

JPLA 34.2047 -118.1710  LA   -0.013  0.008     0.004  0.005    -0.004  0.005   0.000
JPLM 34.2048 -118.1732  LA   -0.012  0.001     0.005  0.001    -0.004  0.004  -0.045
JPLM 34.2048 -118.1732  NR    0.006  0.001    -0.006  0.001    -0.004  0.003  -0.008
JPLM 34.2048 -118.1732  JP   -0.002  0.001     0.002  0.001     0.000  0.003   0.010
JPLM 34.2048 -118.1732  HM   -0.003  0.001     0.002  0.000    -0.002  0.002   0.001
code  lat      long     Eq     Edis   Eerr      Ndis   Nerr      Vdis   Verr    rho

code

the station code.

lat

the geographical latitude, in degrees.

long

the east longitude, in degrees.

Eq

the earthquake. The codes are JT for Joshua Tree, LA for Landers, NR for Northridge, and NA for a large Northridge aftershock, JP for a separate post-post-Northridge rate at JPLM, and HM for Hector Mine.

Edis

the east displacement, with associated error Eerr.

Ndis

the north displacement, with associated error Nerr.

Vdis

the vertical displacement, with associated error Verr.

rho

the correlation between the east and north displacements.

Stations (monuments)

The station_list gives information about the individual sites. Some sample lines are

PIN2     33.612148  -116.457617 1258.41 Pinyon 2         [SCIGN]
PIN3     33.612153  -116.457996 1256.12 UCSD 1992 PIN3C
PINY     33.609249  -116.458801 1235.53 PINYON FLAT NCMN 1981

code     lat         long       ht      stamping/description

code

the monument 4-character ID used by SCEC. The list is alphabetical in this ID.

lat

the geographical latitude, in degrees.

long

the east longitude, in degrees.

height

the ellipsoid height. Note that thsese coordinate values are not created according to leggalkl accepted survey procedures, and should not be used for reference for surveying or engineering purposes.

stamping/description

which is, if in ALL CAPS, what is stamped on the monument; if this is partly in lowercase it is the description or name of the monument. Permanent GPS sites in SCIGN or the IGS are indicated.

In general, these coordinates should be good to the sub-meter level, although there are indications that the adjustment for positions of sites only in the EDM network has systematic errors in a few locations.

Observation Times

The table_of_times_of_observation gives information about when sites were observed. Some sample lines are

PINY_GPS 1986.4660
PINY_GPS 1989.3620
PINY_GPS 1991.2781
PINY_GPS 1991.3685
PINY_GPS 1992.1981
PINY_GPS 1992.3525
PINY_GPS 1992.4413
PINY_GLA 1992.8661
PINY_GLA 1993.4123
PINY_GLA 1993.6452
PINY_GLA 1994.4575
PINY_GLA 1994.5342
PINY_GLA 1995.5685
PINY_GLA 1997.0794
PINY_GLA 1998.3315
PINY_GLA 1998.5918
PINY_GLA 2001.1699
LAE1_GPS 1992.5355 not used
LAE1_GPS 1992.6093 not used
LAE1_GPS 1992.8661 not used
LAE1_GPS 1993.7726 not used
LAE1_GPS 1994.3808
LAE1_GPS 1995.1219
LAE1_GPS 1995.9164
LAE1_GPS 1997.0301
LAE1_GPS 1998.1233
LAE1_GPS 1999.7973 not used
LAE1_GPS 1999.8110 not used
LAE1_GPS 1999.8123 not used
LAE1_GPS 1999.8247 not used
LAE1_GPS 1999.8384 not used
BEAR_GPS 1991.8370 East and North downweighted
CLAR_GPS 1996.5123 North downweighted
CLAR_GPS 1996.5792 North downweighted

code     time (CE)  comment

code

the station designator.

time

the time in decimal years; note that this is the time of the data after being aggregated into monthly combinations, and so may not be the exact time of observation.

comment

indicates if the data were not used (for example, to avoid postseismic signals) or were downweighted.