We apply a spectral decomposition approach to isolate the source spectra from propagation and site effects and, in turn, to estimate the source parameters of small‐to‐moderate earthquakes that occurred in central Italy. The data set is composed of about 400,000 waveforms relevant to 4111 earthquakes in the moment magnitude range 1.5–6.5, recorded by a high‐density network of stations installed in the study area. We first investigate the reliability of the source parameters for small magnitudes through numerical simulations. We generate synthetic spectra for different source scaling models and near‐surface attenuation effects, considering the source–station geometry and the data availability of the central Italy data set. Our analysis with synthetics shows that the spectral decomposition is effective in isolating the source contributions from other factors. Moreover, the analysis of the residual distributions suggests that moment magnitude 1.8 is the lower bound for the retrieval of reliable Brune’s source parameters, although we observe an increase of residual’s variability below magnitude 3, and the estimated source parameters could be biased below magnitude 2.3. Remarkably, the assessment of the stress drop Δσ for small events is strongly hampered by site‐specific attenuation near the surface. In view of the results with synthetics, we analyze the source parameters of earthquakes recorded in central Italy. The corner frequency versus seismic moment relationship describes a source scaling in which Δσ increases with increasing moment magnitude Mw⁠, the mean Δσ varying from 0.1 MPa for Mw<2 to 7.9 MPa for Mw>5⁠. In particular, Δσ increases mainly for Mw in the ranges 2.5–3 and 4.5–5.2. The corner frequencies estimated from the apparent source spectra do not show any dependence on hypocentral distance and magnitude, confirming that uncorrected anelastic attenuation effects do not significantly bias the results.

中文翻译：

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意大利中部小事件源参数的可靠性：光谱分解分析在合成数据和真实数据中的应用

我们采用频谱分解方法将源频谱与传播和站点效应隔离开来，然后估算意大利中部发生的中小地震的震源参数。该数据集由大约400,000个与1.511-6.5矩范围内的4111地震有关的波形组成，由安装在研究区域中的高密度台站网络记录。我们首先通过数值模拟研究小幅值源参数的可靠性。考虑到源站的几何形状和意大利中部数据集的数据可用性，我们为不同的源比例模型和近地表衰减效应生成了合成光谱。我们对合成物的分析表明，光谱分解可有效地将源的贡献与其他因素隔离开。此外，对残差分布的分析表明，矩量为1.8是检索可靠的Brune源参数的下界，尽管我们观察到残差的可变性在量级3以下有所增加，并且估计的源参数可能会在量级2.3以下偏移。值得注意的是，小事件的应力下降Δσ的评估受到地表附近特定位置的衰减的强烈阻碍。根据合成的结果，我们分析了意大利中部记录的地震震源参数。拐角频率与地震力矩的关系描述了震源标度，其中Δσ随着力矩大小Mw？的增加而增加，平均Δσ从Mw <2的0.1 MPa到Mw>5⁠的7.9 MPa不等。特别是，Δσ主要在2.5-3和4.5-5.2范围内的Mw处增加。从视在源频谱估计的转折频率不显示与震中距离和震级的任何依赖关系，从而证实了未经校正的弹性衰减效应不会明显偏向结果。