Active tectonics in Taiwan: insights from a 3-D viscous finite element model

Abstract

Taiwan is a young orogenic belt with complex spatial distributions of deformation and earthquakes. We have constructed a three-dimensional finite element model to explore how the interplays between lithospheric structure and plate boundary processes control the distribution of stress and strain rates in the Taiwan region. The model assumes a liberalized power-law rheology and incorporates main lithospheric structures; the model domain is loaded by the present-day crustal velocity applied at its boundaries. The model successfully reproduces the main features of the GPS-measured strain rate patterns and the earthquake-indicated stress states in the Taiwan region. The best fitting model requires the viscosity of the lower crust to be two orders of magnitude lower than that of the upper crust and lithospheric mantle. The calculated deviatoric stress is high in regions of thrust faulting and low in regions of extensional and strike-slip faulting, consistent with the spatial pattern of seismic intensity in Taiwan.

Seismotectonics of the Philippine and Taiwan Subduction Systems and Implications for Seismic Hazards

“…A prominent example of shallow intraslab activity is the normal faulting observed in southern Taiwan (Figure 9). The normal faulting observed here is generally inconsistent with the collisional tectonic setting and has been previously determined to be a result of plate bending forces within the subducted Eurasian plate beneath Taiwan (Hayes et al., 2017; Sun et al., 2015). The largest shallow intraslab event since January 2000 was the M w 7.1 Pingtung earthquake in December 2006 (Figure 9b), which occurred between ∼20 and 44 km depth (Ekström et al., 2012; Lee et al., 2008) and caused notable damage (U.S. Geological Survey, 2021).…”

“…Crustal thrust and reverse faulting are common sources of seismicity in the Philippines‐Taiwan region. Much of the seismicity across Taiwan exhibits thrust mechanisms (Figure 9; Sun et al., 2015; Yang et al., 2018), and the island hosts several N‐S trending thrust faults that reflect primarily compressive tectonics (Figure 9a; Sun et al., 2015; Yang et al., 2018). Most thrust activity is concentrated on the eastern margin of the island near the junction with the Ryukyu trench where the suture zone between the colliding Eurasian and Philippine Sea plates is present (Figure 9a; Sun et al., 2015; Yang et al., 2018).…”

“…Much of the seismicity across Taiwan exhibits thrust mechanisms (Figure 9; Sun et al., 2015; Yang et al., 2018), and the island hosts several N‐S trending thrust faults that reflect primarily compressive tectonics (Figure 9a; Sun et al., 2015; Yang et al., 2018). Most thrust activity is concentrated on the eastern margin of the island near the junction with the Ryukyu trench where the suture zone between the colliding Eurasian and Philippine Sea plates is present (Figure 9a; Sun et al., 2015; Yang et al., 2018). Several recent thrust events in Taiwan have exceeded M w 6.0 (Figure 9b), some of which caused notable damage, such as the M w 7.1 northeast Taiwan event in March 2002 (Figure 9b; Loh et al., 2003), and more recently a M w 6.7 earthquake in southeast Taiwan in March 2022, and the April 2024 M w 7.4 Hualien earthquake (Table 3).…”

“…Arc-continent collision is active across Taiwan, and seafloor spreading is active within the Okinawa trough. Major plate boundaries and faults are obtained from Besana and Ando (2005), Tsutsumi and Perez (2013), Sun et al (2015), Fan et al (2016), Liu et al (2016), Hall (2018), and Yang et al (2018). Blue arrows represent the motion of the Philippine Sea plate relative to the Eurasian plate from the MORVEL velocity model (DeMets et al, 2010).…”

Crustal Stress State in Taiwan: Moderately Strong Crust Supporting Gravitational and Flexural Loading

“…We adopt this very simple model to examine the first-order distribution of stress orientations and magnitudes in the crust. More sophisticated lithospheric modeling of the Taiwan stress state that incorporates inelastic rheology has been conducted by others (e.g., Kaus et al, 2009;Sun et al, 2015); however, these finite element models do not seem to have the resolution in the crust to test the stress distribution inferred in our study.…”