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Anderson, M.L., Roberts, C.W., and Jachens, R.C., 2000, Principal Facts for Gravity Stations in the Vicinity of San Bernardino, Southern California: U.S. Geological Survey Open-File Report 00-193, U.S. Geological Survey, Menlo Park, CA.Online Links:
This is a Vector data set. It contains the following vector data types (SDTS terminology):
Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.01 minutes. Longitudes are given to the nearest 0.01 minutes. Latitude and longitude values are specified in Degrees and decimal minutes.
The horizontal datum used is North American Datum of 1927.
The ellipsoid used is Clarke 1866.
The semi-major axis of the ellipsoid used is 6378206.4.
The flattening of the ellipsoid used is 1/294.98.
We would like to thank Jeff Davidson and Geoff Phelps of the USGS for their help gathering field data. We would also like to thank the West San Bernardino County Municipal Water District, the City of Colton, and the City of Rialto for supporting this project. Thanks to Jonathan Matti, Jerry Treiman, and Mike Rymer of the USGS for their tips on geologic and seismic data and James Hunter (Rialto City Public Works) for providing some elevation control data. Field work is not possible without the access provided by the consent of land owners. Thanks to the many unnamed people who allowed us access onto their land and a special thanks to the following helpful people: Al Cunningham and family, Cemex Materials Corp., Richard Scanlan (Rialto Municipal Airport), Lytle Creek Ranger Station, Sally McGill (California State University, San Bernardino), Mike Seal (San Bernardino County Flood Control), Steve Lowe (San Bernardino National Forest), Tom Fujiwara (City of Redlands), and Crafton Hills College.
650-329-5308 (voice)
mlanderson@usgs.gov
The purpose of the survey was to locate more precisely and characterize the Rialto-Colton fault, a strand in the San Jacinto fault zone. The information developed during this study will be used in ground-water models by the USGS Water Resources Division and for the purposes of deciphering the complex basin geometry and tectonic history in this area to help understand the development of similar strike-slip basins.
Tang, R.W., and Ponce, D.A., 1982, Principal facts, accuracies, sources, and base station descriptions for 4915 gravity stations on the San Bernardino 1°x2° quadrangle, California: U.S. Geological Survey Open-File Report 82-004.
Sikora, R.F., Langenheim, V.E., Biehler, Shawn, Beyer, L.A., and Chapman, R.H., 1993, Principal facts and base station descriptions for gravity data compiled for the Santa Ana 1° by 2° quadrangle, California: U.S. Geological Survey Open-File Report 93-217A,B.
Observed gravity data are accurate to 0.05 mGal; reduced anomalies are accurate to 1-2 mGal. Data are more accurate in the flat areas than in the mountains because of uncertainties in the terrain correction. Terrain corrections are accurate to 0.2 mGal in the flat areas and to 0.4-1.5 mGal in the mountains. Grain density measurements are accurate to 0.01 g/cm3; susceptibility measurements to 0.01 x 10-3 cgs units.
Accuracy of the point data is roughly 10m.
Accuracy of the point data is roughly 5-10cm.
Dataset based on geophysical analysis.
Sources of error in our data set encompass several aspects. Elevation
uncertainty of 5-10 cm (2-4 in) causes an uncertainty in the Bouguer
and isostatic anomalies that is typically 0.01- 0.02 mGal. There is
some uncertainty in observed gravity from our assumptions of meter
drift, though our system of base ties keeps this uncertainty typically
less than 0.05 mGal. Our largest source of uncertainty is in the
terrain corrections. Our terrain corrections are estimated to be
accurate to within 10% of the value of the correction. Therefore,
there is very little uncertainty in the values for our stations
located on the flats of the San Bernardino basin (typically 0.2 mGal
or less), but there is a larger uncertainty associated with the
stations in the surrounding mountains and hills (0.4-1.5 mGal),
because the terrain corrections are much higher.
Our data across the Rialto-Colton fault are quite uniform; contouring
yields a smooth, consistent, linear gradient that indicates that the
error for the data over the Rialto-Colton fault is probably much less
than the maximum error given above. Also, data obtained from other
agencies and surveys fits in very well with our newly acquired data.
In cases where there was a misfit, we analyzed all involved data sets
for possible sources of error and corrected them if possible. In a
couple of cases, we double-checked our corrections on older data sets
by reoccupying several previously established stations. The contour
gravity maps (figs. 6 and 7) include data sets from the following
surveys/agencies: 114 stations from the Defense Mapping Agency, 940
stations from University of California, Riverside (Tang and Ponce,
1982; Sikora and others, 1993), 171 stations from R.H. Chapman
(written commun.; Tang and Ponce, 1982), 86 USGS stations, 102
stations from J.L. McWhirter (Tang and Ponce, 1982), 12 stations from
R.B Grannell and R.B. Greenwood (Tang and Ponce, 1982), 449 stations
from Tien-Chang Lee (written commun., 1998), and 2 stations from the
California high-precision gravity network (Roberts and Jachens, 1986).
Are there legal restrictions on access or use of the data?
- Access_Constraints: none
- Use_Constraints: none
650-329-5308 (voice)
mlanderson@usgs.gov
USGS Open-File Report 00-193
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Data format: |
Gravity station data and physical properties of samples
in format ASCII
Fixed-field ASCII; FORTRAN format statement descriptors
for the field names (in this order) are
for Gravity station file: STATION NAME (a8) LAT (f3.0,f6.3) LON (f4.0,f6.3) ELEV (f8.2) OG (f10.3) FAA (f9.3) SBA (f8.3) ITC (f7.3) TC (f7.3) TC CODE (a1) CBA (f8.3) ISO (f8.3)for Physical properties file: STATION NAME (a8) LAT (f3.0,f6.3) LON (f4.0,f6.3) GRAIN DENSITY (f7.2) SATURATED BULK DENSITY (f6.2) DRY BULK DENSITY (f6.2) MAGNETIC SUSCEPTIBILITY (f7.2) GEOLOGIC MAP UNIT (a10) ROCK TYPE (a32) |
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Network links: |
<http://geopubs.wr.usgs.gov/open-file/of00-193/sb-gravity-of00-193.txt> <http://geopubs.wr.usgs.gov/open-file/of00-193/sb-prop-of00-193.txt> |
650-329-5308 (voice)
mlanderson@usgs.gov