The Longitudinal Valley in eastern Taiwan represents the present plate suture between Eurasian and Philippine plates. How is the significant deformation (more than 2 cm/yr horizontal shortening across the Longitudinal Valley) distributed across the plate suture valley, and how much attributed to a single major fault zone are our main questions.

       A geodetic measurement using trilateration network (by Yu S.B. and his colleagues) carried out in 1983-1988 first showed a substantial horizontal shortening occurred across the LVF. Based on these data, we carried out a further analysis by introducing a discontinuous rigid-block model so that the location of fault zone as well as the moving vectors can be defined [Lee and Angelier, 1993].

　

　

We carried out geological field investigations along the active Chihshang active fault, one of the most active segments of the LVF, for characterizing and measuring the fault motion at the outcrops. Concrete retaining walls, which revealed thrust-type surface ruptures of the creeping Chihshang fault, provide a good opportunity for the outcrop quantitative analysis. We obtained a steady shortening rate of about 2 cm/yr during 1990-2000. The surface rupture of active faulting concentrated within a 30-100-m-wide narrow deformation zone. [Angelier et al., 1997; Angelier et al., 2000]

　

        　

       Strain partitioning on the southern Longitudinal Valley was characterized by geodetic data analysis (discontinuous model) and geologic information [Lee et al., 1998], as well as by numerical modeling [Hu et al., 2001]. The surface deformation in this area is partitioned into two parallel N-S trending fault zone: pure thrusting with a high-friction fault surface to the west and strike-slip shearing with a low-friction fault surface to the east with a Plio-Pleistocene molasse conglomerate deposits in-between. 

　

　

We developed rod-type creepmeters and set up across the surface breaks for monitoring of the creeping Chihshang fault [Lee et al., 2000]. One-year results (1998-1999) reveal that the surface deformation of the Chihshang fault, though distributed, continuously moving along the surface ruptures. This annually steady motion also confirmed the result from previously field investigation. On the other hand, the detailed creep data, revealed by creepmeters,  shows a seasonal variation of fault motion which was closely linked to the rainfall [Lee et al., 2001; Lee et al., 2003]. 

      

Local geodetic networks were deployed at five different sites to across the surface ruptures zones of the Chihshang fault since 1998. The measurements which include leveling, distance-angle measurements and GPS are generally carried out twice a year.  These measurements allow not only characterize the deformation and fault kinematics near the fault, but also provide the opportunity to quantify the co- and post-seismic deformation of the 2003 Chengkung earthquake along the Chihshang fault [Lee et al., 2006].

　

　

The  2003 Mw=6.5 Chengkung earthquake resulted from rupturing of the Chihshang fault. The main shock together with numerous aftershocks likely distributed along a fault patch of 35 km long and 25 km wide. Combining the far field GPS data with our near fault investigation, including field observation, measurements on local geodetic networks (GPS, leveling and distance-angle), creep meters, we found a much larger post-seismic slip occurred along the surface ruptures of the Chihshang fault, compared to a smaller co-seismic slip [Lee et al., 2006].   

　

　

　

　

　

Below publications list our efforts on Active Tectonics of the LVF

Lee, J.C. & Angelier, J., 1993. Localisation des déformations actives et traitements des données géodésiques: l'example de la faille de la Vallée Longitudinal, Taïwan. Bull. Soc. géol. France, t. 164, n° 4, pp. 533-540. (SCI)

Yu, M.S., Chu, H.T., Hou, C.S., and Lee, J.C., 1994. The Chengkung earthquake of May 29, 1992 and the Chihshang Fault (in Chinese): Bull. Cent. Geol. Sur., v. 9, 107-121.

Angelier, J., Chu, H.T., and Lee, J.C., 1997. Shear concentration in a collision zone: kinematics of the active Chihshang Fault, Longitudinal Valley, eastern Taiwan: Tectonophysics, 274, 117-144. (SCI)  [Full Text (PDF)]

Lee, J.C., Angelier, J., Chu, H.T., Yu, S.B., and Hu, J.C., 1998. Plate-boundary strain partitioning along the sinistral collision suture of the Philippine and Eurasian plates: Analysis of geodetic data and geological observation in southeastern Taiwan: Tectonics, 17, 6, 859-871. (SCI)   [Full Text (PDF)]

Lee, J.C., Jeng, F.S., Chu, H.T., Angelier, J. and Hu, J.C., 2000. A rod-type creepmeter for measurement of displacement in active fault zone: Earth, Planets, and Space, 52, 5, 321-328. (SCI)   [Full Text (PDF)]

Angelier, J., Chu, H.T., Lee, J.C., and Hu, J.C., 2000. Active faulting and earthquake risk: the Chihshang Fault case, Taiwan: Jour. Geodynamics, 29, 151-185. (SCI)  [Full Text (PDF)]

 Lee, J.C., Angelier, J., Chu, H.T., Hu, J.C., and Jeng, F.S., 2001. Continuous monitoring of an active fault in a plate suture zone: a creepmeter study of the Chihshang active fault, eastern Taiwan, Tectonophysics, 333, 219-240. (SCI)   [Full Text (PDF)]

Chow, J., Angelier, J., Hua, J.J., Lee, J.C., and Sun, R., 2001. Paleoseismic event and active faulting: from ground penetrating radar and high-resolution seismic reflection profiles across the Chihshang Fault, eastern Taiwan, Tectonophysics, 333, 241-259. (SCI)   [Full Text (PDF)]

Hu, J.C., Angelier, J., Homberg, C., and Lee, J.C., 2001. Three-dimensional modeling of the behavior of the oblique convergent boundary of southeast Taiwan: friction and strain partitioning, Tectonophysics, 333, 261-276. (SCI)  [Full Text (PDF)]

Lee, J.C., Chu, H.T., Angelier, J., Hu, J.C., Yu, S.B., Chen, H.Y., Jeng, F.S. Lin, C.H., Rau, R.J., Chow, J.D., Chang, S.H., and Jiang, G.C., 2002. Crustal deformation and Active faulting in relation with seismic hazard: Study of the active Chihshang fault in Longitudinal Valley , eastern Taiwan (in Chinese). Ti-Chih, 21, 2, 31-52.[Full Text (PDF)]

Lee, J.C., Angelier, J., Chu, H.T., Hu, J.C., Jeng, F.S. and Rau, R.J., 2003. Active Fault Creep Variations at Chihshang, Taiwan, Revealed by Creepmeter Monitoring, 1998-2001. Journal of Geophysical Research, 108, B11, 2528, doi:10.10129/2003JB002394. (SCI) [Full Text (PDF)11.2MB]

Lee, J.-C., J. Angelier, Chu, H.T., Hu, J.C., Fu-Shu Jeng, 2005. Monitoring active fault creep as a tool in seismic hazard mitigation. Insights from creepmeter study at Chihshang, Taiwan, C.R. Geosciences, 337(13), 1200-1207. (SCI) [Full Text (PDF) 950K]

Lee, J.-C., Chu, H.T., J. Angelier, Hu, J.C., Chen, H.Y., Yu, S.B., 2006. Quantitative analysis of co-seismic surface faulting and post-seismic creep accompanying the 2003, Mw=6.5, Chengkung earthquake in eastern Taiwan, Journal of Geophysical Research, 111, B02405, doi:10.1029/2005JB003612. (SCI) [Full Text (PDF) 11.0MB]

Hu, J.C., Cheng, L.-W. Chen, H.-Y., Wu, Y.-M., Lee, J.-C., Chen, Y.-G., Lin, K.-C., Rau, R.-J., Kuochen, H., Chen, H.-H., Yu, S.-B., Angelier J., 2007. Coseismic deformation revealed by inversion of strong motion and GPS data: the 2003 Chengkung earthquake in eastern Taiwan. Geophys. J. Int., 169, 667-674, doi: 10.1111/j.1365-246X.2007.03359.x. (SCI)  [Full Text (PDF) 11.9MB]