A growing structure near the deformation front in SW Taiwan as
deduced from SAR interferometry and geodetic observation
Mong-Han Huang,1Jyr-Ching Hu,1Chia-Sheng Hsieh,2Kuo-En Ching,3Ruey-Juin Rau,3 Erwan Pathier,4Be´ne´dicte Fruneau,5 and Benoıˆt Deffontaines5
Received 25 December 2005; revised 7 May 2006; accepted 24 May 2006; published 30 June 2006.
[1] We apply the D-InSAR technique to monitor the active
growing structure on the Tainan Tableland near the deformation front in SW Taiwan using ERS SAR images in the period of 1996 – 2000. Interferometric processing of six SAR images reveals the average slant range displacement (SRD) to be 12.5 mm/yr, and it increases from the west edge of the Tainan Tableland and decreases across the Houchiali fault. The GPS campaign data indicate an average horizontal movement of 12 ± 4 mm/yr in the direction of N44W for the Tainan Tableland with respect to the western coastline. Five precise leveling surveys across the Tainan Tableland over two years show an uplift rate of 14 mm/yr for the benchmarks on the Tableland. By combining the horizontal velocity of GPS data and the SRD of D-InSAR we transfer the SRD into vertical deformation and discuss the deformation pattern and seismic hazards in the Tainan area. Citation: Huang, M.-H., J.-C. Hu, C.-S. Hsieh, K.-E. Ching, R.-J. Rau, E. Pathier, B. Fruneau, and B. Deffontaines (2006), A growing structure near the deformation front in SW Taiwan as deduced from SAR interferometry and geodetic observation, Geophys. Res. Lett., 33, L12305, doi:10.1029/2005GL025613.
1. Introduction
[2] Taiwan is one of the most active seismic regions in
the world. Historical records indicate more than 12 large (Mw > 6) earthquakes since 1900, including the 1999 Mw 7.6 Chi-Chi earthquake (Figure 1) which occurred in Taiwan and resulted in serious damage and causalities in densely populated areas. The newly initiated blind fault system in the coastal plain area is due to the on-going arc-continent collision and increases potential earthquake haz-ards in the western alluvial plain where it was once considered less of a threat in comparison with other regions of the island. Tainan Tableland is a significant morpholog-ical feature of an active growing structure near the defor-mation front located in SW Taiwan (Figure 2a). The Tainan City (the fourth largest) with more than 700,000 people is situated on the active structure. Recent research suggests
that the Houchiali fault, which located in the east portion of the Tainan Tableland, was an active fault [Lin et al., 2000]. Based on a study of the Holocene sea-level curve and the C14 dating of driftwood and mollusc samples of coastal sediments, the long-term (Holocene) uplift rate of the Tainan Tableland is 5 mm/yr [Chen and Liu, 2000]. However, the preliminary result of an InSAR (Interferomet-ric Synthetic Aperture Radar) scan revealed a ground motion of 2.8 cm along the radar line of sight toward the satellite during the period of 1996 – 1998 [Fruneau et al., 2001]. Under constraints of the measurement of only one campaign mode GPS, they pointed out that the displacement vector of vertical and horizontal components are 32 mm/yr and 16 mm/yr respectively in a period of about two years. Their result indicated an uplift rate of16 mm/yr. A dense GPS network survey and precise leveling mode around the Tainan Tableland was established by the Central Geological Survey in Taiwan. The goal of this study is to characterize the deformation pattern and uplift rate of the Tainan Tableland using the InSAR technique within the constraint of the geodetic measurements.
2. Tectonic Setting
[3] The tectonic environment in Taiwan is the result of
the collision of the Eurasian Plate (EU) and Philippine Sea Plate (PSP). The PSP moves toward the northwest with respect to the stable EU (Penghu Islands) at the rate of 78.7 mm/yr and the polarity of subduction between the EU and PSP flipped near the central part of Taiwan (Figure 1). The investigated area of SW Taiwan corresponds to the southern part of a Plio-Pleistocene foreland basin which developed in response to lithospheric flexure due to the tectonic loading of the Central Range orogenic belt [Lin and Watts, 2002]. The westernmost surface exposures of the fold-and-thrust belt reach the boundary between the Foot-hills region near the Tainan Tableland [Sun et al., 1998; Chen and Liu, 2000]. The Tainan plain can be divided into three major structural grains of different geomorphic fea-tures. From the west to the east, there are the Tainan Tableland, the Tawan Lowland and the Chungchou Terrace (Figure 2a). The major part of the Tainan city is on a 30 m high and N-S elongated tableland that is 12.5 km long and 4 km wide with a N20E trending axis and shows an east-west asymmetry. Its western slope gently dips westward, while the eastern region is obviously steeper and considered as a fault scarp and is mapped as the Houchiali fault [Chen and Liu, 2000]. The Tawan Lowland has an average altitude of about 6 m above see-level and the elevation increases eastward and gradually merges with the third unit, the Chungchou Terrace, located between Taiwan Lowland and
GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L12305, doi:10.1029/2005GL025613, 2006
1Department of Geosciences, National Taiwan University, Taipei,
Taiwan.
2Department of Civil Engineering, National Chiao Tung University,
Hsinchu, Taiwan.
3
Department of Earth Sciences, National Cheng Kung University, Tainan, Taiwan.
4
Department of Earth Sciences, University of Oxford, Oxford, UK.
5Laboratoire Ge´omate´riaux et Ge´ologie de l’Inge´nieur, Universite´de
Marne-la-Valle´e, Marne-la-Valle´e, France.
Copyright 2006 by the American Geophysical Union. 0094-8276/06/2005GL025613
