Quantitative Seismicity Analysis for the Risk of Historical Large Earthquake Rupture Zones:Applied to the Midnorth Segment of the South-North Seismic Belt

Although seismic gap theory plays an important role in mid-long term earthquake prediction,the potential risk of the non-seismic gap,historical rupture area,need to be take into consideration at the same time,during the study of mid-long term earthquake prediction,due to the clustering or non-linear behavior of the large earthquake recurrence time.In order to explore technical methods which can be based on observational data,and can indentify historical earthquake rupture zone(including historical,seismic gap of prehistoric earthquake rupture),we select 8 historical large earthquake ruptures with different elapsed times in the South-North Seismic Belt,analyzing the quantitative characteristics of the modern seismicity of these ruptures,to determine the seismicity method of potential earthquake hazard urgency.The results mainly show that,p value,which reflects the attenuation of the earthquake sequence,and a value,which reflects the seismicity rate,are well related to the elapsed time of the latest earthquake in the rupture,that the corresponding relationships in some rupture areas are not clear may due to the complex fault structure and movement behavior.b value,which represents the state of tectonic stress accumulation,is difficult to reflect the elapsed time information of different evolution stages.b value temporal scanning shows that most of the rupture zone evolution is steady over time,but in the rupture zone of the 1879 Wudu M8 earthquake,the b value is manifested in significant fluctuations,and there is a decreasing trend for 20 years.By comparative analyzing,we conclude that the ruptures of the 1933 Maoxian 7.5,the 1976 twin Songpan-Pingwu 7.2 earthquakes,are still in the sequence decay period.Low b values in the Maqu segment,which locates at the north margin of the 842 Diebu M7 rupture,is more dangerous than the Diebu segment.Continued reduction of b value in the 1879 Wudu M8 earthquake rupture may also reflect a new round of seismogenic period.