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Earthquakes used in this study Blue dots represent ISC earthquake locations. The red star shows the location of the Mariana trench.
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The water cycle at subduction zones remains poorly understood, although subduction is the only mechanism for water transport deep into Earth. Previous estimates of water flux1–3 exhibit large variations in the amount of water that is subducted deeper than 100 kilometres. The main source of uncertainty in these calculations is the initial water cont...
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It has been believed that early Earth featured higher mantle temperature. The mantle temperature affects the geodynamic processes, and, therefore, the production of the continental crust, which has been a stable environment for the developing of life since Earth's infancy. However, our knowledge of the processes operating dur...
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... Although such studies have high accuracy and precision in velocity structure, they cover only a very small portion of the ocean area due to high cost and harsh environment (Chen et al., 2022;Guo et al., 2022;Zhu et al., 2021). Both laboratory experiments (e.g., Guillot et al., 2001;Spandler et al., 2014) and geophysical observations (e.g., Cai et al., 2018;Ivandic et al., 2008Ivandic et al., , 2010Naif et al., 2015) show that hydration of mantle peridotites produces serpentinites with low seismic velocities, and thus low-velocity anomalies in the shallow oceanic mantle of the outer-rise region are considered as indicators of fluids. However, most water is thought to be trapped within the upper oceanic crust, and the low permeability of the gabbroic-rich lower oceanic crust and peridotite upper mantle makes these parts of the lithosphere relatively dry (e.g., Jarrard, 2003;Wallmann, 2001). ...
Accurate earthquake source parameters are crucial for understanding plate tectonics, yet, it is difficult to determine these parameters precisely for offshore events, especially for outer‐rise earthquakes, as the limited availability of direct P or S wave data sets from land‐based seismic networks and the unsuitability of simplified 1D methods for the complex 3D structures of subducting systems. To overcome these challenges, we employ an efficient hybrid numerical simulation method to model these 3D structural effects on teleseismic P/SH and P‐coda waves and determine the reliable centroid locations and focal mechanisms of outer‐rise normal‐faulting earthquakes in northeastern Japan. Two M6+ events with reliable locations from ocean bottom seismic observations are utilized to calibrate the 3D velocity structure. Our findings indicate that 3D synthetic waveforms are sensitive to both event location, thanks to bathymetry and water reverberation effects, and the shallow portion of the lithospheric structure. With our preferred velocity model, which has Versus ∼16% lower than the global average, event locations are determined with uncertainties of <5 km for horizontal position and <1 km for depth. The refined event locations in a good match between one of the nodal strikes and the high‐resolution bathymetry, enabling the determination of the causative fault plane. Our results reveal that trench‐ward dipping normal faults are more active, with three parallel to the trench as expected, while five are associated with the abyssal hills. The significant velocity reduction in the uppermost lithosphere suggests abundant water migrating through active normal faults, enhancing both mineral alteration and pore density.
... Water can be transported into Earth's interior via subduction processes and subsequently be liberated into the overlying mantle wedge [1][2][3][4][5][6] . Before subduction, seawater could extensively hydrate oceanic crust and sediments through hydrothermal circulation, representing approximately 2% of global seawater volume 7 . ...
... Mariana has long been recognized as one of the coldest subduction zones 63 , with substantial amounts of water transported into the deep mantle by subduction 3,64 . Based on the water solubility P-T diagram and the thermal structure of the Mariana subduction zone, it appears that most of the water in the peridotitic layer can survive beneath the arc and may be released at much greater depth or even transported into the lower mantle 1,4 . ...
Fluids released from subducting slabs profoundly affect mantle composition, rock melting points, and arc magma generation. However, identifying fluid sources (sediments, crust, or mantle) and their ascent paths remains challenging. Magnesium isotopes are potential tracers for subduction-related fluids, though their behavior during hydrous peridotite dehydration remains unclear. Here we determined the equilibrium magnesium isotope fractionation factors between aqueous fluids and hydrous peridotitic minerals using first-principles calculations. Aqueous fluids prefer heavy magnesium isotopes relative to mantle silicate minerals, indicating that fluids released during hydrous peridotite dehydration are enriched in heavy magnesium isotopes relative to the residual minerals. Our simulations proposed that magnesium isotope variations in arc lavas from different subduction zones could be attributed to different dehydration reactions influenced by subduction zone thermal structures. This study highlights the potential of magnesium isotopes for tracing fluids originating from subducting hydrated mantle, providing insights into the thermal structure of various subduction zones.
... The literature dealing with Wilson Cycles is substantial and many authors discuss details related to each stage (Wilson et al. 2019;Kawamoto et al. 2012Kawamoto et al. , 2013Huang et al. 2020;Manning 2018;Coumou et al. 2008;Lecumberri-Sanchez et al. 2015). There is a common understanding that water plays a significant role in many of these stages, and that the entry point for this water is during the formation of oceanic crust, from which the water migrates deep into the Earth's mantle by the subduction process (Glassley 2001;Lamb 2004;van Keken et al. 2011;Cai et al. 2018;Grove et al. 2006;Worzewski et al. 2010;Garth and Rietbrock 2017). Although the source, role, and fate of water are largely undisputed and the presence of salinity in deep geological systems is commonly observed, very few authors have concluded that salt deposits may be linked to deep saline fluids derived from previously subducted seawater. ...
The Global Salt Cycle (GSC) model is based on the Wilson Cycle concept and predicts that deep subduction of seawater-laden oceanic crust leads to dehydration, with the expulsion of saline fluids that migrate into the overlying mantle wedge. This may result in mantle upwelling and delamination in the lower crust, which eventually leads to crustal uplift, lithospheric and continental break-up. A key to understanding the endogenic GSC-model, is to understand how pressured and heated fluids can sustain the vertical movements of the mantle: It has been shown by Watson and Brenan (1987), Holness and Graham (1991), Huang et al. (2020), Holness (2006), and Kenji et al. (1998), that a combination of saline fluids at high pressures and temperatures will create self-sustaining porosity and permeability in mantle rocks at these depths. Over time, any subduction zone will/may, therefore, accumulate vast amounts of saline fluids at depth, that are NOT expelled by the prevailing pressure conditions. For the salts to return to the surface, the mantle itself must initially move upwards to be depressurized with all its contents. This upwelling may cause the expulsion of saline vapours, brines, and melts that migrate in hydrothermal systems towards the surface through newly formed faults and fractures. The Red Sea area has gone through all the geological stages for this to happen, and it is concluded that the Red Sea, the East African Rift (EAR) and the Afar Triple Junction are in different stages of the GSC processes. Thus, they produce large volumes of salts, both on and below the surface. Observed salt (mainly halite) features in the Red Sea area include seismically opaque ‘diapirs’, ‘walls’ or ‘rises’, and thick layered salt deposits associated with diapirs and volcanoes. In addition, mobile ‘carpets of salt flows’ are observed at the ocean's flanks and abundant collapse features are observed along the Red Sea floor. These features are associated with high heat-flow regions, including submarine volcanism and hydrothermal processes. It is concluded that the GSC model is highly applicable to explain the formation of the salt deposits in the Red Sea area.
... For example, expanding to global OTF events would advance our understanding of OTF earthquake mechanics (e.g., Boettcher & Jordan, 2004;Shi et al., 2022). It is also straightforward to use this computationally efficient SEM-DSM code for modeling teleseismic waves from earthquakes at outer-rise regions of subduction zones, where the associated hydration processes could have substantial impacts on deep Earth material recycling (Cai et al., 2018;Chen et al., 2022;Emry & Wiens, 2015), and in subducted zones, which could generate serious seismic hazards Lay & Rhode, 2019;Wang & Yue, 2022). ...
Accurate source parameters of global submarine earthquakes are essential for understanding earthquake mechanics and tectonic dynamics. Previous studies have demonstrated that teleseismic P coda waveform complexities due to near‐source 3‐D structures are highly sensitive to source parameters of marine earthquakes. Leveraging these sensitivities, we can improve the accuracy of source parameter inversion compared to traditional 1‐D methods. However, modeling these intricate 3‐D effects poses significant computational challenges. To address this issue, we propose a novel reciprocity‐based hybrid method for computing 3‐D teleseismic Green's functions. Based on this method, we develop a grid‐search inversion workflow for determining reliable source parameters of moderate‐sized submarine earthquakes. The method is tested and proven on five Mw5+ earthquakes at the Blanco oceanic transform fault (OTF) with ground truth locations resolved by a local ocean bottom seismometer array, using ambient noise correlation and surface‐wave relocation techniques. Our results show that fitting P coda waveforms through 3‐D Green's functions can effectively improve the source location accuracy, especially for the centroid depth. Our improved centroid depths indicate that all the five Mw5+ earthquakes on the Blanco transform fault ruptured mainly above the depth of 600°C isotherm predicted by the half‐space cooling model. This finding aligns with the hypothesis that the rupture zone of large earthquakes at OTFs is confined by the 600°C isotherm. However, it is noted that the Blanco transform fault serves as a case study. Our 3‐D source inversion method offers a promising tool for systematically investigating global oceanic earthquakes using teleseismic waves.
... Bell et al. (2015) extended the idea by developing a model for the tilt noise which depends on the tilt angle and direction of the instrument. The technique of noise removal for the vertical records is applied to analyze oceanbottom seismic data and study the Earth's structure (e.g., Bowden et al., 2016;Cai et al., 2018;Janiszewski et al., 2019;Wei et al., 2015;Zha & Webb, 2016). Besides, based on the mechanism of water waves deforming the elastic Earth, an inverse approach has been developed to constrain the Earth's elastic properties using recordings of vertical compliance noise and ocean-bottom pressure (e.g., Crawford et al., 1998;Yamamoto & Torii, 1986;Zha et al., 2014). ...
The horizontal records of ocean‐bottom seismometers (OBS) are usually highly noisy, generally due to ocean‐bottom currents tilting the instrument, which greatly limits their practical usage in ocean‐bottom seismology. In shallow water, water waves with energy concentration around 0.07 Hz induce additional noise on OBSs. Such noise is not well understood. In this article, we propose a noise model to explain the horizontal noise around 0.07 Hz. The noise model consists of three types of noise, that is, water‐wave‐induced noise, current noise with a relatively constant orientation, and background random noise. The wave‐induced horizontal acceleration is theoretically shown to be proportional to the time derivative of ocean‐bottom pressure. We validate the noise model and related theories using realistic observations. Results are potentially applicable to determine the propagation direction of water waves nearshore, and also provide constraints on the underlying Earth structure. The results can also be applied to the removal of wave‐induced noise, achieving a typical maximum improvement in the signal‐to‐noise ratio of 10–20 dB for time periods with strong wave noise.
... Faulting of downgoing slabs prior to subduction is thought to have several influences on subduction processes: (a) faults provide pathways for seawater infiltration into and hydration of the oceanic lithosphere (Cai et al., 2018;Contreras-Reyes et al., 2008;Faccenda, 2014;Fujie et al., 2018;Hacker, 2008;Van Keken et al., 2011;Wei et al., 2021); (b) bending-related faulting contributes to frictional heterogeneity on the megathrust once subducted (Wang & Bilek, 2014); and (c) faults host normal-faulting earthquakes both outboard and within the subduction zone (Lay et al., 2009(Lay et al., , 2011Ranero et al., 2005). Water has been interpreted to be stored in the upper mantle of the downgoing plate (e.g., Cai et al., 2018;Grevemeyer et al., 2018;Ivandic et al., 2008;Lefeldt et al., 2012;Ranero et al., 2003;Shillington et al., 2015) in the form of serpentinite, the hydrous alteration of peridotite in the upper mantle. ...
... Faulting of downgoing slabs prior to subduction is thought to have several influences on subduction processes: (a) faults provide pathways for seawater infiltration into and hydration of the oceanic lithosphere (Cai et al., 2018;Contreras-Reyes et al., 2008;Faccenda, 2014;Fujie et al., 2018;Hacker, 2008;Van Keken et al., 2011;Wei et al., 2021); (b) bending-related faulting contributes to frictional heterogeneity on the megathrust once subducted (Wang & Bilek, 2014); and (c) faults host normal-faulting earthquakes both outboard and within the subduction zone (Lay et al., 2009(Lay et al., , 2011Ranero et al., 2005). Water has been interpreted to be stored in the upper mantle of the downgoing plate (e.g., Cai et al., 2018;Grevemeyer et al., 2018;Ivandic et al., 2008;Lefeldt et al., 2012;Ranero et al., 2003;Shillington et al., 2015) in the form of serpentinite, the hydrous alteration of peridotite in the upper mantle. Water can also be stored as pore fluids in fault zones in the crust and mantle of the incoming plate, and contained in seafloor sediments (Canales et al., 2017;Faccenda, 2014;Iyer et al., 2012;Miller et al., 2021). ...
... One major importance of bending-related faulting is its role in allowing ingress of seawater and hydration of the crust and upper mantle of the incoming plate (Cai et al., 2018;Faccenda, 2014;Faccenda et al., 2009;Grevemeyer et al., 2018;Ivandic et al., 2008;Korenaga, 2017;Nishikawa & Ide, 2015;Peacock, 2001;Ranero et al., 2003;Shillington et al., 2015). Extensional faults on the incoming plate are thought to act as conduits for seawater to percolate several kilometers through the crust and into the upper mantle of the incoming plate. ...
Oceanic plates experience extensive normal faulting as they bend and subduct, enabling fracturing of the incoming lithosphere. Debate remains about the relative importance of pre‐existing faults, plate curvature and other factors controlling the extent and style of bending‐related faulting. The subduction zone off the Alaska Peninsula is an ideal place to investigate controls on bending faulting as the orientation of the abyssal‐hill fabric with respect to the trench and plate curvature vary along the margin. Here, we characterize faulting between longitudes 161°W and 155°W using newly collected multibeam bathymetry data. We also use a compilation of seismic reflection data to constrain patterns of sediment thickness on the incoming plate. Although sediment thickness increases over 1 km from 156°W to 160°W, most sediments were deposited prior to the onset of bending faulting and thus should have limited impact on the expression of bend‐related fault strikes and throws in bathymetry data. Where magnetic anomalies trend subparallel to the trench (<30°) west of ∼156°W, bending faults parallel magnetic anomalies, implying that bending faults reactivate pre‐existing structures. Where magnetic anomalies are highly oblique (>30°) to the trench east of 156°W, no bending faults are observed. Summed fault throws increase to the west, including where pre‐existing structure orientations are constant (between 157 and 161°W), suggesting that another factor such as the increase in slab curvature must influence bending faulting. However, the westward increase in summed fault throws is more abrupt than expected for gradual changes in slab bending alone, suggesting potential feedbacks between pre‐existing structures, slab dip, and faulting.
... Passive-source studies, on the other hand, are able to image the deeper structure of the incoming plate and place constraints on the depth of serpentinization. A passive source study in the Mariana subduction zone found that the mantle hydration at the Mariana trench extends to ∼24 km below the Moho (Cai et al., 2018), suggesting the total amount of water input into the Mariana trench is at least 4.3 times more than previous estimates (van Keken et al., 2011). Since the Alaska subduction zone differs from Mariana in terms of incoming plate age (∼50 Ma, as opposed to ∼150 Ma for Mariana), and shows extensive along-strike variation in incoming plate fabric and faulting, it represents an excellent target to test the possible widespread occurrence of deeper incoming plate hydration. ...
... The velocities decrease toward the trench and show significant along-strike variations. Low-velocity zones at the top of the incoming plate mantle have been observed at many other subduction zones and are generally attributed to the serpentinization of mantle peridotite (Cai et al., 2018;Ivandic et al., 2008;Mark et al., 2023;Shillington et al., 2015;Van Avendonk et al., 2011) and/or to the effects of water in plate-bending faults (Korenaga, 2017;Miller & Lizarralde, 2016). The Shumagin segment shows a distinct low-velocity zone (∼3.65 km s 1 ) at the top of the incoming plate mantle, suggesting strong hydration if the velocity reduction is due to serpentinization. ...
... It is worthwhile to compare the Alaska Trench results with the central Mariana Trench (Cai et al., 2018) and the southern Mariana Trench (Zhu et al., 2021). Since the studies use similar techniques, we can directly compare the V S profiles. ...
We develop a 3‐D isotropic shear velocity model for the Alaska subduction zone using data from seafloor and land‐based seismographs to investigate along‐strike variations in structure. By applying ambient noise and teleseismic Helmholtz tomography, we derive Rayleigh wave group and phase velocity dispersion maps, then invert them for shear velocity structure using a Bayesian Monte Carlo algorithm. For land‐based stations, we perform a joint inversion of receiver functions and dispersion curves. The forearc crust is relatively thick (35–42 km) and has reduced lower crustal velocities beneath the Kodiak and Semidi segments, which may promote higher seismic coupling. Bristol Bay Basin crust is relatively thin and has a high‐velocity lower layer, suggesting a dense mafic lower crust emplaced by the rifting processes. The incoming plate shows low uppermost mantle velocities, indicating serpentinization. This hydration is more pronounced in the Shumagin segment, with greater velocity reduction extending to 18 ± 3 km depth, compared to the Semidi segment, showing smaller reductions extending to 14 ± 3 km depth. Our estimates of percent serpentinization from VS reduction and VP/VS are larger than those determined using VP reduction in prior studies, likely due to water in cracks affecting VS more than VP. Revised estimates of serpentinization show that more water subducts than previous studies, and that twice as much mantle water is subducted in the Shumagin segment compared to the Semidi segment. Together with estimates from other subduction zones, the results indicate a wide variation in subducted mantle water between different subduction segments.
... The converted S-wave velocity and results from Zhu et al. (2021) using surface wave tomography of the POBS data were compared with our results. We also included the velocity profile in central Mariana from Cai et al. (2018) in the comparison after adding the same water depths (Figure 10). The comparison was conducted in three different subregions, as marked in Figure 1b, that is, the rifting zone, forearc, and incoming plate, from northwest to southeast of the southernmost Mariana Trench. ...
... This velocity pattern is stable with different inversion parameters and initial models ( Figure S4 in Supporting Information S1). The low-velocity feature also appears at the top of the incoming plate mantle according to the results of Zhu et al. (2021) and Cai et al. (2018). However, our results show much lower velocity compared to other models (Figure 10c), indicating greater hydration than in previous studies Zhu et al., 2021). ...
Ocean bottom seismometers (OBSs) have been used to detect submarine structural and tectonic information for decades. According to signal source controllability, OBS data have generally been classified into active and passive source data categories. The former mainly focuses on the compressional wave (P‐wave) velocity inversion and always lacks valid information about the shear wave (S‐wave) velocity structure. While the latter provides structural information with limited resolution due to the aperture of the stations. Overcoming the barriers between processing these two data types will allow the reuse of a vast amount of data from active source experiments to explore the submarine S‐wave velocity structural properties. Here, we creatively applied ambient noise interferometry to invert the S‐wave velocity structure using data from active source OBS deployment conducted in the southernmost Mariana subduction zone, which had already been utilized to detect submarine P‐wave velocity structure. Considering the short time duration and relatively low quality of this type of data, a combined method of short‐segment cross‐correlation and selected time‐frequency domain phase‐weighted stacking was adopted to obtain stable cross‐correlation functions, which were subsequently used to invert S‐wave velocity structures. Compared to previous studies using different methods, our result sheds new light on the crust and upper mantle structure of the southernmost Mariana subduction zone. This method could be used to detect more information based on the reutilization of existing active source OBS data.
... The sediments in the Mariana Trench are primarily sourced from two inputs: the overriding plate contributing to forearc sediment from the inner-trench slope and ash from arc volcanoes, and the subducting plate supplying pelagic sediment and seamount-related volcaniclastics. The trench sediments are <1 km thick (Figs. 2 and 4) and particularly lower than 0.2 km at the trench axis (Cai et al., 2018). Moreover, the bathymetric and seismic data show no accretionary wedge, as confirmed by dredging and deep-sea drilling data (Hussong and Uyeda, 1982). ...
... With further subduction of the oceanic plate, the relief of the graben structure caused by faulting gradually intensifies to accommodate more materials. Consequently, in comparison to other margins, the subducting Pacific plate carries more water into the Mariana subduction zone, approximately 4.3 times than previously estimated (Cai et al., 2018). Subsequent carrier dewatering elevates the pore pressure in the interplate interval, and allows a large volume of fluid into the bottom of the overriding plate, eventually triggering a special type of basal erosion known as hydrofracturing ( Fig. 7; Pichon et al., 1993;von Huene et al., 2004). ...
... The antigorite stability limit is roughly placed at the pressure of the lithospheric mantle beneath OO volcano, indicating that an elevated slab component signal towards the back arc occurs by increasing participation of the lithospheric mantle in the release of f luids from the slab (Straub & Layne, 2003;John et al., 2004;Barnes et al., 2008;Herms et al., 2012;John et al., 2012;Konrad-Schmolke & Halama, 2014;Martin et al., 2016;Yamada et al., 2019;Martin et al., 2020). The potential of slab f luid enrichment in back-arc magmas would then be controlled by the level of hydration of the lithospheric mantle, which occurs during normal faulting of the outer rise (Ranero et al., 2003;Faccenda et al., 2008;Cai et al., 2018;Grevemeyer et al., 2018). Furthermore, hotter subduction zones have a higher potential to release f luid compared to colder subduction zones (Syracuse et al., 2010), as colder subduction zones can retain up to c. 4 wt% H 2 O in the alpha-phase beyond 8 GPa (Fig. 11). ...
The stability and breakdown of mineral phases in subducting slabs control the cycling of trace elements through subduction zones. Stability of key minerals and the partitioning of trace elements between these minerals and liquid phases of interests have been charted by natural sample analysis and experimental constraints. However, systematic study from arc front to far back-arc has rarely shown that the expected geochemical variations of the slab liquid are actually recorded by natural samples. Complexities arise by uncertainties on the nature of the slab component (melts, fluids and supercritical liquids), source heterogeneities and transport processes. Using data from olivine-hosted melt inclusions sampled along and across the NE Japan and southern Kurile arcs, we demonstrate that experimentally and thermodynamically constrained phase stabilities in subducted materials indeed control the trace element signatures as predicted by these models and experiments. The main reactions that can be traced across arc are progressive breakdown of light rare earth element-rich accessory phases (e.g., allanite), enhanced dehydration of the lithospheric mantle (serpentine breakdown) and changes in the nature of the slab component. This work elucidates subduction zone elemental cycling in a well-characterized petrogenetic setting and provides important constraints on the interpretation of trace element ratios in arc magmas in terms of the prograde metamorphic reactions within the subducting slab.
