Development of an Ocean Bottom Seismometer handled by a submarine

本文介绍了京都大学的III型海底地震仪的研制情况。和海底地震仪（京都大学的Model IV），及其在北海道近海地震观测中的应用。模型IV的OBS的特点是：（1）三分量力平衡传感器，具有高达40秒的速度输出的平坦响应，（2）地震计的倾斜度可以通过记录垂直分量的直流偏移来测量，这使得我们能够安装在海底的斜坡上。然而，这种设计也存在缺点：（1）力平衡传感器单元需要较大的直流电流，使得OBS的可观测期短至10天;（2）30 kg的金属压力容器（铝）需要相当大的浮力，使得整个地震计单元重至100 kg。为了克服这些困难，我们重新设计并制造了一台京都大学的IV型地震仪。我们采用了磁光记录器和玻璃抗压容器，使地震仪的重量大大减轻，并具有较长的观测周期。事实上，这艘外太空船的玻璃容器易碎，不能用潜水船处理。为了解决这个问题，我们现在正计划使一个金属抗压力容器具有显着降低costs.The本研究开发的基本思想和概念的OBS处理的潜水船。

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.