A new method to estimate ocean-bottom-seismometer orientation using teleseismic receiver functions

摘要

The orientation of an ocean-bottom-seismometer (OBS) is a critical parameter for analysing three-component seismograms, but it is difficult to estimate because of the uncontrollable OBS posture after its deployment. In this study, we develop a new and effective method to estimate the OBS orientation by fitting the amplitude of direct P wave of teleseismic receiver functions. The reliability of this method is verified using synthetic data and observed waveforms recorded at land seismic stations in Shandong Province, China. Our extensive synthetic tests show that our new method is little affected by a thin sedimentary layer that has a low S-wave velocity. The orientations of OBS stations that we deployed in the Yap subduction zone in the Western Pacific Ocean are estimated and corrected using our new method. After the correction, the direct P waves of teleseismic receiver functions show very good consistency. The effects of white and coloured noise in different levels, epicentral distance and backazimuth arc also investigated, and the results show that these factors have small effects on the new method. We also examine the effect of sensor tilting on estimation of the OBS orientation, and find that a tilting correction should be made before the misorientation correction. We compare the OBS orientations determined with the new method and other methods and find that they are generally consistent with each other. We also discuss advantages and shortcomings of various methods, and think that our new method is more robust than the existing methods.