Seismic Velocity Changes of the 2025 Myanmar M7.9 Earthquake
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摘要: 地震波速度变化是表征地下介质应力状态演化的关键指标，对理解地震孕育机制、破裂过程及震后调节行为具有重要意义.利用2025年3月28日缅甸M7.9级地震震源区4个固定台站的连续波形数据，采用背景噪声自相关方法分析了地震波速在震前、同震及震后三个阶段的动态变化特征.结果表明，在0.1~2 Hz频段范围内，震前阶段所有台站均观测到显著的地震波速下降现象，推测可能与实皆大型走滑断裂带在临震阶段的预滑活动或介质物理性质的渐进性改变有关.同震阶段地震波速变化呈现明显的空间差异性，震中距较近的台站表现出更大的波速变化幅度，表明近场区域受强地面运动的影响更为显著.震后阶段地震波速随时间呈现逐渐恢复的趋势，可能反映了台站下方介质的自愈合过程.研究结果为深入认识大型走滑断裂的孕震机理及震后介质愈合机制提供了新的观测依据.Abstract: Seismic velocity change serves as a crucial indicator for characterizing the evolution of stress states in subsurface structure, providing significant insights into earthquake nucleation mechanisms, rupture processes, and postseismic adjustments. This study utilizes continuous waveform data from four permanent stations located in the source region of the March 28, 2025, Myanmar M7.9 earthquake. By applying the ambient noise autocorrelation method, we analyze the dynamic changes in seismic wave velocity during the pre-seismic, co-seismic, and post-seismic phases. The results reveal that all stations observed a notable decrease in seismic wave velocity within the frequency range of 0.1-2 Hz during the pre-seismic phase, which may be attributed to pre-seismic slip or progressive changes in the physical properties of the media along the Sagaing large-scale strike-slip fault zone. During the co-seismic phase, the velocity changes exhibit significant spatial heterogeneity, with stations closer to the epicenter showing more pronounced variations, indicating stronger near-field ground motion effects. In the post-seismic phase, the wave velocity gradually recovers over time, likely reflecting the self-healing process of the subsurface media beneath the seismic stations. These findings provide new observational evidence for understanding the seismogenic mechanisms of large strike-slip faults and the post-seismic healing processes of subsurface structure.
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Key words:
- Myanmar M7.9 earthquake /
- autocorrelation /
- seismic velocity changes /
- Sagaing fault /
- geophysics
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图 1 区域地质构造、台站及历史强震(M > 6.5)分布
红色五角星为2025年3月28日缅甸M7.9级地震震中位置，蓝色三角形为台站位置，震源机制结果代表历史M > 6.5级的地震（Xiong et al.，2017）
Fig. 1. Regional tectonic setting, seismic stations and historical strong earthquake (M > 6.5) in the study region
图 2 区域地震活动性
灰色圆圈为1964年-2021年的地震目录，黑色五角星为缅甸M7.9级主震，彩色圆圈为其余震，左下角附图为缅甸地震序列M-T图
Fig. 2. Regional seismic activity
图 3 NGU台5小时叠加窗口的自相关函数(黑色实线为缅甸地震发震时刻)
Fig. 3. The autocorrelation functions with a 5-hour stacking window at station NGU (the black solid line indicates the origin time of the Myanmar earthquake)
图 4 压缩拉伸法进行波速测量示例
右侧红色曲线为参考波形，蓝色曲线为不同经过不同拉伸系数处理后的波形
Fig. 4. An example of velocity measurement using compression/stretching method
图 5 NGU台不同频率范围随时间的相对波速变化
黑色实线为缅甸地震发震时刻
Fig. 5. Temporal variations in relative velocity changes at station NGU for different frequency bands
图 6 NGU台0.1~2 Hz频率范围不同滑动窗口的相对波速变化
黑色实线为缅甸地震发震时刻
Fig. 6. Relative velocity changes at NGU station with different stacking time length in a frequency band of 0.1‒2 Hz
图 7 NGU台2025年3月28日自相关函数变化
Fig. 7. The autocorrelation function variations at NGU station on March 28, 2025
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