Evolution of the Southern Segment of the Philippine Trench: Constraints From Seismic Tomography

Abstract

A high‐resolution model of three‐dimensional P wave tomography of the crust and upper mantle beneath the southern part of the Philippine Trench is determined by inverting 22,960 arrival times of 2,789 local earthquakes and 4,660 traveltime residuals of 751 teleseismic events simultaneously. The tomographic method TOMOG3D is used to obtain the tomographic model that has a lateral resolution of 0.6° or better, as shown by extensive checkerboard resolution tests. A model‐recovery synthetic test is also performed, which indicates that main features of our tomographic images are quite robust. Our results show that the Philippine Sea slab has subducted down to depths of 450–600 km with an overturned dip angle along the southern segment of the Philippine Trench, indicating that the subduction of the Philippine Sea Plate along the southern segment of the Philippine Trench initiated at 20–25 Ma, contemporaneous with the Sangihe Trench. The subduction initiation of the Philippine Sea Plate at the central Philippine Trench resulted from the collision between the Philippines and the Palawan block at ~10 Ma. The subduction completion of the Molucca Sea slab propagated from the south to the north at ~5 Ma, which presumably resulted in the subduction reorganization of the Philippine Sea Plate along the southern segment of the Philippine Trench and subduction initiation of the Philippine Sea Plate along the northern segment of the Philippine Trench.

The Seismicity of Indonesia and Tectonic Implications

“…Farther south (∼3°N), where arc‐arc collision remains active (Widiwijayanti et al., 2004), Figure 6d shows the Wadati‐Benioff zone of the Halmahera slab dipping steeply eastward, with the Sangihe slab exhibiting a moderate dip compared to Figure 6c. These orientations are consistent with recent tomography modeling and the orientation of the Molucca Sea plate (Fan & Zhao, 2018; Hall & Spakman, 2015). The Halmahera slab is estimated to have initiated subduction ∼10 Ma (Hall & Spakman, 2015).…”

“…However, recent tomography modeling by Fan and Zhao (2018) imaged the Philippine Sea slab extending aseismically to ∼450-600 km depth near Mindanao, implying subduction in the southern Philippine trench is older than originally believed and likely initiated around the same time as the Sangihe slab (∼20-25 Ma; Fan & Zhao, 2018;Hall, 2018;Hall & Spakman, 2015). Conversely, the Cotabato slab, dipping moderately eastward (Hayes, 2018) and seismically active to <100 km depth has been considered a younger feature, with the Wadati-Benioff zone likely representative of the extent of subduction (Figure 6c; Cardwell et al, 1980;Fan & Zhao, 2018;Hall, 2018).…”

“…The cause of this seismic gap is not clear from available literature. Tomography models (e.g., Chen et al., 2020; Fan & Zhao, 2018) tend to show a continuous slab near 6°N, and so one possibility is that the slab is aseismic due to ambient mantle temperatures or neutral internal stress in the slab. Another possibility is slab tearing and detachment, which typically follows a cease in subduction (Wortel & Spakman, 2000).…”

Slab Transport of Fluids to Deep Focus Earthquake Depths—Thermal Modeling Constraints and Evidence From Diamonds

“…In some cases, transects were omitted or moved along trench strike to ensure that all of our modeled transects complied with the two aforementioned constraints. For example, transects along the Philippine Trench appear to show deep earthquakes, but seismic tomography studies indicate that these may be due to the completely subducted Molucca Sea slab, not the currently subducting Philippine Sea plate (e.g., Fan & Zhao, 2018). Further to the north, where the Philippine plate subducts along the Ryukyu trench, seismic imaging and plate reconstructions suggest the down‐going slab collides with a stagnated portion of the Pacific plate within the transition zone, making the attribution of deep seismicity to one slab or the other difficult (Wu et al., 2016).…”

Cenozoic Evolution of the Sulu Sea Arc‐Basin System: An Overview

“…Timing of the (Proto)‐SCS seafloor spreading and subduction remains unclear (e.g., Advokaat et al., 2018; Briais et al., 1993; Pubellier & Morley, 2014; Sibuet et al., 2016), and so is the collision of the Palawan Continental Terrane (including northern Palawan, western Mindoro(‐Tablas), NW Panay, Reed Bank‐Dangerous Grounds) with the Philippine Mobile Belt and northern Borneo. Suggested ages of the collision range widely from late Early Miocene (∼20 Ma) (Yumul, Dimalanta, et al., 2009) to Late Miocene (∼10 Ma) (Fan & Zhao, 2018). Different hypotheses on the timing of ocean basin opening/subduction and terrane collision are not necessarily mutual exclusive, as such events can be diachronous, particularly across such a vast region.…”