Studies of Regional Phases and Discriminants in Asia

摘要

The following conclusions were obtained from studies under this contract: Lgpropagation in eastern Asia is fairly complex because of the presence of tectonic provinces with distinctive waves propagation characteristics. At the Chinese Kirnos stations, WMQ and KSH, high frequency Lg waves from Semipalatinsk are recorded well. At more distant stations, such as LZH and BJI, Lg amplitudes are small even for Mb>6.0 events. The low magnification of the Chinese Kirnos stations is a limiting factor. The recently installed CDSN stations provide excellent signal to noise ratios for eastern Asian events with magnitude greater than 4.5 or so across the network. Some events smaller than 4.5 may provide very clear surface waves. Regional phases are very prominently developed for paths that do not cross the Tibetan Plateau. A path with less than three hundred kilometers in the Plateau often means little discernible Lg waves. Regionalization studies of surface waves have allowed us to determine the dispersions in many tectonic provinces. This seems to be the most suitable way to determine the crustal structures of this area, with a high quality, but sparse, network. (jhd)