Shear waveQstructure and its lateral variation in the crust of China and surrounding regions

Abstract

SUMMARY We have obtained three-layer crustal models of shear wave Q (Qμ) for several surface wave paths in China and peripheral regions using a single-station, multimode method in which amplitude spectra of fundamental-mode and higher-mode Rayleigh waves, computed for known source depths and mechanisms, are compared to measured spectra. The three layers, totaling 60 km in thickness, roughly comprise the entire crust in the Tibetan plateau and include both the crust and part of the uppermost mantle in other regions where the crust is thinner. Qμ in the shallowest layer, 10 km thick, is lowest (about 40) in the western portion of the Tibetan plateau and highest (about 250) in southeastern China. In the middle layer, at 10–30 km depth, Qμ is lowest (60–80) beneath Tibet and the Pamir thrust system and highest (120–140) in central China and parts of the Sino-Korean platform. Uncertainties of Qμ in the deepest layer, at 30–60 km depth, are much greater than in the upper two layers but available results suggest that Qμ is lowest (about 80) under the Pamir thrust system and highest (about 180) under southern Mongolia. The densities of event and station coverage, although wanting in some regions, allow us to develop the first regionalized maps of crustal Qμ variation for continents. The maps, for depth ranges 0–10 km and 10–30 km, generally show good agreement with Q results obtained earlier with other phases and good correlation with the tectonics of this active region.