云南地区地壳各向异性及其动力学意义

Crustal anisotropy beneath the Yunnan region and dynamic implications

本文使用中国地震局地壳应力研究所2010—2011年期间在云南地区布设21个宽频带野外流动地震台记录到的波形资料,经时间域迭代反褶积求取远震接收函数,并挑选高质量Pms(莫霍面转换)震相,利用切向能量最小化方法获得283对高信噪比的径向和切向对应的Pms分裂参数,从而得到云南地区各台下方地壳各向异性.结果显示,研究区内慢波时间延迟量在0.125s和0.40s之间变化,平均为0.25s,且各向异性强弱与构造分布有一定相关性.在扬子地台和保山地块表现为相对较强的各向异性,而思茅地块相对弱些,说明这些块体受下地壳流的影响作用各不相同.从各向异性快波方向分布来看,在扬子地台和思茅地块除红河断裂带和澜沧江断裂带走向变化明显地区(如YNL04和YNL12台)外,各向异性方向均与断裂带走向近似平行,说明研究区内大型断裂带控制着下地壳流的构造变形.腾冲地区的各向异性与其他三个块体均不相同,在该块体内部各向异性快波方向近似呈现出以火山为中心发散状分布,可能说明腾冲火山下方地幔热物质上涌到达下地壳后受上地壳的阻挡作用向四周发散的原因.

In this study, we chose high-quality Pms （Moho converted） phases from the receiver functions which were obtained by using the time domain iterative deconvolution of waveforms. These waveform data were recorded by the 21 temporary seismic stations in the Yunnan region during 2010 and 2011, which were deployed by the Institute of Crustal Dynamics, CEA. Using the transverse energy minimal method, we obtained the crustal anisotropy beneath the Yunnan region from the 283 pairs of splitting parameters with high signal-to-noise ratios and unambiguous Pms phases. Our results show that delay times between fast and slow Pms range from 0. 125 to 0.40 s with an average of 0.25 s, and the strength of anisotropy is related to the tectonics. The Yangtze and Baoshan blocks show a relative stronger anisotropy, whereas the Simao block has a weaker one, suggesting the different effects of the lower crustal flow. Except for the region （stations YNL04 and YNL12） where the orientations of the Red River and Lancang River faultschange rapidly, the polarization direction of the fast wave is approximately parallel to the orientation of faults, implying that the large-scale faults may control the deformation of the lower crustal flow. Distinguished from other blocks, the Tengchong block shows a scatter-shaped direction in the fast polarization, possibly suggesting that the upwelling flow has been obstructed when it meets the upper crust.