In this study, we simulated the strong ground motion from the M_S6.4 earthquake that occurred in Yangbi, Yunnan Province on May 21, 2021, with stochastic finite fault method. The peak ground acceleration(PGA)distribution within the range of (25.25°~26.15°N, 98.5°~100.8°E) of 920grid points was synthesized and the impact field of this earthquake ground motion was also obtained. According to the information of strong ground motion records released officially by Institute of Engineering Mechanics, China Earthquake Administration, it can be seen that stations are sparse in the area near the epicenter, therefore, we chose 4 strong motion stations(53YBX, 53YPX, 53BCJ, 53LKT)with horizontal peak ground acceleration(PGA)greater than 10cm/s² in the range of 150km of epicentral distance to simulate the strong ground motions and obtained the synthetic acceleration time series and acceleration response spectrum(PSA)with a damping ratio of 5%for the four stations. Simultaneously, we compared the synthetic results with observed ones and found that the value of synthetic peak ground acceleration and the shape of accelerograms fit well with the records of stations 53YBX, 53YPX, and 53BCJ. Besides, the simulated acceleration response spectrums for the above three stations are consistent with the observed ones, and the average logarithmic error is between ±0.5, which suggests a good agreement for both high and low frequency. However, for station 53LKT, although the value of synthetic peak ground acceleration fits well with the observed one, the shape of acceleration time series has some differences with the observed, and the fitting degree is not as good as other three stations. Besides, there is a better agreement for high frequency than low frequency in the acceleration response spectrum, the simulated result is higher than the observed in low frequency for station 53LKT. The reason for this phenomenon is complex and may be associated with the site condition and so on, so further study is needed for the specific reasons. For the above mentioned four stations, the results show that there are some differences in duration between the synthetic acceleration time series and the recorded data. The cause for such differences may be described as follows: In the stochastic finite fault method, a time window is added to white Gaussian noise to control its shape and make sure that the windowed white Gaussian noise is similar to the real acceleration time series, and also, the path duration is expressed by a simplified theoretical duration, thus there are something different between the windowed white Gaussian noise and the real acceleration time series. Therefore, the simulation results cannot reflect the complex propagation process of seismic waves well. The result of PGA distribution shows a maximum peak ground acceleration of 875cm/s² located near the epicenter. The value of simulated maximum peak ground acceleration is beyond the range of 186~372cm/s², which is the peak ground acceleration range corresponding to intensity Ⅷ. The peak ground acceleration of 720.3cm/s² recorded by station 53YBX is also beyond the range of 186~372cm/s². To a large extent, the cause of this phenomenon may be related to the topography of the region of Yangbi County. About 98.4% of the area of Yangbi County is mountainous area. Consequently, mountain topography is the most widely distributed terrain in this county, and geological disasters are frequent. However, most buildings around the epicenter are not high, the intensity obtained from the damage degree could not reflect the value of peak ground acceleration clearly. Other earthquakes in Yunnan also have similar phenomena. For example, the Ludian M_S6.5 earthquake that happened in Yunnan in 2014 had a maximum intensity of Ⅸ, but the actual peak acceleration recorded by strong motion station reached 949.1cm/s², which is also beyond the peak ground acceleration range corresponding to intensity Ⅸ. The impact field of ground motion obtained in this study is approximately(25.25°~26.15°N, 99.3°~100.5°E), which is consistent with both the predicted ground motion influence area for Yunnan Yangbi M_S6.4 earthquake from Institute of Geophysics, China Earthquake Administration and the area shown in the seismic intensity map issued by Yunnan Earthquake Agency for the Yangbi M_S6.4 earhtquake, which suggest the effectiveness of the simulation results. Although the simulation results are consistent with the observed ones on the whole, there are still a few stations that have a little deviation. The main reason is that some parameters in the process of simulation are obtained by empirical formula and the site conditions are not well reflected, these are the aspects that need to be improved in the process of simulation. And it’s necessary to establish a more accurate model in order to realize accurate simulation and forecast the strong ground motions in the future. Using stochastic finite fault method to simulate ground motion can fill the gap of strong motion records to some extent and the synthetic ground motion results of this study can provide a scientific basis for post-earthquake relief, post-disaster reconstruction, and seismic design in this area.

The time-dependent probabilistic seismic hazard assessment of the active faults based on the quantitative study of seismo-geology has the vital practical significance for the earthquake prevention and disaster management because it describes the seismic risk of active faults by the probability of an earthquake that increases with time and the predicted magnitude. The Poisson model used in the traditional probabilistic method contradicts with the activity characteristics of the fault, so it cannot be used directly to the potential earthquake risk evaluation of the active fault where the time elapsing from the last great earthquake is relatively short. That is to say, the present Poisson model might overestimate the potential earthquake risk of the Xiadian active fault zone in North China because the elapsed time after the historical M8 earthquake that occurred in 1679 is only 341a. Thus, based on paleoearthquake study and geomorphology survey in the field, as well as integrating the data provided by the previous scientists, this paper reveals two paleo-events occurring on the Xiadian active fault zone. The first event E₁ occurred in 1679 with magnitude M8 and ruptured the surface from Sanhe City of Hebei Province to Pinggu District of Beijing at about 341a BP, and the other happened in (4.89±0.68)ka BP(E₂). Our research also found that the average co-seismic displacement is ~(1.4±0.1)m, and the predicted maximum magnitude of the potential earthquake is 8.0. In addition, the probabilistic seismic hazard analysis of great earthquakes for Xiadian active fault zone in the forthcoming 30a is performed based on Poisson model, Brownian time passage model(BPT), stochastic characteristic-slip model(SCS)and NB model to describe time-dependent features of the fault rupture source and its characteristic behavior. The research shows that the probability of strong earthquake in the forthcoming 30a along the Xiadian active fault zone is lower than previously thought, and the seismic hazard level estimated by Poisson model might be overestimated. This result is also helpful for the scientific earthquake potential estimation and earthquake disaster protection of the Xiadian active fault zone, and for the discussion on how to better apply the time-dependent probabilistic methods to the earthquake potential evaluation of active faults in eastern China.

It is of great significance to determine the factors and causes that affect the recurrence of major earthquakes. This paper introduces the influence of strong earthquake on the recurrence of major earthquakes according to elastic rebound theory, and then proposes to calculate the impact time Δt respectively from the effect of strong earthquakes on the same and surrounding faults on the major earthquake recurrence by using seismic moment release rate method and Coulomb stress change. In this paper, we studied the change amount of major earthquake recurrence by taking four earthquakes with magnitude greater than 6.5 occurring at different fracture sections of the Xianshuhe fault zone as an example, they occurred on Daofu, Changcu, Zhuwo Fault, respectively. We used seismic moment rate method to calculate the impact time Δt of strong earthquake on the recurrence of major earthquakes on the Daofu-Qianning Fault. We further discussed the effect of the Coulomb stress change due to the interaction between faults on the recurrence of subsequent major earthquakes. The co-seismic and post-seismic Coulomb stress changes caused by strong earthquake on the surrounding faults on the Ganzi-Luhuo Fault are calculated. With the fault interaction considered, the importance of the interaction between faults in the middle-north section of the Xianshuihe fault zone to change the recurrence of large earthquakes is retested and evaluated. The results indicate that the two strong earthquakes occurring along Xianshuihe Fault in 1904(M=7.0) and 1981(M=6.9) resulted in a delay of 80 years and 45 years of major earthquake recurrence on the Daofu-Qianning Fault respectively, and the M7.3 earthquake in 1923 and the M6.8 earthquake in 1967 resulted in an advance of 35 years of major earthquake recurrence on the Ganzi-Luhuo Fault.

The Toupo Fault,located in the southern Anhui Province,strikes N60°～70°E in a linear route that is clear on satellite image. It plays an important role in controlling the tectonics,topography and distribution of Mesozoic-Cenozoic basins and strata. Detailed field investigation was carried out along the Toupo Fault about its activity. Profiles as well as a trench excavated reveal that the Quaternary superstratum above the fault has not been offset. The stratum was sampled and dated with TL methods to be the Mid-Pleistocene time,implying that the fault has been no longer active since then. Three stages can be divided since the fault was formed,namely,the first stage (late Yanshan Movement),when the fault movement was of reversal left-lateral strike-slipping and the tracks formed then are still clear today; the second stage (early Himalayan Movement-the late Cretaceous-early Tertiary),when the fault movement turned to be normal faulting and the southern wall became a tensile basin and received clastic sediments; and the third stage (since the late Tertiary),when the tectonic movement was very week. No late Tertiary sediments were formed and the Quaternary sediment is only as thick as tens meters. The topography also suggests an old-age form. Neither vertical nor horizontal displacement was evident along Toupo Fault during this stage,though fault gouge dating suggests the Toupo Fault might have been active during the Middle Pleistocene.

In this paper, the definition of the lower-limit magnitude is recommended, then on the basis of analysis of its determination in connection with real data of some earthquakes, the difference between the lower-limit magnitude and the minimum magnitude considered in seismic harzard evaluation is pointed out. The lower-limit magnitude is commonly 4, but the minimum magnitude may be lower. Thus, for the facilities with specific safety requirement, such as nuclear power plant, a substitution of lower-limit magnitude 4 for the minimum magnitude may be unsafe.

In this paper, the fundamental theory and basic principle of the seismotectonic approach to evaluation of design basis ground motion are introduced firstly, then the difference between the new Safety Guide of IAEA and the old one is anlysed, The defects in this method are discussed, and the actual problems which in using this method appear in nuclear power plants siting are discussed too. Finally, the development and improvement of the seismotectonic approach are suggested.