Waveform similarity reveals the relationship among pressure, acceleration and velocity in shallow water: a study based on seismic records from different sensors

Abstract

Globally, countries along oceans attach great importance to research involving oceanic observations. In the past 60 years, the United States and Canada, Japan, and the European Community have continued to promote development of ocean Seafloor seismic observations. The first Seafloor seismic station in China was built in Fujian in 2018,  the Wuyu Island Seafloor seismic station, has recorded more than 100 earthquakes since it began operations more than a year ago. A far-field spherical wave incidence, which can be approximately considered a plane wave, and the sound pressure and vibration velocity are in phase; In the low frequency range (0.1-10Hz), The theory of "forced oscillation" describes that the change of water pressure is proportional to the vertical component of ground acceleration. We demonstrate the equivalence of the acceleration, velocity in shallow water and water-pressure signals for a set of local earthquakes .The cross spectrum method is used to analyze the similarity characteristics of velocity and acceleration with pressure signals at different frequencies. In addition, The similarity relationship between sound pressure and velocity acceleration in different frequency ranges is visually displayed through similarity probability distribution. The results show that with the decrease of frequency, the influence of hydrostatic pressure on the pressure detector gradually increases, and the pressure detector gradually changes from high-velocity correlation to high-acceleration correlation. Our work is not only to prove the existence of "forced oscillation" frequency, but also to explain the reason for high similarity of different types of waveforms by using formulas. Finally, we analyze the position of conversion frequency points through probability density distribution. This work can put forward a new design idea for the future research and development of hydrophone type Seafloor seismometer.