[S-SS03] Seismological advances in the ocean

[SSS03-P10] Seafloor Rayleigh ellipticity, measured from unoriented data, and its significance for passive seismic imaging in the ocean

*Sanxi AI¹ (1.China University of Geosciences)

キーワード：Rayleigh Ellipticity, OBS Orientation, Oceanic Lithosphere

Observations of the seafloor Rayleigh ellipticity contribute to seismic imaging in the ocean. To extract such observables from the arbitrarily oriented ocean-bottom seismometer (OBS) data, we develop an orthogonal-regression based approach to measure the waveform amplitude ratios of the unoriented horizontal and vertical components. The amplitude ratios are then used to calculate the Rayleigh ellipticity (and the sensor orientation angle). The robustness of our method is verified by applications to both the unoriented OBS data and the well oriented on-land seismic data. As we propose to calculate the Rayleigh ellipticity directly from the unoriented three-component data, the measurement process avoids the complexity arising from the surface wave non-great circle effects and uncertainties of the OBS sensor orientation angles. Overall the Rayleigh ellipticity measurements from our method are systematically greater than those by conventional analysis. We also observe that the seawater layer affects the depth sensitivities of the ocean bottom Rayleigh ellipticity to the lithospheric structure. Compared to the continental Rayleigh ellipticity, the seafloor measurements are more effective to image the lithosphere structure. We show the potential of seafloor Rayleigh ellipticity for seismic imaging in the ocean through a case study of the Japan Basin, the Sea of Japan and associated synthetic tests. Considering the insufficient station coverage in the ocean, the single-station measurement of seafloor Rayleigh ellipticity is of significance for OBS community.