REGIONAL WAVE-PROPAGATION IN CHINA AND ITS SURROUNDING REGIONS

A comprehensive study of the gross characteristics of high-frequency s eismic-wave propagation in China and its surrounding regions was accom plished to learn more about how regional geology affects high-frequenc y phases, Amplitudes of the regional seismic waves Sn and Lg relative to P coda were used to map lateral variations of shear-wave attenuatio n in the crust and upper mantle. Over 7000 digital seismogram from 13 broadband stations of the Chinese Digital Seismic Network and Global S eismic Network in the frequency range 0.5 to 5.0 Hz were visually exam ined. Propagation efficiencies of Sn and Lg were qualitatively analyze d by ranking their amplitudes relative to the P-wave coda. Efficient S n propagation is observed in the Tien Shan, Tarim Platform, southern T ibet, Yangzi Paraplatform, and Sino-Korean Platform, We have confirmed results of previous studies by finding a lack of Sn transmission in n orth central Tibet, the Ryukyu and Japan Arcs, Burma, and the Baikal R ift, An important observation, which has not been previously reported, is that Sn does not propagate across Mongolia The elimination of Sn a nd the occurrence of recent volcanism in north central Tibet and Mongo lia suggest that there is partial melt in the uppermost mantle beneath those regions. High-frequency Lg waves propagate efficiently for most of China, Indochina, and Mongolia. Lg signals are attenuated within c entral Tibet as well as along its southern boundary. Crustal structure variations along with an anomalously low-e crust are primarily respon sible for weakened Lg amplitudes in Tibet, Propagation paths across oc eanic crust in the Sea of Japan and the Andaman Sea show blockage of t he Lg phase as well. This investigation has relevance to Comprehensive Test Ban Treaty monitoring by showing where certain regional phases w ill or will not propagate efficiently.