Notice that a series of red tick marks appears on the displayed traces. Click on the Ok button on the next two menus to accept the default parameters.ġ8 18 EXERCISE 2: First Break Picking In this exercise, we will pick first breaks from the input seismic data. Select it from the menu as shown above and click on Ok. The geometry file needed for this guide session is called accept.geo. This file contains a single text line for each trace in the dataset, describing the x-y location of the trace, its elevation and the pick time, if it has already been picked. The geometry file that is required for the GLI3D PICKER is in the HRS ASCII format. The Load Geometry selection box then appears.

From the pulldown menu select Open Files. Click on the File option of the GLI3D PICKER window. To do this, we need to read in two files: a geometry file and a SEGY seismic file.

We will get these picks by picking a seismic dataset within the GLI3D PICKER window. You do not need to have a pick time from every trace, but you should ensure that your picks provide a reasonable sample of the survey. Start the program by typing: gli3d Two windows now appear, as shown below:ġ2 12 GLI3D requires you to provide coordinates for every shot and receiver location in your survey and first arrival times at some of the traces. This can dramatically increase the runtimeĨ 8 Land data sources and receivers are often grouped to improve the signal to noise ratio This should be taken into account when calculating the travel time, especially at short offset distancesĩ 9 time time x x The result of not specifying arrays is to underestimate the travel time (right) Actual first break picks will show a bulk time shift when compared to the model derived valuesġ0 10 EXERCISE 1: Reading Data and Starting the Project In this exercise, we will start a new GLI3D project and read data into it. 5 5 Geometry data comprises shot and receiver numbers and locations, elevation data, shot depth and uphole times (if available) First break picks can be imported if picked in external packageĦ 6 The ray trace method of model based First Break pick analysis can be computer intensive when dealing in 3D Ray tracing can be speeded up if the survey area is rotated to a north-south orientation which simplifies the trigonometryħ 7 The data in the survey are extrapolated to a north-south grid if a rotation is not applied.

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