Extraction Of Gravity Change Signals From Earthquakes Using ICA Method And GRACE Data

Earthquake is a kind of serious natural disaster,which poses a great threat to the safety of human life and property in our country and even in the world.Ground gravity observation technology limited by observing environment conditions,the amount of data and dynamic update ability is insufficient,can't meet the needs of earthquake monitoring,and GRACE to make the space gravity satellite large scale detecting gravity change is possible,for those conditions,environment,land measurement provides a new technology is not easy to reach.In view of the shortcomings of the traditional difference method and least square method for seismic signal analysis based on GRACE data that require seismic prior information,the purpose and main contents of this paper are carried out,and the Independent Component Analysis(ICA)method is proposed to extract seismic gravity change information from GRACE data without seismic prior information.The main work of this paper is as follows:This paper introduces the background and significance of seismic gravity change research,analyzes the current research status and shortcomings of GRACE data extraction methods for seismic signals,summarizes and analyzes the application of GRACE gravity satellite in earthquake at home and abroad,and puts forward the advantages and feasibility of Independent Component Analysis method in seismic signal extraction.Under the premise of studying the change of seismic gravity,this paper firstly describes the research methods involved in the post-processing of GRACE time-varying gravity field data,introduces the calculation method of gravity disturbance,and points out the main filtering methods to remove the north-south abnormal bands in GRACE time-varying signals,and gives the method of time series analysis.This paper introduces the method of extracting the information of the change of the theoretical co-seismic gravity based on the dislocation theory,and explains the method of using the software and the matters needing attention of the required data.Aiming at the problem that the amplitude of the theoretical co-seismic gravity change is tens or even hundreds of times of the amplitude of the global gravity change extracted by GRACE,which cannot be directly compared and analyzed,the method of spherical harmonic expansion and spatial filtering is proposed to realize the mathematical transformation from the theoretical value to the observed value.The methods of using GRACE data to extract seismic gravity variation are given:Difference method,Least Square method,Principal Component Analysis(PCA/EOF),Rotation Empirical Orthogonal Function(REOF)and Independent Component Analysis(ICA).According to the advantages and disadvantages of each statistical method,the simulation experiment proves that the Independent Component Analysis is better than the Principal Component Analysis and the Rotation Empirical Orthogonal Function in extracting and separating the information of seismic gravity change.Three typical large earthquakes,namely the 2004 Sumatra M_w9.1 earthquake,the 2011Japanese M_w9.1 earthquake and the 2012 Sumatra M_w8.6 earthquake,were studied by the above methods.Dislocation model is used to calculate the theory of three earthquake coseismic gravity change,expand the spheric after add space filtering processing with reference to the results and the finite Difference method,the Least Squares and Principal Component Analysis(PCA/EOF),Rotated Empirical Orthogonal Function(REOF)and Independent Component Analysis(ICA)method to extract the seismic information of GRACE gravity disturbance data,comparison analysis,studies show that Independent Component Analysis can accurately extract the three earthquake coseismic gravity changes and trends,the former after the gravity of the 2004Sumatran earthquake for inland-oceans are negative shear form,The change range of gravity is-7.7?gal?8.8?gal,and the positive and negative co-seismic gravity step is+4.7?gal and-7.8?gal.Before the 2011 earthquake in Japan,the gravity of the western region was positive for a long time,while the eastern side of the ocean was negative for a long time.When the earthquake occurred,the gravity changed significantly and the gravity changed alternately.In the northeast of Honshu and the Japanese waters west of the source center,there is a large range of negative gravity changes,and there is a certain positive gravity change in the east of the epicenter and on both sides of the north and south.From the west to the east,there is a negative to positive distribution after the earthquake,that is,the southeast side is positive and the northwest side is negative.The 2012 Sumatran earthquake co-seismic gravity change appears as one compression zone and two tension zone seismic features four quadrant strike-slip type,through analysis and comparison,the accuracy of the independent component analysis to extract the seismic than principal component analysis and rotated empirical orthogonal function,shows that in the independent component analysis to extract type strike-slip earthquakes of time-space effect is better than principal component analysis and rotated empirical orthogonal function.The conclusion shows that the method of independent component analysis can successfully extract the seismic gravity signal from GRACE data.