The power of interferometric SAR （InSAR） is to clarify spatial distributions of crustal deformation thoroughly, and by performing time-series analysis, it is possible to detect displacement even at several mm/year. However, as accuracy of satellite InSAR observations and analyses has increased, error factors, which were not conspicuous in the past, have become obstacles to the crustal deformation observations. One of them is phase delay of the SAR microwave in a medium caused by the dielectric properties of the medium. In the case of soil or trees, apparent line-of-sight （LOS） changes depending on difference in vegetation and land use, such as urban areas and forest areas, appears in SAR interferograms. In addition, the difference in LOS exceeding several centimeters can occur depending on positional relationship between the satellite and directions of the ground slope. There are two mechanisms for the changes in LOS caused by changes in the dielectric constant depending on the water content of the medium. In general land, effects of the changes in penetration depth of microwaves into the medium are not observed, and the apparent changes in LOS are due to changes in the propagation velocity of microwaves in the medium. However, there are cases where the depth-of-penetration change is noticeable in snow cover, which cannot be interpreted simply. Even if this is mitigated by statistical processing such as the InSAR time-series analysis, the result may remain as an error of several mm/year. Therefore, when discussing minute changes, paying attention to such systematic errors contained in the InSAR results is necessary.

　The FG5 absolute gravimeter yields estimates of the gravity acceleration typically at the height of 130 cm above the floor. In order to transfer the gravity value to another height such as the surface of the floor, precise knowledge of a vertical gradient of gravity acceleration is necessary. Gravity gradients are commonly measured by using relative gravimeters, but limited precision in relative gravity measurements leads to less precise values of the transferred gravity. In this study, a trial was made to measure the vertical gravity gradient using the FG5 absolute gravimeter. Absolute gravity measurements were made at two different heights with vertical separation of about 13 cm at the gravity station in Mount Fuji Research Institute, Yamanashi, Japan. As a result, relative precision of about 0.5％ was established for the estimate of the vertical gradient of gravity.

　We analyzed the “spatial distribution of trends” utilizing high-rate GNSS data, analogous to that employed in a preceding study reporting pre-slip antecedent to the 2011 Tohoku-Oki earthquake. Our analysis focused on the temporal window encompassing the four hours preceding the mainshock. The data revealed a predominance of positive trend values across Eastern Japan. Notably, in the coastal vicinities surrounding Miyagi Prefecture （near the epicenter of the earthquake）, these positive trend values did not exhibit any systematic augmentation. Furthermore, these observed positive values spanning Eastern Japan could be effectively represented as the first principal component.