Research On Larger Earthquake Magnitude Estimation Using GPS Data

Magnitude is a measure of the earthquake,which is one of the basic parameters of the earthquake.The accurate and timely determination of the magnitude can provide a reliable basis for the emergency relief work after the earthquake,and help make the appropriate response to the relevant departments,thus reducing the losses caused by the disaster.When the earthquake occurs,near-field seismometer recording will appear amplitude saturation,resulting in underestimation of magnitude.Although the strong motion seismograph is not easy to limit,baseline drift phenomenon of the record remains to be resolved,and its research in the determination of the magnitude has not yet carried out.At present,high-frequency GPS(Global Positioning System)is widely used in obtaining instantaneous surface movement,which has features of all-weather,high precision and non-limiting,and it can expanse of seismic network monitoring capabilities effectively.The ability of GPS to obtain the displacement of the surface directly is expected to realize the rapid and accurate assessment of the earthquake magnitude.Therefore,it is of great practical significance to study the application of GPS in the determination of large earthquake magnitude.Based on GPS data of large earthquake,the application of GPS in surface wave magnitude and moment scale determination is studied.The main work and innovation of this paper are as follows:1?This paper introduces the research significance of the paper,and reviews the methods of calculating the earthquake magnitude and the application of GPS data to the seismic magnitude determination.2?The basic principle of high precision GPS positioning is studied,and the source model and GPS data type based on surface wave magnitude and moment scale determination are described respectively.3?Based on the principle of seismograph and the principle of dynamic response of single-degree-of-freedom system,this paper presents a method to simulate GPS data to record-based(SK)seismograph.Through the amplitude and phase frequency analysis of the simulation formula,it is recognized that the minimum sampling rate of GPS is 1Hz when the simulation can guarantee the amplitude error within 5%.Subsequent algorithm test shows that the simulation algorithm in this paper has no phase difference with Jinxing's,and the amplitude is basically the same,which shows the reliability of the algorithm.Then,using the 1Hz GPS data of the Mw 9.0 earthquake in Japan on March 11,2011 and the Mw7.2 earthquake on April 4,2010,the GPS is simulated to seismograph.The maximum amplitude and the corresponding period are measured on the seismograph,and the surface wave magnitude of the two cases is calculated.The calculated surface wave magnitude of Mexico earthquake is 7.6,which is 0.1 units larger than that of the China Earthquake Network Center.The calculated surface wave magnitude of the Japanese earthquake is 8.5,which is 0.2 units smaller than that of the China Earthquake Network Center.The results show that the simulation algorithm can make the 1Hz GPS record used to calculate the surface wave magnitude of earthquake,and it has a small error compared with the result of the seismic network.4?Based on the theory of rectangular fault dislocation proposed by Okada,a single rectangular fault model is constructed and nine unknown parameters are set to specify the specific location of the fault under the ground.The inverse problem is established by the function of the fault parameter and the observed data,and the residual root mean square of the observed data and the theoretical data is taken as the objective function.In this paper,two mathematical models are established by the different constraints with the given fault parameters.Ihe inversion method is used as the "interior point-parallel-multi-initial point" method,and a virtual earthquake case is used to test the reliability and efficiency of the algorithm.Then,two mathematical models are applied to four earthquake cases.The inversion results show that: 1.In addition to the Mexican earthquake,the two models can reflect the more reliable fault direction information and moment magnitude;2,Both models can't reflect information of fault dip.5?In this paper,we study the real-time inversing parameters with high frequency GPS,and take the Mw9.0 earthquake in Japan on March 11,2011 as an example.Firstly,the epicenter information is given to coordinate the displacement of the GPS stations.At the same time,the pseudo-quasi-displacement is extracted from the original GPS record,and then the fault parameters and moment magnitude are calculated by the inversion process of the fourth chapter.The inversion results show that the high frequency GPS can give the first moment magnitude Mw7.8 after the earthquake occured 22 seconds,and the magnitude is increased to Mw8.8 after 100 seconds,reaching the maximum magnitude Mw9 around 120 seconds.Compared with the results of JMA's warning magnitude,at the same time point,the moment magnitude in this paper is larger than that of JMA,and the JMA warning magnitude reaches 8.1,which no longer increases after 112 seconds.However,the final fault direction and fault inclination are unreliable,and the final magnitude Mw9.4 is too overestimated.The reasons may be that the GPS stations are caused by the fault side.Subsequently,this paper uses the coseismic displacement data of Wenchuan earthquake,and intends to select five kinds of GPS stations distributtions to carry out inversion.Five inversion tests of the fault direction,inclination and moment magnitude all are greater error,which shows that the distribution of GPS stations are not surround the fault lead to the larger deviation of Mexican earthquake and the Japanese earthquake inversion results.