1. A method for monitoring vertical seafloor movements by measuring the ambient seawater pressure at a plurality of locations adjacent to the seafloor comprising generating asynchronous pressure signals by a plurality of pressure sensors mounted at different locations on the seafloor over a prolonged period of time(t), and deriving tide-free relative height differences from the asynchronous pressure signals wherein the asynchronous pressure signals are corrected for harmonic tide-related pressure variations by an algorithm comprising a mathematical equation that models spatial and temporal pressure variations in an objective function and minimizing said objective function.