GeoTom - Version CG - Seismic Tomography Software
GeoTomCG can process and display 2-D and 3-D crosshole or VSP seismic or radar data. The display below shows calculated seismic velocities from a dam in Taiwan being investigated for earthquake damage1. S and R indicate source and receiver positions, respectively. The crosshatch pattern indicates areas with few raypaths. The investigators reported that the seismic velocities were consistent with results obtained by other geophysical methods.
GeoTomCG GPR and seismic tomography software provides:
- Efficient processing of 2-D and 3-D data.
- Versatile methods for using site information for more reliable results.
- Practical, easy to use.
- Many years of program development guided by processing field data.
- Instrucciones sumarias en español e inglés.
User’s suggestions led to the optional color spectrum shown below for quickly highlighting zones of low velocity (red-magenta) in concrete. 3-D displays can be rotated and tilted. Low velocity zones inside a 3-D volume can be displayed with a cutoff velocity. Only zones where the velocity is below the cutoff velocity are colored.
GeoTomCG can export results for display by commercial 2-D and 3-D graphics programs such as Surfer®, Voxler®, Tecplot®, and SlicerDicer®. A 3-D display from Tecplot of results calculated by GeoTomCG is shown below. This display shows questionable locations (velocity 3.0 to 3.6 m/ms, green-yellow) in a dam that suffered earthquake damage in Taiwan1.
1Application of Elastic Wave Tomography for Dam Safety. Sheng-Hsung Hsieh, Chih-Hsin Hu, Chih-Hsien Hsieh , Jen-Kai Huang, Cheng-Yang Yen, Wen -Lung Chi, and Chao-Ming Lin. Presented at SAGEEP 2012, Tucson, AZ, USA, Mar. 25-29, 2012, Poster Session Two, Wed. Mar. 28.
GeoTomCG features and options
Traveltimes (or amplitudes) can be processed to calculate velocities (or attenuation). Sources and receivers can be in anywhere within a 3-D grid. Anisotropy can be specified for each grid point. Raypaths can be straight or curved. Options for using site information to improve the reliability of results include:
- Maximum and minimum calculated velocities.
- Constant velocity in user-selected areas or volumes in the grid.
- Groups of nodes with similar velocities, such as horizontal layers or vertical columns.
- Constraints that take into account the uncertainty in site knowledge.
- Adjustable damping and smoothing to reduce small-scale variations in calculated velocity.
GeoTomCG runs under Windows© and provides graphical displays of velocities, raypaths, raypath densities, and other parameters for inspecting results and preparing preliminary reports. These displays can be copied and pasted with the Windows clipboard. Quality control plots include traveltime vs. distance, residual vs. raypath angle, velocity vs. raypath angle, common-source and common-receiver gathers, and others. It also provides 3-D numerical results and 2-D slices of the 3-D grid as ASCII files that can be read by commercial 3-D and 2-D visualization programs for preparing formal reports and presentations. Two sets of results can be compared by differences or ratios. The user’s manual describes processing seismic and electromagnetic data. Examples with files allow the user to practice traveltime and amplitude data processing. The separate time and amplitude picking program TomTime provides output in the format used as input for GeoTomCG. It provides versatile filtering and display options for noisy data and for S-wave overlays. TomTime is described in a separate information sheet.