High seismicity coupled with high population density creates a recipe for high seismic risk in Taiwan. Taiwan is located at the convergences of the Eurasian and Philippine Sea plates. These convergences result in the development of an accretionary wedge. A basal decollemont bounds the NE-SW trending thrust packages. The most Eastern thrust package, the Central Range, experiences high erosion rates and exhumation rates which may induce high seismicity. Paleoseismic indicators improve the ancient seismic history and may aid in the constraint of geologic processes of an accretionary wedge. Pseudotachylytes, known as earthquake fossils, form by frictional melting during seismic slip. Cataclasites form by comminution during sliding. Frictional melts serve as a window to the fault plane. Pseudotachylytes may allow for the assessment of focal parameters through the utilization of fault plane geometry and slip surface properties. This study provides the first microstructural evidence for fault pseudotachylytes at the Hoping River locality in Eastern Taiwan. The 3.3 Ma Hoping River frictional melt evidences an ancient Mw 6.4 ±0.40 earthquake. This pseudotachylyte demonstrates an oblique fault with a reverse component which corresponds to the orientation of the thrust packages in the accretionary wedge. Sense of slip of both pseudotachylytes and cataclasites suggest a uniform stress field. Narrow fault cores suggest high strain localization. Coeval pseudotachylyte and quartz-calcite veins suggest shear heating as a mechanism, if a fluid reservoir along the basal decollemont in Taiwan exists.