3.2. Data Preparation
Before chronostratigraphy is calculated the data needs to be prepared. Specifically horizons must exist everywhere, they cannot cross each other nstead they should truncate against each other as and where appropiate. For these purposes utilities exist to fill up holes and check crossings respectively.
Also, for the data driven chronostratigraphy computations a smooth dip-azimuth field is needed. This can be achieved by median filtering the steering cube.
3.2.1. Horizon preparation
To solve crossing horizons conflicts select check crossings submenu (SSIS - Data preparations - Horizons - Check crossings). The Horizon relation window pops up. Select all horizon that need checking (Read Horizons ...). The horizons are sorted automatically from top to bottom. Now press Check crossing...
To solve crossing conflicts select the horizon that will be modified. The software will check the number of positions where a conflict exits and modify the horizon by removing the conflict points or by changing the values to be equal to the overlying/underlying horizon.
Note: To honour the requirement that horizons cannot coincide the actual values are not exactly equal, but they are within one sample position accuracy.
The figure below sketch what will happen to horizon B if you select shift (1) or remove (2). Figures (3) and (4) show the results for shifting (3) and removing (4) when horizon A is the one to be modified. The software verifies that removing and shifting operations are executed properly and the correct chronostratigraphy calculation results are reached.
Holes in horizons can lead to unexpected chronostratigraphy results. It is therefore recommended to work with continuous horizons. The fill holes utility fills holes using an iterative application of an inverse distance algorithm. In successive steps holes are interpolated which means that the algorithm stays local in each step.
The options are:
Extrapolate outward. If set to yes the horizon is extrapolated to match the dimension of the survey area, or specified work area, as the case may be.
Maximum fill size(nodes). In some cases, you do want to keep large holes. If so, select specify maximum fill size (nodes) and set it to the maximum size in nodes you still want to be filled.
Maximum interpolation steps. Restricting the number of interpolation steps facilitates in partially filling the holes. This is useful when filling holes of a particular shape.
Save interpolated horizon. The horizon can be saved as new horizon or is overwritten.
3.2.2. Filtering the steering cube
The steering cube can be improved by smoothing. A better steering cube improves chronostratigraphy calculations. Use the option Filter SteeringCube... to apply a median filter to the steering cube. Adjust the needed parameters: inline and crossline step-out, time gate size, and maximum dip according to your dataset. Filtering of the steering cube is described in Section 2.2.3