Depth to the Juan De Fuca Slab Beneath the Cascadia Subduction Margin-- A 3-D Model for Sorting Earthquakes By Patricia A. McCrory, J. Luke Blair, David H. Oppenheimer, and Stephen R. Walter 2004 U.S. Geological Survey Data Series 91, Version 1.0 OVERVIEW OF THE SLAB-GRID PROJECT We present an updated model of the Juan de Fuca slab beneath southern British Columbia, Washington, Oregon, and northern California, and use this model to separate earthquakes occurring above and below the slab surface. The model is based on depth contours previously published by FlŸck and others (1997). Our model attempts to rectify a number of shortcomings in the original model and to update it with new work. The most significant improvements include (1) a gridded slab surface in geo-referenced (ArcGIS) format, (2) continuation of the slab surface to its full northern and southern edges, (3) extension of the slab surface from 50-km depth down to 110-km beneath the Cascade arc volcanoes, and (4) revision of the slab shape based on new seismic-reflection and seismic-refraction studies. We have used this surface to sort earthquakes and present some general observations and interpretations of seismicity patterns revealed by our analysis. In addition, we provide files of earthquakes above and below the slab surface and a 3-D animation or fly-through showing a shaded-relief map with plate boundaries, the slab surface, and hypocenters for use as a visualization tool. FILES 1_README.txt Overview of the slab-grid project - this file 2_TEXT.pdf Project description and references in Adobe Reader format 3_FIGURES A folder containing the figures for this report in Adobe Reader PDF format as well as a set of small JPG files of the same illustrations 4_DATA A folder containing GIS data, metadata, and animations: above_points.txt Sorted earthquakes above slab surface in tab-separated-ASCII format. List of North American seismic events selected from ANSS catalog earthquakes. See text for explanation of parameters used to select earthquakes. below_points.txt Sorted earthquakes below slab surface in tab-separated-ASCII format. List of Juan de Fuca seismic events selected from ANSS catalog. See text for explanation of parameters used to select earthquakes. contours_dd.txt File of slab contours in tab-separated ASCII format. Geo-referenced GIS grid of depth to Juan de Fuca slab surface in XYZ format using decimal degrees and kilometers. See text for explanation of method used to create grid. GIS_data A folder containing 36 GIS files metadata A folder containing 4 metadata files: newslab_dd.ascii Slab grid file in ASCII format. Geo- referenced GIS grid of depth to Juan de Fuca slab surface in XYZ format using decimal degrees and kilometers. See text for explanation of method used to create grid. newslab_dd.prj Slab projection file in ASCII format PNW_animation.avi 3-D animation in Microsoft Media Player format PNW_animation.mov 3-D animation in Apple QuickTime format slab.grd Slab grid file. 5_SOFTWARE A folder containing: Acrobat Installer for Adobe Reader for Macintosh and Windows ArcReader_install ArcReader is part of the ArcGIS Desktop installation autorun.inf Windows auto-launch file usgsid.ico Windows icon file, USGS version_history.txt Citation and release information SYSTEM REQUIREMENTS This CD-ROM (DS_91) was produced in accordance with the ISO 9660 Level 2 standard and Apple Computer's(R) hierarchical file system (HFS) standard. 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FOR SALE BY: USGS Information Services Box 25286 Denver Federal Center Denver, CO 80225 Telephone: (888) ASK-USGS The bibliographical reference for this publication is: McCrory, P.A., Blair, J.L., Oppenheimer, D.H., and Walter, S.R., 2004, Depth to the Juan de Fuca slab beneath the Cascadia subduction margin--A 3-D model for sorting earthquakes: U.S. Geological Survey Data Series 91 (CD-ROM and URL http://pubs.usgs.gov/ds/ds-91). ISBN: 0-607-97922-4 This report and any updates to it are available on line at http://pubs.usgs.gov/ds/ds-91/ DISCLAIMERS This Compact Disc Read-Only Memory (CD-ROM) publication was prepared by an agency of the U.S. Government. 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