川滇地区Lg波Q值层析成像

利用云南和四川数字地震观测台网记录的数字化地震资料，开展了川滇地区不同频率的Q_Lg层析成像研究，反演结果的空间分辨率小于100 km.反演结果表明，川滇地区介质的横向不均匀性强烈，Q_Lg高低值差异显著.川滇地区显著的高衰减区有川滇菱形块体的东南边界（即沿鲜水河至安宁河以及思茅—澜沧—普洱区），滇西北地区、龙门山断裂以西松潘—茂文地区、巴塘及理塘强震区等，Lg波高衰减区的分布与构造活动强烈、强震活动或大震破裂造成介质破碎区、低速区等相关，表明构造活动强烈或大震破裂造成的介质破碎、热物质沿活动断裂上涌等可能是川滇地区低Q_Lg的主要成因.显著的低衰减区有川东盆地、滇东南地区以及金沙江、怒江断裂的中段区域，滇中块体内部也呈现出相对的低衰减特征.Lg波低衰减区与地震活动性弱、速度正异常等相关，表明川滇地区Lg波的低衰减区与地壳变形、地震活动性及水热活动弱、块体稳定等有关.

Tomography of QLg in Sichuan-Yunnan Zone

In this study we obtained the tomography results of Q_Lg in Sichuan-Yunnan region, separately for each frequency, by using seismic wave data recorded by Yunnan and Sichuan seismic networks. The spatial resolution of our result is less than 100 km. Our results demonstrate that strong heterogeneity exists in the studied region, showing large difference between the highest and lowest Q value. The obvious high attenuation regions include the southeast edge of Sichuan-Yunnan rhombic block from Xianshuihe fault zone to Anninghe fault zone, the Simao-Lancang-Pu′e region, the Songpan-Maowen region to the west of Longmenshan fault zone, as well as the Batang and Litang strong earthquake region. According to our result, high attenuation of Lg waves corresponds to strong seismic active zones, ruptured area of large earthquakes, high terrestrial heat activity, and low velocity. It demonstrates that broken medium caused by strong tectonic activity or large earthquakes and heat flow upwelling along active faults may be the main reasons of low Q_Lg in Sichuan-Yunnan region. The obvious low attenuation regions include the Sichuan basin, the eastern block of Yunnan region, and the middle part of Jinshajiang and Nujiang fault zones. The interior of Dianzhong block also shows lower attenuation than the nearby area. Low attenuation regions correspond to the stable tectonic block, weak tectonic activity and high velocity. It shows that low attenuation of Lg wave in Sichuan-Yunnan region is correlated with small crustal deformation, low seismic activity, weak hydrothermal activities and stable block.