Research On Marine Seismic Noise And Ground Motion Attenuation Based On Wuyu Island Station

In order to develop abundant marine resources,countries around the world have successively carried out the construction of seabed observation networks.Since the "Eleventh Five-Year Plan",China has also initiated research on the construction of submarine observation networks.With the support of national projects and the development of domestically-made submarine seismometers,my country's submarine observatories and observation networks in the East China Sea and South China Sea have also been established.In 2018,a cable-type submarine seismic observation station on Wuyu Island was built on Wuyu Island,Zhangzhou.During the operation of the station,a large amount of data was recorded,which provided a data basis for the study of marine earthquakes and the construction of seabed observation networks.This paper uses the data recorded by the Wuyu Island station to analyze the clock difference through the method of instrument cross-correlation to detect the domestic OBS clock that has been working on the seabed for a long time.Through time-domain and frequency-domain analysis of the recorded noise,the abnormal phenomenon in the noise record is found,and the abnormal phenomenon is explained by the instrument self-noise analysis.Based on the judgment of whether the data recorded by the instrument is normal or not during noise processing,the seismic signal peaks(PGV,PGA)of the normal data are picked up,and the horizontal component is polarized.Combined with the Fujian medium and small ground motion attenuation model,the attenuation relationship suitable for marine earthquakes is fitted,and the model is compared with the data recorded by land stations.The main content of the paper are as follows:1.On the basis of data preprocessing,perform cross-correlation processing on simultaneous segment data of different instruments to determine the clock difference between different instruments.Using the cross-correlation between ocean stations and land stations,the clock status of the instruments is judged,and it is found that there is a clock difference in each instrument,but it does not affect the seismic signal pickup.2.The noise root mean square curve is calculated,the noise recorded by the instrument changes with time,the noise power spectral density graph is drawn,and the problems appearing in the root mean square curve are analyzed in the frequency domain.The self-noise of the instrument is calculated based on the classic two-channel cross-correlation analysis method,and the influence of self-noise on the noise record of the instrument is obtained.3.Use the waveform diagram to determine whether the instrument has recorded the seismic signal,and draw the Fourier spectrum diagram to determine the strength of the seismic signal compared to the noise.Calculate the magnitude using seismic data,compare the calculated magnitude with the catalog magnitude,and judge the ability of the instrument to record seismic signals.On this basis,artificially pick up seismic peak signals PGV and PGA.For the PGV and PGA of the E-W and N-S components,the polarized horizontal component is obtained through the horizontal component rotation method.4.Using the data records of marine seismic signals from ocean stations and land stations,calculate the standard deviation of the difference between the model and the recorded value to determine whether the Fujian medium and small ground motion attenuation model is applicable.According to the picked peak velocity and peak acceleration,a two-step method is used to fit the model parameters.Compare and analyze the applicability of ocean models to ocean station data and land station data.