2020 Volume 73 Pages 23-32
Ocean bottom gravimery can acquire precise gravity data as same as gravimetry on land, and it can acquire clear and large gravity anomalies compared with sea surface gravimetry by using ships due that the ocean bottom gravimetry is conducted near exploration target. We have developed an ocean bottom gravimeter (OBG-3) to use for explorations of offshore deep basement structures and submarine resources such as seafloor massive sulfide (SMS).
As a part of “Next-Generation Technology for Ocean Resources Exploration (Zipangu-in-the Ocean Project)” as a part of the “Strategic Innovation Promotion Program (SIP)” of the Cabinet Office of Japan, ocean bottom gravimetry utilized the OBG-3 was carried out at the “Hakurei Site” in the middle Okinawa Trough. As a result, the observed gravity anomalies at the “Hakurei Site” can be explained by the gravity anomalies calculated from two-dimensional density structure models which referred SMS sections of the boring core samples by the D/V “Chikyu” of JAMSTEC. The measurement time for each station was only 30 minutes including moving time to the next station 100 m away. This high efficiency of the measurements was achieved by introducing the ROV towing-type exploration system newly developed for SIP.
