This is a surface representation based on a collection of evenly spaced Locations (a discretized surface). Specifically, this is any entity that can provide the following information:

• Average Strike
• Average Dip
• Discretization Interval (or grid spacing)
• 2D Array of Locations that represent a discretized version of the rupture surface (where the first row represents the upper edge, or trace, and the other rows represent down-dip Locations):

loc 1,1	loc 1,2	loc 1,3	...
loc 2,1	loc 2,2	loc 2,3	...
loc 3,1	loc 3,2	loc 3,3	...
:	:	:	:

An example use of this is determining the shortest distance between a Site and a Rupture Surface (represented as an Evenly Gridded Surface), which simply involves computing the distance to all Locations in this array and keeping the smallest value.

The way in which the surface Locations are evenly spaced depends on the particular type of Evenly Gridded Surface. Those currently supported in OpenSHA include:

• Point Surface
• Frankel Fault Surface
• Stirling Fault Surface
• Subset Surface