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Nishimura T.,Geography and Crustal Dynamics Research Center | Nishimura T.,Kyoto University | Matsuzawa T.,Japan National Research Institute for Earth Science and Disaster Prevention | Obara K.,University of Tokyo
Journal of Geophysical Research: Solid Earth | Year: 2013

We detected short-term slow slip events (SSEs) previously observable only with tilt and strain data along the Nankai Trough, southwest Japan, using GNSS (Global Navigation Satellite System) data. Offsets detected in GNSS time series using Akaike's information criterion helped automatically identify 207 episodes with a motion direction opposite to that of the relative plate motion from June 1996 to January 2012. By nonlinear inversion of the detected displacement, we estimated rectangular fault models for 133 probable and 25 possible short-term SSEs over 15 years. The SSE moment magnitudes range from 5.5 to 6.3. Most SSE fault models are located in a narrow band of non-volcanic tremors on the interfaces of the subducting Philippine Sea Plate. Large SSEs (moment magnitude, Mw, ≥6) often occur in western and central Shikoku. The cumulative slip is distributed heterogeneously along the strike, generally decreasing eastward with the maximum slip (~50 cm) in western Shikoku. No definite short-term SSEs were found in the Kii Channel, but several short-term SSEs occurred in Ise Bay. Both regions are known as tremor gaps. The local maximum of the cumulative slip fills in the tremor gap located in Ise Bay. The long-term rate of short-term SSE cumulative moment increased by threefold around 2003 in eastern Shikoku, whereas it was almost constant in other regions. Comparison with short-term SSE catalogues using tilt data suggests that both this study and previous studies missed some SSEs along the Nankai Trough. A combination of geodetic data is important in the monitoring of the spatiotemporal distribution of short-term SSEs. Key Points Short-term slow slip events along the Nankai Trough are detected using GNSS data Non-uniformly distributed SSEs (>150) occurred along the strike over 15 years The ETS zone had a gap in cumulative SSE slip in Kii Channel, but not in Ise Bay ©2013. American Geophysical Union. All Rights Reserved. Source


Nishimura T.,Geography and Crustal Dynamics Research Center
Tectonophysics | Year: 2011

We examined GPS data in the northwestern Pacific region, which includes the Izu-Ogasawara (Bonin)-Mariana (IBM) arc and the Japan arc. GPS velocity vectors on the Izu Islands, including Hachijo-jima and Aoga-shima, show systematic eastward movement deviating from that predicted by the rigid rotation of the Philippine Sea plate; this deviation supports the active back-arc spreading model suggested by previous geological studies. The results of a statistical F-test analysis with 99% confidence level showed that the forearc of the Izu Islands arc has an independent motion with respect to the rigid part of the Philippine Sea plate. We developed a kinematic block-fault model to estimate both rigid rotations of crustal blocks and elastic deformation due to locked faults on the block boundaries. The model suggests that the back-arc opening rate along the Izu back-arc rift zone ranges from 2. mm/yr at its southern end to 9. mm/yr near Miyake-jima, its northern end. It also predicts 23-28. mm/yr of relative motion along the Sagami Trough in the direction of ~. N25°W, where the Izu forearc subducts beneath central Japan. The orientation of this motion is supported by slip vectors of recent medium-size earthquakes, repeated slow-slip events, and the 1923 M = 7.9 Kanto earthquake. © 2011 Elsevier B.V. Source


Nakano T.,Geography and Crustal Dynamics Research Center | Sakai H.,University of Toyama | Kato M.,Niigata Archaeological Artifacts Research Association
Proceedings - 2014 IIAI 3rd International Conference on Advanced Applied Informatics, IIAI-AAI 2014 | Year: 2014

Land liquefaction triggered by huge earthquake occurs repeatedly at the same area ([1]). Therefore, it is important to grasp the land liquefaction occurrence area in the past for taking measures against land liquefaction disaster. Reference [6] produces the map data for historic liquefaction sites in Japan based on recent field survey and historical document from the 8th century to 2008. Also, though Reference [13] completed information on land liquefaction vestiges found on archaeological ruins in Japan at that time, later information on land liquefaction vestiges isn't made into database, except for Kanto district, Japan. Therefore, we created a geographic information system (GIS) dataset about information on archaeological ruins with land liquefaction vestiges in Niigata Prefecture, Japan, and analyzed a characteristic of spatial distribution of the ruins by associating with landform classification and/or distance from river by GIS. The result of this analysis indicated a clear trend, and it has great significance because the distribution tendency of land liquefaction in ancient period, which is not included in the 'Maps for historic liquefaction sites in Japan', was comprehended. © 2014 IEEE. Source


Nishimura T.,Kyoto University | Suito H.,Geography and Crustal Dynamics Research Center | Kobayashi T.,Geography and Crustal Dynamics Research Center | Dong Q.,EduScience Research Institute Corporation | Shibayama T.,Computational Mechanics Inc
Geophysical Journal International | Year: 2016

Coseismic deformation depends on both the source fault and on the elastic properties of the crust. Large coseismic deformation associated with the 2011 Mw 9.0 Tohoku-oki earthquake enabled us to investigate strain anomalies from crustal inhomogeneity. Concentrated contractional strain was observed in the Echigo Plain (Niigata-Kobe Tectonic Zone) before the Tohoku-oki earthquake, whereas continuous and campaign global navigation satellite system measurements show a widespread distribution of coseismic extensional strain in and around the plain. A 1-D displacement profile shows high strain (7.2 ± 0.7 microstrain) in a 17 km long section across the Echigo Plain and low strain (3.3 ± 0.4 microstrain) along a 15 km long section east of the plain, despite the latter being closer to the megathrust fault source. We performed numerical modelling of coseismic deformation using a heterogeneous subsurface structure and successfully reproduced excess extension in the plain, which is filled by low-rigidity sediments. This study demonstrates the importance of considering heterogeneous crust in deformation modelling. © The Authors 2016. Source


Koarai M.,Geography and Crustal Dynamics Research Center | Okatani T.,Geography and Crustal Dynamics Research Center | Nakano T.,Geography and Crustal Dynamics Research Center | Nakamura T.,Geospatial Information Authority of Japan | Hasegawa M.,Geospatial Information Authority of Japan
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences - ISPRS Archives | Year: 2012

The great earthquake occurred in Tohoku District, Japan on 11th March, 2011. This earthquake is named "the 2011 off the Pacific coast of Tohoku Earthquake", and the damage by this earthquake is named "the Great East Japan Earthquake". About twenty thousand people were killed or lost by the tsunami of this earthquake, and large area was flooded and a large number of buildings were destroyed by the tsunami. The Geospatial Information Authority of Japan (GSI) has provided the data of tsunami flooded area interpreted from aerial photos taken just after the great earthquake. This is fundamental data of tsunami damage and very useful for consideration of reconstruction planning of tsunami damaged area. The authors analyzed the relationship among land use, landform classification, DEMs data flooded depth of the tsunami flooded area by the Great East Japan Earthquake in the Sendai Plain using GIS. Land use data is 100 meter grid data of National Land Information Data by the Ministry of Land, Infrastructure, Transportation and Tourism (MLIT). Landform classification data is vector data of Land Condition Map produced by GSI. DEMs data are 5 meters grid data measured with LiDAR by GSI after earthquake. Especially, the authors noticed the relationship between tsunami hazard damage and flooded depth. The authors divided tsunami damage into three categories by interpreting aerial photos; first is the completely destroyed area where almost wooden buildings were lost, second is the heavily damaged area where a large number of houses were destroyed by the tsunami, and third is the flooded only area where houses were less destroyed. The flooded depth was measured by photogrammetric method using digital image taken by Mobile Mapping System (MMS). The result of these geographic analyses show the distribution of tsunami damage level is as follows: 1) The completely destroyed area was located within 1km area from the coastline, flooded depth of this area is over 4m, and no relationship between damaged area and landform classification. 2) The heavily damaged area was observed up to 3 or 4km from the coastline. Flooded depth of this area is over 1.5m, and there is a good relationship between damaged area and height of DEMs. 3) The flood only area was observed up to 4 or 5km from the coastline. Flooded depth of this area was less than 1.5m, and there is a good relationship between damaged area and landform. For instance, a certain area in valley plain or flooded plain was not affected by the tsunami, even though an area with almost the same height in coastal plain or delta was flooded. These results mean that it is important for tsunami disaster management to consider not only DEMs but also landform classification. Source

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