High‐Resolution 3‐D P Wave Velocity Structures Under NE Taiwan and Their Tectonic Implications

Abstract

First P wave arrival-time data from local earthquakes recorded by a dense geophone array deployed on the Ilan Plain and by existing permanent stations were combined to invert for high-resolution P wave velocity structures under northeast Taiwan. With relatively high resolution, we were able to examine the structures in more detail and to investigate their significance and tectonic implications. We introduce two distinct groups of proposals for mechanisms of subduction polarity flipping in Taiwan, referred to as the "tear model" and "breakoff model." While the predicted Philippine Sea Plate boundaries differ between the two models, those of the breakoff model and the related subducting indenter model are geodynamically similar. The surface junction and the west edge of the imaged high V p anomalous Philippine Sea Plate comply with those predicted by the subducting indenter model and thus favor the breakoff model over the tear model. While the observed high V p anomalous region in the mantle wedge can be explained as eclogitization of previously subducted crust, eclogitization of the overriding continental crustal roots cannot be ruled out. Those beneath the Taipei Basin and the Tatun Volcano Group exhibit a pattern potentially connected to the low V p anomalies in the mantle wedge, suggesting the involvement of the Philippine Sea slab, either by asthenospheric upwelling due to extensional collapse or by fluid migration due to slab dehydration. Those beneath the Ilan Plain exhibit a low V p pattern extending to deeper origins in the eastern offshore region, suggesting a connection with the opening of the Okinawa Trough.

SASSIER22: Full‐Waveform Tomography of the Eastern Indonesian Region That Includes Topography, Bathymetry, and the Fluid Ocean

“…In particular, we observe a westward dipping slab beneath the southern end of the Philippine Trench and an eastward dipping slab that exhibits a reversal in subduction polarity from 100 km down to the mantle transition zone. Such a subduction polarity flip has previously been suggested for settings where two oceanic plates collide (Gasser et al., 2021; Su et al., 2019). Furthermore, P.‐F.…”

Relocation of the April 2017 Batangas, Philippines, earthquake sequence, with tectonic implications

“…Recent P-wave tomography indeed exhibits a detached slab and apparent tearing in central and north Mindoro, respectively (Fan et al 2017). Using high Vp anomalies for subducting slab (Su et al 2019) and low Vp anomalies for positions of slab detachment beneath Mindoro and SW Luzon (Fan et al 2017) and invoking results of 3D numerical modeling (Menant et al 2016), we were able to infer the pattern of toroidal asthenospheric flow and location of overriding-plate stretching in the study region ( Fig. 8).…”

Tectonic deformation of northeastern Taiwan revealed by geomorphic indices

“…The Nanao drainage basin enters the collapse post-collision zone, and the WEP boundary projected across through the Heping and Liwu drainages may induce uplift and subsidence on the surface in these areas. Therefore, regional activity and intensity can be evaluated from variations in values, which can provide a sensitive measure of the uplift rate (Wang et al, 2019). From the distribution of knickpoints, the magnitude of knickpoint drop height and the variation in values in medium to high classes can also observe the in uence of long-term uplift tendency in the study drainages (Figs.…”

“…Taiwan is situated at the convergent boundaries between the Philippine Sea Plate (PSP) and the Eurasian Plate (EUP), where the northwestward convergence rate is approximately 80 mm/yr (Yu et al, 1997) resulting in southward subduction and collisional processing on the island. The western edge of the PSP (WEP) boundary is beneath northern and northeastern Taiwan (Wu et al, 2009;Su et al, 2019). The oblique projected WEP boundary across these areas might re ect different tectonic activities on the surface.…”