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.
Original language | English |
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Pages (from-to) | 3311-3334 |
Number of pages | 24 |
Journal | Tectonics |
Volume | 38 |
Issue number | 9 |
DOIs | |
State | Published - 1 Sep 2019 |
Keywords
- Taiwan
- active folding
- fault-bend folding
- fold-and-thrust belt
- seismic reflection