Utility of Regional Chinese Seismograms for Source and Path Studies in Central Asia

摘要

Regional surface waves recorded at the Urumchi station located about 700 km north of the Tibetan Plateau in the Sinkiang Province are used to study East Kazakh explosions and wave propagation in central Asia. The data consist of broadband (flat to displacement between 0.1 and 10 Hz), photographic records from an SK Kirnos galvanometric system. Simultaneous inversion of Rayleigh wave phase and group velocities for the path from East Kazakh through the Dzhungarian Basin yields a crustal model dominated by the presence of very low velocities and a strong positive velocity gradient above 15 km depth. Velocities below 15 km depth are not significantly different from other continental structures underlain by Paleozoic or Precambrian basement. This model is consistent with geologic evidence indicating that most of the path is characterized by the presence of up to 10 km of sediments overlying a Paleozoic basement. Source studies were made on seven East Kazakh explosions detonated in the time period between June 1980 and April 1981. These studies involved estimation of seismic moments using models of explosion sources with associated tectonic release. The largest explosion studied occurred on 9/14/80 and had an m/sub b/ of 6.2 and a seismic moment of 2.7 x 10 exp 23 dyn-cm. The observed amplitude spectra of Rayleigh waves are richer in high frequencies than predicted by explosion source models with tectonic release. This could be caused by a path effect involving seismic wave focusing by the large sedimentary basin between East Kazakh and the Urumchi station, although source medium effects cannot be ruled out. 30 references, 5 figures, 2 tables. (ERA citation 09:031834)