On 8 July 2020, an ML 4.2 earthquake occurred in the Xiaojiang fault zone along the eastern margin of the Tibetan Plateau. Applied ambient noise monitoring technique to the continuous waveforms from a near-fault small-aperture array, we obtain daily high-resolution variations in seismic velocity before and after the earthquake. When compared with environmental observations, we exclude these factors such as groundwater level, precipitation, temperature, and atmospheric pressure that might significantly influence the seismic velocity changes. We propose that the observed ∼10-day transitional phase from relatively high velocity to low velocity following the ML 4.2 earthquake, signifies a transition within the fault zone from a relatively compressional state to an extensional one. This transition could be an indicator of transient dilatation deformation during the long-term strike-slip process of the Xiaojiang fault, which is not easily detected by space geodetic measurements. When the fault zone is in extensional state, there is stronger strain-velocity sensitivity, which is verified by local long-period tidal strain.

中文翻译：

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青藏高原东南缘 ML 4.2 地震伴随的瞬态地震速度变化及其对断层滑移过程的影响


2020 年 7 月 8 日，青藏高原东缘的小江断裂带发生 ML 4.2 级地震。将环境噪声监测技术应用于近断层小孔径阵列的连续波形，我们获得了地震前后地震速度的每日高分辨率变化。与环境观测相比，我们排除了这些因素，例如地下水位、降水、温度和大气压力，这些因素可能会显着影响地震速度变化。我们提出，在 ML 4.2 地震后观察到的从相对高速到低速的 ∼10 天过渡阶段，意味着断层带内从相对压缩状态过渡到伸展状态。这种转变可能是小江断层长期走滑过程中瞬态膨胀变形的指标，空间大地测量不容易检测到。当断裂带处于伸展状态时，应变-速度敏感性更强，这可以通过局部长周期潮汐应变进行验证。