The present paper is a preliminary technical report of the development of ocean-bottom seismograph observation in the Bohai Sea area of China, conducted under financial support from Japan Foundation for Shipbuilding Advancement.
This report mainly includes the following contents:
(1) The seismicity and seismic risk assessment of the Bohai Sea area and its vicinity.
(2) Conditions for sea-bottom seismograph observation in the Bohai Sea area.
(3) Some results of preliminary study on instruments and techniques for ocean-bottom seismograph observation in the Bohai Sea area.
(4) The results of experimental modelling researches on the noises of ocean-bottom seismograph observation in the case of shallow sea.
The historical and present seismicity, the long-term seismic risk, and the relation between large earthquakes which occurred in North China and Japan have been studied. The problems on influences of a strong earthquake and tsunami upon the Bohai Sea navigation routes and near populated areas were discussed. Based on the result the necessity of sea-bottom seismograph observation in the Bohai Sea area was explained.
The conditions in the Bohai Sea area, introduced in this paper, include the sea-bottom geomorphology, strong waves and meteorological conditions, and the sea navigation and Sea work condition in this sea area.
Some problems on the instruments and techniques for sea-bottom seismograph observation in the Bohai Sea area were studied and discussed. The preliminary seismograph observation test at the platform of an oil well in the Bohai Sea area was made by the Seismological Bureau of Tianjin, Some new techniques, and successes in noise reduction and signal transmission etc. of sea-bottom seismograph observation advanced by the Meteorological Research Institute of Japan Meteorological Agency (JMA) may be applied to the sea-bottom seismograph observation in the Bohai Sea area. On the basis of these results, a preliminary project to develop the sea-bottom seismograph observation in the Bohai Sea area of China was proposed.
To study the noises of sea-bottom seismograph observation in the case of shallow sea, a new experimental modelling research has been completed. The noises caused by sea surface source and sea interior source were studied separately. Some important experimental results have been presented.
The preliminary results, obtained in this paper, may be useful to develop the sea-bottom seismograph observation in the Bohai Sea area and its vicinity.