Abstract
SUMMARYIn this paper we test whether or not structural and morphological features inherited from the Eurasian continental margin are affecting the contemporary stress and strain fields in south-central Taiwan. Principal stress directions (σ1, σ2 and σ3) are estimated from the inversion of clustered earthquake focal mechanisms and the direction of the maximum compressive horizontal stress (SH) is calculated throughout the study area. From these data the most likely fault plane orientations and their kinematics are inferred. The results of the stress inversion are then discussed together with the directions of displacement, compressional strain rate and maximum shear strain rate derived from GPS data. These data show that there is a marked contrast in the direction of SH from north to south across the study area, with the direction of SH remaining roughly subparallel to the relative plate motion vector in the north, whereas in the south it rotates nearly 45° counter-clockwise. The direction of the horizontal maximum compression strain rate (εH) and associated maximum shear planes, together with the displacement field display an overall similar pattern between them, although undergoing a less marked rotation. We interpret the southward change in the SH, εH and the dextral maximum shear plane directions, together with that of the horizontal displacement field to be related to the reactivation of east–northeast striking faults inherited from the rifted Eurasian margin and to the shelf/slope break. Inherited faults in the basement are typically reactivated as strike-slip faults, whereas newly formed faults in the fold-and-thrust belt are commonly thrusts or oblique thrusts. Eastwards, the stress inversions and strain data show that the western flank of the Central Range is undergoing extension in the upper crust. SH in the Central Range is roughly parallel to the relative plate convergence vector, but in southwestern Taiwan it undergoes a marked counter-clockwise rotation westwards across the Chaochou fault. Farther north, however, there is no significant change across the Lishan fault. This north to south difference is likely due to different margin structures, although local topographic effects may also play a role.
Highlights
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, 2017; Alvarez-Marron et al 2014; Camanni et al 2014, 2016; Biete et al 2018)
The continental margin of Eurasia that is involved in the Taiwan fold-and-thrust belt evolved from a subcontinental subduction system in the Late Cretaceous (Li et al 2007; Lan et al 2008) to a rifting margin by the Early Eocene, with seafloor spreading starting in the South China Sea by the late Early Oligocene (e.g. Briais et al 1993)
In the north of the study area, and along the entire western flank of the Central Range, the SH and the εH directions are subparallel to the direction of relative plate motion (306◦) between the Philippine Sea and the Eurasian plates
Summary
The determination of the stress and strain fields in a fold-and-thrust belt is important because these are necessary parameters for the understanding of its mechanic, geometric and kinematic evolution (e.g. Angelier et al 1986; Oncken 1988; Erslev 1993; Becker 2000; Homberg et al 2002; Saintot & Angelier 2002; Lacombe et al 2006; King et al 2009; Peyret et al 2011; Tavani et al 2015). Knowledge of the stress and strain fields can, play an important part in a data set aimed at deciphering the role of reactivation of inherited structures in the development of a 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, 2017; Alvarez-Marron et al 2014; Camanni et al 2014, 2016; Biete et al 2018).
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