A Significant Change in Ocean Bottom Pressure Off Eastern Taiwan, Southwestern Ryukyu Subduction Zone

Three real-time permanent observatories (EOS02–EOS04) connected by a submarine cable were constructed and deployed to monitor seismicity, tsunamis, and other geophysical phenomena off eastern Taiwan, southwestern Ryukyu subduction zone. In this study, we process the pressure data (January 26, 2017, to December 31, 2019) recorded by three ocean bottom pressure gauges. After removing of tidal and short-period oceanographic effects and the linear trend caused by long-term sensor drift, overall, the variation patterns of the ocean bottom pressure (OBP) records at stations EOS02 and EOS03 are similar, while that at station EOS04 (located on a slope) exhibits different characteristics. The amplitude fluctuations of the OBP records are very large, even reaching approximately 3 × 102 mbar at station EOS02. In addition, we observe a significant permanent change in the OBP data at station EOS04 where the pressure variation reaches approximately 4.2 × 102 mbar (approximately equals a 4.2 m water column variation). Considering the seismicity and background tectonic characteristics of station EOS04, we speculate that this permanent pressure change may have been caused by submarine landslides and/or slumps (triggered by nearby earthquakes).