基于重复地震的松潘—甘孜地块边界断层滑移速率和波速变化研究

The Songpan-Ganze terrane located in the northeastern part of the Tibetan Plateau, is bounded by the Xianshuihe-Yushu-Mani fault zone in the south, the East Kunlun fault zone in the north and the Longmenshan in the east. As the transition zone from the Tibetan Plateau to the Yangtze platform, the Songpan-Ganze terrane underwent extensive tectonic deformation and faulting movement during the uplift process of the Tibetan Plateau, since the strong Sichuan basin at the eastern edge of the plateau blocked the eastward movement of the plateau. Thus, the Songpan-Ganze terrane has high seismic activities and many strong earthquakes occurred in this region. In this project, by collecting a huge amount of seismic data recorded at stations close to the fault zones at the edge of the Songpan-Ganze terrane, we will first use a weighted waveform template matching technique to identify more microearthquakes to complete the earthquake catalogue. Then the waveform cross-correlation technology together with the double-difference location method will be used to extract repeating earthquakes. Based on the seismic moments and repetition intervals of the repeating earthquakes, the fault slip rates at different depths can be obtained. By analyzing the waveform shape and delay time of the repeating earthquakes, we can obtain the spatial and temporal change of fault zone characteristics. The results will provide important information and basis for better understanding the seismogenic tectonic environments and assessing the seismic risks in the Songpan-Ganze. The results will be of great significance to understand the deep dynamic mechanism of strong earthquakes in the Tibetan Plateau and the dynamics of the Tibetan Plateau.

松潘—甘孜地块位于青藏高原东北部，南以玛尼—玉树—鲜水河断裂带为界，北以东昆仑断裂带为界，东以龙门山断裂带为界。松潘—甘孜地块作为青藏高原向扬子地台的过渡带，在以高原为中心的隆升过程中，高原东缘由于受到相对坚硬而稳定的四川盆地阻挡，经历了强烈的构造变形和断裂错动，因此松潘—甘孜地块也是中国大陆强震频发地区。本项目拟通过收集松潘—甘孜地块边界断层附近台站多年地震观测资料，通过改进的加权波形模板匹配技术进行微震识别和定位，完善地震目录，采用波形互相关技术结合地震精定位来提取重复地震，然后利用重复地震的地震矩和重复间隔计算断层不同深度的滑移速率，分析重复地震的波形和到时获取断层介质的波速变化，从而为深入探讨松潘—甘孜块体边界断层的大震孕震环境和地震危险性评估提供重要依据。相关结果对认识青藏高原强震活动的深部动力机制和青藏高原动力学研究也都具有重要的科学意义。

松潘—甘孜地块位于青藏高原东北部，南以玛尼—玉树—鲜水河断裂带为界，北以东昆仑断裂带为界，东以龙门山断裂带为界。松潘—甘孜地块作为青藏高原向扬子地台的过渡带，在以高原为中心的隆升过程中，高原东缘由于受到相对坚硬而稳定的四川盆地阻挡，经历了强烈的构造变形和断裂错动，因此松潘—甘孜地块也是中国大陆强震频发地区。本项目收集了松潘—甘孜地块边界断层附近青海省和四川省数字地震台网共327个台站记录的多年地震观测资料，通过改进的加权波形模板匹配技术，结合基于深度学习的地震去噪技术进行微震识别和筛选，获得研究区青海甘孜—玉树断裂带、东昆仑断裂带东段、龙门山断裂带附近的完备的地震目录，采用波形互相关技术结合地震精定位来识别重复地震，然后利用重复地震的地震矩和重复间隔计算断层不同深度的滑移速率。重复地震的结果表明，在四川龙门山断裂带附近获得10组重复地震，断层滑动速率为2.5-9mm/yr, 平均滑动速率约为5mm/yr；在青海甘孜—玉树断裂带识别6组重复地震，滑动速率为3.3-10.8mm/yr，平均断层滑动速率为7.4mm/yr。基于完备的地震目录进行地震活动性分析，四川龙门山断裂带附近在汶川地震震后一年的b值整体较低，2016年b值变高，反映了龙门山断裂带的震后愈合。我们的结果为深入探讨松潘—甘孜块体边界断层的大震孕震环境和地震危险性评估提供重要依据，对认识青藏高原强震活动的深部动力机制和青藏高原动力学研究也都具有重要的科学意义。