Ambient Noise Interferometry Using Ocean Bottom Seismometer Data From Active Source Experiments Conducted in the Southernmost Mariana Trench.

Ocean bottom seismometers (OBSs) have been used to detect submarine structural and tectonic information for decades. According to signal source controllability, OBS data have generally been classified into active and passive source data categories. The former mainly focuses on the compressional wave (P‐wave) velocity inversion and always lacks valid information about the shear wave (S‐wave) velocity structure. While the latter provides structural information with limited resolution due to the aperture of the stations. Overcoming the barriers between processing these two data types will allow the reuse of a vast amount of data from active source experiments to explore the submarine S‐wave velocity structural properties. Here, we creatively applied ambient noise interferometry to invert the S‐wave velocity structure using data from active source OBS deployment conducted in the southernmost Mariana subduction zone, which had already been utilized to detect submarine P‐wave velocity structure. Considering the short time duration and relatively low quality of this type of data, a combined method of short‐segment cross‐correlation and selected time‐frequency domain phase‐weighted stacking was adopted to obtain stable cross‐correlation functions, which were subsequently used to invert S‐wave velocity structures. Compared to previous studies using different methods, our result sheds new light on the crust and upper mantle structure of the southernmost Mariana subduction zone. This method could be used to detect more information based on the reutilization of existing active source OBS data. Plain Language Summary: Active source ocean bottom seismometer (OBS) data are usually used to detect P‐wave velocity information of submarine areas using signals from air‐gun shootings. However, most of the waveform recording ambient noise has yet to be utilized. A large amount of valuable data needs to be fully exploited for the high cost of OBS experiments. In addition, we still lack shear wave velocity information in many critical marine areas due to the rarely picked shear wave phases. However, this information is of great importance for marine tectonic analysis, such as magmatism, dehydration or serpentinization. Using the recorded ambient noise in OBS data from active source experiments can afford the opportunity to obtain shear‐wave velocity structures. We adopted different processing methods to calculate high‐quality surface wave dispersion data, which were subsequently used to invert shear wave structures in the southernmost Mariana Trench. This method can also provide structural information with a different resolution that is lacking using passive source OBS data. Key Points: Ambient noise interferometry was applied to ocean bottom seismometer data from an active source deployment to invert the shear‐wave velocity structureA selected time‐frequency domain phase‐weighted stack was adopted to improve the quality of cross‐correlationsWater content and hydrated layer thickness of the subducting plate were estimated in the southernmost Mariana Trench [ABSTRACT FROM AUTHOR]