| Earthquake disasters are one of the most serious natural disasters facing mankind,and as the economy grows and cities become more and more modern,the number of earthquake disasters increases exponentially.China is one of the countries with the strongest seismic activity and the most serious seismic disasters in the world,and more than 500 strong and large earthquakes have occurred in China from the last century to the present.Since earthquakes are random,short-lived and sudden,it is difficult to accurately predict the time,location and size of their occurrence.As a technical means to predict earthquake intensity using a small amount of information after the occurrence of an earthquake,earthquake early warning provides a new development direction and idea for earthquake disaster mitigation.The Propagation of Local Undamped Motion Method(PLUM method)is an earthquake early warning method that uses the observed ground motion for direct ground motion prediction,which can achieve good earthquake early warning effect in simultaneous multiple earthquakes and earthquakes with severe rupture zone extension.At present,China’s earthquake early warning business is developing rapidly.In this paper,three aspects of early warning performance,warning area size and improvement methods are studied for the local undamped vibration-based earthquake early warning method,in order to provide some reference for the introduction of t the method into the earthquake early warning system in China.The main research work is summarized as follows:1.The principles of earthquake early warning technology,earthquake early warning models are introduced,and the current progress of earthquake early warning systems in three countries,Japan,the United States,and Mexico,as well as in China,are summarized,in addition to an overview of the current global earthquake early warning system construction status.2.The basic principles of the PLUM method,the warning release guidelines and the evaluation index of earthquake warning results that have been adopted in the earthquake warning system of the Japan Meteorological Agency are introduced,and the composition of the Japanese earthquake observation network is summarized.Also,the work of the Southern California research group for the PLUM method is summarized and concluded.3.The early warning performance of the PLUM method is evaluated by retrospective simulation of the M_w 9.0 Tohoku-Oki earthquake on March 11,2011 and the M_w 7.3Honshu earthquake on February 13,2021 in Japan,based on the evaluation indicators such as prediction timeliness,early warning time,prediction score,precision and recall.4.Taking Japan,which is rich in data,as an example,the whole area is divided into grids of different sizes,and each grid is used as an early warning area to simulate the earthquake cases based on the PLUM method,and the influence of the warning area size on the warning performance of the PLUM method is discussed,so as to provide reference for regional division and station layout density in China.In addition,a simple warning area division was made for Beijing with reference to Japan.5.In view of the deficiency of PLUM method in the number of stations and the division of warning region into small areas,an earthquake warning method centered on the warning region is proposed.Through the simulation of the M 9.0 magnitude earthquake on March 11,2011 in Japan,the performance of PLUM method and the warning region-centered warning method are compared.The recommended number of stations is given based on the early-warning issuing criteria of the two early-warning methods. |
