本文应用ISOLA近震全波形方法，以2017年1月4日西藏仲巴4.7级地震为例，反演稀疏台网记录的中小地震震源机制解。该地震反演所得最佳双偶机制参数为：节面Ⅰ的走向109°/倾角85°/滑动角-177°，节面Ⅱ的走向19°/倾角88°/滑动角-4°，最佳矩心位置为30.590°N、83.784°E，最佳质心深度为6km，矩震级M_W4.6。震源机制反演结果表明此次地震是一次走滑型为主的事件，其与震源区域附近历史地震震源机制解具有相同性质。本文还应用CSPS初动扫描法，利用P波初动资料和近震波形联合约束反演此次地震的震源机制，并与ISOLA近震全波形反演结果进行比较，结果表明，联合少量台站的的三分量波形数据，能够定量地判断最佳震源机制解，降低了P波初动反演结果的非唯一性，同时也约束了由于少量台站参与全波形反演引起的解的不稳定性。本文研究为中小地震震源参数测定提供了一种简单有效的方法，具有较高的稳定性和可靠性。

We take an M_S4.7 earthquake that occurred at Zhongba, Tibet on January 4, 2017 as an example. The focal mechanism solution is inverted with the broadband waveform from a sparse network of Tibetan Regional Digital Seismic Network using the ISOLA full-waveform method. The best double-couple solution of the earthquake for two nodal planes is:strike=109°/dip=85°/Rake=-177° for Noodle 1 and strike=19°/dip=88°/Rake=-4° for Noodle 2. The centroid location and depth is 30.590°N, 83.784°E/6km;the moment magnitude is M_W=4.6, which shows a strike-slip faulting mechanism. The joint constraint inversion is conducted using the CSPS method with the P-wave polarity and local and near regional waveform data. The comparison of the results from two methods, including ISOLA and CSPS, shows that combining with the three-component waveform from a few stations can not only determine quantitatively the best solution but also avoid the non-uniqueness from the P-wave polarity inversion and constrain the instability due to the inversion with data from very few stations. A simple but effective way with high stability and reliability is provided in this paper to determine the focal mechanism solution of a small and moderate earthquake with the data from a sparse network.

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国家重点研发计划重点专项“海洋重大灾害预报技术研究与示范应用”（2016YFC1401506）资助