Readme for Open-File Report 00-193

Data Contents

The two data tables included in Open-File Report 00-193 are given as ascii 
data files on the web site 
URL http://geopubs.wr.usgs.gov/open-file/of00-193/.  The format of the data 
files (sb-gravity-of00-193.txt and sb-prop-of00-193.txt) is described below.  
The horizontal and vertical locations for the stations are on the North 
American Datum 1927 (NAD27) and the North American Vertical Datum 1929 
(NAVD29), respectively.  

The gravity stations (sb-gravity-of00-193.txt) were referenced to the 
International Gravity Standardization Net 1971 (IGSN71) datum and the 
reference ellipsoid is the Geodetic Reference System 1967 (GRS67).  The 
free-air anomalies were calculated using a modified version of formulas 
from Swick (1942).  The complete Bouguer anomalies were calculated from the 
free-air anomalies using the Bouguer correction, terrain corrections, a 
curvature correction, and a reduction density of 2.67 g/cc.  Isostatic 
corrections were calculated using an Airy-Heiskanen model of isostatic 
compensation.  The depth of the crust-mantle boundary was controlled using 
the following parameters:  a crustal thickness at sea level of 25 km, a 
density contrast of 0.40 g/cc between the crust and mantle, and a crustal 
density of 2.67 g/cc.

The physical property measurements (sb-prop-of00-193.txt) consist of 3 
density measurements (grain density, saturated bulk density, and dry bulk 
density) and a magnetic susceptibility measurement for each station.


     EXPLANATION OF PRINCIPAL FACT FORMAT FOR GRAVITY STATIONS


Item                                     Explanation

STATION NAME (a8):  An alphanumeric combination of up to 8 characters used 
				for station identification.

LAT (f3.0,f6.3):  Latitude in degrees and minutes, to 0.01 minute.

LON (f4.0,f6.3):  Longitude in degrees and minutes, to 0.01 minute.

ELEV (f8.2):  Elevation, to 0.1 ft.

OG (f10.3):  Observed gravity, to 0.01 mGal.

FAA (f9.3):  Free-air anomaly to 0.01 mGal.

SBA (f8.3):  Simple Bouguer anomaly to 0.01 mGal.

ITC (f7.3):  Inner terrain correction out to a radius of 68 m from the 
				station, for a density of 2.67 g/cc, to 0.01 mGal.

TC (f7.3):  Total terrain correction from the station to 166.7 km for a 
				density of 2.67 g/cc, to 0.01 mGal.

TC CODE (a1):  Letter denoting the extent of the correction, according to the 
				Hayford-Bowie template (e.g. 'D' means 590 meters).

CBA (f8.3):  Complete Bouguer anomaly reduced for a density of 2.67 g/cc, to 
				0.01 mGal.

ISO (f8.3):  Isostatic residual anomaly values, to 0.01 mGal.


                 Example of format for gravity file

51636676 36 12.16 114 29.15  2480.0 979579.35   -23.18 -107.77   3.13   5.96 D -102.71   -3.14   -2.91

STATION NAME:     51636676
LAT:              36 degrees 12.16 minutes North
LON:              114 degrees 29.15 minutes West
ELEV:             2480.0 feet
OG:               979579.35 mGal
FAA:              -23.18 mGal
SBA:              -107.77 mGal
ITC:              3.13 mGal
TC:               5.96 mGal
TC CODE:          D (590 m)
CBA:              -102.71 mGal
ISO:              -3.14 mGal
ISO-COR:          -2.91 mGal


     EXPLANATION OF PRINCIPAL FACT FORMAT FOR GRAVITY STATIONS

Item                                     Explanation

STATION NAME (a8):  An alphanumeric combination of up to 8 characters used 
				for station identification.

LAT (f3.0,f6.3):  Latitude in degrees and minutes, to 0.01 minute.

LON (f4.0,f6.3):  Longitude in degrees and minutes, to 0.01 minute.

GRAIN DENSITY (f7.2):  In grams per cubic centimeter.

SATURATED BULK DENSITY (f6.2):  In grams per cubic centimeter.

DRY BULK DENSITY (f6.2):  In grams per cubic centimeter.

MAGNETIC SUSCEPTIBILITY (f7.2):  In 10-3 cgs units.

GEOLOGIC MAP UNIT (a10):  An alphanumeric combination of up to 10 characters 
				for corresponding geologic map unit when plotted on 
				the 1:24,000 geologic map, see open-file report for 
				map references.

ROCK TYPE (a32):  Description of hand sample.



         Example of format for physical property file

RI162    34  2.68 117 25.04   2.71  2.68  2.66   0.01   s        cataclastic gneiss/gneiss
 

STATION NAME:              RI162
LATITUDE:                  34 degrees 2.68 minutes North
LONGITUDE:                 117 degrees 25.04 minutes West
GRAIN DENSITY:             2.71 grams per cubic centimeter
DRY BULK DENSITY:          2.68 grams per cubic centimeter
SATURATED BULK DENSITY:    2.66 grams per cubic centimeter
MAGNETIC SUSCEPTIBILITY:   0.01 x 10-3 cgs units
GEOLOGIC MAP UNIT:         s
ROCK TYPE:                 cataclastic gneiss and gneiss