Statistics on Directional Data

Abstract

Methods for analyzing circular and spherical data are widely used in earth sciences. For instance, structural geologists measure and analyze the orientation of slickensides (or striae) on fault planes. Circular statistics is also common in paleomagnetic applications. Microstructural investigations include the analysis of grain shapes and quartz c-axis orientations in thin sections. Paleoenvironmentalists also reconstruct paleocurrent directions from fossil alignments (Fig. 10.1). In principle, two types of directional data exist in earth sciences: directional data sensu stricto, and oriented data. Directional data have a true polarity, such as the paleocurrent direction of a river as documented by flute marks, or the flow direction of a glacier as indicated by glacial striae. Oriented data describe axial data and lines without any sense of direction, such as the orientation of joints.