A. Surfer assigns NoData values to the grid cell when a fault BLN line crosses the cell, therefore the grid cells around the fault line will contain NoData values. There is not a way to work around this, however, you can minimize the NoData area around the fault lines by decreasing the size of the grid cells. To do this, you can click Home | Grid Data | Grid Data and regrid the data with the fault file, specifying smaller grid cells (increase the # of Nodes or decrease the Spacing in the Grid Data dialog).
Alternatively, you can try increasing the width of the fault line in the contour map to cover some of the NoData area.
Updated September 18, 2017