Characteristics of Seismic-source Spectral Parameters of Small Earthquakes in Yishu Fault Zone
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摘要: 利用山东台网记录的2010—2020年沂沭断裂带范围内的地震波形资料,基于高频截止模型,以理论震源谱对观测震源谱之间的最小绝对残差值作为目标函数,使用稳健的最小二乘法估计模型参数,得到93个地震震源谱的特征参数和震源参数,对不同震源参数之间的定标关系及视应力的时空特征进行分析。研究结果表明,高频截止模型的理论震源谱对观测震源谱有较好的拟合效果,能够明显改善拐角频率识别效果,因此该模型更适用于观测震源谱;沂沭断裂带中小地震的拐角频率为2~15 Hz,与矩震级有较好的相关关系,震级越大,拐角频率越低;地震矩
$ {M}_{0} $ 与震级$ {M}_{{\mathrm{L}}} $ 在单对数坐标系下存在较好的线性关系,利用稳健函数线性拟合,可表示为$ \mathrm{log}{M}_{0}=1.096{M}_{{\mathrm{L}}}+9.78 $ ;地震视应力的时间分布特征表明,沂沭断裂带2012—2014年地震视应力偏高,地震强度和频次明显增加,2016年后地震视应力有所降低,地震强度和频次有所降低;沂沭断裂带地震多发生在高视应力内部和边缘地区,断裂带中南部的莒南-临沂和断裂带北段的安丘段存在明显高视应力集中区,这些区域为沂沭带未来可能发生中强地震的潜在震源区,有必要对高视应力区的地球物理特征进行监测。Abstract: Using the seismic waveform data in the Yishu fault zone during 2010-2020 recorded by the Shandong Seismic Network, based on the High-cut model, the minimum absolute residual between the theoretical source spectrum and observed source spectrum is taken as the objective function, and the model parameters are estimated by the robust least squares method, the characteristic parameters of the source spectrum and source parameters of 93 earthquakes were obtained. Through the analysis and discussion of the scaling relationship between different source parameters and the spatiotemporal characteristics of apparent stress, the following conclusions are obtained. The results show: (1) The theoretical spectrum of the High-Cut source model has a good fitting effect on the observation spectrum, which can be significantly improve the corner frequency identification, indicating that the theoretical model is more suitable for observing the source spectrum; (2) The corner frequency of medium and small earthquakes in Yishu belt is in the range of 2~15Hz, which has a good correlation with MW, The greater the MW, the lower the corner frequency; (3) There is a good linear relationship between${M}_{0}$ and${M}_{{\rm{L}}}$ , can be expressed as$\mathrm{log}{M}_{0}=1.096{M}_{{\rm{L}}}+9.78$ ; (4) Variation of apparent stress with time show that, with high apparent stress in 2012—2014, the intensity and frequency of earthquakes also increased significantly; The apparent stress decreased after 2016, the intensity and frequency of earthquakes also decreased significantly. (5) The spatial distribution characteristics of apparent stress indicate that there are obviously high apparent stress concentrations between Jvnan-Linyi in the central and southern Yishu belt, and Anqiu part in the northern section of the Yishu belt. These locations mean the potential source areas of moderate-strong earthquakes in the Yishu zone in the future. It is very necessary to continue to track and monitor the geophysical characteristics of areas with high apparent stress.-
Key words:
- Yishu fault zone /
- High-cut model /
- Corner frequency /
- Apparent stress
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图 2 山东地区56个台站的场地响应(苗庆杰等,2016)
Figure 2. The site responses of 56 stations in Shandong province(Miao et al., 2016)
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