Application of noise HVSR method in OBS detection: A case study of OBS array off the Pearl River Estuary

The horizontal-to-vertical spectral ratio (HVSR) method, generally used to determine the thickness of sedimentary strata, is rarely applied to estimate the marine sediment thickness by Ocean Bottom Seismometer (OBS). In this paper, the HVSR method was applied to the OBS array off the Pearl River Estuary (PRE) to verify the reliability of the method for OBS detection. The HVSR curves for 27 OBSs off the PRE were obtained by processing the three-component seismic noise records. The peak frequency associated with the thickness of sedimentary strata can be obtained from the HVSR curves of 23 OBSs, and the thickness of the sedimentary strata could be calculated using an empirical equation. The results show that the thickness of the sedimentary strata (Cenozoic strata) off the PRE varies from about 100 m to about 3500 m, with sedimentary strata in the northwest thinner than that in the southeast of the study area, and the sediment thickness is controlled by the NEE trending Littoral Fault Zone. The results obtained in this paper are generally consistent with those obtained from previous drillings and reflection seismic profiles. Further analysis shows that Cenozoic strata in the study area have multi-layer structures, and most HVSR curves have peaks with the largest amplitude at 5 similar to 12 Hz, which is considered to be the peak frequency related to Quaternary strata, and then the thickness of Quaternary strata is determined to be 20 to 50 m. This study expands the application fields of the HVSR method and provides a new and reliable approach to measure the thickness of sub-marine sedimentary strata.