Little Cottonwood Water Treatment Plant Gravity & Magnetic Survey

Links
• Final report (PDF) - 616 kB
• Final report (PS) - 7.8 MB
• Lab exercise for Exploration Seismology class
• Principal Facts for all gravity stations, in USGS SWFO gravity format.
• CBGA values for all stations, for a variety of densities (2.67, 2.0, 2.2, 2.3, 2.4, 2.5 g/cc)
• Gravity reduction software available upon request to the report authors; the code is free, but not yet packaged for distribution.
• Gravity modeling code is commercially produced by Northwest Geophysical Associates

Principal Fact format of gravity data

This format is given as FORTRAN read() statement format specifiers; translation to C scanf() format string codes is trivial. Note that the columns are indexed starting from 1. Help with reading/writing this format is available from the report authors.

cols    format          field name
-------------------------------------------------------------------
1-8     a8              station identification, alphanumeric
9-12    i4              latitude degrees, +/-xx
13-19   f7.3            latitude minutes, xx.xxx
20-25   f6.3            latitude uncertainty, min, xx.xxx
26-30   i5              longitude degrees, +/-xxx
31-37   f7.3            longitude minutes, xx.xxx
38-43   f6.3            longitude uncertainty, xx.xxx
44-45   1x,a1           altitude units: 'm' meters, 'f' feet
46-53   f8.2            altitude, xxxxx.xx
54-58   f5.2            altitude uncertainty, xx.xx
59-69   f11.3           observed gravity, mGals, xxxxxxx.xxx
70-75   f6.3            observed gravity uncertainty, xx.xxx
76-81   f6.2            inner zone terrain correction, mGals, xx.xx
82-88   f7.2            total terrain correction, mGals, xx.xx
89-92   f4.2            uncertainty in ttc, as fraction of ttc, e.g.
                        0.10 means 10 % of total terr. corrn.
93-103  f11.4           time of observation in days since 1200 hrs 31 dec 1899

Gravity Anomaly format for CBGA data

This format is defined, and maintained, by the Southwest Field Office of the USGS. The specification used in the LCWTP project is reproduced here. Format codes are for FORTRAN; translation to C should be trivial. Help with this format can be obtained from the report authors.

cols    format          field name
-------------------------------------------------------------------
1-8     a8              station identification, alphanumeric
9-18    f10.4           northing in km (UTM or Lambert Conf. Conic)
19-28   f10.4           easting in km (UTM or Lambert Conf. Conic)
29-32   i4              latitude degrees, + N, - S
33-39   f7.3            latitude minutes
40-44   i5              longitude degrees, - W, + E
45-51   f7.2            longitude minutes
52-53   1x,a1           altitude units, f - feet, m - meters
54-61   f8.2            altitude
62-69   f8.2            free air agravity anomaly, mgals
70-77   f8.2            simple Bouguer gravity anomaly at 2.67 g/cc
78-85   f8.2            complete Bouguer gravity anomaly 
                        (sbga + tc - curv.corrn) at 2.67 g/cc
86-93   f8.2            cbga at alternate density 1
94-101  f8.2            cbga at alternate density 2
102-109 f8.2            cbga at alternate density 3
110-117 f8.2            cbga at alternate density 4
118-125 f8.2            cbga at alternate density 5
126-133 f8.2            inner terrain correction, mgals, at 2.67 g/cc
134-141 f8.2            total terrain correction
142-149 f8.2            uncertainty in cbga at 2.67 g/cc, mgals