Frictional fusion due to coseismic landsliding during the 1999 Chi-Chi (Taiwan) M_L 7.3 earthquake

Fused materials (pseudotachylytes) generated from landsliding during the 1999 Chi-Chi (Taiwan) M_L 7.3 earthquake are found on the glide plane in Mio-Pliocene interbedded shale and siltstone. The pseudotachylytes occur as thin layers on the glide plane and as veins injected into cracks in the host rocks, which are a few mm to 1 cm in thickness. Typical melting textures within the pseudotachylyte include vesicles, glassy matrices, flow structures, and rounded and embayed clast shapes. Powder X-ray diffraction analysis has revealed a glass content of up to 50 wt% within the pseudotachylyte. Physical conditions of pseudotachylyte formation are estimated to have been <1.5 MPa corresponding to ca. 40 m depth, at a temperature of at least 1100-1600 °C. The geological and petrological data suggests that these pseudotachylytes formed by frictional melting generated from coseismic landsliding during the Chi-Chi earthquake.