Suito H.,Geospatial Information Authority of Japan
Earth, Planets and Space | Year: 2017
This study develops a three-dimensional viscoelastic model using the finite element method to understand the postseismic deformation that followed the 2011 Tohoku-Oki earthquake. The question of understanding which elements of the viscoelastic media affect the surface deformation is of particular importance. We first examined the individual effects of two different viscoelastic media, the mantle wedge and the oceanic mantle, which produce almost opposite deformation patterns. The mantle wedge controls eastward motion, uplift of the Pacific coastal and offshore regions, and extension across a broad area. In contrast, the oceanic mantle controls dominantly offshore westward motion, subsidence across a broad area, minor uplift of the surrounding areas, and contraction offshore. These differences are the most important issues for understanding the viscoelastic relaxation caused by subduction earthquakes. We then developed four different models to clarify which elements of the viscoelastic media affect the observed surface deformation. The simplest model, with uniform viscosity for all viscoelastic media, could explain the horizontal deformation but not the vertical deformation. The second model, with different viscosities for the mantle wedge and the oceanic mantle, could explain the onshore observations but could not explain the seafloor observations. The third model, which includes a thin weak layer beneath the subducting slab, could essentially explain the near-field onshore and seafloor observations but could not explain the far-field data. The final depth-dependent model was able to explain the far-field data as well as the near-field data. In these typical models, it is of particular importance to consider the different viscosities between the mantle wedge and the oceanic mantle and to include a thin weak layer beneath the slab, which has a dramatic impact on the seafloor deformation. Far-field data as well as near-field data are also important for constraining the viscoelastic structure; the former is sensitive to viscoelastic relaxation at greater depths. Clearly, viscoelastic relaxation alone cannot explain the observed deformation. A combined viscoelastic and afterslip model is necessary for constructing a complete postseismic deformation model.[Figure not available: see fulltext.] © 2017 The Author(s).
News Article | July 13, 2017
As G20 Summit 2017 drew to a close, the issue of climate change divided the world. As it happened, 19 of the 20 leaders were able to agree on all points made in the joint declaration (known as the communique)--with the exception of Donald Trump, who could not agree on climate change; thus resulting in 'G19' (i.e. G20 sans the United States) releasing a joint statement on climate change. Leaving politics aside, for the people around the world who inhabit as much as 71% of the world's coastlines and are surrounded by oceans, this is not just a statement on a piece of paper, but a commitment of world leaders to take the wellbeing of our further generations to heart, to tackle the burning of fossil fuels and global warming collectively. Climate change can cause a range of effects on coastal environments. Some of the effects are related to erosional processes such as a decrease in sediment supply, changes in the intensity and frequency of extreme events (storms and cyclones, among others), and changes in sea levels and in the wave climate. The estimation of changes due to sea level rise (SLR) and climate change is a major issue with respect to future coastal management decisions. No one is more concerned than the Japanese, who are surrounded by seas; about 73% of Japan is forested, mountainous, and unsuitable for agricultural, industrial, or residential use, as a result, the habitable zones are mainly located in or near coastal areas, so much so that, there are growing concerns in Japan of the impact of climate change on their coastal surroundings, prompting the Japanese government to set up an Intergovernmental Panel on Climate Change (IPCC) to undertake a study on climate change, to provide future projections of coastal erosion based on representative concentration pathway (RCP) scenarios. So far, the study indicates that rising sea levels (SLR) and increasing maximum wave heights due to climate change would lead to shoreline retreat. Japan's coasts have already undergone significant erosion due to rapid national development after World War II; future beach erosions would significantly affect areas behind the coasts where both population and property are densely concentrated. The first projection of future beach erosion all along Japanese coasts was published in 1994 by Mimura et al. (1994), who calculated that beach erosion caused by SLR would occur in values of 0.30, 0.65, and 1.00m based on the projections of the IPCC First Assessment Report (IPCC, 1990). Twenty years later, Udo and Takeda (2014) projected the rate of beach loss at SLR values of 0.1 to 1.0m using the same method as Mimura et al. (1994), further refined with a different beach data set obtained from 1/25,000 scale maps issued by the Geospatial Information Authority of Japan (GSI) (Kishida and Shimizu, 2000). In their investigation, Udo and Takeda (ibid) determined beach-loss rates of 49% for an SLR of 0.3m and 93% for an SLR of 1.0m. Yoshida et al. (2013), had projected future beach erosion using the Bruun rule (Braun, 1962) due to SLR for SRES A1B to have the greatest effect on beach erosion. In the study by Keiko Udo and Yuriko Takeda, published in Coastal Engineering Journal on 29th May 2017, the authors projected beach losses in the 77 coastal zones throughout Japan caused by future SLR (2081 to 2100) relative to a reference period (1986 to 2005) using 21 CMIP5 models, and constructed a beach-loss curve for SLR averaged along the entire coastline of Japan. Uncertainties due to different SLR projections and sediment sizes were also taken into consideration. Finally, temporal changes in beach loss rates from 2007 to 2100 were given for the projections of GMSLR for each RCP scenario, and the histograms of mean beach width in the 77 coastal zones were projected for the future. The beach-loss rate in the future (2081 to 2100) was projected by the Bruun rule to be 62% for the ensemble mean RCP2.6 scenario, 71% for RCP4.5, 73% for RCP6.0, and 83% for RCP8.5; the rates projected by the 21 models for RCP4.5 ranged widely from 61% (MRI-CGCM3) to 87% (MIROC-ESM). Although the effect of the spatial distribution of SLR in each CMIP5 model on beach loss rate in Japan is insignificant, the effects of differences in the SLR values among the RCP scenarios and CMIP5 models are significant. The maximum uncertainty caused by the sediment size (0.2-0.6mm) against the same SLR was 38%. Projections of the beach-loss rate from 2007 to 2100 for GMSLR of the different RCP scenarios revealed that the rates were between 18% and 79% and differed by 60% in the near future and between 28% and 96% differed by 70% in the future. Large uncertainties were caused by the GMSLR scenario and sediment size; however, the minimum projected rate of beach loss was 18% in the near future, and this rate of loss is expected to have significant implications for coastal management. For the upper bound scenario in the near future, the projected beach width in more than half of the 77 coastal zones is 0-10 m, which would cause serious damage to coastal areas in consideration of coastal protection, environmental concerns, and beach utilization. Hence, in conclusion, the authors stated that beach loss due to SLR is an urgent issue that must be addressed through the development of better coastal management strategies to combat beach loss. World Scientific Publishing is a leading independent publisher of books and journals for the scholarly, research, professional and educational communities. The company publishes about 600 books annually and about 130 journals in various fields. World Scientific collaborates with prestigious organizations like the Nobel Foundation and US National Academies Press, amongst others, to bring high quality academic and professional content to researchers and academics worldwide. To find out more about World Scientific, please visit http://www. . For more information, contact Dr Yan-Hong Ng at email@example.com
Ozawa S.,Geospatial Information Authority of Japan
Geophysical Research Letters | Year: 2014
A slow slip event occurred off the coast of the Boso peninsula, Japan, from approximately 28 December 2013 to 10 January 2014. The estimated aseismic slip expanded slightly southward and westward over time with a moment magnitude of 6.5, which was the smallest value since 1996. The recurrence interval has decreased from approximately 6.4 to 2.2years from 1996 to 2014. One explanation of this shortening is the change in Coulomb failure stress due to the 2011 Mw9.0 Tohoku earthquake and its afterslip. Another interpretation is related to a scenario observed in several numerical simulation studies, in which the recurrence interval of slow slip becomes shorter as the time nears a large earthquake. This case will constrain the physical processes of a slip cycle. The Boso slow slip events together with the Tohoku earthquake and its afterslip changed the stress state for the anticipated interplate earthquake near the Sagami trough. Key Points Spatial and temporal slow slip process in Boso slow slip, Japan Shortening of the recurrence interval DCFS is increasing after the Tohoku earthquake ©2014. American Geophysical Union. All Rights Reserved.
Kobayashi T.,Geospatial Information Authority of Japan |
Morishita Y.,Geospatial Information Authority of Japan |
Yarai H.,Geospatial Information Authority of Japan
Earth, Planets and Space | Year: 2015
We have successfully detected widely distributed ground displacements for the 2015 Gorkha earthquake by applying a ScanSAR-based interferometry analysis of Advanced Land Observing Satellite 2 (ALOS-2) L-band data. A major displacement area extends with a length of about 160 km in the east-west direction, and the most concentrated crustal deformation with ground displacement exceeding 1 m is located 20-30 km east from Kathmandu. A quasi-vertical displacement estimated by combining the ascending and the descending data indicates upheaval of about 1.4 m at maximum. We inverted the synthetic aperture radar interferometry (InSAR) data including both of the main shock (moment magnitude (Mw) 7.8) and the largest aftershock (Mw 7.3) to construct a slip distribution model. Our model shows a nearly pure reverse fault motion with a slip amount of approximately 6 m at maximum, and the spatial extent is zonally distributed within a distance of 50 to 100 km from the surface along downdip direction. The downdip end of the slip is quite consistent with that of the interseismic coupling area geodetically inferred in previous studies. On the other hand, there is no significant slip at shallow depth in spite of the fact that the plate interface is thought to be fully locked there, may be suggesting that there still remains a potential of fault slip. The slip distribution unnaturally bifurcates in the east, and we can identify a clear-cut slip deficit area with a radius of ~10 km just west side of the Mw 7.3 event, where the slip amount reaches only 20 cm at most. This area is presumably subjected to a strong shear stress which should promote a reverse fault slip. There is a possibility to produce a fault slip equivalent to Mw ~7.0 in the future although we do not know if the slip heterogeneity would be smoothed out by a seismic event or an aseismic event. © 2015 Kobayashi et al.
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.
Yarai H.,Geospatial Information Authority of Japan |
Ozawa S.,Geospatial Information Authority of Japan
Journal of Geophysical Research: Solid Earth | Year: 2013
The time evolution of afterslip on a plate boundary experiencing interplate earthquakes is expected to show logarithmic decay. The global positioning system network in Japan has been monitoring transient deformation since the occurrence of two large interplate earthquakes with moment magnitudes of 6.8 and 6.7 in the Hyuga-nada area, southwest Japan, in 1996. The spatial and temporal evolution of aseismic interplate slip based on crustal deformation data indicates that afterslip followed the two earthquakes and gradually declined to background rates by around 2004 with total moment magnitude of 7.3. However, quasi-periodic slow slip events suddenly began within the afterslip area in 2005 with approximately one year duration and two-year recurrence interval. The moment magnitudes of the three slow slip events since January 2005 range from 6.7 to 6.8. This differs greatly from the expected behavior of logarithmic decay over time. Both velocity-strengthening and velocity-weakening rate-and-state modes have been implicated as the cause of afterslip, whose location is complementary to the main shock area of velocity-weakening, while a slow slip event occurs in the velocity-weakening area with different frictional properties from those of an afterslip area. In light of the seemingly different frictional properties, the coexistence of afterslip and slow slip events in the same area would provide additional information about precisely how the plate interface is behaving. The monitoring of these slow slip events should give the clues to understanding the coexistence of long-term afterslip and slow slip events and the increasing risk of earthquakes in neighboring areas. © 2013. American Geophysical Union. All Rights Reserved.
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.
Kuroishi Y.,Geospatial Information Authority of Japan
Nature Photonics | Year: 2016
According to Einstein's theory of relativity, the passage of time changes in a gravitational field. On Earth, raising a clock by 1 cm increases its apparent tick rate by 1.1 parts in 1018, allowing chronometric levelling through comparison of optical clocks. Here, we demonstrate such geopotential measurements by determining the height difference of master and slave clocks separated by 15 km with an uncertainty of 5 cm. A subharmonic of the master clock laser is delivered through a telecom fibre to synchronously operate the distant clocks. Clocks operated under such phase coherence reject clock laser noise and facilitate proposals for linking clocks and interferometers. Taken over half a year, 11 measurements determine the fractional frequency difference between the two clocks to be 1,652.9(5.9) × 10-18, consistent with an independent measurement by levelling and gravimetry. Our system demonstrates a building block for an internet of clocks, which may constitute ‘quantum benchmarks’, serving as height references with dynamic responses. © 2016 Nature Publishing Group
Tobita M.,Geospatial Information Authority of Japan
Earth, Planets and Space | Year: 2016
The time series of a postseismic deformation is commonly fitted by a logarithmic or exponential decay function. However, the high-quality postseismic Global Navigation Satellite System (GNSS) time series of the 2011 Mw 9 Tohoku-Oki earthquake indicates that a single decay function cannot be used to represent the postseismic behaviour. We therefore combined the logarithmic (log) and exponential (exp) decay functions and developed methods for obtaining global solutions using nonlinear least squares calculations for such complex functions. Our models significantly improved the fitting performance of the postseismic time series and the prediction performance of the evolution of postseismic deformation. The solutions obtained by the proposed models and methods enabled distinction between the contributions of the log and exp functions, and explanation of characteristic phenomena such as the subsidence that occurs immediately after an earthquake is reversed to an uplift. The analysis of the solutions may suggest that there has been a continuous increase in the contribution of viscoelastic relaxation to postseismic deformation in eastern Japan, whereas the contribution of afterslip has rapidly decreased. The short-term prediction performance and the universal applicability of the proposed models to the Tohoku-Oki earthquake have contributed to the detection of a slow-slip event in the Tokai region. Rather than the existence of a unique single relaxation time for each surface site, our results suggest a unique single relaxation time for each postseismic deformation mechanism at a given subsurface location. Although the predictions were highly dependent on the assigned steady velocities and the long-term relaxation time constants, they indicate that the coseismic subsidence of the Yamoto station in Miyagi prefecture will recover around the year 2020. The estimated relaxation time constants of the present models appeared to be uniform throughout eastern Japan. © 2016 Tobita.
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.