Study On The Determination Of Earthquake Magnitude From Initial P-Wave Recordings

Earthquake early warning(EEW)system is a new and effective method for seismic prevention and disaster mitigation,and the key problem is how to determine the earthquake magnitude by the initial P wave information.The current magnitude estimation methods have some problems such as having relatively large discreteness,underestimating the large earthquakes and overestimating small earthquakes.Therefore,the technical aspect not only involves the method of estimating magnitude based on the P phase,but also involves a hot problem of seismology which is whether the size of the earthquake can be determined by the limited energy from the initial source rupture and the initial P information recorded by stations or not.Based on the above issues and problems,the theoretical relationship between the information contained in the first P arrivals and the source parameters for moderate and small earthquakes is discussed,and the common methods for the estimation of the earthquake magnitude is analyzed and summarized.The differences in the characteristics of the initial information of the earthquake strong motion records in different areas is researched,and a new parameter and method for estimating magnitude is proposed.Further a magnitude estimation method with more effectiveness and accuracy is recommended.The main contents of this dissertation are as follows:(1)This paper discusses the relationship between the information of the initial P wave displacement field and the magnitude of the earthquakes and show that the quantitative relation between ground motion parameters including amplitude and half period of frist P arrivals and the focal parameters including the focal radius and the body wave velocity,based on the model of the disk source in the medium and small earthquakes.Here we analyze and summarize the common methods in the estimation of the magnitude in the earthquake early warning system.The results of different methods behave some extent discreteness,large earthquakes "saturation" and overestimate small earthquakes.The reliability difference of different early warning magnitude parameters in practical application is analyzed.(2)In this paper,we study the different seismic events in different regions of strong motion records for the P wave in the initial period of the existence of differences: first of all,this paper discusses the characteristics at the beginning of the Wenchuan mainshock and aftershock events dynamic waveform,to determine the correlation between the motion of moderately strong earthquakes in the early half cycle parameters and the earthquake magnitude;.Secondly,we consider the effect of attenuation relations studied in the P wave seismic phase to S-wave phase time range,peak displacement with the time window length increases the variation characteristics,and different magnitude between peak displacement curve regularity of.Finally,similarly studied characteristics of cycle parameters in the same time Fan Wai with the variation of the time window.According to the research results,it is shown that there is a difference in the initial rupture of the earthquake with different sizes.In addition,this chapter also discusses the relationship between the initial moving half period,the characteristic period and the source scale.(3)This paper explains the physical principles of alignment shift peak curve of the initial slope;researches new parameters and the formula for real-time estimation of the magnitude;selects the appropriate magnitude epicenter distance range of seismic record to discuss real-time application effect on the slope parameter irS for magnitude estimation;studies the requirements of the timeliness and the stability of the slope parameters irS for the early-warning magnitude estimation.