Tilt Observations at the Seafloor by Mobile Ocean Bottom Seismometers

We have developed a broadband ocean bottom seismometer (BBOBS) and its new generation (BBOBS-NX) with the penetrator sensor system since 1999. With them, we performed many practical observations to create research category of seismology. As next step in seafloor geophysical observation, BBOBS BBOBS-NX can be breakthrough realizing geodetic observation network on seafloor. Although vertical displacement by absolute pressure gauge has been widely conducted recent years, other are rarely performed. A few trials measure tilt were performed, but those looked inadequate for observations. Note that our BBOBSs mass position signal output, which used change. horizontal component noise level is good at long period range, expected it adequate measurement. At first evaluation, comparison water-tube tiltmeter. The result was comparable resolution better than 1 µ radian. south Boso Peninsula (KAP3 site) as in-situ study from April, 2013. In January, 2014, slow slip event (SSE) occurred near this site. data processed removing steps, mechanical relaxation, tides. results show clear peak started late December Two more 2 year-long began 2015: one KAP3 site another off Miyagi Prefecture slope Japan Trench. latter recovered 2017 about 1.5 years data, indicate large continuous up several tens This amount explained similar already estimated SSE. Mobile measurement powerful tool SSEs, they located above source area also possible build an array because low cost ease deployment compared borehole