Abstract:Source parameters calculations are generally carried out in the frequency domain.Seismic wave data from station records can be used for site response,instrument response,geometric diffusion path attenuation,and focal radiation directivity factor correction.A genetic algorithm can be used to obtain the parameters of low-frequency spectral amplitude limit and corner frequency,and thus,the theoretical formula for calculating stress drop,source radius,and seismic moment.The geological structure of Jiaodong Peninsula is complex.The area spread by the Jiaodong fault was uplifted,and the area of the northern Yellow Sea fault was bent,so the Jiaodong Peninsula fault structure is mainly monoclinic or relief synclinic.Brittle faults are well developed,mainly related to the eastern section of the Yanshan-Bohai fault zone.In contrast,at the intersection with the Tan-Lu fault in the Bohai are two sets of faults in the NNE-NE and NWW directions.The faults in the area are strong,and the structure is extremely complex;this was a high activity area in the North China earthquake.In recent years,the seismic activity has concentrated and strengthened.Regional stress changes have been analyzed in recent years in order to study the risk to Jiaodong Peninsula of strong earthquakes.Based on digital seismograms of Jiaodong Peninsula and the surrounding areas recorded by the Shandong digital seismic network since 2010,the Brune model,combined with a genetic algorithm,has been used to calculate the spectral parameters of 134earthquakes above 2.0in the Jiaodong Peninsula.Results show that seismic moments were between 9.76×1011 N·m and 5.9×1014 N·m;pressure drops were between 0.017MPa and 25MPa(0.97MPa mean);and apparent pressures were between 0.06 MPa and 10.2MPa(0.396MPa mean).Seismic moment,stress drop,and apparent stress were positively correlated with magnitude,with the magnitude of the rise increasing.By using a linear fit of robust regression functions,aquantitative relationship has been developed for the Jiaodong Peninsula,which is consistent with the findings of other scholars.The relationship between corner frequency and magnitude is not obvious;seismic moment and corner frequency were negatively correlated.According to the quantitative statistical relationships between the Jiaodong Peninsula source parameters and magnitude(in addition to the effect of magnitude),and by the changes in stress drop and apparent stress over time,we can clearly see that a Jiaodong Peninsula stress adjustment has caused the stress to currently be in a period of weakening,compared to its previous high-stress state.
