Displaying strike and dip information on a Surfer map is a good way to show field data and geologic orientation of surfaces or planes (i.e. bedding surfaces, fault planes, sills, dikes, fractures, etc).
If you have strike and dip measurements already from literature, field measurements, or borehole data, you can display the measurements directly on a map using a post map. All you need is a data file with the XY location, the azimuth of the strike line, and the dip amount for each point.
NOTE: This article assumes the azimuth measurement conforms to the American “right hand rule”, which is to always report the strike azimuth so that the dip direction is on the right side of the strike line (if you make an “L” shape with your right hand, palm down, then your index finger points down dip and your thumb points to the strike azimuth).
To create the post map with the strike and dip symbols, follow these steps:
- First, the strike azimuth data needs to be manipulated slightly to be compatible with Surfer so that the strike/dip symbols are rotated correctly. This manipulation can be done in the Surfer worksheet. Click File | Open, select the data file and click Open. The data opens in the Surfer worksheet.
- To make the strike azimuth be compatible, the data needs to have 90 subtracted from it, and the result multiplied by -1. To do this, click Data | Data | Transform.
- In the Transform equation box, enter the function G=(C-90)*-1, where C is the column containing the strike azimuth data and G is the column that you want to save the new data in.
- Click OK and the new column of data is created. Now when the symbols in the post map are rotated by the azimuth value, they are rotated to the correct orientation.
- Click File | Save and File | Close.
- In a plot window, click Home | New Map | Post | Post (or Home | Add to Map | Layer | Post to add this to another map layer), select the data file, and click Open.
- Select the Post layer in the Contents window.
- In the Properties window, click the General tab:
- Set the appropriate data columns for X Coordinates and Y Coordinates.
- If you created the strike and dip data file by converting a grid file to a DAT file, you may want to adjust the Frequency number to reduce the number of symbols.
- To change the symbols to strike/dip symbols, click the Symbol tab:
- Expand the Symbol Properties section by clicking the + sign.
- Change the Symbol Set to GSI Geologic Symbols.
- Change the Symbol to a strike/dip symbol. For example, for non-vertical and non-horizontal orientations, you could use Symbol 0 for bedding (), Symbol 26 for foliation (), or Symbol 14 for joints (). In the attached SRF, Symbol 26 is selected.
- In the Symbol Angle section, set the Angle column to be the column containing the transformed azimuth or strike direction (i.e. Column G).
- In the Symbol Size section, change the Symbol size to something a little larger (i.e. 0.400 in).
- If you want to show the labels for the dip amount, click the Labels tab:
- In the Label Set 1 section, change the Worksheet column to the column containing the dip amount (i.e. Column D).
- To adjust the label position relative to the symbol, change the Position relative to symbol from Above to another option (i.e. Right).
- If desired, the font properties can be adjusted by expanding the Font Properties sub-section and changing the options. For example, change the Size (points) to 12 and the Foreground color to Blue.
- You can click the Add button in the Label Sets section to add another label set if you also wish to display a label for the strike direction. After creating Set 2, simply set the Worksheet column to the column containing the original strike direction. Again, you may need to adjust the label position relative to the symbol.
- You may also want to fine-tune the label positions. There is not a way to automatically place the dip labels in the location they are usually depicted (with the dip label in front of the symbol, regardless of rotation). All labels in Surfer are positioned relative to the symbol XY point location, and not adjusted for any rotation. You can either find the best placement using one of the predefined or custom Position relative to symbols options, or you can manually edit the position of each label. If you choose to manually edit the labels, be sure to do this after any changes to the coordinate system of the map (as in the previous step), as changing the map’s coordinate system will eliminate the custom label positions. To manually edit the labels, follow these steps:
- Right click over the Post layer in the Contents window and click Edit Post Labels.
- Drag and drop the labels to the desired positions.
- Press ESC on the keyboard when you are finished.
- Turn off the leader lines by clicking the Labels tab in the Properties window and unchecking Enable for dragged labels in the Leader Lines section.
Please see attached SRF and DAT files for example. The SRF file is saved in Surfer 12 SRF format.
If you don’t have field data with strike and dip information but you have a grid file, you can calculate the strike and dip information from the grid file in Surfer and then display it on your map. To calculate the strike and dip values of a grid file, please see the instructions in this article: How can I find the strike and dip values for my grid file and display it on a map?
Updated January 11, 2017