How the structural architecture of the Eurasian continental margin affects the structure, seismicity, and topography of the south central Taiwan fold‐and‐thrust belt

Abstract

Studies of mountain belts worldwide show that along‐strike changes are common in their foreland fold‐and‐thrust belts. These are typically caused by processes related to fault reactivation and/or fault focusing along changes in sedimentary sequences. The study of active orogens, like Taiwan, can also provide insights into how these processes influence transient features such as seismicity and topography. In this paper, we trace regional‐scale features from the Eurasian continental margin in the Taiwan Strait into the south central Taiwan fold‐and‐thrust belt. We then present newly mapped surface geology, P wave velocity maps and sections, seismicity, and topography data to test the hypothesis of whether or not these regional‐scale features of the margin are contributing to along‐strike changes in structural style, and the distribution of seismicity and topography in this part of the Taiwan fold‐and‐thrust belt. These data show that the most important along‐strike change takes place at the eastward prolongation of the upper part of the margin necking zone, where there is a causal link between fault reactivation, involvement of basement in the thrusting, concentration of seismicity, and the formation of high topography. On the area correlated with the necking zone, the strike‐slip reactivation of east northeast striking extensional faults is causing sigmoidal offset of structures and topography along two main zones. Here basement is not involved in the thrusting; there is weak focusing of seismicity and localized development of topography. We also show that there are important differences in structure, seismicity, and topography between the margin shelf and its necking zone.

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

“…Historical earthquake records in Tainan area clearly do not match this hypothesis. The records attest for four destructive earthquakes (M w~6 -7) in the region between 1655 and 1721 and little activity afterward (Ng et al, 2009), until the M w 6.3 earthquake that ruptured the Hsinhua fault in 1946 (Bonilla, 1975). Historical accounts do not allow determining the fault responsible for these events, yet they imply that the Houchiali fault did not produce a significant earthquake since at least 300 years.…”

“…The surface trace of the Houchiali fault, as extrapolated from Seismic Lines D1 and D5, is very close to the tip of the 1946 M6.3 earthquake surface rupture along the Hsinhua fault (Figures 1a and 7a). The Hsinhua fault is identified as a right-lateral, subvertical fault (Bonilla, 1975;. It is inferred as a former Paleogene normal fault, reactivated as a tear fault during orogeny, as other approximately E-W strike-slip faults in western Taiwan (Brown et al, 2017;Pathier, 2003;Yang et al, 2016).…”

“…They trend ~N60°E offshore, along the shelf edge and within the Tainan Basin down the continental slope, and ~N75°E within the Coastal Plain north of Tainan (Figure a). Therefore, they are oblique to nearly parallel to the direction of convergence and at the origin of a southward deepening of the basin, with some irregularities that probably affected the development of the foreland basin and of the fold‐and‐thrust belt during the Pliocene and the Quaternary (Biete et al, ; Brown et al, ; Lin et al, ; Yang et al, ).…”

The influence of inherited continental margin structures on the stress and strain fields of the south-central Taiwan fold-and-thrust belt

“…With this in mind, in this paper we continue to explore the possible effects that the morphology and inherited structures of the Eurasian continental margin are having on the fold-and-thrust belt in southcentral Taiwan (Fig. 1), which we have investigated in a series of recent publications (Brown et al 2012(Brown et al , 2017Alvarez-Marron et al 2014;Camanni et al 2014Camanni et al , 2016Biete et al 2018). In these studies, we used seismicity data, P-wave velocity models and geodetic data, together with geometric analyses of surface and subsurface geological structures to propose that there is a causal link between along-strike changes in these features and the reactivation of fault systems inherited from the margin's outer shelf and necking zone.…”

“…Lin et al 2003). Throughout this paper, we follow the scheme of Alvarez-Marron et al (2014) and Brown et al (2017), when describing the geology of the continental margin, defining the pre-Eocene rift-related rocks as its basement, the area of basement thinning towards the South China Sea ocean basin as the necking zone (see Mohn et al 2012 for a definition of necking zone) and the slope as the morphological feature where the sediments were deposited on the necking zone. Today's shelf/slope break is defined as the 200 m bathymetry contour (Fig.…”