Visualizing Multiple Earthquake Focal Mechanisms

If you select a group of faults in an area, you can see the similarities in their orientations on the stereonet.

Earthquake Focal Mechanisms Option on Stats button of  on table display window.

 

Focal planes on stereonet.  There are earthquakes produced from normal and strike slip faults, each with two focal planes.

  • The normal faults (green) mostly have strikes of about N45E to N90E, and dips either to the NW or the SE.  There is a fair amount of scatter.
  • The strike slip faults (blue) have strikes that are either about N10E or N80W, 90 degrees apart.  The dips are all very steep.

Poles to focal planes.  The pole is the line normal/perpendicular to the plane, and plots as a point on the stereonet.

  • The normal faults (green) have poles  in two groups, toward the north, and toward the south.
  • The strike slip faults (blue) have poles in two groups.  This looks like four groups, because a gently dipping line to the north is very close to a gently dipping line to the south.

 

  Dir directions for focal planes.  The dip direction lies on the plane, so the line will plot as a point on the great circle. 
  • The normal faults (green) have poles (normal to the fault plane) into two groups, toward the north, and toward the south.  While these look superficially like the poles to the focal planes, the dip directions are actually 90 degrees away from the poles.
  • The strike slip faults (blue) have poles in basically one group in the center of the net, because the dips are all very close to vertical.  However, there are dips to both the E-W, and to the N-S

This diagram can be used to set limits for looking for fault scarps in digital topography.

   

Earthquake Focal Mechanisms Option on Stats button of  on table display window.


Last revision 11/28/2015