Abstract: The W-phase is a long period phase arriving between the P and S wave phases of a seismic source, theoretically representing the total near-and far-field long-period wave-field. Recent study suggests that the reliable source properties of earthquake with magnitude greater than ~M_W4.5 can be rapidly inverted by using the W-phase waveform data. With the advantage of W-phase, most of major earthquake research institutes in the world have adopted the W-phase based inversion method to routinely assess focal mechanism of earthquake, such as the USGS and GFZ. In this study, the focal mechanism of the August 8, 2017 M7.0 Sichuan Jiuzhaigou and August 9, 2017 M6.6 Xinjiang Jinghe earthquakes were investigated by W-phase moment tensor inversion technique using global seismic event waveform recordings provided by Incorporated Research Institutions for Seismology, Data Management Center. To get reliable focal mechanism, we strictly select raw waveform data and carry out inversion in stages. At first, we discard waveform without correct instrument information. Then we carry out an initial inversion using selected waveform data to get primary results. Using the preliminary results as input, we carry out grid-search based inversion to find the final optimal source parameters. The inverted results indicate that the August 8, M7.0 Sichuan Jiuzhaigou shock resulted from rupturing on a NW-trending normal fault with majority of strike-slip movement. The parameters of two nodal planes are strike 152.7°, dip 61.4°, rake -4.8° and strike 245.0°, dip 85.8°, rake -151.3° respectively, and focal depth is 14.0km. The August 9, Xinjiang Jinghe M6.6 shock resulted from rupturing on a south-dipping thrust fault with left-lateral strike-slip. The parameters of two nodal planes are strike 100.6°, dip 27.5°, rake 114.1° and strike 259.3°, dip 65.1°, rake 78.0°, and the focal depth is 16.0km. The direction of two nodal planes is consistent with regional seismotectonic background.

Key words: W-phase, moment tensor inversion, Jiuzhaigou earthquake, Jinghe earthquake

摘要： 文中利用地震学联合研究会（IRIS）数据管理中心提供的全球地震事件波形资料，基于W-Phase震相资料，采用矩张量反演方法研究2017年8月8日和9日分别发生在四川省九寨沟的M7.0地震和新疆精河M6.5地震的震源机制。反演结果显示2017年8月8日发生的四川省九寨沟M7.0地震的2个节面分别为走向152.7°、倾角61.4°、滑动角-4.8°和走向245.0°、倾角85.8°、滑动角-151.3°，震源深度为14km，该结果表明九寨沟地震以走滑型为主，2个节面分别呈NW向和SE向展布。2017年8月9日发生的新疆精河M6.6地震的2个节面分别为走向100.6°、倾角27.5°、滑动角114.1°和走向253.9°、倾角65.1°、滑动角78.0°，震源深度为16km，该结果表明精河地震为以逆冲型为主的地震破裂事件，2个节面均为近EW向，震源性质与区域地震构造背景一致。

关键词: W-Phase震相, 矩张量反演, 九寨沟地震, 新疆精河地震