Compact tiltmeter for ocean bottom and other frontier observations

Long-term observations conducted with large arrays of tiltmeters deployed in ocean bottom boreholes, on the seafloor, are expected to provide rich information useful in geosciences, social engineering, resource monitoring, and other applications. To facilitate such observations, we designed and built a compact, highly sensitive tiltmeter with sufficient performance, comparable to that of much larger instruments that are difficult to operate in the target locations. This paper describes its key technologies, including a compact and long-period folded pendulum and an optical fiber readout. Preliminary results of test observations conducted using a prototype tiltmeter are compared with a conventional water-tube tiltmeter.