Isostatic gravity map of the Los Angeles 30 x 60 minute quadrangle, California

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Metadata:

Identification_Information:
Citation:
Citation_Information:
Originator: R.J. Wooley
Originator: R.F. Yerkes
Originator: V.E. Langenheim
Originator: F.C. Chuang
Publication_Date: 2003
Title:
Isostatic gravity map of the Los Angeles 30 x 60 minute quadrangle, California
Edition: rev 1.0
Geospatial_Data_Presentation_Form: map
Series_Information:
Series_Name: U.S. Geological Survey Open-File Report
Issue_Identification: 03-269
Publication_Information:
Publication_Place: U.S. Geological Survey, Menlo Park, CA
Publisher: U.S. Geological Survey
Online_Linkage: http://pubs.usgs.gov/of/2003/0269/
Description:
Abstract:
Gravity data were compiled, collected, and edited to produce an isostatic gravity map of the Los Angeles 30 x 60 minute quadrangle, California. This record focuses primarily on the principal facts, that is, gravity observations, and the corrections made to those values to reflect the effects of elevation and terrain, and deep crustal structure.
Purpose:
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.
Supplemental_Information:
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 2
Time_Period_of_Content:
Time_Period_Information:
Range_of_Dates/Times:
Beginning_Date: 1994
Ending_Date: 2001
Currentness_Reference: Data collection period
Status:
Progress: Complete
Maintenance_and_Update_Frequency: None planned
Spatial_Domain:
Bounding_Coordinates:
West_Bounding_Coordinate: -119.0
East_Bounding_Coordinate: -118.0
North_Bounding_Coordinate: 34.5
South_Bounding_Coordinate: 34.0
Keywords:
Theme:
Theme_Keyword_Thesaurus: USGS Thesaurus
Theme_Keyword: geophysics
Theme_Keyword: maps and atlases
Theme_Keyword: bulk density
Theme_Keyword: isostatic anomaly
Theme_Keyword: geospatial datasets
Theme:
Theme_Keyword_Thesaurus: ISO 19115 Topic Categories
Theme_Keyword: geoscientificInformation
Place:
Place_Keyword_Thesaurus: none
Place_Keyword: Southern California, Los Angeles, San Gabriel Mountains
Place:
Place_Keyword_Thesaurus: Augmented FIPS 10-4 and FIPS 6-4
Place_Keyword: f06111 = Ventura
Place_Keyword: f06037 = Los Angeles
Access_Constraints: none
Use_Constraints: none
Point_of_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Victoria E Langenheim
Contact_Organization: U.S. Geological Survey, GEO-WRG-NGM
Contact_Address:
Address_Type: mailing address
Address:
Mail Stop 989
345 Middlefield Rd
City: Menlo Park
State_or_Province: CA
Postal_Code: 94025
Country: USA
Contact_Voice_Telephone: 650-329-5313
Contact_Facsimile_Telephone: 650-329-5133
Contact_Electronic_Mail_Address: zulanger@usgs.gov
Data_Set_Credit:
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).
Native_Data_Set_Environment: data was stored and analysed on a SUN Ultra4000 UNIX platform
Data_Quality_Information:
Attribute_Accuracy:
Attribute_Accuracy_Report:
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.
Logical_Consistency_Report:
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.
Completeness_Report:
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.
Positional_Accuracy:
Horizontal_Positional_Accuracy:
Horizontal_Positional_Accuracy_Report:
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
Vertical_Positional_Accuracy:
Vertical_Positional_Accuracy_Report:
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.
Lineage:
Source_Information:
Source_Citation:
Citation_Information:
Originator: Hanna, W.F.
Originator: Rietman, J.D.
Originator: Biehler, S.H.
Publication_Date: 1975
Title: Bouguer gravity map of California, Los Angeles sheet
Edition: first edition
Series_Information:
Series_Name: California Division of Mines and Geology
Source_Scale_Denominator: 250000
Type_of_Source_Media: paper
Source_Citation_Abbreviation: Hanna and others (1975)
Process_Step:
Process_Description:
Gravity data in the Los Angeles 1:100,000-scale quadrangle and vicinity include 428 gravity stations obtained by the U.S. Geological Survey from 1994 to June, 2001; 2536 stations from a previously published Bouguer Gravity Map of California--Los Angeles sheet compiled by W.F. Hanna and others, (1974); and 950 gravity stations obtained from the Defense Mapping Agency (written communication, 1994). Gravity stations collected by the U.S. Geological Survey for the Los Angeles Regional Seismic Experiment line II (LARSE II) are also included. More detailed information on recent U.S. Geological Survey data collection in the Los Angeles area is contained in Wooley and Langenheim (2001). The datum of observed gravity for this map is the International Gravity Standardization Net of 1971 (IGSN 71) as described by Morelli (1974); the reference ellipsoid used is the Geodetic Reference System 1967 (GRS67; International Association of Geodesy and Geophysics, 1971).
The observed gravity data were reduced to free-air anomalies using standard formulas (e.g. Telford and others, 1976). Bouguer, curvature, and terrain corrections to a radial distance of 166.7 km) were applied to the free-air anomaly at each station to determine the complete Bouguer anomalies at a standard reduction density of 2.67 g/ cm3 (Plouff, 1977). An isostatic correction was then applied to remove the long-wavelength effect of deep crustal and/or upper mantle masses that isostatically support regional topography. The isostatic correction assumes an AiryHeiskanen model (Heiskanen and Vening-Meinesz, 1958) of isostatic compensation; compensation is achieved by varying the depth of the model crust-mantle interface, using the following parameters: a sea-level crustal thickness of 25 km, a crust-mantle density contrast of 0.40 g/cm3, and a crustal density of 2.67 g/cm3 for the topographic load. These parameters were used because (1) they produce a model crustal geometry that agrees with seismically determined values of crustal thickness for central California, (2) they are consistent with model parameters used for isostatic corrections computed for the rest of California (Roberts and others, 1990), and (3) changing the model parameters does not significantly affect the resulting isostatic anomaly (Jachens and Griscom, 1985). The computer program ISOCOMP (Jachens and Roberts, 1981) directly calculates the attraction of an Airy-Heiskanen root by summing the attraction of individual mass prisms making up the root and thus calculating the isostatic correction; the resulting isostatic residual gravity values should reflect lateral variations of density within the mid- to upper crust.
Process_Date: 1994 - 2001
Process_Step:
Process_Description: Creation of original metadata record
Process_Date: 20030915
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Victoria E Langenheim
Contact_Organization: U.S. Geological Survey, GEO-WRG-NGM
Contact_Address:
Address_Type: mailing address
Address:
Mail Stop 989
345 Middlefield Rd
City: Menlo Park
State_or_Province: CA
Postal_Code: 94025
Country: USA
Contact_Voice_Telephone: 650-329-5313
Contact_Facsimile_Telephone: 650-329-5133
Contact_Electronic_Mail_Address: zulanger@usgs.gov
Spatial_Data_Organization_Information:
Direct_Spatial_Reference_Method: Point
Point_and_Vector_Object_Information:
SDTS_Terms_Description:
SDTS_Point_and_Vector_Object_Type: Entity point
Point_and_Vector_Object_Count: 3914
Spatial_Reference_Information:
Horizontal_Coordinate_System_Definition:
Geographic:
Latitude_Resolution: 0.00017
Longitude_Resolution: 0.00017
Geographic_Coordinate_Units: decimal degrees
Geodetic_Model:
Horizontal_Datum_Name: North American Datum of 1927
Ellipsoid_Name: Geodetic Reference System 1967
Semi-major_Axis: 6378160
Denominator_of_Flattening_Ratio: 298.25
Entity_and_Attribute_Information:
Detailed_Description:
Entity_Type:
Entity_Type_Label: station
Entity_Type_Definition: Point at which gravity anomaly was measured
Attribute:
Attribute_Label: STAT
Attribute_Definition:
Station Name--An alphanumeric combination of up to 8 characters used for station identification
Attribute_Domain_Values:
Unrepresentable_Domain: textual identifier without scientific significance
Attribute:
Attribute_Label: LaD
Attribute_Definition: Degree Latitude North
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 34
Range_Domain_Maximum: 34
Attribute_Units_of_Measure: degrees
Attribute_Measurement_Resolution: 1
Attribute:
Attribute_Label: LaM
Attribute_Definition: Decimal Minute
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 0.00
Range_Domain_Maximum: 60.00
Attribute_Units_of_Measure: minutes
Attribute_Measurement_Resolution: 0.01
Attribute:
Attribute_Label: LoD
Attribute_Definition: Degree Longitude West
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 117
Range_Domain_Maximum: 118
Attribute_Units_of_Measure: degrees
Attribute_Measurement_Resolution: 1
Attribute:
Attribute_Label: LoM
Attribute_Definition: Decimal Minute
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 0.00
Range_Domain_Maximum: 60.00
Attribute_Units_of_Measure: minutes
Attribute_Measurement_Resolution: 0.01
Attribute:
Attribute_Label: ELEV
Attribute_Definition: Elevation in feet
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 16.0
Range_Domain_Maximum: 7111.0
Attribute_Units_of_Measure: feet
Attribute_Measurement_Resolution: 0.1
Attribute:
Attribute_Label: acc
Attribute_Definition: accuracy indicator?
Attribute_Domain_Values:
Enumerated_Domain:
Enumerated_Domain_Value: (no value)
Attribute_Domain_Values:
Enumerated_Domain:
Enumerated_Domain_Value: A
Attribute_Domain_Values:
Enumerated_Domain:
Enumerated_Domain_Value: b
Attribute_Domain_Values:
Enumerated_Domain:
Enumerated_Domain_Value: m
Attribute_Domain_Values:
Enumerated_Domain:
Enumerated_Domain_Value: t
Attribute_Domain_Values:
Enumerated_Domain:
Enumerated_Domain_Value: U
Attribute:
Attribute_Label: OG
Attribute_Definition: Observed gravity, in mGal
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 979151.31
Range_Domain_Maximum: 979650.10
Attribute_Units_of_Measure: mGal
Attribute_Measurement_Resolution: 0.01
Attribute:
Attribute_Label: FAA
Attribute_Definition: Free-air anomaly, in mGal
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: -98.01
Range_Domain_Maximum: 140.77
Attribute_Units_of_Measure: mGal
Attribute_Measurement_Resolution: 0.01
Attribute:
Attribute_Label: SBA
Attribute_Definition: Simple Bouguer anomaly, in mGal
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: -121.18
Range_Domain_Maximum: 3.93
Attribute_Units_of_Measure: mGal
Attribute_Measurement_Resolution: 0.01
Attribute:
Attribute_Label: ITC
Attribute_Definition:
Inner terrain correction for a density of 2.67 g/cc, in mGal. See Code column for radius of correction.
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 0.00
Range_Domain_Maximum: 11.00
Attribute_Units_of_Measure: mGal
Attribute_Measurement_Resolution: 0.01
Attribute:
Attribute_Label: TTC
Attribute_Definition:
Total terrain correction from the station to 166.7 km for a density of 2.67 g/cc, in mGal.
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 0.00
Range_Domain_Maximum: 31.97
Attribute_Units_of_Measure: mGal
Attribute_Measurement_Resolution: 0.01
Attribute:
Attribute_Label: Code
Attribute_Definition: Letter denoting the zone (radius) of the correction
Attribute_Domain_Values:
Enumerated_Domain:
Enumerated_Domain_Value: (no value)
Attribute_Domain_Values:
Enumerated_Domain:
Enumerated_Domain_Value: D
Enumerated_Domain_Value_Definition: 0.59 km
Attribute_Domain_Values:
Enumerated_Domain:
Enumerated_Domain_Value: G
Enumerated_Domain_Value_Definition: 3.52 km
Attribute_Domain_Values:
Enumerated_Domain:
Enumerated_Domain_Value: M
Enumerated_Domain_Value_Definition: 58.8 km
Attribute:
Attribute_Label: CBA
Attribute_Definition:
Complete Bouguer anomaly reduced for a density of 2.67 g/cc, in mGal.
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: -115.45
Range_Domain_Maximum: 6.83
Attribute_Units_of_Measure: mGal
Attribute_Measurement_Resolution: 0.01
Attribute:
Attribute_Label: ISO
Attribute_Definition:
Isostatic residual anomaly,in mGal,assuming an Airy model for isostatic compensation of topographic loads. This model assumes a crustal thickness of 25 km, a topographic load density of 2.67 g/cc, and a density contrast across the base of the model crust of 0.4 g/cc. Isostatic correction would be difference between CBA and ISO values.
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: -71.31
Range_Domain_Maximum: 17.10
Attribute_Units_of_Measure: mGal
Attribute_Measurement_Resolution: 0.01
Distribution_Information:
Distributor:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: USGS Information Services
Contact_Address:
Address_Type: mailing address
Address: Box 25286 Denver Federal Center
City: Denver
State_or_Province: CO
Postal_Code: 80225
Country: USA
Contact_Voice_Telephone: 1-888-ASK-USGS
Contact_Facsimile_Telephone: 303-202-4693
Contact_Electronic_Mail_Address: ask@usgs.gov
Resource_Description: USGS Open-File Report 03-269
Distribution_Liability:
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.
Standard_Order_Process:
Digital_Form:
Digital_Transfer_Information:
Format_Name: ASCII
Format_Specification:
 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 2
Format_Information_Content: Gravity observation data
Transfer_Size: 0.3691
Digital_Transfer_Option:
Online_Option:
Computer_Contact_Information:
Network_Address:
Fees: none
Metadata_Reference_Information:
Metadata_Date: 20160205
Metadata_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Peter N Schweitzer
Contact_Organization: USGS Midwest Area
Contact_Position:
Collection manager, USGS Geoscience Data Clearinghouse, http://geo-nsdi.er.usgs.gov/
Contact_Address:
Address_Type: mailing address
Address:
Mail Stop 954
12201 Sunrise Valley Dr
City: Reston
State_or_Province: VA
Postal_Code: 20192-0002
Country: USA
Contact_Voice_Telephone: 703-648-6533
Contact_Facsimile_Telephone: 703-648-6252
Contact_Electronic_Mail_Address: pschweitzer@usgs.gov
Metadata_Standard_Name: Content Standard for Digital Geospatial Metadata
Metadata_Standard_Version: FGDC-STD-001-1998

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