Characteristics of strong earthquake evolution around the eastern boundary faults of the Sichuan-Yunnan rhombic block

Based on the existing materials of fault segmentation, characteristic earthquakes, and their empirical relationships, we calculated the parameters of the fault segments, such as length, width, magnitudes of characteristic earthquakes, etc. Constrained by GPS velocity field, the slip rates of these fault segments in depth were inversed using the 3-D half-space elastic dislocation model. As not all of the recurrence periods and co-seismic displacements of characteristic earthquakes are known, we selected the fault segments with these two parameters known and calculated the accumulation rate of average co-seismic displacement, which shows the faults’ slip rate in seismogenic layer. Then, the slip rate in depth was compared with that in seismogenic layer, the relationship between them was obtained, and this relationship was used to get the recurrence periods and co-seismic displacements of all fault segments. After the studies above, we calculated the co-seismic deformation field of all the earthquakes larger than Ms6.8 from AD 1700 one by one and inversed the potential displacement in the co-seismic deformation field. Then, we divided the potential displacement by the slip rate from GPS inversion to get the influences of these fault segments, added the influences into the elapsed time of the characteristic earthquakes, and obtained the earthquake hazard degree of all the segments we studied in the form of the ratio of elapsed time to recurrence period; so, we name the ratio as the Impending Earthquake Risk (IER). Historical earthquake cases show that the fault segment is in safety when the IER is less than 1 but in danger after the IER becomes larger than 1. In 2009, the IER is larger than 1 on the following segments, 1.35 on the Tagong segment of Xianshuihe fault, 1 on the Menggu-Dongchuan segment, 1.04 on the Dongchuan-Xundian segment, and 1.09 on the Yiliang-Chengjiang segment of Xiaojiang fault.