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Seismic Refraction Method

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Interpex offers five packages that apply to seismic refraction data. FIRSTPIX v4 is a data processing package. GREMIX v2, GREMIX 15, GREMIX S and GREMIX 15 S interpret seismic refraction data. Used together, FIRSTPIX v4 and any GREMIX package provide an integrated software system for editing and interpreting your seismic refraction data.


FIRSTPIX is an interactive, graphically oriented, seismic refraction trace processing, display, and first arrival picking program. The main functions are as follows:

  • selecting files and importing the trace data
  • defining the field recording geometry and elevation information
  • identifying first arrival information for use in the GREMIX
  • interpretation program
  • producing hard copy output of the original field records
  • merging adjacent records to create up to 48 channels per record, from 6, 12, or 24 channel records
  • combining opposite polarity shear wave shot to cancel P-wave arrivals to improve selection of the shear wave arrivals
  • produce common offset plots


    Digitally recorded seismic data are transferred from the input records to an internal database. Up to 20 shots, recorded by as many as 48 geophones per shot, can be used.

    Geophones cannot be placed coincident with the shot source locations. You can merge seismic records to create larger spreads from several smaller ones, or to display common offset refraction or reflection data. When merging records, it is assumed that the geophone locations do not overlap, and that the shot locations, the sample rates and trace length are the same for each spread.

    You can edit the arrangement of the source and receiver locations (geometry) to depict the actual field data collection parameters. Shot and geophone locations, and uphole times for downhole shots are included.

    Geometry as well as shot records can be viewed on screen. Select from several display parameters, including trace scaling, trace clipping, variable area, zoom, and vertical or horizontal display orientation of the shot record. You can pick first breaks automatically or manually to create the travel time curve set for the spread.

    Travel time curves are the visual relationship between the spread geometry and the first arrival times picked from the displayed shot records. First arrivals are a function of the survey geometry and the travel time of the seismic waves along the geological refraction interfaces. These travel time curves can be displayed on screen to be checked for relevancy and possible picking or geometry errors.

    After the travel time curves appear satisfactory, you can print or plot the data, and produce a plate style plot of the travel time curves.

    The following is a list of the features that were added or enhanced from previous FIRSTPIX programs

  • Automatically detects recording formats of instrument files
  • Interactive spreadsheet like geometry editor with automatic geometry generation
  • Automatic generation of positions for constant or irregular spaced and symmetrical or asymmetric tapered spreads.
  • Reads elevation data from generic ASCII or SEG P1 files
  • Appends records to existing spreads.
  • Data export in GREMIX, SEGY and SEG2 format.
  • Graphical view and plotting of spread layout.
  • Graphical view and plotting of common offset/long data with optional use of firstbreaks as static shift
  • Accepts up to 20 shot records
  • Provides interactive graphics operation
  • Automatically or interactively picks first arrivals, and enables you to adjust first arrivals
  • Enables you to merge and combine seismic records
  • Firstbreak picking with traveltime curves displayed
  • Processing screen showing enlarged windows for firstbreak picking


    Picking of firstbreaks is accomplished via interactive graphical mouse picking in an enlarged windows. The picking window is user definable for both trace length and gain. Record selection can be made directly from picking screen. Traveltime curves can be displayed while picking.

    Autopicking allows for automatic picking of all records at once or for individual records. Picking can also be done by displaying all relevant traveltime curves and selecting a point on a curve. The program then displays a window with five applicable traces from the selected record. Gain and length of these displayed traces are user controllable.

    Picking is then done interactively on the displayed traces. Changes to the traveltime curves are made in real time. This feature is especially useful to repick traces while taking other records into consideration.

    FIRSTPIX now also features combining of records using an interactive analysis window displaying traces from the records to be combined. By changing the combination factor interactively the user can see the combined effect in real time. This feature allows users to do shear wave analysis and picking interactively.

    Traces can be displayed with AGC on or off and traces can be filtered with a user selectable low pass filter. Time ranges as well as trace width and overlap can be set for global operation or can be changed for each record.

    The program also features all the usual INTERPEX features including screen attribute control, color control over plotting colors, command mode, user definable plot labels and outputs to all popular plotting and printing devices including Laser printers and Postscript files.

    Supported Seismographs

    ABEM Geophysics
    BISON Instruments Inc.
    - Geopro - 1 8000 series
    - Geopro - 2 7000 & 9000 series
    - Seisview w/ math coprocessor format
    - Seisview w/o math coprocessor format
    - ES-2401 (pseudo-SEG2 format)
    - Other instruments that support SEG2
    OYO Corporation
    - McSEIS
    - DAS1
    Scintrex Ltd
    - ECHO-2
    SEG2 Standard Format

    GREMIX Family Features


    GREMIX interprets seismic refraction data. It is a powerful, easy to use tool for interpreting laterally varying layered earth structure as well as for detecting hidden layers. GREMIX lets you enter, edit, interpret and plot seismic refraction first arrival data.


    It incorporates the slope-intercept method, parts of the Plus-Minus Method of Hagedoorn (1959), Time-Delay Method, and features the Generalized Reciprocal Method (GRM) of Palmer (1980).

    GREMIX Features:

  • Up to four layers, one deduced from direct arrivals and three deduced from refractions.
  • Interactive editing of the traveltime data including geophone elevations, uphole and system delay times,
  • Interactive assignment of arrival times to layers
  • Interactive graphical editing of reciprocal times
  • Implicit phantoming through examination of all possible travel time pairs.
  • Listings that display interpreted velocities and time depths for each layer
    Four velocity analysis methods
    Full GRM
    Partial GRM
    Optimum X-Y
    Time delay
  • Plate style output of traveltime curves with or with out layered earth fits, velocity section, time depth section and annotated interpreted depth section with or without arcs.

    Plots will display up to 16 spreads and a maximum of 9 shots on one plot, each with 69 geophones for a maximum of 1104 geophones.


    GREMIX S allows for surface topography (elevations) to be imported from SEG-P1 files with multiple header records. Interpreted results (up to 200 spreads) can be merged with SEG-P1 files to produce a data file giving shot/geophone point and estimated static value at each point in the SEG-P1 file. Static value can be weathering correction only or full datum plus weathering static correction. These results can then be imported to a processing package as a first estimate of static corrections.

    GREMIX 15

    GREMIX 15S

    GREMIX 15 and GREMIX 15S has all the features of GREMIX V2 and GREMIX S respectively but its data handling capacities has been increased. Please refer to the product selection table for the data handling capacities of each program.


    Product Selection Table

    Max number of Shots 16 16 16 16
    Max number of Shots/spread 9 15 9 15
    Max number of Geophones/Shot 96 96 69 96
    Statics N N Y Y



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