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Gunawan E.,Nagoya University | Sagiya T.,Nagoya University | Ito T.,Nagoya University | Kimata F.,Tono Research Institute of Earthquake Science | And 7 more authors.
Journal of Asian Earth Sciences | Year: 2014

We investigate the postseismic deformation of the 2004 Sumatra-Andaman earthquake (SAE) using 5years of Global Positioning System (GPS) data located in northern Sumatra. Continuous GPS data from northern Sumatra suggest that the relaxation time in the vertical displacement is longer than horizontal displacements. This implies that there are multiple physical mechanisms that control the postseismic deformation, which refer to afterslip and viscoelastic relaxation. In this study, we introduce an analysis strategy of postseismic deformation to simultaneously calculate multiple mechanisms of afterslip and viscoelastic relaxation. The afterslip inversion results indicate that the distribution of the afterslip and the coseismic slip are compensatory of each other. Also, afterslip has a limited contribution to vertical deformation in northern Sumatra. In our rheology model, we use a gravitational Maxwell viscoelastic response and the result indicates that the elastic layer thickness is 65±5km and the Maxwell viscosity is 8.0±1.0×1018Pas. We find that afterslip plus Maxwell viscoelastic relaxation are appropriate to explain the deformation in northern Sumatra. We also find that our rheology model reproduces the long-term features of the GPS time series in Thailand. Applying our rheology model to the data in Andaman Islands our afterslip estimation is located at the down-dip part of the plate boundary. Finally, we showed that our rheology model is applicable to the GPS datasets of postseismic deformation of the 2004 SAE located in northern Sumatra, Thailand, and Andaman-Nicobar, respectively. © 2014 Elsevier Ltd.

Furukawa A.,Kyushu University | Spence R.,University of Cambridge | Ohta Y.,Tono Research Institute of Earthquake Science | So E.,University of Cambridge
Bulletin of Earthquake Engineering | Year: 2010

Collapse of adobe buildings during an earthquakes with various earthquake intensities is analyzed using the 3-dimensional distinct element method code developed by the first author. Firstly, we evaluate structural damage with damage index, interior-space damage with w score, and human casualties in the collapsing buildings with three casualty criteria. Secondly, we investigate relationships between the earthquake intensity, the structural damage, the interior-space damage, and the casualties. It is found that the casualties have stronger correlation with the interior-space damage than the structural damage, and three vulnerability functions, namely, structural, interior-space and casualty vulnerability functions, are proposed. Effects of reinforcing methods on these functions are also examined. Finally, a series of analytical procedures to develop vulnerability functions and to estimate casualties using the functions are described. © 2009 Springer Science+Business Media B.V.

Takano K.,Geospatial Information Authority | Kimata F.,Tono Research Institute of Earthquake Science
Earth, Planets and Space | Year: 2013

The ground deformation and fault slip model for the 1891 M 8.0 Nobi earthquake, central Japan, have been reexamined. The Nobi earthquake appears to have occurred mainly due to the rupture of three faults: Nukumi, Neodani, and Umehara. Since triangulation and leveling had been performed around the Umehara fault, the two geodetic datasets from 1885-1890 and 1894-1908 have been reevaluated. Maximum coseismic horizontal displacements of 1.7 m were detected to the south of the Neodani fault. A fault model of the Nobi earthquake was estimated from the geodetic datasets, taking into account the geometry of the fault planes based on the known surface ruptures. The best fit to the data was obtained from three and four divided fault segments running along the Nukumi, Neodani, and Umehara faults; although, in past studies, the Gifu-Ichinomiya line has been suggested as a buried fault to explain the ground deformation. The detected ground deformation can be well reproduced using a slip model for the Umehara fault, dipping at 61° toward the southwest, with a maximum slip of 3.8 m in the deeper northwestern segment. As this model suitably explains the coseismic deformation, the earthquake source fault does not appear to extend to the Gifu-Ichinomiya line.

Duong N.A.,Vietnam Academy of Science and Technology | Sagiya T.,Nagoya University | Kimata F.,Tono Research Institute of Earthquake Science | To T.D.,Vietnam Academy of Science and Technology | And 4 more authors.
Earth, Planets and Space | Year: 2013

We present a horizontal velocity field determined from a GPS network with 22 sites surveyed from 2001 to 2012 in northwestern Vietnam. The velocity is accurately estimated at each site by fitting a linear trend to each coordinate time series, after accounting for coseismic displacements caused by the 2004 Sumatra and the 2011 Tohoku earthquakes using static fault models. Considering the coseismic effects of the earthquakes, the motion of northwestern Vietnam is 34.3 ± 0.7 mm/yr at an azimuth of N1080 ± 0.7°E in ITRF2008. This motion is close to, but slightly different from, that of the South China block. The area is in a transition zone between this block, the Sundaland block, and the Baoshan sub-block. At the local scale, a detailed estimation of the crustal deformation across major fault zones is geodetically revealed for the first time. We identify a locking depth of 15.3 ± 9.8 km with an accumulating left-lateral slip rate of 1.8 ± 0.3 mm/yr for the Dien Bien Phu fault, and a shallow locking depth with a right-lateral slip rate of 1.0 ± 0.6 mm/yr for the Son La and Da River faults. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS).

Queitsch M.,Institute of Geosciences | Jentzsch G.,Institute of Geosciences | Weise A.,Institute of Geosciences | Ishii H.,Tono Research Institute of Earthquake Science | Asai Y.,Tono Research Institute of Earthquake Science
International Association of Geodesy Symposia | Year: 2014

Tilt meters are a widely used tool for monitoring long-term and small-scale deformations. Therefore, they are perfectly suited to test potential subsurface waste repositories. Since November 2005 a high sensitive tilt meter of the ASKANIA-type is recording at a distance of 300m from Mizunami Underground Research Laboratory, where two vertical shafts are under construction. During the construction of those shafts large pumps were used to reduce the groundwater level, leading to two large- and several small-scale pore pressure induced tilt signals. Due to the fault system nearby, the tilt direction does not coincide with the direction towards the pump as would be expected in homogeneous media. In this study we analyze the main surface tilt direction caused by pore pressure induced deformation. Our results show two main directions which are both nearly perpendicular to the fault. Also, the long-term signals show a high correlation with the short-term pore pressure induced tilt signals. © Springer-Verlag Berlin Heidelberg 2014.

Ohkura T.,Kyoto University | Tabei T.,Kochi University | Kimata F.,Tono Research Institute of Earthquake Science | Bacolcol T.C.,Institute of Volcanology and Seismology | And 8 more authors.
Journal of Disaster Research | Year: 2015

We conducted yearly Global Positioning System (GPS) campaigns in the eastern part of Mindanao from March 2010 to March 2014. The obtained station velocities with respect to the Sunda plate (SU) show that WNW motions are dominant due to the convergence of the Philippine Sea plate (PHS). However, it was found that elastic deformations caused by a full coupling of the plate interface down to 80 km could explain a maximum of only 29% of the observed station velocities. In order to interpret the displacement pattern, we applied a rigid block rotation model and determined the Euler vector. As a result, we determined that Mindanao Island could be divided into at least three blocks and that the Philippine fault is one of the block boundaries. Although it was not possible to determine the coupling ratio at the Philippine trench, the dislocation pattern of the Philippine fault showed along-strike variation in Mindanao Island. © 2014 Fuji Technology Press. All rights reserved.

Nakashima T.,Tono Research Institute of Earthquake Science | Okada S.,Hokkaido University
AIJ Journal of Technology and Design | Year: 2010

For the purpose of simplify the method on death toll, this paper proposes the simple method on population for effectively and efficiently selecting the seismic hazard maps having significant impact on Nagoya city, Japan, as an example area in this study. We select the extensive distribution of population exposure seismic intensity by use of the simple method on population, and estimate the effectiveness and the efficiency of selected it. The result shows that nearly 95% of estimated victims in Nagoya city is able to be covered by only 2 maps selected in the strategic choice approach.

Hanifa N.R.,Nagoya University | Sagiya T.,Nagoya University | Kimata F.,Tono Research Institute of Earthquake Science | Efendi J.,Geospatial Information Agency | And 2 more authors.
Earth and Planetary Science Letters | Year: 2014

We present an interplate coupling model of the Australia-Java plate interface off the southwestern coast of Java, Indonesia, based on data from the Indonesian Permanent GPS Station Network from 2008 to 2010. The majority of vertical data indicate uplift, while the baseline change rate indicates coastal contraction in the middle of the network and coastal extension in the eastern part of the network. Using the rate of baseline length changes and the absolute rate of vertical displacements, we apply a geodetic inversion method by Yabuki and Matsu'ura (1992). From the inversion result, we interpret the main source of the observed velocity in West Java as resulting from contributions of (1) interplate coupling off Ujung Kulon-Pelabuhan Ratu at 20 to 40 km depth, with a slip rate range from 48 to 56 mm/yr, (2) interplate coupling off Pangandaran at 37 to 45 km depth with a slip rate of 48 to 55 mm/yr, (3) afterslip off Pangandaran within the rupture area of the 2006 M7.8 Java earthquake, in the depth range of 15-20 km, with a slip excess rate of 57-61 mm/yr. The absence of a megathrust earthquake for at least 300 years in this region implies seismic moment accumulation during this time period of 1.6 × 1021Nm (~Mw8.7) off Ujung Kulon-Pelabuhan Ratu, and 3.9 × 1021Nm (~Mw8.3) off Pangandaran, unless episodic slow slips release tectonic stress. © 2014 Elsevier B.V.

Shimizu H.,Kanazawa University | Hiramatsu Y.,Kanazawa University | Kawasaki I.,Tono Research Institute of Earthquake Science
Polar Science | Year: 2015

Continuous waveform records of STS-1 seismometers of the Incorporated Research Institutions for Seismology (IRIS) and superconducting gravimeters of the Global Geodynamics Project (GGP) obtained during the 2004 Sumatra-Andaman, the 2010 Chile, and the 2011 off the Pacific coast of Tohoku earthquakes are examined to search for latitudinal variations of the spectral peak frequencies of 0S0, 1S0, and 0S2. No latitudinal variation is determined. The observed spectral peak frequencies are identical to those of the Preliminary Reference Earth Model (PREM). © 2014 Elsevier B.V. and NIPR.

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