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The NNR (No-Net-Rotation)-MORVEL (Mid-Ocean Ridge VELocity) 56 is a set of angular velocities describing the motions of 56 plates relative to a No-Net-Rotation reference frame. These plates can be adjusted in terms of non overlapping polygonal regions, separated by plate boundaries on a unit sphere. During the calculation on the kinematic parameters for these 56 plates in a NNR reference frame using the International Terrestrial Reference Frame (ITRF) velocity field, the geometric parameters of tectonic plates play a significant role in establishing an absolute plate motion model based on space geodesy results. The computational method for these geometric parameters implemented as a FOR TRAN90 program is described in this paper, allowing an evaluation of the area and the inertia tensor of a polygonal region on a unit sphere. This program is mainly built on a triangulation algorithm and the adaptive Simpson's double integral method for spherical polygons, which produces highly reliable results for all 56 modern plates.

NNR-MORVEL56板块运动模型描述了全球56个构造板块在无整体旋转参考架下的角速度运动参数。这些板块可以近似描述为单位球上的无重叠球面多边形区域。用ITRF速度场计算这56个板块相对于无整体旋转参考架下的绝对运动时,板块的几何参数起着至关重要的作用。详细给出了计算板块几何参数的方法并且编写了FORTRAN90程序以供参考,使得计算单位球上板块的面积和转动惯性张量得以实现。文中的计算方法和程序主要采用球面三角算法和自适应辛普森双积分算法,并对全球56个板块的几何参数进行了计算,得到了较为可靠的计算结果。