Mantle Wedge Corner Research Articles

Fault‐Valve Instability: A Mechanism for Slow Slip Events

AbstractGeophysical and geological studies provide evidence for cyclic changes in fault‐zone pore fluid pressure that synchronize with or at least modulate slip events. A hypothesized explanation is fault valving arising from temporal changes in fault zone permeability. In our study, we investigate how the coupled dynamics of rate and state friction, along‐fault fluid flow, and permeability evolution can produce slow slip events. Permeability decreases with time, and increases with slip. Linear stability analysis shows that steady slip with constant fluid flow along the fault zone is unstable to perturbations, even for velocity‐strengthening friction with no state evolution, if the background flow is sufficiently high. We refer to this instability as the “fault valve instability.” The propagation speed of the fluid pressure and slip pulse, which scales with permeability enhancement, can be much higher than expected from linear pressure diffusion. Two‐dimensional simulations with spatially uniform properties show that the fault valve instability develops into slow slip events, in the form of aseismic slip pulses that propagate in the direction of fluid flow. We also perform earthquake sequence simulations on a megathrust fault, taking into account depth‐dependent frictional and hydrological properties. The simulations produce quasi‐periodic slow slip events from the fault valve instability below the seismogenic zone, in both velocity‐weakening and velocity‐strengthening regions, for a wide range of effective normal stresses. A separation of slow slip events from the seismogenic zone, which is observed in some subduction zones, is reproduced when assuming a fluid sink around the mantle wedge corner.

Subducted carbon weakens the forearc mantle wedge in a warm subduction zone

Subducting oceanic plates carry large amounts of carbon into the Earth’s interior. The subducted carbon is mobilized by fluid and encounters ultramafic rocks in the mantle wedge, resulting in changes to the mineral assemblage and mechanical properties of the mantle. Here, we use thermodynamic modeling of interactions between carbon-bearing multi-component fluids and mantle rocks to investigate the down-dip variation in mineral assemblage in the forearc mantle along subduction megathrusts. We found that fluids rich in aqueous carbon are preferentially generated in a warm subduction zone (e.g., Nankai, SW Japan), causing a change in mineral assemblage from serpentine-rich at the mantle wedge corner to talc + carbonate-rich at greater depths. The transition caused by the infiltration of aqueous carbon may influence the depth of the boundary between the seismogenic and aseismic zones, and the down-dip limit of episodic tremor and slip.

Mantle Flow Induced by the Interplay of Downgoing Slabs Revealed by Seismic Anisotropy Beneath the Sula Block in Eastern Indonesia

AbstractThe North Sulawesi subduction zone is characterized by southward subduction of the Celebes Sea slab to a depth of ∼250 km, mainly overlying the Sangihe slab that subducts west from the Molucca Sea and penetrates the mantle transition zone. The palaeo‐subducted Sula slab dips northward and partially underlies both the Sangihe and Celebes Sea slabs. Adjacent subduction zones with horizontal overlapping subducting slabs in the upper mantle have unclear dynamic interactions. An extensive strike‐slip fault forms the western boundary of the active North Sulawesi subduction zone, providing an ideal setting to study mantle flow between overlapping slabs. We use local S‐wave and teleseismic S and SK(K)S waveform splitting analysis to measure seismic anisotropy in the northern Sulawesi region. Our observations reveal typical mantle wedge corner flow within the Sangihe subduction system. In the Gulf of Tomini, the observed trench‐oblique fast‐axis orientations above the Celebes Sea slab are likely a consequence of the interaction between two subducting slabs. The southernmost measurement with an E–W‐trending fast direction in the mantle wedge might be related to the subduction of the Sula slab. Furthermore, fault‐parallel fast‐axis orientations of anisotropy near the southern segment of the Palu‐Koro fault are attributed to large‐scale shearing across this lithospheric‐scale strike‐slip fault system. Overall, our observations suggest that the strain caused by lithospheric and asthenospheric deformation is mainly confined within the microplate, displaying a restricted flow pattern and localized effects due to the size of the plate boundaries, such as the Palu‐Koro fault.

Detection of a recent large Hyuga-nada long-term slow slip event and estimation of its spatiotemporal slip distributions

Using horizontal and vertical GNSS time series data from the GSI in sotheastern Kyushu from January 1, 2017 to June 30, 2022, we detected a recent long-term slow slip event (L-SSE) that occurred in the Hyuga-nada region, southwest Japan, and estimated its spatiotemporal slip distribution. We performed such analysis considering the piecewise evolution of slip over time with time windows of 0.8 years to ensure a good signal-to-noise ratio in the horizontal displacements in each time window. The results showed that a slip of more than 2 cm occurred in the central part of Miyazaki Prefecture from 2018.5 to 2019.3 (the units were 0.1 years = 36.5 days). Then, the amount of slip increased and expanded slightly to the southern part of Miyazaki Prefecture from 2019.3 to 2020.1, and the amount of slip reached a maximum of 3.9 cm in the subsequent period (2020.1–2020.9). A smaller slip occurred at almost the same location in the following 0.8 years. Therefore, the duration of the L-SSE was approximately 3.2 years from approximately 2018.5 to 2021.7. The annual average maximum slip rate was approximately 4.9 cm/yr (3.9 cm/0.8 yr) during the period from 2020.1 to 2020.9. The maximum total slip was estimated to be approximately 12.9 cm, and the equivalent release moment was 4.9 × 1019 Nm, corresponding to Mw7.1. Compared to previous L-SSEs that occurred in the Hyuga-nada region, the annual average maximum slip rate was relatively low, and the main total slip was estimated at almost the same location on the plate interface. On the other hand, the slip duration of this L-SSE was the longest, and the release moment and moment magnitude were the greatest. The total slip area of more than approximately 10 cm in the Hyuga-nada L-SSE estimated in this study almost overlapped with the afterslip area of the December 3, 1996 Hyuga-nada earthquake, with a depth range of approximately 30–40 km. Short-term SSEs also occurred in the same depth range. These coincidental same depth ranges of interplate seismic events stem from large thermal gradients. The large thermal gradients play an important role in narrowing the depth range of frictional parameters (a–b) at the plate interface. In addition, the pore pressure and normal stress are closely related to the critical stiffness. In particular, contrasting values of pore pressure and normal stress at the shallow and deep sides of the mantle wedge corner may also contribute to transient aseismic slip within the same depth range.

Formation of the eclogites of the Atbashi complex, Kyrgyzstan, in a subduction zone mélange diapir

Much debate exists concerning mechanisms of crustal material transfer from subducting slab to overlying mantle. Formation of mélange rocks by physical mixing of slab components within subduction plate interface is predicted to transfer their compositional signal to source of arc magmas by ascending as diapirs from slab-top. Despite being supported conceptually and through modeling, existence of these diapirs in global subduction architecture remains inconclusive. Here we use petrological observations, thermometry and thermodynamic modeling, combined with geochemical constraints and compilation of massive existing data, to investigate eclogites from a deeply buried mélange “package” in Kyrgyz Tianshan, southern Altaids. We find that various slab components physically mixed to form eclogitic mélange rocks at threshold depth of the subarc (i.e., ≥85 km). Index mineralogical and Pressure-Temperature records indicate a thermal history with substantial heating after peak burial to condition crossing wet solidus. Such translation, toward hot corner of mantle wedge, is short-lived around several hundred thousand to few million years, serving as first tangible evidence substantiating mélange diapirs propagate and dynamically mix with overlying mantle. Contemporaneous Late Carboniferous flare-up of regional arc magmatism with mélange diapir melting signal also advocates that non-negligible process of mantle wedge hybridization by buoyant mélange materials, to transfer volatile, generate arc lavas and regulate terrestrial geochemical cycles, stands.

Metasomatism at a metapelite–ultramafic rock contact at the subduction interface: Insights into mass transfer and fluid flow at the mantle wedge corner

Metasomatism at a metapelite–ultramafic rock contact at the subduction interface: Insights into mass transfer and fluid flow at the mantle wedge corner

Margin-wide variations in slab dehydration in Cascadia and their relationship to slow slip

Slow slip events are observed in subduction zones globally, with a wide range of variations in behaviour, including the periodicity and magnitude of events. These variations are observed both within and across different subduction zones. Due to their role in controlling strain accumulation and potential nucleation of regular earthquakes, understanding the physical environment of slow slip events and the source of their observed variability is critical to understanding seismogenic processes. Here we calculate thermal models for 10 trench-normal profiles along the entirety of the Cascadia subduction zone. The models incorporate lateral changes in incoming plate age and sediment input, as well as slab geometry and overriding plate structure. Temperatures at the location of peak slow slip and tremor occurrence (depths of 30–40 km) vary from 525 °C in southern Cascadia, to 475 °C in central Cascadia, to 550 °C in northern Cascadia. The variability in thermal structure and slab geometry leads to changes in the rate of calculated fluid flux in the vicinity of the mantle wedge corner where slow slip events are observed. Fluid flux rates calculated within 25 km and 50 km downdip of the mantle wedge corner show an inverse relationship with the recurrence time of slow slip with highest value observed in southern Cascadia, followed by northern Cascadia, and then central Cascadia. Other along-strike variability in tremor behaviour, such as tremor strength, correlates spatially with changes in calculated fluid flux pattern but the relationship between these parameters is not readily defined. This study provides support for models where variations in the rate of fluid production in the vicinity of the mantle wedge corner are a potential mechanism controlling the rate of pore fluid pressure buildup and fluid release during slow slip. • Changes in subduction parameters affect fluid release along Cascadia. • Major sites of slab dewatering are observed beneath the mantle wedge corner. • Fluid flux rates show an inverse relationship with the recurrence time of slow slip. • Variability in tremor strength and density correlate spatially with flux pattern.

Megathrust Shear Modulated by Albite Metasomatism in Subduction Mélanges

AbstractAseismic megathrust slip downdip of the seismogenic zone is accommodated by either steady creep or episodic slow slip events (SSEs). However, the geological conditions defining the rheology of megathrust slip remain elusive. We examined exhumed subduction mélanges on Kyushu, Japan, which deformed at ∼370–500°C under greenschist to epidote‐amphibolite facies conditions, comparable to warm‐slab environments. The mélanges recorded fluid release and viscous shear localization associated with metasomatic reactions between juxtaposed metapelitic and metabasaltic rocks. Metasomatic reactions caused albitization of metapelite, resulting in depth‐dependent changes to megathrust rheology. In a mélange deformed at ∼370°C, very fine grained reaction products (metasomatic albite) facilitated grain boundary diffusion creep at stresses of ∼45 MPa, less than those in the surrounding metabasalt. Mineralogical and chemical changes during metasomatic reactions, and their field content, imply an onset of albite metasomatism at ∼350°C. Albite metasomatism therefore potentially contributed to decreased megathrust strength around the inferred thermally controlled base of the seismogenic zone. In a mélange deformed near the mantle wedge corner at ∼500°C, metasomatic reactions promoted local quartz vein formation and localized viscous shear at slow slip strain rates, during which the coarse‐grained metasomatic albite behaved as relatively rigid blocks in a viscous matrix. We suggest that albite metasomatism can facilitate changes in a megathrust slip mode with depth and may explain why slip mode changes from creep to SSEs with tremor with increasing depth.

Consistent detachment of supracrustal rocks from a fixed subduction depth in the Cyclades

While subduction zones recycle Earth's crust back into the mantle, high pressure metamorphic rocks exposed at the surface testify to occasional crustal subduction failure. Balancing the budget of Earth's recycling factory requires a fundamental comprehension of how and when some crustal rocks are returned to the surface. Here, we constrain the timing and conditions for rocks that were subducted, exhumed and now exposed on Syros and Sifnos islands (Cyclades, Greece). Detailed petrochronology on domains of supracrustal oceanic, passive margin and continental provenance shows that progressive subduction and exhumation has resulted in imbrication of a former continental margin. The consistency of age groups in 2–4 Myr intervals across two islands suggests episodic triggering of exhumation of coherent slices, similar to nappe stacking in the upper levels of orogens. Similar maximum burial conditions across the domains indicate that their highly variable material properties have not exerted a control on the depth from which they were recovered, and supracrustal exhumation was instead triggered by a steady state mechanism operating at ∼65–70km depth in the subduction zone. We propose that for mechanically strong rocks, consistent exhumation may have been triggered by thermal weakening at the depth of coupling between the subducting slab and mantle wedge corner flow in an extended back-arc. For weakly coupled supracrustal rocks, consistent exhumation may have been triggered by a stepped buoyancy increase for subducting rocks at the crust mantle boundary of a thickened overlying plate. These models help to understand the mechanisms and conditions by which supracrustal rocks may be systematically detached from a downgoing plate.

Seismological Structures on Bimodal Distribution of Deep Tectonic Tremor

AbstractDeep tectonic tremors occur at the downdip extent of the seismogenic zone due to fluid processes. Beneath the northeastern Kii Peninsula, southwestern Japan, there is an along‐dip bimodal distribution of tremor. However, no constraint exists on the structures controlling that distribution. We extract detailed seismological structures from multi‐band receiver functions and evaluate conditional differences in the distribution. To achieve high resolution images along the plate interface, we utilize records of regional deep‐focus earthquakes from the Pacific slab. Cross‐section images show the subducting oceanic plate with depth‐dependent phases along the bimodal distribution, revealing a conspicuous plate interface at the updip portion and an inconspicuous interface below the mantle wedge at the downdip portion. This indicates that episodic tremors occur in the high pore‐fluid plate interface below the impermeable forearc crust, and that continual tremors occur at the permeable mantle wedge corner, owing to continuous fluid supply from the oceanic crust.

Subcretionary tectonics: Linking variability in the expression of subduction along the Cascadia forearc

A number of seismic and other geophysical phenomena exhibit significant lateral heterogeneity along the strike of the Cascadia forearc. Both the overriding and downgoing plate have been invoked to play the dominant role in controlling along-strike correlations between seismogenic behavior, potential field measurements, morphological/tectonic characteristics, and seismic structure; however, significant feedbacks likely exist between the two. In this study, we apply a 3D velocity correction to receiver function data and interpret the resulting discontinuity model alongside a recently published shear-wave velocity model to understand the possible causative relationships between correlative along-strike variations. Our discontinuity model indicates that the forearc crust thickens as it approaches the mantle wedge corner before progressively thinning toward the magmatic arc, likely due to the basal accretion of material from the downgoing plate to the overriding plate. In the northern and southern portions of the forearc, this “subcreted” material is characterized by thick (∼10 km) anomalously low shear-wave velocity zones. The thickness, high internal reflectivity, and low Bouguer gravity signatures associated with the low velocity zones likely indicate that this subcreted material is composed of dominantly (meta)sedimentary material that has been emplaced through successive subcretion events over geologic timescales. Furthermore, the anomalously low velocities and spatial correlation with high non-volcanic tremor (NVT) density and short slow slip recurrence intervals indicate that these regions are fluid-rich. While first-order variations in the fluids that control NVT and slow slip likely result from differences in the permeability of the downgoing slab as inferred from its stress state and the distribution of intraslab seismicity, these subcreted packages likely represent thick, vertically-impermeable regions in the lower crust that further accentuate this correlation. Variability in the amount of subcretion explains patterns of exhumation and uplift along the Cascadia margin and the resulting forearc topography over geologic timescales, and is likely controlled by some combination plate interface geometry/rheology and overriding plate architecture.

The development of seismic anisotropy below south-central Alaska: evidence from local earthquake shear wave splitting

SUMMARYThe Transportable Array in south-central Alaska spans several subduction zone features: backarc, forearc and volcanic arc, making it an ideal tool to study subduction zone anisotropy. Shear wave splitting analysis of 157 local earthquakes of mb ≥ 3.0 that occurred between 2014 and 2019 yields 210 high-quality measurements at 23 stations. Splitting delay times (δt) are generally small (δt ≈ 0.3 s), increasing with distance from the trench. Arc-parallel fast directions, ϕ, are only seen in the forearc, but rotate to arc-perpendicular ϕ in the backarc. Observed ϕ values generally do not parallel teleseismic SKS splitting results, implying that the latter is sensitive primarily to subslab mantle flow, not mantle wedge dynamics. The forearc local-earthquake signal likely originates from anisotropic serpentinite in fractures atop the subducting Pacific Plate, with possible additional signal coming from fractures in the North American crust. Mantle wedge corner flow, potentially with additional arc-perpendicular anisotropy in the subducting slab, explains backarc anisotropy.

Role of Serpentinized Mantle Wedge in Affecting Megathrust Seismogenic Behavior in the Area of the 2010 M = 8.8 Maule Earthquake

AbstractWhat controls subduction megathrust seismogenesis downdip of the mantle wedge corner (MWC)? We propose that, in the region of the 2010 Mw = 8.8 Maule, Chile, earthquake, serpentine minerals derived from the base of the hydrated mantle wedge exert a dominant control. Based on modeling, we predict that the megathrust fault zone near the MWC contains abundant lizardite/chrysotile‐rich serpentinite that transforms to antigorite‐rich serpentinite at greater depths. From the MWC at 32–40 km depth to at least 55 km, the predominantly velocity‐strengthening megathrust accommodated dynamic propagation of the 2010 rupture but with small slip and negative stress drop. The downdip distribution of interplate aftershocks exhibits a gap around the MWC that can be explained by the velocity‐strengthening behavior of lizardite/chrysotile. Interspersed velocity‐weakening and dynamic weakening antigorite‐rich patches farther downdip may be responsible for increased abundance of aftershocks and possibly for some of the high‐frequency energy radiation during the 2010 rupture.

Seismic Anisotropy in the Java‐Banda and Philippine Subduction Zones and its Implications for the Mantle Flow System Beneath the Sunda Plate

AbstractThe Sunda Plate is a minor tectonic plate bounded by tectonically active convergent boundaries, below which are subducting: the Philippine Sea Plate to the east and the Indo‐Australian Plate to the south and west. It is thus an ideal tectonic setting for investigating the interaction between subduction and asthenospheric flow. To better understand mantle interactions within the two nearly perpendicular subduction zones, we characterize seismic anisotropy by conducting a source‐side sS splitting analysis, which allows us to improve spatial resolution of anisotropic fabrics, in particular underneath the backarc regions, which are poorly constrained by previous studies. In the backarc of the Java‐Banda subduction zone, a gradual fast‐axis rotation from trench normal in the west to trench parallel in the east is clearly observed. We attribute this rotation to the interactions between the 2‐D corner flow in the Java wedge and a squeezed asthenospheric flow by the highly arcuate Banda slab. In the backarc of the Philippine subduction zone, the fast‐axis direction transitions from trench normal in the central south to trench oblique in the north; the trench normal is attributed to the mantle wedge corner flow, whereas the trench oblique is likely deflected by the eastward subduction of the South China Sea Plate. Hence, the mantle flow system beneath the Sunda Plate is composed of various types of flow developed in the mantle wedges. Their interactions play an important role in influencing greatly the regional geodynamics in the upper mantle above the 670‐km discontinuity.

A Strong Seismic Reflector within the Mantle Wedge above the Ryukyu Subduction of Northern Taiwan

AbstractMajor structures within the mantle wedge are often revealed from seismic velocity anomalies, such as low‐velocity zones at magma reservoirs, partial melting regions, or the upwelling asthenosphere. However, no significant seismic boundaries have been reported in the shallow mantle wedge beneath volcanic arcs. Here, we present evidence for a strong seismic reflector dipping in the opposite direction of the subducting slab in the mantle wedge beneath northern Taiwan in the western end of the Ryukyu subduction system. We find that two unambiguous P waves generated by a deep earthquake (ML 5.1) at a depth of 132.5 km were clearly recorded by the dense seismic array (Formosa Array), composed of 140 broadband seismic stations with a station spacing of approximately 5 km in northern Taiwan. Forward modeling using both raytracing and travel times shows that a seismic reflector exists beneath the Tatun volcano group (TVG) around depths of 80–110 km. The reflector dips in the opposite direction of the subducting slab and is unlikely to be associated with mantle wedge corner flow. Instead, it probably belonged to parts of possible structures such as the asthenospheric flow, the mantle diapir, or other undiscovered structures above the subducting slab. No matter what the seismic boundary is exactly, it might be associated with the active volcanism in the TVG. The detailed geometry and mechanism of the seismic boundary in the mantle wedge will be obtained as the Formosa Array collects more seismic data in the near future.

Along‐Arc Heterogeneity in Local Seismicity across the Lesser Antilles Subduction Zone from a Dense Ocean‐Bottom Seismometer Network

AbstractThe Lesser Antilles arc is only one of two subduction zones where slow‐spreading Atlantic lithosphere is consumed. Slow‐spreading may result in the Atlantic lithosphere being more pervasively and heterogeneously hydrated than fast‐spreading Pacific lithosphere, thus affecting the flux of fluids into the deep mantle. Understanding the distribution of seismicity can help unravel the effect of fluids on geodynamic and seismogenic processes. However, a detailed view of local seismicity across the whole Lesser Antilles subduction zone is lacking. Using a temporary ocean‐bottom seismic network we invert for hypocenters and 1D velocity model. A systematic search yields a 27 km thick crust, reflecting average arc and back‐arc structures. We find abundant intraslab seismicity beneath Martinique and Dominica, which may relate to the subducted Marathon and/or Mercurius Fracture Zones. Pervasive seismicity in the cold mantle wedge corner and thrust seismicity deep on the subducting plate interface suggest an unusually wide megathrust seismogenic zone reaching ∼65 km depth. Our results provide an excellent framework for future understanding of regional seismic hazard in eastern Caribbean and the volatile cycling beneath the Lesser Antilles arc.

Magma generation conditions at the Akita-Komagatake volcano, Northeast Japan arc: Implications of across-arc variations in mantle melting parameters

Akita-Komagatake is an active volcano in the Northeast Japan arc with a slab depth (H) of ∼110 km. In this study, magma generation conditions were estimated for basaltic products from the volcano to examine the thermal structure of the sub-arc mantle and the across-arc variations in the parameters related to magma genesis. The studied basalts have the highest MgO content (∼6 wt%) among the products from the volcano and contain ∼15% plagioclase phenocrysts, ∼5% olivine phenocrysts, and <1% pyroxene phenocrysts. The water content of the melt was estimated to be ∼4 wt% by melt inclusions in the phenocrysts using plagioclase–melt hygrometry. Multi-component thermodynamic analyses suggest that the primary magma was generated by ∼14% melting of the source mantle with ∼0.5 wt% H2O at ∼1275 °C and ∼1.3 GPa. The estimated pressure condition of ∼1.3 GPa coincides well with the low-velocity anomaly observed in the mantle at ∼40 km depth beneath the volcano. By comparing the results from Akita-Komagatake to the published results of the frontal-arc Iwate volcano (H = ∼90 km) and the rear-arc Sannome-gata volcano (H = ∼150 km), which are arranged along a cross-arc line in the Northeast Japan arc, we found that the pressure conditions of the magma generation are ∼1.3 GPa at both Iwate and Akita-Komagatake, which are significantly lower than the ∼1.8 GPa at the rear-arc Sannome-gata volcano. The source mantle temperature of ∼1275 °C at ∼1.3 GPa beneath Akita-Komagatake is higher than the ∼1250 °C at ∼1.3 GPa beneath Iwate, which suggests that the ascending flow of the mantle wedge corner flow may reach the shallowest levels beneath Akita-Komagatake. It was also demonstrated that the depth at which fluid was released from the subducting slab tends to increase for the volcanoes with increasing H.

Interseismic Coupling and Slow Slip Events on the Cascadia Megathrust

In this study, we model geodetic strain accumulation along the Cascadia subduction zone between 2007.0 and 2017.632 using position time series from 352 continuous GPS stations. First, we use the secular linear motion to determine interseismic locking along the megathrust. We determine two end member models, assuming that the megathrust is either a priori locked or creeping, which differ essentially along the trench where the inversion is poorly constrained by the data. In either case, significant locking of the megathrust updip of the coastline is needed. The downdip limit of the locked portion lies ∼ 20–80 km updip from the coast assuming a locked a priori, but very close to the coast for a creeping a priori. Second, we use a variational Bayesian Independent Component Analysis (vbICA) decomposition to model geodetic strain time variations, an approach which is effective to separate the geodetic strain signal due to non-tectonic and tectonic sources. The Slow Slip Events (SSEs) kinematics is retrieved by linearly inverting for slip on the megathrust the Independent Components related to these transient phenomena. The procedure allows the detection and modelling of 64 SSEs which spatially and temporally match with the tremors activity. SEEs and tremors occur well inland from the coastline and follow closely the estimated location of the mantle wedge corner. The transition zone, between the locked portion of the megathrust and the zone of tremors, is creeping rather steadily at the long-term slip rate and probably buffers the effect of SSEs on the megathrust seismogenic portion.

Deformation of a Half‐Space from Anelastic Strain Confined in a Tetrahedral Volume

Deformation in the lithosphere-asthenosphere system can be accommodated by faulting and plastic flow. However, incorporating structural data in models of distributed deformation still represents a challenge. Here, I present solutions for the displacements and stress in a half-space caused by distributed anelastic strain confined in a tetrahedral volume. These solutions form the basis of curvilinear meshes that can adapt to realistic structural settings, such as a mantle wedge corner, a spherical shell around a magma chamber, or an aquifer. I provide computer programs to evaluate them in the cases of anti-plane strain, in-plane strain, and three-dimensional deformation. These tools may prove useful in the modeling of deformation data in tectonics, volcanology, and hydrology.

Seismic imaging of mantle wedge corner flow and arc magmatism.

I reviewed studies on the inhomogeneous seismic structure of the mantle wedge in subduction zones, in relation to corner flow and its implications for arc magmatism. Seismic studies in Tohoku clearly imaged the descending flow portion of the corner flow as a thin seismic low-velocity layer right above the slab. Slab-derived H2O is fixed to the layer as hydrous minerals, which are brought down by the slab and eventually decompose. The released H2O rises and encounters the ascending flow, formed to fill the gap caused by the descending flow. The combination of H2O addition and adiabatic decompression causes partial melting within the ascending flow. For many subduction zones, seismic tomography has distinctly imaged the ascending flow of the corner flow as a seismic low-velocity and/or high-attenuation layer in the mantle wedge inclined nearly parallel to the slab. These observations indicate that the volcanic front in subduction zones is formed both by the ascending flow and the addition of slab-derived H2O.