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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).

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.

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.

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.

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.

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