In view of the clustering of earthquakes with Ms
≥5.0 in Ludong-Huanghai active block in recent years, the research on the period of medium strong earthquakes, space-time evolution, energy release and the impact of large earthquakes around the block is carried out. The period of historical earthquake activity is determined by wavelet analysis. The nowcasting method is used to evaluate the risk of moderate and strong earthquakes. Through the above research, the following understandings are obtained. By qualitative analysis and quantitative calculation of historical earthquake periods, there are active-quiescent characteristics with an active period of about 66.1-78.6 years, for Ms
≥5.0 earthquakes in the west of Ludong-Huanghai block.
Since 1997, the western part of the Ludong-Huanghai block has entered the late stage of the active period of earthquakes (weak release stage). The results of the frequency and magnitude difference of earthquakes Ms
≥5.0 indicate that the current period may transition from the end of the active period to the quiescence period. Although the active period has lasted for about 48 years (exceeded the duration of the previous active period), the energy release of Ms
≥5.0 earthquakes is insufficient. In the next few years, seismicity may be dominated by earthquakes with magnitude of 5.0-5.9. At present, the main active area in the active period is the southern depression of the Yellow Sea and its vicinity. According to the assessment results of strong earthquake risk in Nowcasting method, the potential risk score of Ms
≥5.5 earthquakes in the west of Ludong -Huanghai block is 100% indicating that there is a strong background of earthquakes with Ms
≥ 5.5 in this area. At present, Ms
≥ 5.0 earthquakes in the west of Ludong-Huanghai block and its vicinity are weakly active, while Ms
≥ 6.0 earthquakes in North China are remarkably quiet. There is a background of synchronous activity in these two regions. In recent years, the seismicity in the west of the Ludong-Huanghai block is mainly Ms
4.0-5.0 earthquakes. Without significant concentration of Ms
≥ 5.0 earthquakes within 5 years in the west of Ludong-Huanghai block, there is little possibility of Ms
≥ 6.0 earthquakes at present.