Synchronizing Intercontinental Seismic Networks Using the 26 s Persistent Localized Microseismic Source

Abstract Accurate instrument clocks are essential for quantitative studies in seis-mology. Recent studies demonstrate that ambient seismic noise can be used to detect clock time drift for ocean-bottom seismometers (OBSs) or inland seismometers with internal hardware or software problems, but the short-period (<20 s) interstation Ray-leigh waves extracted from ambient seismic noise are too weak for intercontinental seismic station-pair correlations and thus are less effective for synchronizing sparse global seismic networks. The 26 s persistent localized microseismic source in the Gulf of Guinea radiates strong seismic signals that can be recorded on global stations, thus providing an alternative approach for synchronizing seismometers at large interstation distances. In this study, we test the feasibility of synchronizing seismic stations in Africa, North America, and Europe using the 26 s signals in the noise cross-correlation functions. We find that the clocks at the TAM and OBN stations are relatively stable during the years from 2002 to 2009; an ∼1 s time shift occurred at the CCM station from 2006 to 2009, and the clock drift was not constant. We also detected about 150 s time shifts at the KOWA station in October 2012 and up to 500 s in January 2013. We validate our results via comparison with the ambient noise method by Stehly et al. (2007) and teleseismic P-wave arrival-time residuals. The method proposed in this study can be used to calibrate the OBSs in the north Atlantic by synchronizing their clocks with the precisely calibrated inland seismometers