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It has long been recognized that ocean gravity waves can generate microseisms through their interactions and coupling with the solid earth. Their generation mechanisms, wave types, and propagation have been studied and debated intensively. In this study, we focus on the characteristics of microseisms in South China Sea (SCS) and compare them with globally observed microseisms. We use data from six ocean bottom seismometers, 10 publicly available broadband land seismometers near SCS, and a reanalyzed global wave height model from 1 May 2012 to 20 August 2012 (UTC), the time span of ocean bottom seismometers' data. We apply three techniques including power spectral density, correlation, and frequency dependent polarization analysis. Our results show that (1) microseisms observed in SCS are dominated by sources from adjacent oceans, instead of the common global sources from the Pacific, Atlantic, or Indian Ocean; (2) the split of double-frequency microseisms (DFMs) is observed in SCS, especially on land stations: the sources are located near the central sea basin for long-period DFMs (0.1-0.25 Hz) and are local near stations for short-period DFMs (0.25-0.5 Hz); (3) typhoons both strengthen microseisms and affect the source locations of microseisms with the biggest influence on the short-period DFMs; and (4) microseisms in or near SCS are a mixture of Love and Rayleigh waves and the relative dominance of Love and Rayleigh waves changes with locations.As early as the 1900s when microseisms were still treated as one group, there were mainly two candidates on the source locations: one was coastal region (e.g., Gutenberg, 1931;Haubrich, 1963) and the other was open ocean (e.g., Banerji, 1930; Haq, 1954). Although Stehly et al. (2006) back-projected the source of SFMs to the XIAO ET AL. 3923

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The crust near an extinct mid‐ocean ridge provides unique constraints on how its accretion and deformation responded to the cessation of spreading. Here we present crustal thickness and Vp/Vs measurements beneath 11 Ocean Bottom Seismograph sites that cross the South China Sea's extinct spreading axis. We find that the oceanic crust, which generally had only slight thickness changes once spreading started, abruptly thins at sites close to the extinct ridge axis. Abnormally high Vp/Vs ratios are obtained at several sites south of the ridge, indicating the presence of serpentine. These observations imply that, in its final stage, spreading changed to an ultraslow accretion style. As the axial crust thinned, normal faults and/or detachment faults began to form. Water could penetrate more deeply through these faults, and large fault slip could raise ultramafic peridotites to near or at the seafloor, creating favorable conditions for their enhanced serpentinization.