Research Of The Rapid Magnitude Estimation Parameters And Models In Earthquake Early Warning System Of Southwestern China

To mitigate the potential seismic disasters in Southwestern China region,building up the suitable magnitude estimation models for Earthquake Early Warning system?EEWs?is important.Based on the above problems,the theoretical relationship between the information contained in the short time seismic records and the magnitude estimation parameters is discussed,and the common methods for the rapid estimation of the earthquake magnitude is analyzed and verified.The differences in the characteristics of magnitude estimation models in different areas are researched and new parameter and method is introduced.Our works offer an insight into the feasibility of the EEWs in southwestern China.The main contents of this dissertation are as follows:?1?The records from the main-and after-shocks of the 2008 Wenchuan?M_w 7.9?and 2013 Lushan earthquakes?M_w 6.6?,occurred in Sichuan region,were used to develop the maximum predominant and characteristic periods(?_p^max and?_c)and peak displacement?P_d?parameters for estimating earthquake magnitude.The developed correlations were evaluated and compared with previous studies in other region.The?_p^maxax parameter is correlated with magnitudes in the 4–6 range and 6-8 range,while?_c parameter scales with the entire magnitude range without evident saturation.Nevertheless,the linear slope is slightly lower than the previous studies in other region.As for P_d parameter,it is confirmed as a good estimator and performs most similarly with the compared regions of the magnitude range in 4-6.Indeed for large magnitude,we observe the saturation effect.The longer time window length and narrowing the filtering bandwidth can improve the saturation;however,the linear slope decreases.?2?We do the research and verify on rapid magnitude estimation models,which are developed in last chapter,based events in the Yunnan region in 2014.The results show that three models can be effectively used for magnitude estimation in a short time.All of three models do not underestimate the magnitude in large earthquake events.However,at that moment it is difficult to get the accurate epicentral/hypocentral distance in a short time.Hence,?_p^max or?_c models are recommended to apply in EEWs in southwestern China.The developed correlations were evaluated and compared with previous studies in other region.Speculatively,the different performances perhaps can be attributed to the regional characteristics in southwestern China region.?3?We introduced a new magnitude estimation parameter,?_log,and studied the correlation between magnitude and this parameter obtained from the early portion of P-and S-waves for the main-and after-shocks of Wenchuan earthquake.And we compared the estimation models with?_p^max and?_c methods in the previous research.The result shows that this method can effectively avoid the false?and miss?alarm rate in small scale earthquakes in the practical application of EEWs.In order to overcome the magnitude underestimation,we learn from displacement spectrum inversion method and discuss the applicability of the earthquake magnitude estimation of displacement spectrum from P-waves of single stations.Furthermore,this research focuses on the influence of this method by different hypocentral distances and site conditions.The result shows that the displacement spectrum inversion method can estimate large scale earthquake magnitudes well,solving the problem of magnitude saturation.In addition,with the condition of different hypocentral distance and site conditions,this method can provide stable magnitude estimation.