TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 58 (No. 12), pp. 1617-1620, 2006


Postseismic deformation following the 2005West Off Fukuoka Prefecture Earthquake (M7.0) derived by GPS observation

Shigeru Nakao1, Hiroaki Takahashi2, Takeshi Matsushima3, Yuhki Kohno3, and Masayoshi Ichiyanagi2

1Faculty of Science, Kagoshima University, Kagoshima 890-0065, Japan
2Institute of Seismology and Volcanology, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan
3Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, Shimabara 855-0843, Japan

(Received August 10, 2005; Revised March 13, 2006; Accepted March 16, 2006; Online published February 2, 2007)

Abstract: We constructed a temporary GPS network around the aftershock area of the 2005West Off Fukuoka Prefecture Earthquake (M7.0) in order to investigate the characteristics of its postseismic deformation. Our GPS network data, as well as the GEONET data, were analyzed using Bernese GPS software. We detected notable postseismic deformation in horizontal components close to the fault plane. The observed maximum displacement was 5.6 cm at the GNKI site on Genkaijima Island. A logarithmic law was adapted to the coordinate time series data, revealing decay times from 2 to 23 days, similar to those obtained for the 2003 Tokachi-oki Earthquake (M8.0). The amount of postseismic slips on the fault was assessed using the coseismic fault model proposed by the Geographical Survey Institute (GSI). We derived an optimum fault model of postseismic slip on the shallow (less than 3 km depth) portion of the fault. Our findings indicate that postseismic slip occurred only in shallow parts of the coseismic fault.
Key words: Postseismic deformation, Postseismic slip, 2005 West Off Fukuoka Prefecture Earthquake, GPS.

Corresponding author E-mail: nakao@sci.kagoshima-u.ac.jp

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