Borehole monitoring systems can be classed into two types: permanent systems, which remain below the seafloor forever; and recoverable systems, which can be replaced or recovered to the surface after a period of time. The NanTroSEIZE Long-term borehole monitoring system (LTBMS) is an example of a permanent system, while the Japan Trench Fast Drilling Project (JFAST) is an example of a recoverable system.