Ocean Bottom Seismometer (OBS)

An ocean-bottom seismometer (OBS) is a seafloor instrument that records ground motion and pressure to image crustal structure and offshore seismicity. It carries a three-component geophone for ground velocity and a hydrophone for acoustic pressure, free-falls to the seabed, and is recovered by acoustic release. OBS networks record natural earthquakes and controlled air-gun shots; the travel times feed seismic refraction and reflection models of layer velocities at passive margins, subduction zones, and mid-ocean ridges. Deployment depth reaches 6,000 to 7,300 m and missions run from days to over a year. OBS data underpins offshore tectonic and hazard studies.