Investigation for geodetic detection of variation in crustal deformation near the subduction plate boundary

该研究项目的目标是通过俯冲板块边界附近的海底大地观测，调查俯冲板块运动引起的地壳形变的时空变化，并评估海底大地观测的重复性。岩手县和宫城县外已开展基于海面KGPS定位和水声测距的重复精确海底定位，并已在福岛县外启动。从福岛附近的地震活动来看，该地区板块边界的地震耦合可能相对较弱。然而，这几年的陆上GPS观测表明，福岛附近和宫城附近都存在强烈的耦合。尽管两年观测得到的地壳形变估计误差较大，但结果表明，福岛附近的地震耦合与宫城附近的地震耦合一样强。福岛附近的耦合可能表现出时间上的变化。全球定位系统/声学(GPS/A)在基伊半岛附近的海底定位探测到了与2004年在基伊半岛附近发生的地震(M7.4级)相关的30厘米的大同震地壳运动。通过两天的观测获得的定位的重复性估计约为3-5厘米。这个值大于我们的GPS/A站点与2005年宫城县附近地震相关的估计位移。我们证实，通过更高的GPS采样可以提高该值。在岩手县附近，在用于测高的卫星轨道的两个交叉点下进行了长期的海底压力监测。根据8个主成分向量差的均方根，结果与最近5个1.3 cm范围内的海潮模型相吻合。虽然我们已经掌握了长期海底压力监测的技术诀窍，但要获得压力监测的长期稳定性，还需要进行更多的研究工作。

The objectives of this research program are to investigate for spatial and temporal variations in crustal deformation induced by the subducting plate motion through seafloor geodetic observation in the vicinity of the subduction plate boundary, and to estimate the repeatability of the seafloor geodetic observation.Repeated precise seafloor positioning based on sea surface KGPS positioning and underwater acoustic ranging has been carried out off Iwate and Miyagi prefectures, and has been initiated off Fukushima Prefecture. Judging from seismic activities off Fukushima, seismic coupling on the plate boundary in the region can be relatively weak. However, land-based GPS observation in these several years suggests strong coupling off Fukushima as well as off Miyagi. Although the estimated error is fairly large in the crustal deformation obtained from two-year observations, the result shows that the seismic coupling off Fukushima is as strong as that off Miyagi. The coupling off Fukushima may possibly show temporal variation.GPS/Acoustic (GPS/A) seafloor positioning off Kii Peninsula detected a large co-seismic crustal movement up to 30 cm associated with the 2004 earthquake (M7.4) off Kii Peninsula. The repeatability of the positioning obtained from an observation for two days is estimated to be about 3-5 cm. This value was larger than the estimated displacements at our GPS/A sites associated with the 2005 earthquake off Miyagi Prefecture. We confirmed that the value can be improved with higher GPS sampling.Long-term ocean bottom pressure monitoring was carried out off Iwate Prefecture under two crossover points of the satellite tracks for altimetry. The results coincide with recent five ocean tide models within 1.3 cm in terms of root sum square of vector differences for eight principal constituents. Although we have acquired know-how for long-term ocean bottom pressure monitoring, we need more research works to get long-term stability of pressure monitoring.