收集、整理四川省地震台网2013年5月至2017年9月产出的震相观测报告数据，采用单台多震和达法，重点分析2017年8月8日九寨沟MS 7.0强震前龙门山断裂带中北段地区波速比变化特征。结果表明：龙门山断裂带中段西侧的茂县地震台，在发震前2年左右，波速比出现一次持续时间约一年半的下降异常；发震前半年左右，波速比出现明显回返特征，波速比回返至均值上下时即发生九寨沟MS 7.0地震；震源区周边其他6个地震台波速比在发震前变化较平稳。茂县地震台波速比低值异常对判定九寨沟MS 7.0强震前龙门山断裂带中北段可能存在孕震体具有重要参考价值。
Based on the seismic phase data recorded by Sichuan Digital Network from May of 2013 to Septemper of 2017, the variation of wave velocity ratio vP/vS in the middle-northern Longmenshan fault before Jiuzhaigou MS 7.0 earthquake that occurred on Aug.8, 2017 is analyzed by using Wadati method of single station and multi-earthquake. The results show that at MXI station, which is in the western side of middle Longmenshan fault, the velocity ratio decreased for a duration of almost 1.5 years in two years before the earthquake, and it appeared a obvious recovery of vP/vS ratio half a year before the earthquake, which occurred when the vP/vS went up to the mean value, while the ratio did not show abnormal variation at the other six stations. The low wave velocity ratio of MXI before the earthquake may have important reference value for the possible existence of the seismogenic body in the middle-northern Longmenshan fault before Jiuzhaigou earthquake.
2018,39(3): 39-44 收稿日期：2018-03-27
DOI：10.3969/j.issn.1003-3246.2018.03.006
基金项目：河南省地震局数字地震学研究创新团队科研项目
作者简介：邢康(1989-),男,助理工程师,主要从事测震台网监测和分析预报工作。E-mail:1063368465@qq.com
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