Production‐induced earthquakes in the Groningen gas field caused damage to buildings and concerns for the population, the gas‐field owner, and the local and national authorities and institutions. The largest event (⁠ML=3.6⁠) occurred in 2012 near Huizinge, and, despite the subsequent decision of the Dutch government to reduce the gas production in the following years, similar magnitude events occurred in 2018 and 2019 (⁠ML=3.4⁠). Thanks to the improvement of the local seismic networks in the last years, recent events provide a large number of recordings and an unprecedented opportunity to study the characteristics of induced earthquakes in the Groningen gas field and related ground motions.In this study, we exploit the S‐wave Fourier amplitude spectra recorded by the 200 m depth borehole sensors of the G network from 2015 to 2019 to derive source and attenuation parameters for ML≥2 induced earthquakes. The borehole spectra are decomposed into source, attenuation, and site nonparametric functions, and parametric models are then adopted to determine moment magnitudes, corner frequencies, and stress drops of 21 events. Attenuation and source parameters are discussed and compared with previous estimates for the region. The impact of destructive interference of upgoing and downgoing waves at borehole depth on the derived parameters is also discussed and assessed to be minor.The analysis of the apparent source spectra reveals that several events show rupture directivity and provides clear observations of frequency‐dependent directivity effects in induced earthquakes. The estimated rupture direction shows a good agreement with orientation of pre‐existing faults within the reservoir. Our results confirm that rupture directivity is still an important factor for small‐magnitude induced events, affecting the amplitude of recorded short‐period response spectra and causing relevant spatial ground‐motion variability.

中文翻译：

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钻孔记录的频谱反演对格罗宁根气田地面运动的衰减，应力降和诱发事件的方向性

格罗宁根（Groningen）气田的生产性地震造成建筑物损坏，并给居民，气田所有者以及地方和国家主管部门和机构造成困扰。最大的事件（ML =3.6⁠）发生在2012年的Huizinge附近，尽管荷兰政府随后决定在接下来的几年中减少天然气产量，但在2018年和2019年发生了类似规模的事件（⁠ML=3.4⁠ ）。由于最近几年当地地震网络的改善，最近发生的事件提供了大量记录，并且为研究格罗宁根气田诱发地震的特征和相关地面运动提供了前所未有的机会。我们利用2015年至2019年G网络的200 m深钻孔传感器记录的S波傅里叶振幅谱来推导ML≥2诱发地震的震源和衰减参数。井眼频谱被分解为震源，衰减和现场非参数函数，然后采用参数模型确定21个事件的矩量，拐角频率和应力降。讨论了衰减和源参数，并将其与该区域的先前估计值进行了比较。还讨论了井深处上行波和下行波的破坏性干扰对导出参数的影响，并将其影响较小。对表观震源频谱的分析表明，一些事件显示了破裂方向性，并提供了对诱发地震中频率相关方向性影响的清晰观察。估计的破裂方向与储层内已存在的断层的方向显示出良好的一致性。我们的结果证实，破裂方向性仍然是小震级诱发事件的重要因素，影响记录的短周期响应谱的振幅并引起相关的地面运动变化。