Upper Mantle Hydration Indicated by Decreased Shear Velocity Near the Southern Mariana Trench From Rayleigh Wave Tomography

Abstract

The properties of incoming oceanic plates, such as their geometry and water content closely influence various processes in subduction zones, including the generation of earthquakes and arc magmatism (Grove et al., 2009;Shillington et al., 2015). Water content is especially important because water transported by the incoming plate cools the subduction zone, promotes forearc metamorphism, and facilitates the generation of arc magmatism (Fujie et al., 2016;Hyndman & Peacock, 2003). Since the subducting slab is the primary channel through which water can enter the Earth's interior, estimating hydration of the incoming plate at subduction zones is important for studying these processes (Hirschmann, 2006;Van Keken et al., 2011). Especially at the trench-outer rise bending region on the incoming plate, substantial normal faults can extend into the uppermost mantle, and thus water can penetrate through the bending faults into the mantle, leading to a pervasively serpentinized region (Ranero et al., 2003).Seismic imaging significantly contributes to constraining the hydration of subduction zones, since mineral hydration leads to a reduction in seismic velocity (

Building Precise Local Submarine Earthquake Catalogs via a Deep-Learning-Empowered Workflow and its Application to the Challenger Deep

“…If plate rupture occurs, a positive fault is created, which can be observed by earthquake localization. Seismic velocity models obtained from previous surface wave imaging results show a significant low-velocity anomaly in the subducted slab that extends to a depth of about 25 km inside the mantle, indicating that the southern Marianas subducted slab carries a large amount of water into the Earth's interior (Zhu et al, 2021). Compared with central Mariana (Kato et al, 2003), the velocity reduction of the southern arc-front mantle is not as obvious, suggesting that the degree of serpentinization of the arc-front mantle is lower in the south.…”

Deep Outer‐Rise Faults in the Southern Mariana Subduction Zone Indicated by a Machine‐Learning‐Based High‐Resolution Earthquake Catalog

“…For example, Z. Zhou et al. (2015) conducted 2‐D elastoplastic modeling and suggested that the maximum depth extent of outer‐rise normal faults in the trench was around 30 km below the seafloor, close to the depth of serpentinization within the incoming plate that was inferred from tomographic results (G. Zhu et al., 2021). The focal depths of extensional earthquakes have also been used as indicators.…”

“…Incoming plates at subduction zones are the major regions where water can be transferred into the Earth's depths. Estimating the degree of hydration of the incoming plates usually requires high‐resolution tomographic images based on near‐field observations (Cai et al., 2018; Fujie et al., 2013; Shillington et al., 2015; Van Avendonk et al., 2011; G. Zhu et al., 2021). Since the outer‐rise normal faults serve as pathways for water penetrating into the oceanic plate before subduction (Grevemeyer et al., 2007; Ivandic et al., 2010; Peacock, 2001; Ranero et al., 2003), the depth extent of outer‐rise normal faults has been regarded as a good indicator of the water input in the subduction zones.…”

“…High-resolution seismic tomographic images derived from recent OBS experiments in the Southern Mariana Subduction Zone indicate hydration of the upper mantle near the trench (Wan et al, 2019;G. Zhu et al, 2021).…”

The effects of plateau subduction on plate bending, stress and intraplate seismicity

“…Plate bending may cause active trench-parallel normal faulting, providing important pathways for seawater to hydrate the incoming plate (e.g., Cabrera et al, 2021;Cai et al, 2018;Zhang et al, 2021;Zhou et al, 2015;Zhu et al, 2021) and generating tensional earthquakes at outer rise. A thin plate model was most often used to investigate the plate deflection and bending stress, and the corresponding outer rise intraplate earthquakes (Garcia-Castellanos et al, 2000;Watts, 2001;Contreras-Reyes & Osses, 2010;Emry et al, 2014;Zhou et al, 2015Zhang et al, 2014;.…”