Damage mechanism of single-layer reticulated domes under severe earthquakes

To study the damage mechanism of single-layer reticulated domes subject to severe earthquakes, three limit states of single-layer reticulated domes under earthquakes are defined firstly in this paper. Then, two failure modes are presented by analyzing damage behaviors, and their characteristics are pointed out respectively. Furthermore, the damage process is analyzed and the causes of structural damage in different levels are studied. Finally, by comparing deformation and vibration status of domes with different failure modes, the principles of different failures are revealed and an integrated frame of damage mechanism is set up.

Effect of tidal stress on fault nucleation and failure of the 2007 Ms6.4 Ning＇er earthquake

Based on calculations of the tidal Coulomb failure stress and investigations of the correlation between the Earth tide and the Ning＇er earthquake sequence, the processes of fault nucleation and failure were simulated. In these simulations we consider the influence of tidal stresses using the rate- and state-dependent friction laws. Furthermore, the effects on tidal trig- gering due to the stress amplitude and periodic oscillation properties were investigated, and the triggering effects between the tidal normal and tidal shear stresses were compared. The results showed that the Ning＇er earthquake sequence was a physical consequence of tidal effects. A transition period To exists between the nucleation and failure processes of a seismic fault. When the period T of stress is equal to or becomes larger than To, the fault response becomes dependent on the periodic features of the loading stress; however, for T 〈 To, the response of the fault is nearly independent of the period. Both the tidal normal and tidal shear stresses have similar effect in the nucleation and failure processes; the clock changes generally increase with the maximum amplitudes of the tidal stresses. Tidal normal and tidal shear stresses with positive amplitudes mainly induce earth- quake triggering; however, the triggering effects induced by negative tidal stresses are smaller and faults are not sensitive to negative tidal stresses. Our results primarily reveal the physical mechanisms of tidal stress triggering.

Heterogeneous destruction of the North China Craton： Coupled constraints from seismology and geodynamic numerical modeling

The prevailing academic view regards mantle flow and the metasomatism triggered by the subduction of the Pacific plate as the cause and mechanism for the destruction of the North China Craton(NCC). However, the geodynamic destruction process remains ambiguous, necessitating detailed information at this stage. Combining the structural images obtained by the exploration of dense seismic arrays and the geodynamic simulations inspired by numerical modeling, this paper arrives at the following conclusions: the spatial variation of the P-and S-wave velocities, as well as their velocity ratio in the mantle transition zone, are key evidences of the nonuniform dehydration of the Pacific plate, the subducted plate induces hot upwellings in the mantle transition zone(MTZ), resulting in the heterogeneous distribution of the melt/fluid beneath the craton, characterized by small scale anomalies in the seismic velocity field, and as revealed by dense seismic array observation, the heterogeneities in the upper mantle structure and deformation are the synthetic results of lithospheric strain localization and the heterogeneous distribution of the melt/fluid. It is known that the nonuniform dehydration of the Pacific slab and the heterogeneous distribution of the melt/fluid have occured in the Cenozoic. If these scenarios could have already occurred in the Early Cretaceous, their interaction with the NCC lithosphere would be the dynamic mechanism for the heterogeneous lithospheric destruction of the NCC. The inference in this study is significant for further reconciling the multidisciplinary evidences in the NCC.