GPS Earth Observation Network Research Articles

GEONETデータから求めた伊豆半島～富士山付近の地殻水平歪とテクトニックな考察

In order to understand the active tectonics in the Izu collision zone, the Pacific coast of central Japan, we analyzed the daily coordinate data from GEONET (GPS Earth Observation NETwork), which is a nationwide dense network of continuous GPS observation operated by Geographical Survey Institute (GSI), in the Kanto-Tokai districts surrounding the collision zone for the period from January 1997 to January 2003. In the collision zone the Izu Peninsula, the northern cusp of the Izu-Bonin volcanic arc, is colliding against Honshu as the northernmost part of the Philippine Sea plate, and an active volcanic chain is crossing the collision boundary. For six successive one-year intervals we obtained distributions of principal axes of horizontal crustal strain rate, dilatation rate, and maximum shear strain rate in the Kanto-Tokai districts based on velocity vectors at every 0.1 degrees which were interpolated from observed velocity vectors. We examined the distributions of dilatation rate in particular, and found that all remarkable seismic and volcanic activities in the study area were detected in the distributions, proving the reliability of analyzed results. The notable feature in the distribution of dilatation rate is the existence of positive areas around Mt. Fuji, the most remarkable volcano to the north-northwest of the Izu Peninsula. One possibility for the cause of the positive dilatation is an inflation of magma chamber beneath Mt. Fuji. The other possibility is the regional tectonic effect due to the collision process. The crustal strain in the northern part of the Izu Peninsula is rather small, whereas that in the southern part is considerably large, which seems to reflect the present stage of the Izu collision process.

Regional ionosphere map over Japanese Islands

Based on the high time and spatial resolution total electron content (TEC) data, which is estimated from the phase and code observables obtained by using GPS (Global Positioning System) Earth Observation Network (GEONET), the TEC distribution and its time variation over Japanese Islands are scaled into 0.5° × 0.5° grid data for each 10 minutes. The TEC daily map time series are arranged in an array to show the TEC evolution. Based on the spherical harmonics expansion of global ionospheric TEC model (GIM), which is estimated from global GPS observation, the TEC maps are expanded firstly through as high as 60 degrees and orders for a spherical harmonic function as a regional ionosphere map (RIM). The evolution history of medium scale traveling ionospheric disturbances (MSTIDs), i.e. polarward intense TEC enhancement and pre-noon rapid irregular fluctuations near the geomagnetic equator, are identified and confirmed in a quiet geomagnetic period.

稠密GPS観測網により観測された東北奥羽脊梁山地の地殻変動

A dense GPS network was established in 1997 around Ou Backbone Range (OBR), northeastern Japan, by deploying 9 new continuous GPS stations so as to complement the sparse portion of GEONET (GPS Earth Observation Network) operated by Geographical Survey Institute (GSI), Japan. This new observation network is aimed to investigate the present deformation and to understand the relationship between the occurrence of intraplate earthquakes and the deformation process of an island-arc crust.GPS data are analyzed using a precise point positioning strategy of GIPSY/OASIS-II. Coordinates of the GEONET stations in daily SINEX files have been supplied by GSI. A map of the intraplate deformation field derived by combining the two data sets and by subtracting the motion of the North American Plate demonstrates displacements toward WNW along the Pacific coast. This is caused by the interplate coupling between the Pacific and North American Plates. Displacements along the Japan Sea coast, on the other hand, are considerably small in magnitude, and directed to NW and N in the southern and northern area, respectively. OBR lies halfway between the two coasts and shows the transitional pattern of both deformation characteristics.By producing grid data of displacement velocities and taking spatial derivatives, we obtained a map of strain rate distribution. We found that the region between 38.8°N and 39.8°N in OBR demonstrates notable concentration of EW contraction. The region coincides with the area of active seismicity and includes the focal areas of 1896 (M7.2), 1962 (M6.5), 1970 (M6.2), and 1998 (M6.1) events. The observed strain is larger than can be explained by the total moment release of earthquakes that occurred in the same period of this study. Possible sources of the strain concentration may be viscoelastic deformation due to the large earthquakes and/or aseismic slip along the deeper extension of active faults.

Three-dimensional distribution of water vapor estimated from tropospheric delay of GPS data in a mesoscale precipitation system of the Baiu front

Three-dimensional distributions of water vapor in a mesoscale precipitation system, which developed on 7 July 1996 in the Baiu front, were estimated directly from the GPS data of ‘GPS Earth Observation Network’ (GEONET) of the Geographical Survey Institute. In estimating the three-dimensional distribution of water vapor from the GPS data, we used the tropospheric delays along each path from GPS satellites to GPS receivers on the ground. The result showed that the moist air extended up to the height of 6 km in the precipitation region in the early stage of the precipitation system and that a dry air intruded into the precipitation system from the northwest in the middle-level (from 3 km to 5 km altitude) in the later stage. This dry air intrusion in the middle-level was supported by numerical simulations.

High resolution mapping of TEC perturbations with the GSI GPS Network over Japan

Two‐dimensional total electron content (TEC) perturbations over Japan are mapped with the Geographical Survey Institute (GSI) GPS network, GEONET (GPS Earth Observation Network). Its spatial resolution is 0.15° latitude × 0.15° longitude and temporal resolution is 30 seconds. Two‐dimensional TEC observations with these high resolutions revealed spatial structures and temporal evolutions of traveling ionospheric disturbances (TIDs) in the nighttime mid‐latitude ionosphere on July 03, 1997. A preliminary result of the TEC perturbation mapping indicates that it would be a strong tool to investigate the ionospheric structures in detail. Coordinated observations with other ionospheric observation techniques, such as incoherent scatter (IS) radars, airglow imagers, and ionosondes, are needed to clarify the vertical structure of the ionosphere.

ＧＰＳ連続観測システムとその応用

ＧＰＳ連続観測システムとその応用