Hierarchical Cluster Analysis of Dense GPS Data and Examination of the Nature of the Clusters Associated With Regional Tectonics in Taiwan

Collision of the Luzon Volcanic Arc is the primary causative factor behind the creation of Taiwan Island. Additionally, the indention of the Peikang basement highs in the Taiwan Strait and the back arc spreading of the Okinawa Trough are responsible for the characteristic tectonics in Taiwan. Identification of active tectonic boundaries is important for understanding neotectonics in Taiwan. We analyzed Global Positioning System (GPS) horizontal velocity data in Taiwan with a hierarchical cluster analysis method. We also developed a statistical scheme introducing information entropy to quantitatively assess the fuzziness of the obtained cluster boundaries, which enables us to distinguish a trustworthy discontinuity. The hierarchical representation, which is expressed by a dendrogram, suggests the relative importance of tectonic sources in this region. The major clusters, which appear at higher hierarchy, are likely to represent major tectonic features such as the Longitudinal Valley fault and lateral extrusion in southwest Taiwan. Those at lower hierarchy suggest velocity discontinuities associated with local geological structures such as active faults. For example, boundaries in east offshore Taiwan and southern Taiwan are identified without using geological information by this analysis. In addition to the identification of these clear tectonic boundaries, our statistical cluster assessment shows the existence of fuzzy cluster boundaries along the Coastal Plain and the Western Foothills, reflecting continuum deformation in west Taiwan.