Webservice of Fault Traces Associated with Alquist-Priolo Fault Zones

Attribute_Accuracy_Report: Prior to 2016 digital GIS files delivered did not contain any entity attributes other than a unique identifier. As of 2016 the format of the digital GIS files has been changed and there are now four feature classes, each with associated attributes. For the most part, the attribute values were automatically generated and populated via Python scripts. The date values in FAULT_ZONE.RELEASED and FAULT_ZONE.PREV_DATES were verified against Table 3, Official Maps of Earthquake Fault Zones issues 1974 through August 2007, in Special Publication 42, Interim Revision 2007, Fault-Rupture Hazard Zones in California.  

Quantitative_Attribute_Accuracy_Assessment:

   FAULT_TRACE—Geometry validation and topological checks were performed and duplicate trace segments and near-duplicate trace segments were deleted. Any multipart geometries were expanded into their respective components and kinks/kickbacks were corrected. This feature class contains occurrences of unbroken intersecting geometry, (i.e. fault traces that overlap but the overlapping traces do not share a vertex/node at the point of intersection), which have not been corrected.  

Completeness_Report: The dataset contains Alquist-Priolo Earthquake Fault Zones and faults as shown on the 2018 Official Map of Alquist-Priolo Earthquake Fault Zones for California. The topographic base map, which was included on the published map, is not included.

Horizontal_Positional_Accuracy
Horizontal_Positional_Accuracy_Report: No systematic control surveys have been conducted to characterize the positional accuracy of the fault traces and earthquake fault zones. The mapping of fault traces and earthquake fault zone boundaries began in the early 1970’s and has continued into the present. The processes used to generate these data span a wide range of techniques from hand drawn maps on 7.5’ topographic sheets to heads up digitizing on LiDAR derived shaded relief base maps. The data have been interpreted and mapped as accurately as possible given the type of source data, and the time, staff and technology available at the time of mapping. More detailed information on mapping processes and base maps used may be available in the Fault Evaluation Report or for older maps, in the references used to compile the fault data.

Process_Description: For maps released from 1974 – 1995 the following processes were completed to convert the clear film overlays into digital format.

 The original hardcopy maps (clear film overlays) used to reproduce Official Maps of Earthquake Fault Zones were the basis for developing the original GIS files. Each hardcopy map was scanned at full scale using an Anatech large-format scanner. The scanned image was translated to cit file format, geo-referenced (California State Plane Coordinate System (feet), North American Datum 1927), and digitized using Microstation v5.0 software to create vector files in dgn format. The digital files were printed at 1:24,000 scale and compared with the original clear-film overlay for completeness and accuracy. Digital files were then converted to dxf format, using individual layers to display specific line-styles as follows:

    Layer 1: Corner registration tics for individual quadrangle map and most text data
    Layer 3: Corner registration tics for oversized quadrangle maps (not present for most maps)
    Layer 7: EFZ boundary polygons
    Layer 8: Solid lines (accurately located fault traces)
    Layer 9: Long dashed lines (approximately located fault traces)
    Layer 10: Short-dashed lines (inferred fault traces)
    Layer 11: Dotted lines (concealed fault traces)
    Layer 12: Thin dashed and dotted lines (aerial photo lineament)

Process_Description: In 2016 CGS updated the existing digital GIS data to meet the following goals: 1) a consistent projection and datum for all quadrangles, 2) uniform attribution, and 3) updated metadata. This process step included all GIS data released prior to July 1, 2016.
   
   Four ArcSDE feature classes and the necessary supporting domain tables were defined and created in an ArcGIS 10.3 enterprise geodatabase. The individual shapefiles for each quadrangle were then processed using Python scripts to 1) reproject from California State Plane Zone (feet), NAD 27 to California Albers (meters), NAD 83, 2) add attributes as needed depending on the target feature class, and 3) load the reprojected, attributed data into the appropriate ArcSDE enterprise feature class. Forty three of the 556 quadrangles were loaded using FME Workbench due to data that would not load via Python script or to deal with formatting differences.

   The data layers previously created were loaded to the four feature classes as follows:

    Layers 1&3    FAULT_LEADERLINE
    Layer 7     FAULT_ZONE
    Layers 8-12, polyline geometry  FAULT_TRACE
    Layers 8-12, text annotation  FAULT_LABEL
    
   Once loaded into the enterprise feature classes, QA/QC procedures were run to identify any geometry errors and standardize attributes. See Logical_Consistency_Report. For the FAULT_TRACES feature, the FAULT_NAME and FAULT_ZONE fields were updated by CGS staff by comparing the FAULT_TRACE faults with the CGS Quaternary Fault & Fold database. Where fault traces matched between the two databases, the fault name and fault zone name values from the Quaternary Fault & Fold database were copied to FAULT_TRACE features. Data values for FAULT_NAME and FAULT_ZONE were then updated to use proper case and faults previously named “unnamed” were updated to Null. In addition, inconsistent naming styles for some traces were standardized.
   
   When QA/QC and all updates were complete, Python scripts were used to extract the data from the enterprise ArcSDE feature classes by quad tile, generating potentially four shapefiles per quad. Metadata templates were created and Python scripts used to generate & customize the metadata for each quad. The updated GIS data and metadata for each quad were bundled and zipped via Python scripts and then posted to CGS’s Information Warehouse web site.