Subducting plate

The subducting plate feature provides the user with the ability to add a subducting slab to the GWB world. To define a slab, the user must specify the coordinates where the slab intersects with the surface of the world, which for a subducting plate represents the location of the trench. In the Cartesian coordinate system, coordinates are represented by [x, y] points (in meters), and in the spherical coordinate system coordinates are represented by [longitude, latitude] points (in degrees). Additionally, because the trench is simply a line on the surface, the user must also specify the direction that the subducting plate dips from the trench via the dip point. The dip point is also represented as a surface point ([x, y] in Cartesian, [longitude, latitude] in spherical).

Map-view of a world where a trench is defined with three coordinates (black points), and contains a slab dipping to the left towards the user-specified dip point (white point). The slab is coloured by the depth.

To create a slab that does not change along-strike, the user can simply specify a number of segments. Segments are defined through a length, a thickness, and an angle. When the angle and the thickness are input as single values and not as arrays, the resulting segment is defined by a straight line segment, and dips away from the trench towards the dip point at the specified angle, with a uniform thickness. However, the segment can vary in thickness if the user specifies thickness as an array of two values, in which case the segment will still be represented as a straight line segment, but will linearly vary from the first thickness to the second thickness across the length of the segment. If the user also inputs angle as an array of two values, the segment will be represented as a piece of a circle, where the dip of the segment varies linearly from the first angle to the second angle across the length of the segment. Any given segment can vary in thickness and in angle, and when multiple segments are defined the termination point of a given segment acts as the starting point of the following segment. Combining segments in this way enables a user to define extremely complicated slab geometries down-dip of the trench coordinates.

Cross section of a subducting plate feature showing how segments can create complicated slab geometries down-dip of the trench. Black region represents where the slab is located. The starting point of “Segment 0” is the trench, defined by the user-specified coordinates. The starting point of “Segment 1” is the end point of “Segment 0”, and so on.

Additional complexity can be introduced by specifying sections, which allow the user to vary the shape of the slab along-strike of the trench. If the trench is defined by N surface coordinates, then N sections can be specified, where each section is mapped to the corresponding coordinates of the trench. The sections are made up of M segments (M does not need to be equal to N, but each section MUST be composed of M segments), thereby creating N unique curves along-strike of the trench, and these sections are interpolated along strike using a Bezier interpolation to form a complex 3-dimensional slab that varies along-strike and down-dip.

Side view of the subducting plate feature showing how sections can be used to add along-strike complexity to the slab. Each of the sections are made up of unique segments, which are then interpolated along-strike using a Bezier interpolation. The slab is coloured by the depth.