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 19 99 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 thi n layers on the glide plane and as veins injected into cracks in the host r ocks, which are a few mm to 1 cm in thickness. Typical melting textures wit hin the pseudotachylyte include vesicles, glassy matrices, flow structures, and rounded and embayed clast shapes. Powder X-ray diffraction analysis ha s revealed a glass content of up to 50 wt% within the pseudotachylyte. Phys ical 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 sim ilar to 1600 degreesC. The geological and petrological data suggests that t hese pseudotachylytes formed by frictional melting generated from coseismic landsliding during the Chi-Chi earthquake.