Structure and Deformation History of the Rapidly Growing Tainan Anticline at the Deformation Front of the Taiwan Mountain Belt

Abstract

This study aims at further documenting the mechanisms of shortening at the front of fold‐and‐thrust belts. We focus on an actively growing anticline located at the deformation front of the Taiwan fold‐and‐thrust belt. Based on a multidisciplinary approach combining mainly subsurface data and geodetic techniques, we show that the Tainan anticline is a pure‐shear fault‐bend fold growing above a 38–45° west dipping back thrust, the Houchiali fault, rooted on a 3.8‐km‐deep detachment. The cumulative shortening is estimated at 2–3 km since 310 ± 50 ka, including ~30–50% of horizontal compaction shortening. The significance of the fold is little in terms of total shortening at the scale of the mountain piedmont, yet the Holocene shortening rate of 10.3 ± 1.0 mm/a accounts for 25% of the present‐day shortening rate across the piedmont. Earthquake scaling relationships applied to the Houchiali fault predict Mw~6 earthquakes that would occur a lot more frequently than indicated from historical earthquake catalogs. Hence, the aseismic slip behavior observed from geodetic measurements since two decades is a representative behavior of the fault at least at the scale of a few centuries. Our results bear out the dominance of pure‐shear folding at the front of fold‐and‐thrust belts and support horizontal compaction as a significant shortening mechanism. In contrast, the back thrust wedge structure and the aseismic slip are peculiar characteristics that likely arise from the combination of low friction and high‐pore pressure related to the thick mudstone formation hosting the wedge and of high syntectonic sedimentation rates.

Retracted: Control of Multiple Detachments on Structural Development in the Southern Junggar Fold‐and‐Thrust Belt, Northern Tian Shan: Implications for Seismic Hazard Assessment

“…Then, we focused on the geometry and kinematic evolution of the Hutubi anticline using the ADS analysis method . Assuming conservation of area in a given section, ADS analysis has proven to be powerful in providing constraints on the deformation history of well-imaged contractional structures (Epard & Groshong, 1993;Gao et al, 2020;Gonzalez-Mieres & Suppe, 2011;Groshong, 2015;Le Béon et al, 2019;Schlische et al, 2014). Area is defined as the excess area of each deformed marker horizon above its original depositional position (i.e., the regional level), and depth is the height between the regional level and the reference level that we chose.…”

Updates to the on-land seismogenic structure source database by the Taiwan Earthquake Model (TEM) project for seismic hazard analysis of Taiwan

“…25. We have updated the structural parameters of the Houchiali fault based on recently published information in Le Béon et al (2019). Based on analyses of subsurface data and geodetic observations, Le Béon et al (2019) reconstructed the subsurface structural geometry of the fault as a back thrust originated from the detachment at 3.8 ± 0.4 km deep.…”

“…We have updated the structural parameters of the Houchiali fault based on recently published information in Le Béon et al (2019). Based on analyses of subsurface data and geodetic observations, Le Béon et al (2019) reconstructed the subsurface structural geometry of the fault as a back thrust originated from the detachment at 3.8 ± 0.4 km deep. With a calculated Holocene shortening rate across the fault, they have also constrained the long-term slip rate of the Houchiali fault as 11.8 ± 1.2 mm yr -1 (Le Béon et al 2019).…”

The Chimei Submarine Canyon and Fan: A Record of Taiwan Arc‐Continent Collision on the Rapidly Deforming Overriding Plate

“…The back synclinal axial surface extends to the seafloor indicating that it is geomorphically active, with growth strata showing a fanning of dips. This geometry is classic shear fault‐bend folding geometry (Le Béon et al, 2019; Shaw et al, 2004; Suppe et al, 2004; Yue et al, 2005, 2011). The next two thrust imbrications to the west are less well imaged but sufficiently imaged to identify synclinal axial surfaces that constrain the location of thrust ramps.…”