Maximum entropy spectral characteristics of seismic activity for great earthquakes in China

The maximum entropy spectral characteristics of seismicity in the seismic enhanced region of 11 great earthquakes is analysed in this paper to seek the difference of seismic period spectral structure between the normal and the abnormal stage of seismic activity in this paper. The results show that, during decades or even one hundred years before great earthquakes, only short periods with 6.5～24.3 years appear, and long ones disappear. Otherwise, long periods with 18.5～38.5 years exist chiefly within the normal stages. Decades years after great earthquakes, the period spectra of seismicity are generally about several or ten years. Then the characteristics of great earthquakes is explained physically by applying the strong body seismogenic model, so a method of studying and predicting great earthquakes is offered.

Dynamic simulation for tempo-spatial distribution of strain energy density in inhomogeneous stratified crust

Through simulating the research on dynamic variations of strain energy density (SED) in seismogenic model with hard inclusion, the authors have gained further knowledge to such problems as the process of earthquake preparation, initial rupture, conditions of the initial rupture and fracture propagation direction, etc. Results of the research show that SED (strain energy density) in soft inclusion is very high during the initial period of earthquake preparation. And the increment of SED in the soft area decreases at the later stage of the process. Meanwhile, the increment increases quickly in hard inclusion and in the intersection zone of the inclusion with an erecting fault, where the increment of SED is maximum. Thus, the intersection zone between hard inclusion with larger elastic modulus and erecting fault becomes the place where the initial rupture or earthquake occurs. The fracture in the end part of the hard inclusion spreads along a direction nearly vertical to the erecting fault, so the theoretical fracture direction is consistent with that calculated by digital simulation.

The Geodynamic Mechanism of the M_S8.0 Wenchuan Earthquake

Located on the east boundary of Qinghai-Xizang （Tibet） Plateau, the Ms8.0 Wenchnan earthquake is the strongest event to hit the active block since the 2001 Kunlun Mountains Pass earthquake. In this study, a simplified source model of the Wenchnan earthquake is constructed based on the deep/shallow tectonic settings and crust/mantle structure features of the Longmenshan thrust fault zone. On the basis of dynamic model abstraction, we construct a system of dynamical equations for the seismogenic process and obtain the analytical expressions of stress and strain in the seismogenic process. A preliminary study of the seismogenic process of the Ms8.0 Wenchuan earthquake, based on the analytical solution of the model and observation of tectonic deformation in the Longmenshan region, indicates that the seismogenic process of the Wenchuan earthquake took place over a period of more than 3200 years. The slow process of seismogeny and the long recurrence period of strong earthquakes are attributed to the low deformation rate of the Longmenshan tectonic zone.