CRUST SEISMIC SCATTERING STRENGTH BENEATH THE MIDDLE‐SOUTH SEGMENT OF THE TANCHENG‐LUJIANG FAULT ZONE

Broadband teleseismic waveform data from 10 earthquakes recorded by 134 digital seismic stations were selected to study the seismic scattering strength of the crust in the middle-south segment of the Tancheng-Lujiang fault zone by teleseismic fluctuation wave field method. The results show that strong transverse inhomogeneity exists beneath the middle-south segment of the Tancheng-Lujiang fault zone, and that the spatial distributions of seismic scattering strength exhibit conformity between the upper and lower crusts. Strong seismic scattering strength is found beneath the north China block and the Qinling-Dabie fold system, whereas weak seismic scattering strength is found under the Yangtze block. The peak value of seismic scattering strength is mainly distributed in Lu'an, Junan, Jiashan, and Yantai, among others. The tectonic blocks are correlated with seismic scattering strength. Different blocks show different seismic scattering strengths. Seismic scattering strength, which can be divided into three segments, shows a segmental feature along the Tancheng-Lujiang fault zone. The first segment is from Weifang to Linyi, the second is from Linyi to Jiashan, and the third is from Jianshan to Jiujiang. Earthquake activity is strongly correlated with seismic scattering strength, and the epicenters of moderate earthquakes are located along the gradient zone of seismic scattering strength. Many smaller earthquakes occur along the high gradients of seismic scattering strength throughout the Tancheng-Lujiang fault zone, such as the segment of Linyi to Jiashan, and the segment of Jianshan to Jiujiang. However, the segment of Linyi to Jiashan with fewer earthquakes shows a low gradient of seismic scattering strength. Seismic scattering strength shows coherency with tectonic blocks, deep fault structure, and earthquake activity. Thus, seismic scattering strength reflects the different physical properties of a medium in the crust and is also related to the physical morphology of the medium, substance migration, and variations in stress-strain environment in the deep structure.