Crustal perturbations related to seismic activity can generally be observed with the occurrence of a large magnitude event. For less energetic seismic sequences though, the associated transient crustal variations are questionably measurable, and their observation gets easily obscured by relatively stronger perturbations such as the ones related to hydrological processes. In this study we reveal the significant role that terrestrial water-storage variations play in governing temporal crustal changes in the tectonically active Northern Apennines of Italy, and discuss the potential of accounting for its correction in order to monitor the relatively weaker transient perturbations caused by local seismic swarms. This area is characterized by an extensive level of low-energetic seismic activity, typically clustered in time and space, of which three main seismic swarms outstand during the 12 year period of study (2010–2021). Our analysis compares independent observations and processing methods of Global Navigation Satellite System measurements and ambient seismic noise recordings. We adopt a multivariate statistical approach to discriminate between independent sources of ground deformation, and seismic noise cross-correlation analysis to monitor relative seismic-velocity variations. The result shows how the perturbation effects produced by variations in total water content are dominant in both time series of ground deformations and seismic-velocity variations. After correcting for the water-related variation effects, our monitoring results reveal perturbations in the crustal properties whose activation time and depth range correlate with the occurrences of the seismic swarms.

中文翻译：

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Alto Tiberina 断层带的地壳变形和地震速度扰动（意大利北亚平宁山脉）


与地震活动相关的地壳扰动通常可以在大震级事件的发生时观察到。然而，对于能量较低的地震序列，相关的瞬态地壳变化是值得怀疑的，并且它们的观察很容易被相对较强的扰动（例如与水文过程相关的扰动）所掩盖。在这项研究中，我们揭示了陆地储水变化在控制构造活跃的意大利北亚平宁山脉时间地壳变化中发挥的重要作用，并讨论了解释其校正的潜力，以便监测由局部地震群引起的相对较弱的瞬态扰动。该地区的特点是广泛的低能量地震活动，通常集中在时间和空间上，其中三个主要的地震群在 12 年的研究期间（2010-2021 年）突出。我们的分析比较了全球导航卫星系统测量和环境地震噪声记录的独立观测和处理方法。我们采用多元统计方法来区分独立的地面变形源，并采用地震噪声互相关分析来监测相对地震速度变化。结果表明，总含水量变化产生的扰动效应在地面变形的时间序列和地震速度变化中都占主导地位。在校正了与水相关的变化效应后，我们的监测结果揭示了地壳特性的扰动，其激活时间和深度范围与地震群的出现相关。