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# Seismic Force

Seismic Force can be applied to the wedge by selecting the Seismic check box in the Input Data dialog, and entering the following data:

## Seismic Coefficient

A dimensionless number defines the seismic acceleration as a fraction of the acceleration due to gravity. Typically the Seismic Coefficient might be around 0.1 to 0.2. If a = Seismic Coefficient, g = acceleration due to gravity = 9.81 m/s 2, and m = mass of the wedge, then the Seismic Force applied to the wedge, F = m a g.

## Direction

• Line of Intersection will apply the Seismic Force in the direction (PLUNGE and TREND) of the Line of Intersection of Joint Sets 1 and 2.
• Horiz. & Inters. Trend will apply the Seismic Force horizontally, but with the same TREND as the Line of Intersection of Joint Sets 1 and 2.
• User-Defined allows the user to define any direction for the Seismic Force.

## Display of Seismic Force

If Seismic Force has been applied to a model, the Force will be represented on the model as a yellow arrow at the lowermost wedge vertex on the slope face. The arrow is symbolic and indicates the direction and existence of a Seismic Force. It does NOT indicate the magnitude of the force. The display of this arrow can be turned on or off, and the default arrow colour can be changed, in the Display Options dialog.

Note that the location of the Seismic Force display does NOT indicate the actual location of the force applied in the analysis. As with all other forces in SWedge, a Seismic Force is applied through the centroid of the wedge, during the analysis.