3D Geometry of the Chelungpu Thrust System in Central Taiwan: Its Implications for Active Tectonics

Abstract

This study is aimed at constructing a 3D subsurface geometry of the Chelungpu thrust and its associated structures, as well as examining the implications of the studies results for active tectonics in the area. Nine balanced cross-sections were constructed across the foothills belt in the study area to delineate the subsurface geometry of the major thrusts in the foreland of the fold-and-thrust belt.The Chelungpu thrust cuts down to the subsurface invariably along the base of the Chinshui Shale and is merged with the Changhua thrust into a common décollement at a depth of 5 to 7 kilometers below the sea level. There is a pre-existing normal fault underneath the common décollement of the Changhua and Chelungpu thrusts which accommodates the thickened strata in the hanging wall of the Chelungpu thrust.The restored cross-sections indicate that during its propagation toward the foreland the Chelungpu thrust originally was a low-angle thrust before it met a pre-existing high-angle normal fault, which was then reactivated and became the frontal ramp of the thrust. In the latest stage, displacement along the Changhua thrust left the normal fault behind and kept it underneath the common décollement.The subsurface geometry of the Chelungpu thrust is a uniform curved plane striking N-S, with some local wavy features and a ramp striking E-W Terr. Atmos. Ocean. Sci., Vol. 18, No. 2, June 2007 144 in the northern part of the thrust. To the north of the ramp, the fault plane transforms into a spoon-shaped geometry. In the southern part of the study area, the southern end of the Chelungpu thrust is cut off, and its displacement is transferred into a splay thrust that strikes NE-SW and connects the Chelungpu and Shuangtung-Hsiaomao thrusts.At the hypocenter of the Chi-Chi earthquake, not only is the dip angle of the décollement of the Chelungpu thrust gentler, but the depth much shallower than that of the mainshock. As the hypocenter of the mainshock is very close to the pre-existing normal fault underneath the décollement, a connection between them is highly implied. We also suggest that the ramp in the northern part of the Chelungpu thrust provides a stronger strain guide during the subsurface rupture propagation thereby creating the bended surface rupture.

Three‐dimensional numerical models with varied material properties and erosion rates: Implications for the mechanics and kinematics of compressive wedges

“…Interpreted seismic profiles across the Puli region suggest the combined thickness of synorogenic foreland basin fill (Plio-Pleistocene) is $5 km thick (Figure 9c). In contrast, sections located to the north and south of the Puli Region exhibit thinner sequences of synorogenic fill, capping thrust sheets accreted into the orogen [Yang et al, 2007] (Figure 9c). Because of the lack of induration of these rocks compared to the Miocene Yeh and Yen, 1992].…”

“…Dashed red line shows the location of the Puli Embayment. (c -e) Simplified geological sections from Chinese Petroleum Company (modified from Yang et al [2007] with permission). Location of the sections shown in Figure 9b.…”

The Tiehchanshan structure of NW Taiwan: A potential geological reservoir for CO2 sequestration

“…His balanced cross-section also reveals that the Tunghsiao-Tiehchanshan fold is a fault-propagation fold generated by slip along the Futoukeng fault of listric shape, which cuts off the forelimb of fold upward to the surface. Lately, referring to interpreted seismic lines, a series of balanced cross-sections were constructed by Yang et al (2007) to illustrate lateral variation in subsurface feature in the Tiehchanshan structure and its adjacent area. In their cross-sections, fold vergence is westward in the northern segment of the structure and eastward in the southern segment, with symmetrical geometry in the middle part of the structure.…”

“…As mentioned in the chapter of "Regional Geology", different interpretations in the previous geological cross-sections of the Tiehchanshan structure arise from different interpretations on the geometry of fold-forming thrust cutting through the structure in the subsurface, i.e., models of thrust cutting either low angle (Suppe and Namson 1978;Namson 1981;Hung and Wiltschko 1993;Yang et al 1994Yang et al , 2007 or high angle (Chung 1996) at the strata. A series of interpreted seismic section in our study illustrate a brand new model of fold-forming thrust, in which the high-angle thrusts in the northern and southern parts of the structure change gradually into the low-angle ones in the transfer zone between two anticlines of opposite vergence.…”

“…Although the Tiehchanshan structure was often deemed a fold with simple and intact shape, various interpretations and reconstructions for the subsurface cross-sectional geometry have been proposed (Suppe and Namson 1979;Namson 1981;Hung and Wiltschko 1993;Yang et al 1994Yang et al , 2007 Terr. Atmos.…”