科研之友
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摘要
We imaged the azimuthal anisotropy of Rayleigh wave phase velocity (10-60 s) in northeast North China Craton using the teleseismic data recorded by a dense temporary array, and then inverted for the 3-D azimuthal anisotropy of the crust and uppermost mantle (20-110 km). The results reveal that the azimuthal anisotropy varies both horizontally and vertically. Obvious stratified azimuthal anisotropy is shown in the Central Orogenic Belt, where the fast direction is NE-SW to NNE-SSW in the depth range of 20-40 km and changes to NW-SE to NWW-SEE in the depth range of 60-110 km. In the depth range of 30-40 km, a prominent low velocity belt is shown on the southwest of Zhangjiakou-Penglai fault zone (ZPFZ) and the fast direction is subparallel to the strike of the low velocity belt. Distinct lateral variations of azimuthal anisotropy are clearly shown at 110 km. Our results provide new evidence for the existence of upwelling asthenosphere beneath the Datong volcano and support the assumption that ZPFZ may act as the channel of upwelling asthenosphere. Historical strong earthquakes (M >= 6.0) mainly occurred in the transition zone between low and high velocity anomalies in the upper and middle crust. The upwelling asthenosphere may prompt the generation of large earthquake.
