A seismic sensor station includes a housing 1 containing a fibre optic hydrophone and a fibre optic accelerometer x, y, z that can both be made from a single length of optical fibre 32 arranged inside the housing 1. The fibre optic accelerometer x, y, z is arranged in a liquid/oil filled compartment of the housing 1 for damping of mechanical resonances in the accelerometer due to mechanical disturbances and pressure fluctuations. Cross sensitivity between the hydrophone and the accelerometer is reduced. The accelerometer and hydrophone may include an array of Bragg gratings 41-46 and interferometers. A pressure transfer device 86 may be used to allow low frequency and dc pressure variations into the housing 1 but blocking high frequency ac pressure signals.