MOHO OFFSET ACROSS THE NORTHERN MARGIN OF THE TIBETAN PLATEAU

Anomalous double-pulse teleseismic P-wave arrivals were observed at on e station near the northern margin of the Tibetan Plateau. The azimuth al dependence of the waveform distortion and its absence at nearby sta tions indicated that the distortion was produced by receiver-side crus tal heterogeneity. Modeling of the three-component data revealed a 15- to 20-kilometer Moho offset that occurs over a narrow Lateral range o f Less than 5 kilometers. This east-west-striking offset separates the thick Tibetan Plateau crust from the Qaidam Basin crust. Such a sharp crustal thickness change implies a weak Tibetan Plateau crust that th ickens vertically in response to penetration by India from the south a nd to blockage caused by a strong Qaidam Basin crust to the north.