Development of an Ocean Bottom Seismometer handled by a submarine

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This report summarizes the developments of an Ocean Bottom Seismometer handled by a submersible vessel (Model III of Kyoto Univ.) and an ocean bottom seismometer (Model IV of Kyoto Univ.), and their applications to seismological observations offshore Hokkaido. The OBS of Model IV is characteristic of : (1)three-component force-balanced sensors with a flat response up to 40 sec in velocity output, (2)the inclination of the seismometer can be measured with recording a DC offset from the vertical component which enables us to install even on a slope at the ocean bottom. However, there are demerits in this designing : (1)the force balanced sensor unit needs a relatively large amount of DC current and makes an OBS observationable period as short as 10 days ; (2)the metal pressure containers (aluminum) of 30 kg needs a substantial amount of buoyancy makes the whole unit of seismometer as heavy as 100kg. To overcome these difficulties, we redesigned and produced one unit named Model IV of Kyoto Univ. We adopted a magnetoptical recorder and glass anti-pressure container which made the seismometer considerably lighter in weight and having a longer observational period. As a matter of fact, this OBS cannot be handled by a submersible vessel because of its fragile glass container. To solve this obstacle, we are now planning to make a metal anti-pressure container with a substantially lower cost.The present study developed basic ideas and concepts of OBS handled by a submersible vessel.