Elucidating the geometry of the active Shanchiao Fault in the Taipei metropolis, northern Taiwan, and the reactivation relationship with preexisting orogen structures

Abstract

The Shanchiao Fault is an active normal fault with documented paleoearthquakes in the Taipei metropolis, Taiwan. While posing direct seismic threat on the multimillion population, its crustal-scale fault plane configuration has not been constrained. This study presents the first attempt to resolve the fault plane dip changes of the Shanchiao Fault within the upper crust by forward modeling late Quaternary deformation. Tectonic subsidence over the last~23 ka is estimated from vertical displacements of a rapidly formed alluvial fan horizon deformed into a dramatic rollover monocline. A 2-D profile across the Shanchiao Fault is chosen for elastic half-space dislocation modeling, and the results suggest that the fault is listric in the shallow crust with an abrupt change from subvertical ramp (85°-75°) to near-horizontal flat (10°-15°) at 3-4 km depth, consistent with an origin from the inversion of an orogen-related thrust detachment. Given the presence of rift-related fabrics in the underthrust Chinese Continental Margin basement beneath the Taiwanese orogenic wedge, listric ramp-flat-ramp models with a second deeper bend to 60°dip are also tested. Reasonable fits with the geological observations are produced when the lower ramp is located at greater than 8 km depth, which correlates with the hypocentral location of a moderate earthquake in 2004. Joint reactivation of preexisting thrust and rift faults by the Shanchiao Fault is therefore plausible with implications for seismic hazard in the Taipei area.

Igneous Activity and Structural Development of the Mianhua Terrace, Offshore North Taiwan

“…Accordingly, the deformation front of the Taiwan orogenic wedge roughly separates the foreland basin to the west from the mountain belt to the east in the terrestrial domain (thick black dash line in Figure 1) [11,20], and it separates the less deformed East China Sea continental shelf to the west from the deformed, collapsed Taiwan orogenic wedge to the east in offshore Northern Taiwan (thick blue dash line in Figure 1) [12]. West of the Taipei Basin, the deformation front seems to run approximately along the Shanchiao Fault [23], an active normal fault with documented paleoearthquakes in the Taipei metropolis [24]. Along the northward extension of the Shanchiao Fault, the deformation front runs seemingly along the Chinshan Fault, which has an at-least 7 km extension observed in the underwater domain [25].…”

“…Though there are only three volcanic islets, we should note that volcanism also occurs underwater and may not be visible above sea level. In fact, recent observations have shown some subsurface volcanic features [12] and seafloor edifices [23]. Therefore, the number of volcanoes and the volcanic activity offshore from Northern Taiwan are very likely to have been underestimated.…”

Dense seismic arrays deny a massive magma chamber beneath the Taipei metropolis, Taiwan

“…The TVG is cut in the middle by the Shanchiao fault ( Fig. 1b), an eastward-dipping, listric normal fault 1 . Early studies indicated that the TVG had been active during 2.8-0.1 Ma 2-4 , but has stayed dormant ever since 5 .…”

Ages of ophiolitic rocks along plate suture in Taiwan orogen: Fate of the South China Sea from subduction to collision

“…The collision was achieved in two stages: first the Manila Trench was choked by the arrival of Chinese continental margin after subduction of the South China Sea (Lin et al 2009); then shortening within the upper Philippines Sea Plate, caused by reduced plate interface slip during continental underthrusting, resulted in forearc closure (Malavieille and Trullenque 2009;Shyu et al 2011). Because of the oblique configuration of the Chinese continental margin and the Luzon Arc, the collision commenced in the north in Mio-Pliocene time and propagated southward (Suppe 1984), while northeastern Taiwan has entered post-collisional stage (Chen et al 2014) due to westward propagation of the Ryukyu subduction system with opposite polarity (Teng 1996;Wu et al 2009). The island is divided in two parts ( Fig.…”