Earth Planets Space, Vol. 65 (No. 12), pp. 1399-1410, 2013
Nguyen Anh Duong1,2, Takeshi Sagiya2, Fumiaki Kimata3, Tran Dinh To4, Vy Quoc Hai4, Duong Chi Cong5, Nguyen Xuan Binh1, and Nguyen Dinh Xuyen1
1Institute of Geophysics, Vietnam Academy of Science and Technology, Bldg. A8, 18 Hoang Quoc Viet Street, Cau Giay, Hanoi, Vietnam
2Nagoya University, D2-2 (510), Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan
3Tono Research Institute of Earthquake Science, 1-63 Yamanouchi, Akeyo-cho, Mizunami 509-6132, Japan
4Institute of Geological Sciences, Vietnam Academy of Science and Technology, 84 Chua Lang Street, Dong Da, Hanoi, Vietnam
5Vietnam Institute of Geodesy and Cartography, 479 Hoang Quoc Viet Street, Cau Giay, Hanoi, Vietnam
(Received June 16, 2013; Revised September 2, 2013; Accepted September 16, 2013; Online published December 6, 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 N108° ± 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.
Key words: Crustal movement, GPS, coseismic offset, earthquake, northwestern Vietnam.