Outcome and lessons from the Southern Mariana Ocean Bottom Seismic Experiments

The Challenger Deep in the Southern Mariana subduction zone has attracted enormous attention of scientific investigators and explorers during recent decades. Since late 2016, near-field active and passive source seismic experiments has been carried out in the region by deploying Ocean Bottom Seismographs (OBS) in various terms. Both active and passive source tomographic images clearly indicate a well hydrous incoming plate, which is consistent with the observed pervasive normal faults in the out-rise region. Numerous earthquakes have been detected from the OBS recordings, and their locations delineate the subducting plate as well as deep out-rise faults, showing significant along-trench variations. Earthquake clusters are also found beneath the southwestern Mariana Rift and diminish sharply in the north. In addition to the scientific findings, we have discovered unexpected problems with the OBS data, particularly on the timing accuracies that are crucial on seismic records. To fix the various timing problems, we develop a framework of integrating travel times of teleseismic earthquakes and ambient noise cross correlations in different time segments. Such a framework could be applied on other OBS dataset suffering from irregular timing problems.