Munekane H.,Geospatial Information Authority of Japan
Earth, Planets and Space | Year: 2012
GPS kinematic time series are analyzed to estimate slip distributions for the Mw 9.0 2011 off the Pacific coast of Tohoku Earthquake sequence. Empirical orthogonal function (EOF) analysis is employed to enhance the signal-to-noise ratio of the original time series. The coseismic, and subsequent postseismic, deformations of the foreshock can be described by a single mode, suggesting that the extent of the source for both events must be similar. The total moment magnitude of the afterslip following the foreshock is estimated to be Mw 7.1 with a decay time of 0.63 days. The magnitude of the afterslip was larger for its duration than was anticipated by the scaling law for a typical slow earthquake, although two previous earthquakes in adjacent regions showed the same tendency as that in the present case. The pattern of slip of the mainshock and the subsequent afterslips and aftershocks indicates that each slip occurs in a region adjacent to that of the previous slips in a complementary manner. Finally, in the course of the EOF analysis, the modes representing the thermal expansion of the GPS pillars are clearly identified. © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB.
Munekane H.,Geospatial Information Authority of Japan
Journal of Geodesy | Year: 2013
The sub-daily noise in horizontal global positioning system (GPS) kinematic time series arising from monument tilts is quantitatively evaluated using tiltmeter data at GPS stations from the Japanese nationwide global navigation satellite system network. The estimated tilt-induced monument displacements show characteristics that are typical of those caused by thermal tilts of the monuments. The root mean square of the displacements is typically a few millimetres, with notable inter-seasonal variations. The stacked amplitude spectra of the monument displacements have peaks at the tidal bands S1 and S2, and their higher tones. The peaks at the S1 and S2 bands in the amplitude spectra are reduced by 41 and 43 % for the north-south component and 36 and 53 % for the east-west component, respectively, after correcting for the monument displacements. The monument displacements due to the thermal tilts of the monuments may also be a favourable candidate for sub-daily noise at the S1 and S2 bands found in other GPS networks. © 2013 Springer-Verlag Berlin Heidelberg.
Morishita Y.,Geospatial Information Authority of Japan |
Hanssen R.F.,Technical University of Delft
IEEE Transactions on Geoscience and Remote Sensing | Year: 2015
Temporal decorrelation is one of the main limitations of synthetic aperture radar (SAR) interferometry. For nonurban areas, its mechanism is very complex, as it is very dependent of vegetation types and their temporal dynamics, actual land use, soil types, and climatological circumstances. Yet, an a priori assessment and comprehension of the expected coherence levels of interferograms are required for designing new satellite missions (in terms of frequency, resolution, and repeat orbits), for choosing the optimal data sets for a specific application, and for feasibility studies for new interferometric applications. Although generic models for temporal decorrelation have been proposed, their parameters depend heavily on the land use in the area of interest. Here, we report the behavior of temporal decorrelation for a specific class of land use: pasture on drained peat soils. We use L-, C-, and X-band SAR observations from the Advanced Land Observation Satellite (ALOS), European Remote Sensing Satellite, Envisat, RADARSAT-2, and TerraSAR-X missions. We present a dedicated temporal decorrelation model using three parameters and demonstrate how coherent information can be retrieved as a function of frequency, repeat intervals, and coherence estimation window sizes. New satellites such as Sentinel-1 and ALOS-2, with shorter repeat intervals than their predecessors, would enhance the possibility to obtain a coherent signal over pasture. © 2014 IEEE.
Tobita M.,Geospatial Information Authority of Japan |
Nishimura T.,Geospatial Information Authority of Japan |
Kobayashi T.,Geospatial Information Authority of Japan |
Hao K.X.,Japan National Research Institute for Earth Science and Disaster Prevention |
Shindo Y.,Mitsubishi Group
Earth and Planetary Science Letters | Year: 2011
We present a map of the coseismic displacement field and slip distributions resulting from the Yushu earthquake on 14 April 2010 in Qinghai, China. The wide coverage of ScanSAR data helps in increasing the opportunity of interferometric synthetic aperture radar (InSAR) observations of a specific location on Earth, estimating surface slip, and constraining slip distribution on the fault plane. We increased InSAR sensitivity to the horizontal and vertical surface displacements by combining ascending and descending interferograms. We find that the maximum left-lateral surface slip is 166. cm at ~ 9.7 km WNW of Yushu. The end-to-end length of surface and subsurface faults is about 73 km, and the estimated lengths of the two surface fault lines are 30. km and ~ 9 km. Slip distribution on a fault plane inverted from InSAR data shows an almost pure left-lateral strike-slip, with two slip peaks near the epicentres and Yushu and a maximum slip of ~ 2.6 m. No postseismic deformation is observed southeast of the source region; however, we detected a significant postseismic displacement northwest of the source region. The deformation area is located a few kilometres northwest of the coseismic displacement area observed around Longbao Lake, suggesting that the coseismic slip and the postseismic slips are spatially isolated. © 2011 Elsevier B.V.
Iwahashi J.,Geospatial Information Authority of Japan |
Kamiya I.,Geospatial Information Authority of Japan |
Yamagishi H.,Ehime University
Geomorphology | Year: 2012
We undertake digital terrain analyses of rainfall- and earthquake-induced landslides in Japan, using high-resolution orthoimagery and Light Detection and Ranging (LiDAR) DEMs. Our aims are twofold: to demonstrate an effective method for dealing with high-resolution DEMs, which are often too detailed for landslide assessments, and to evaluate the topographic differences between rainfall- and earthquake-induced landslides. The study areas include the Izumozaki (1961 and 2004 heavy rainfalls), Niihama (2004 heavy rainfalls), Houfu (2009 heavy rainfalls), and Hanokidachi/Kurikoma-dam regions (the 2008. M 7.2 Iwate-Miyagi Nairiku earthquake). The study areas include 7,106 landslides in these five regions. We use two topographic attributes (the slope gradient and the Laplacian) calculated from DEMs in varying window sizes. The hit rates for statistical prediction of landslide cells through discriminant analyses are calculated using the two topographic attributes as explanatory variables, and the landslide inventory data as the dependent variable. In cases of surface failure, the hit rates are found to diminish when the window size of the topographic attributes is too large or too small, indicating that an optimal scale factor is key in assessing shallow landslides. The representative window sizes are approximately 30. m for shallow landslides; the optimal window size may be directly related to the average size of landslides in each region. We also find a stark contrast between rainfall- and earthquake-induced landslides. Rainfall-induced landslides are always most common at a slope gradient of 30°, but the frequency of earthquake-induced landslides increases exponentially with slope gradient. We find that the Laplacian, i.e., the attributes of surface convexity and concavity, and the slope gradient are both important factors for rainfall-induced landslides, whereas earthquake-induced landslides are influenced mainly by slope steepness. © 2012 Elsevier B.V.