Three-component Seismic-wave Gradiometry And Imagination

Seismic-wave gradiometry is a new array data processing technique which uses the spatial variation captured by subarray stations to extract fundamental wave propagation characteristics which include phase velocity,wave directionality,geometrical spreading,and radiation pattern.Recently,seismic dense array developing globally,regionally,or locally.The two most typical examples of a dense array are USArray and ChinArray,from which seismic data can be used to wave gradiometry.In the previous study of seismic-wave gradiometry,most of the vertical components in the three components of the seismograph were used,and there was a lack of research on the horizontal component.This study firstly used seismic-wave gradiometry in the study of three-component surface-wave seismic data.Using the 7.4-magnitude earthquake in Central America on August 27,2012,surface-wave three-component data obtained by the USArray array were used to study the eastern and central United States.First,calculate the waveform gradient of the vertical component seismic data,obtain the angle of wave directionality,and then coordinate rotation of the two components of the seismometer according to the angle to obtain radial and tangential component(SH wave)seismographic record.This study calculates the waveform gradients for the three components after coordinate rotation.Through the filtering of different period and waveform gradient calculations,the four propagation parameters of phase velocities,wave directionality,geometrical spreading,and radiation pattern in the 40-60 s,60-80 s,80-100 s,100-125 s,and 125-150 s periods were obtained.Comparative analysis of different frequency bands and different components have certain understanding of the underground structure in the eastern and central United States.At the same time,we also applied the method of seismic-wave gradiometry to the data of the vertical component of the array formed by the ChinArray's stations and the fixed seismic stations in the study region.Then we can invert S-wave velocity by dispersion curve combining the phase velocities of the respective frequency bands.The S-wave velocity structure in the area has obtained some preliminary results.Probably describes the distribution of low-velocity zone in the study area and compares the existing results with good consistency.Seismic wave propagation images were extracted using an earthquake that occurred on July 27,2014 in the Atlantic Ocean(23.724°N,45.5809°W).The study took 100-125 seconds of filtering and 50-60 seconds of filtering.The vertical component seismic data collected by the USArray array have been studied in the eastern United States.By applying the seismic-wave gradiometry,the seismic data of each grid node with grids of 0.1° and 0.5° was obtained,thereby reconstructing the seismic waves propagated through the wave fields of the array coverage area after the earthquake.At the same time,some simple waveforms have been synthesized for testing seismic-wave gradiometry,and good results have also been obtained.