USGS Geoscience Data Catalog
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Wooley, R.J., Yerkes, R.F., Langenheim, V.E., and Chuang, F.C., 2003, Isostatic gravity map of the Los Angeles 30 x 60 minute quadrangle, California: U.S. Geological Survey Open-File Report 03-269, U.S. Geological Survey, U.S. Geological Survey, Menlo Park, CA.Online Links:
This is a Point 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 0.00017. Longitudes are given to the nearest 0.00017. Latitude and longitude values are specified in decimal degrees.
The horizontal datum used is North American Datum of 1927.
The ellipsoid used is Geodetic Reference System 1967.
The semi-major axis of the ellipsoid used is 6378160.
The flattening of the ellipsoid used is 1/298.25.
textual identifier without scientific significance
Range of values | |
---|---|
Minimum: | 34 |
Maximum: | 34 |
Units: | degrees |
Resolution: | 1 |
Range of values | |
---|---|
Minimum: | 0.00 |
Maximum: | 60.00 |
Units: | minutes |
Resolution: | 0.01 |
Range of values | |
---|---|
Minimum: | 117 |
Maximum: | 118 |
Units: | degrees |
Resolution: | 1 |
Range of values | |
---|---|
Minimum: | 0.00 |
Maximum: | 60.00 |
Units: | minutes |
Resolution: | 0.01 |
Range of values | |
---|---|
Minimum: | 16.0 |
Maximum: | 7111.0 |
Units: | feet |
Resolution: | 0.1 |
Value | Definition |
---|---|
(no value) | |
A | |
b | |
m | |
t | |
U |
Range of values | |
---|---|
Minimum: | 979151.31 |
Maximum: | 979650.10 |
Units: | mGal |
Resolution: | 0.01 |
Range of values | |
---|---|
Minimum: | -98.01 |
Maximum: | 140.77 |
Units: | mGal |
Resolution: | 0.01 |
Range of values | |
---|---|
Minimum: | -121.18 |
Maximum: | 3.93 |
Units: | mGal |
Resolution: | 0.01 |
Range of values | |
---|---|
Minimum: | 0.00 |
Maximum: | 11.00 |
Units: | mGal |
Resolution: | 0.01 |
Range of values | |
---|---|
Minimum: | 0.00 |
Maximum: | 31.97 |
Units: | mGal |
Resolution: | 0.01 |
Value | Definition |
---|---|
(no value) | |
D | 0.59 km |
G | 3.52 km |
M | 58.8 km |
Range of values | |
---|---|
Minimum: | -115.45 |
Maximum: | 6.83 |
Units: | mGal |
Resolution: | 0.01 |
Range of values | |
---|---|
Minimum: | -71.31 |
Maximum: | 17.10 |
Units: | mGal |
Resolution: | 0.01 |
We would like to thank Doug Morton and the Southern California Areal Mapping Project for providing funding for the creation of this map. We would also like to acknowledge and thank Seth Stiles for help in collecting gravity data within the Los Angeles 30' x 60' quadrangle. The map benefited from reviews by David Ponce (U.S. Geological Survey, Menlo Park, CA).
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This isostatic residual gravity map is part of the Southern California Areal Mapping Project (SCAMP) and is intended to promote further understanding of the geology in the Los Angeles 30 x 60 minute quadrangle, California, by serving as a basis for geophysical interpretations and by supporting both geological mapping and topical (especially earthquake) studies. Local spatial variations in the Earth' s gravity field (after various corrections for elevation, terrain, and deep crustal structure explained below) reflect the lateral variation in density in the mid- to upper crust. Densities often can be related to rock type, and abrupt spatial changes in density commonly mark lithologic boundaries.
Hanna, W.F., Rietman, J.D., and Biehler, S.H., 1975, Bouguer gravity map of California, Los Angeles sheet: California Division of Mines and Geology.
Observed gravity data are accurate to 0.05 mGal; reduced anomalies are accurate to 1-2 mGal. Data are more accurate in the valleys than in the mountains because of uncertainties in elevation and in the terrain correction.
Accuracy of the point data is roughly 40 m, as well as the data can be located on a 1:24,000-scale topographic map
Accuracy of the point data vary; most of the elevations are accurate to 10 feet or less. In some of the more mountainous areas, the accuracy may fall to 20 to 40 feet.
Spacing of observation points in the study area is dense but not regular; generally the density of observation points is lowest in the northeast corner of the quadrangle.
The main sources of error are inaccurate terrain corrections and/or inaccurate elevations. Errors associated with terrain corrections may be 5 to 10 percent of the value of the total terrain correction. The average error based on the average terrain correction (2.48 mGal) is thus about 0.2 mGal, but in the most rugged areas of the San Gabriel Mountains, the individual errors may be as large as 3.2 mGal. Errors resulting from elevation uncertainties are probably less than 0.5 mGal for most of the data because the majority of the stations are at or near benchmarks and spot and surveyed elevations, which are accurate to about 0.2 to 3 m. Measurements for which elevations were controlled by contour interpolation are expected to have errors of up to 1.2 mGal. The significance of errors resulting from elevation is greater in mountainous areas, where elevations vary over a relatively short distance, than in the flatter valleys and deserts. In general, the total uncertainties for the data shown on the map are estimated to be less than 2 mGal (or one contour interval), although in many areas the data are considerably more accurate.
Are there legal restrictions on access or use of the data?
- Access_Constraints: none
- Use_Constraints: none
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USGS Open-File Report 03-269
This report is preliminary and has not been reviewed for conformity with the U.S. Geologcial 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 observation data
in format Text
Strict-format ASCII text as follows; here S = start column E = end column (inclusive) T = data type (C character, N numeric) W = width P = "precision", digits to right of decimal Label S E T W P STAT 1 8 C 8 LaD 10 11 N 2 0 LaM 13 17 N 5 2 LoD 19 21 N 3 0 LoM 23 27 N 5 2 ELEV 29 35 N 7 1 OG 37 45 N 9 2 47 47 C 1 FAA 52 58 N 7 2 SBA 60 66 N 7 2 ITC 68 73 N 6 2 TTC 75 80 N 6 2 Code 82 82 C 1 CBA 84 90 N 7 2 ISO 92 98 N 7 2Size: 378 kilobytes |
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Network links: |
<http://geopubs.wr.usgs.gov/open-file/of03-269/la-grav.dat> |
650-329-5313 (voice)
650-329-5133 (FAX)
zulanger@usgs.gov