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The Create time table module computes seismic travel-time tables from a depth velocity model and writes the results to a binary TT file. For every source bin in the survey, the module solves the Eikonal equation — using a fast marching (structured Eikonal) solver — to propagate wave-fronts through the 3D velocity grid and record the travel time from that source to every receiver bin within the specified aperture. The resulting travel-time tables are the primary input for Kirchhoff pre-stack depth migration (PSDM), which uses them to collapse reflection energy to its correct depth position.
Both isotropic and anisotropic (VTI) velocity models are supported. When Thomsen Delta and Epsilon parameters are supplied alongside the P-wave velocity model, the solver accounts for anisotropy in the travel-time computation. The module supports parallel execution on multiple CPU threads as well as GPU (CUDA) acceleration, and can be distributed across computing nodes for large 3D surveys.
Note: This module is deprecated. For new projects, consider using the Time tables calculation module instead.
The path and file name for the output travel-time table file (extension .ttfile). This binary file stores the computed travel times for all source-receiver pairs and is subsequently read by Kirchhoff depth migration modules. Choose a location with sufficient disk space, as TT files can be very large for wide-aperture 3D surveys.
Controls whether an existing TT file at the specified output path is overwritten without prompting. Default: false. When set to false, the module will check if computation for each source bin has already been completed (allowing a previously interrupted run to be resumed). If the existing file is incompatible with the current parameters, the user is asked whether to overwrite it. Enable this option when you want to unconditionally recreate the TT file from scratch.
The P-wave interval velocity model in the depth domain. Each trace in this gather corresponds to one bin (CMP) location; the samples along the trace represent velocity values at successive depth levels. This model defines the medium through which the Eikonal solver propagates wave-fronts. The velocity model must have a geometry (inline/crossline layout) consistent with the survey bins — the product of the number of inlines and crosslines must equal the trace count.
The Thomsen anisotropy parameter delta (δ) model, in depth-domain gather format matching the velocity model. Delta controls the near-vertical anellipticity of the wave-front and primarily affects normal-moveout velocity. This input is optional and is only used when Make anizo is enabled. If not connected, the module assumes an isotropic medium.
The Thomsen anisotropy parameter epsilon (ε) model, in depth-domain gather format matching the velocity model. Epsilon characterizes the degree of anisotropy between the horizontal and vertical P-wave velocities and controls the long-offset travel-time behavior. Like Delta, this input is optional and is only active when Make anizo is enabled.
Selects whether the survey geometry and velocity model are treated as 3D (full inline and crossline extent) or 2D (single line). Default: false (2D mode). Enable this for 3D surveys where the velocity model spans multiple inlines and crosslines. In 2D mode, only the inline dimension is used for wave-front propagation.
The spatial grid spacing in the crossline direction, in meters. Default: 5 m. This value must match the actual bin spacing of the velocity model in the X (crossline) direction. An incorrect value will cause the Eikonal solver to propagate wave-fronts at wrong velocities, leading to mispositioning of events in the migrated image. This parameter is automatically populated from the velocity model geometry when available.
The spatial grid spacing in the inline direction, in meters. Default: 5 m. This value must match the actual bin spacing of the velocity model in the Y (inline) direction. As with DX, an incorrect value directly corrupts the travel-time computation. This parameter is automatically populated from the velocity model geometry when available.
The maximum lateral distance (in meters) from a source bin within which receiver travel times are computed and stored. Default: 500 m. Receiver bins located farther than this distance (measured separately along inline and crossline) from the source are excluded. This aperture must be at least as large as the migration aperture used in the subsequent Kirchhoff migration step. Larger apertures increase disk space and computation time proportionally; set it to the minimum value sufficient to capture all significant reflection contributions at your target depths.
The reference datum elevation, in meters (depth domain). Default: 0 m. Sources and receivers are placed at this depth level in the velocity model for the purpose of Eikonal wave-front initialization. This value should be consistent with the datum used when building the depth velocity model and with the datum assumed in the migration workflow. This parameter is automatically populated from the velocity model and is not directly editable.
Enables anisotropic (VTI) travel-time computation. Default: false (isotropic). When enabled, the Eikonal solver uses the Thomsen Delta and Epsilon parameter models in addition to the P-wave velocity model to compute anisotropic travel times. Use this option in geologic settings with strong shale anisotropy or where isotropic depth migration produces significant structural distortions. Both the Delta param and Epsilon param inputs must be connected for anisotropic mode to function correctly.
An integer decimation factor applied to the depth sampling of the output TT file. Default: 1 (no decimation). Valid range: 1–100. The Eikonal solver always runs at the full depth resolution of the input velocity model. The output is then resampled (decimated) by this factor before writing: for example, a factor of 2 halves the number of depth samples in the TT file, reducing disk space and I/O time during migration at the cost of depth resolution. Use a factor greater than 1 only when disk space or I/O throughput is a constraint and the migration depth step can tolerate the coarser sampling.
Selects the numerical order of the Eikonal finite-difference stencil used to compute travel times. Default: Low. Options:
Low — 1st-order scheme. Fastest computation; suitable for initial quality checks or coarse velocity models.
Medium — 2nd-order scheme. Improved travel-time accuracy with moderate additional cost; recommended for production anisotropic runs.
High — 3rd-order scheme. Highest accuracy; best choice for complex geology with strong velocity contrasts, but requires the most computation time.
This group of parameters defines which source bins have their outgoing travel-time wave-fronts computed. Restricting the source area to a subset of the survey reduces computation time when only part of the TT file needs to be computed or updated (for example, when adding new shot lines to an existing TT file).
The first inline number in the source calculation area. Default: -1 (no lower limit — use all available inlines from the beginning of the survey). Set to a specific inline number to restrict computation to sources at or beyond that inline.
The last inline number in the source calculation area. Default: -1 (no upper limit — use all available inlines to the end of the survey). Set to a specific inline number to restrict computation to sources at or before that inline.
The first crossline number in the source calculation area. Default: -1 (no lower limit). Works together with the inline bounds and the Calculation rule to define the source subset.
The last crossline number in the source calculation area. Default: -1 (no upper limit). Works together with the inline bounds and the Calculation rule to define the source subset.
Controls how the inline and crossline bounds are combined to select source bins. Default: Logical AND. With Logical AND, a bin is included only if it satisfies both the inline range and the crossline range simultaneously — this defines a rectangular sub-area. With Logical OR, a bin is included if it satisfies either the inline range or the crossline range — this defines a cross-shaped (union) region.
The decimation step for source bins along the inline direction. Default: 1 (compute every inline). Setting this to 2 computes every second inline, to 3 every third inline, and so on. Larger step values reduce computation time but result in coarser spatial coverage of source positions in the TT file; the migration step must then interpolate travel times between computed source locations.
The decimation step for source bins along the crossline direction. Default: 1 (compute every crossline). As with the inline step, increasing this value reduces compute time at the cost of sparser source-side travel-time coverage.
This group of parameters defines which receiver bins are included when recording travel times from each source. The receiver subset is further filtered by the Aperture parameter. Restricting the receiver area can reduce TT file size for surveys where receivers cover only a limited portion of the survey grid.
The first inline number in the receiver calculation area. Default: -1 (no lower limit). Set to a specific inline number to restrict which receiver positions are considered during TT computation.
The last inline number in the receiver calculation area. Default: -1 (no upper limit).
The first crossline number in the receiver calculation area. Default: -1 (no lower limit).
The last crossline number in the receiver calculation area. Default: -1 (no upper limit).
Controls how the inline and crossline bounds are combined to select receiver bins. Default: Logical AND. Behaves identically to the Calculation rule in the Source calculation area group: Logical AND defines a rectangular receiver patch; Logical OR defines the union of the inline and crossline ranges.
The decimation step for receiver bins along the inline direction. Default: 1 (include every inline). Increasing this value reduces the number of receiver positions stored per source, reducing TT file size.
The decimation step for receiver bins along the crossline direction. Default: 1 (include every crossline). Increasing this value reduces the number of receiver positions stored per source, reducing TT file size.
Selects the hardware used for the Eikonal solver. Choose GPU to use CUDA-capable graphics cards, which can substantially accelerate TT computation for large 3D surveys. Choose CPU for standard multi-threaded processing. GPU mode is recommended when multiple NVIDIA GPUs are available and the velocity model is large.
Enables distribution of TT computation across a cluster of computing nodes. Source bins are divided into chunks and dispatched to available worker nodes. This is particularly useful for large 3D surveys where total TT computation may take many hours on a single machine.
The number of source bins grouped into a single computational task (chunk) when distributing work across nodes or threads. Larger bulk sizes reduce inter-node communication overhead but may cause uneven load balancing if some chunks take significantly longer than others.
Sets the maximum number of CPU threads used on each distributed worker node. Useful when nodes are shared with other processes and you want to limit the CPU resources consumed by this job.
An optional text suffix appended to the distributed job name for identification in the job queue. Useful for tracking multiple simultaneous TT computation jobs.
When enabled, allows manual specification of CPU core affinity for this process. Use this to pin the computation to specific processor cores, which can improve cache utilization on NUMA systems.
Specifies the CPU core affinity mask when Set custom affinity is enabled. Only active when custom affinity is turned on.
The number of parallel CPU threads used for local (non-distributed) execution. For CPU mode, set this to the number of available physical cores. In GPU mode, each GPU runs as a separate thread, so this value is overridden by the number of detected CUDA devices.
Enables execution of custom shell scripts before and after the TT computation run.
Path to a script that is executed before the TT computation begins. Use this to set up the output directory, copy velocity model files, or configure the compute environment.
Path to a script that is executed after the TT computation completes. Use this for post-processing steps such as archiving the TT file or notifying downstream processes.
When enabled, this module is bypassed during workflow execution without removing it from the processing sequence. Use this to temporarily disable TT computation while testing other parts of the migration workflow.
A bin point vector containing the survey geometry bins that were processed during TT computation. This output can be connected to downstream migration modules to ensure they use the same bin geometry as was used for the TT file, avoiding geometry mismatches at the migration stage.