VLBIを用いたプレート相対運動の検出

抄録

VLBI technique serves us with a very useful tool in finding relative plate motions. The accuracy of distance determination by the technique is now reaching to a few to several centimeters. Therefore, even a few years of repeated VLBI observations may detect plate motions, if station locations are adequate. The present paper examines the capabilities of VLBI technique in monitoring plate motions in case that one of two stations is located in Japan. Numerical simulations are conducted for this purpose based on simple assumptions on the plate motions as follows; 1) Plates move as rigid materials. 2) Relative motions of plates are subject to Minster and Jordan (1978) and Seno (1977). 3) Two different cases are considered as for the plate boundary close to Japan. Three representative locations are considered as for a VLBI station in Japan: they are 1) Hokkaido, 2) Central Honshu, and 3) Kyushu. Simulations are carried out under the condition that the relative plate motion should be recognized by a twice of successive VLBI observations, within ten years and for distances between two stations less than 8000 km. After some numerical simulations, we found several possibilities on the detectabilities of relative plate motions surrounding Japan as follows: 1) If we put stations in Japan, relative plate motions between Eurasian, Pacific, Philippine Sea, North American, Indian and Arabic plates are detectable, while those between a Japanese station and stations on African, Antarctic, Cocos, Nazca and Caribbean plates are not detectable. 2) Motion of Pacific plate can be detected within one year, if we put an accompanied station at Hawaii. 3) Fiducial station in Kyushu would have some advantages in watching Philippine Sea and Arabic plates, 4) Kashima is not a suitable location to watch Philippine Sea plate. 5) It takes three to four years to find relative motion between Eurasian and North American plates, if we put stations in Hokkaido and Kyushu. 6) Indian plate motion could be detected in a few years, if station locations are suitable. These suggestions could be usefully considered when we plan the VLBI station net-work in Japan, although we should be careful in direct applications of these results because of oversimplifications in assumptions.