2:15 PM - 2:30 PM
[J07-3-04] Seafloor deformation due to ocean tidal loading observed by seafloor cabled network
Seafloor observation hosted by seafloor cabled network such as DONET (Dense Ocean-Floor Network for Earthquake and Tsunamis) have potential to observe process of slow crustal deformation occurring at plate margin which in many cases situated in the seafloor. Observation in deep seafloor borehole have recently documented occurrence of slow slip events. Investigation of seafloor broadband seismic records in tidal frequency obtained from DONET observatories, was conducted to see if such events of may be observed in the seafloor. The broadband seismic records (from Guralp CMG3T) have flat velocity response < 360s and were corrected to obtain acceleration response in tidal frequencies between 2 days and 1 hour. The corrected acceleration response in vertical direction were consistent in most of DONET observatories, with estimated tidal gravity change by GOTIC2, indicating these broadband seismometers have good sensitivity to gravity change in tidal frequencies. The horizontal acceleration response, corresponds to tilting, on the other hand, showed differences between sites. The amplitude of diurnal tidal response varied between 0.1 – 2 microradians, significantly larger than those estimated for earth tide. The observed tidal tilt responses were at many sites in phase with seafloor pressure variation in both horizontal axes. This observation indicates significant effect of seafloor deformation due to ocean tide loading in these sites. The linearly correlating tilting were observed in may sites in accretionary prism of dipping subseafloor structure. It is considered that ocean tidal loading at such setting results in horizontal variation of deformation that was observed as the large amplitude tidal tilting. Therefore, seafloor tilt/strain measurement may be used to indicate slow crustal deformation, but with cautious estimate of the effect of ocean loading at each sites.