Crustal Structure of the Jurassic Quiet Zone in the West Pacific Ocean:Insights from 2D Multichannel Seismic Reflection Profiles

The Jurassic oceanic crust is the oldest existing oceanic crust on earth,and although distributed sparsely,carries essential information about the earth's evolution.The area around the Pigafetta Basin in the west Pacific Ocean(also known as the Jurassic Quiet Zone,JQZ)is one of a few areas where the Jurassic oceanic crust is present.This study takes full advantage of high-resolution multichannel seismic reflection profiles in combination with bathymetry,magnetic,and gravity data from the JQZ to examine the structure,deformation,and morphology of the Jurassic oceanic crust.Our results show the following insights:1)The Moho lies at 2–3 s in two-way travel time beneath the seafloor with the segmented feature.The gaps between the Moho segments well correspond to the seamounts on the seafloor,suggesting the upward migration of magma from the mantle has interrupted the pre-existing Moho.2)The oceanic crust is predominantly deformed by crustal-scale thrust faults,normal faults cutting through the top of basement,and vertical seismic disturbance zones in association with migration of thermal fluids.The thrust faults are locally found and interpreted as the results of tectonic inversion.3)Seafloor morphology in the JQZ is characterized by fault scarps,fold scarps,seamounts,and small hills,indicating the occurrence of active faults.4)The oceanic crust in the JQZ and East Pacific Rise has many structural and geometrical variations,such as the thickness of sediments,seafloor topography,basement morphology,fault size and type.

Debris flow runout behaviors considering the influences of densely populated buildings

Debris flows pose serious risks to communities in mountainous areas,often resulting in large losses of human life and property.The impeding presence of urban buildings often affects the runout behavior and deposition of debris flows.But the impact of different building densities and sizes on debris flow dynamics has yet to be quantified to guide urban planning in debris flow risk zones.This study focused on a debris flow that occurred in Zhouqu County,Gansu Province,China on August 7th,2010,which was catastrophic and destroyed many buildings.The FLO-2D software was used to simulate this debris flow in two scenarios,i.e.the presence and the absence of buildings,to obtain debris-flow intensity parameters.The developed model was then used to further analyze the influence of large buildings and narrow channels within the urban environment.The simulation results show that considering the presence of buildings in the simulation is essential for accurate assessment of debris flow intensity and deposition distribution.The layout of buildings in the upstream urban area,such as large buildings or parallel buildings which form narrow channels,can affect the flow velocity and depth of debris flow heading towards downstream buildings.To mitigate damage to downstream buildings,the relative spacing(d/a)between upstream and downstream buildings should not exceed a value of two and should ideally be even lower.These findings provide valuable insights for improving the resistance of mountainous cities to urban debris flows.

Effect of Langmuir circulation on upper ocean mixing in the South China Sea

Effect of Langmuir circulation （LC） on upper ocean mixing is investigated by a two-way wave-current coupled model. The model is coupled of the ocean circulation model ROMS （regional ocean modeling system） to the surface wave model SWAN （simulating waves nearshore） via the model-coupling toolkit. The LC already certified its importance by many one-dimensional （1D） research and mechanism analysis work. This work focuses on inducing LC＇s effect in a three-dimensional （3-D） model and applying it to real field modeling. In ROMS, the Mellor-Yamada turbulence closure mixing scheme is modified by including LC＇s effect. The SWAN imports bathymetry, free surface and current information from the ROMS while exports signifi- cant wave parameters to the ROMS for Stokes wave computing every 6 s. This coupled model is applied to the South China Sea （SCS） during September 2008 cruise. The results show that LC increasing turbulence and deepening mixed layer depth （MLD） at order of O （10 m） in most of the areas, especially in the north part of SCS where most of our measurements operated. The coupled model further includes wave break- ing which will brings more energy into water. When LC works together with wave breaking, more energy is transferred into deep layer and accelerates the MLD deepening. In the north part of the SCS, their effects are more obvious. This is consistent with big wind event in the area of the Zhujiang River Delta. The shallow water depth as another reason makes them easy to influence the ocean mixing as well.

Spreading rate dependence of morphological characteristics in global oceanic transform faults

We quantified the systematic variations in global transform fault morphology,revealing a first-order dependence on the spreading rate.(1)The average age offset of both the full transform and transform sub-segments decrease with increasing spreading rate.(2)The average depth of both the transform valley and adjacent ridges are smaller in the fast compared to the slow systems,reflecting possibly density anomalies associated with warmer mantle at the fast systems and rifting at the slow ridges.However,the average depth difference between the transform valley and adjacent ridges is relatively constant from the fast to slow systems.(3)The nodal basin at a ridge-transform intersection is deeper and dominant at the ultraslow and slow systems,possibly reflecting a lower magma supply and stronger viscous resistance to mantle upwelling near a colder transform wall.In contrast,the nodal high,is most prominent in the fast,intermediate,and hotspot-influenced systems,where robust axial volcanic ridges extend toward the ridge-transform intersection.(4)Statistically,the average transform valley is wider at a transform system of larger age offset,reflecting thicker deforming plates flanking the transform fault.(5)The maximum magnitude of the transform earthquakes increases with age offset owing to an increase in the seismogenic area.Individual transform faults also exhibit significant anomalies owing to the complex local tectonic and magmatic processes.

Influence of Climatic Conditions on the Time Series Fluctuation of Yellowfin Tuna <i>Thunnus albacares</i>in the South Pacific Ocean

Yellowfin tuna (Thunnus albacares) is one of the most commercially important fish species for South Pacific island nations and territories and for effective conservation efforts it is important to understand the factors which affect its time series pattern. Our research was aimed at elucidating the climatic factors which affected the trajectory of the yellowfin tuna stock in the Eastern and Western South Pacific Ocean. We utilized various climatic factors for the years t - n with n = 0, 1, ..., 8 and investigated their statistical relationship with the catch per unit effort (CPUE) of yellowfin tuna stock from 1957-2008 for three South Pacific zones ranging from the East to the West Pacific Ocean within the coverage area of the Western and Central Pacific Convention Area. Results showed that the climatic conditions of: (i) the global mean land and ocean temperature index (LOTI), (ii) the Pacific warm pool index (PWI) and (iii) Southern Oscillation Index (SOI) had significant relationship with the CPUE of yellowfin tuna in all three zones. LOTI, PWI and SOI were used as independent variables and fitted through modeling to replicate the CPUE trajectory of the yellowfin tuna in Zone 1, Zone 2 and Zone 3. Model selection was based on significant parameter estimates (p < 0.05), Akaikes Information Criterion (AIC) and R2 values. Models selected for all three zones had LOTI, PWI and SOI as the independent variables. This study shows that LOTI, PWI and SOI are climatic conditions which have significant impact on the fluctuation pattern of the yellowfin tuna CPUE in the Eastern and Western South Pacific Ocean. From the findings of this study it can be recommended that when management decisions are made for yellowfin tuna fishery conservation and sustainability in the Eastern and Western South Pacific, it is imperative to take the effect of climatic factors into account.

Seismic Images of Shallow Waters over the Shatsky Rise in the Northwest Pacific Ocean

Recent studies have demonstrated the ability of seismic oceanography to reveal finescale vertical structures of water column in the oceans based on multichannel seismic(MCS)reflection data.Such information can clarify the dynamic processes of mixing,exchange,and translation of water mass and energy.In this study,we present four MCS lines and satellite data to show high-resolution seismic images of shallow waters over the Shatsky Rise in the Northwest Pacific Ocean,where the Kuroshio Exten-sion passes and bifurcates.One of our MCS transects crossed the center of an anticyclonic warm eddy on August 28,2010,confirmed by satellite data such as sea level anomaly(SLA),geostrophic current anomaly(GCA),and sea surface temperature anomaly(SSTa).The seismic image showed that the eddy vertical structure featured a bowl-like shape and onion-like internal layering.The slightly tilted(<0.5°)surface of the eddy was 400m below the sea surface,indicating a subsurface eddy.The eddy was inferred to have a radius of 50 km and a maximum thickness of 500m.Other MCS sections demonstrated the submesoscale structure of oceanfronts,characterized by the dipping reflectors(>2°-3°)at the boundaries between water masses with differing properties.In addition,the discrepancies in SLA,GCA,and SSTa between water masses resulted in different seismic reflectivities.The water masses with high SLA,anticyclonic GCA and positive SSTa featured high-amplitude,continuous,clear-layered,and non-linear reflections,whereas those with low SLA,cyclonic GCA,and negative SSTa were associated with weak,fragmented,less stratification,and more linear reflectors.

Evaluation of the submarine debris-flow hazard risks to planned subsea pipeline systems: a case study in the Qiongdongnan Basin, South China Sea

The ever-increasing deepwater oil and gas development in the Qiongdongnan Basin,South China Sea has initiated the need to evaluate submarine debris-flow hazard risks to seafloor infrastructures.This paper presents a case study on evaluating the debris-flow hazard risks to the planned pipeline systems in this region.We used a numerical model to perform simulations to support this quantitative evaluation.First,one relict failure interpreted across the development site was simulated.The back-analysis modeling was used to validate the applicability of the rheological parameters.Then,this model was applied to forecast the runout behaviors of future debris flows originating from the unstable upslope regions considered to be the most critical to the pipeline systems surrounding the Manifolds A and B.The model results showed that the potential debris-flow hazard risks rely on the location of structures and the selection of rheological parameters.For the Manifold B and connected pipeline systems,because of their remote distances away from unstable canyon flanks,the potential debris flows impose few risks.However,the pipeline systems around the Manifold A are exposed to significant hazard risks from future debris flows with selected rheological parameters.These results are beneficial for the design of a more resilient pipeline route in consideration of future debris-flow hazard risks.

Deciphering the Origin of Abiotic Organic Compounds on Earth:Review and Future Prospects

The geologic production of abiotic organic compounds has been the subject of increasing scientific attention due to their use in the global carbon flux balance,by chemosynthetic biological communities,and for energy resources.Extensive analysis of methane(CH_(4))and other organics in diverse geologic settings,combined with thermodynamic modelings and laboratory simulations,have yielded insights into the distribution of specific abiotic organic molecules on Earth and the favorable conditions and pathways under which they form.This updated and comprehensive review summarizes published results of petrological,thermodynamic,and experimental investigations of possible pathways for the formation of particular species of abiotic simple hydrocarbon molecules such as CH_(4),and of complex hydrocarbon systems,e.g.,long-chain hydrocarbons and even solid carbonaceous matters,in various geologic processes,distinguished into three classes:(1)pre-to early planetary processes;(2)mantle and magmatic processes;and(3)the gas/water-rock reaction processes in low-pressure ultramafic rock and high-pressure subduction zone systems.We not only emphasize how organics are abiotically synthesized but also explore the role or changes of organics in evolutionary geological environments after synthesis,such as phase transitions or organic-mineral interactions.Correspondingly,there is an urgent need to explore the diversity of abiotic organic compounds prevailing on Earth.

Recently deepened insights regarding Mg corrosion and advanced engineering applications of Mg alloys

This review summarizes recent insights into the Mg corrosion mechanism, clarifies many critical controversial points regarding the Mg corrosion behaviour, and updates some efforts made to extend the industrial application of Mg alloys. Based on the new understandings gained so far, future research directions are also suggested in the review. This review has the following logic. The first section "1. Scope"is a consolidation of the new understandings or developments regarding the Mg corrosion mechanism and the new applications for Mg alloys. It also highlights some key points for the review. The second section "2. Widely accepted knowledge" briefly summarizes the general understanding of Mg corrosion gained so far, which acts as the foundation for the following sections. The third section "3. Recently deepened insights" mainly briefs on some new insights into Mg corrosion phenomena based on recent findings. Different interpretations on the corrosion behaviours are comprehensively discussed in the fourth section "4. Controversial points" and the conclusions are drawn in the subsection"4.5 Clarified points". Apart from the fundamental understandings, various efforts in the application of Mg alloys are presented in the fifth section "5. New applications". Following the research tendency as indicated in the review, prioritized research areas are suggested in "6.Future directions". The review is concluded with "7. Concluding remarks" at last.

Impact of Climatic Factors on Albacore Tuna <i>Thunnus alalunga</i>in the South Pacific Ocean

Over the years there has been growing interest regarding the effects of climatic variations on marine biodiversity. The exclusive economic zones of South Pacific Islands and territories are home to major international exploitable stocks of albacore tuna (Thunnus alalunga);however the impact of climatic variations on these stocks is not fully understood. This study was aimed at determining the climatic variables which have impact on the time series stock fluctuation pattern of albacore tuna stock in the Eastern and Western South Pacific Ocean which was divided into three zones. The relationship of the climatic variables for the global mean land and ocean temperature index (LOTI), the Pacific warm pool index (PWI) and the Pacific decadal oscillation (PDO) was investigated against the albacore tuna catch per unit effort (CPUE) time series in Zone 1, Zone 2 and Zone 3 of the South Pacific Ocean from 1957 to 2008. From the results it was observed that LOTI, PWI and PDO at different lag periods exhibited significant correlation with albacore tuna CPUE for all three areas. LOTI, PWI and PDO were used as independent variables to develop suitable stock reproduction models for the trajectory of albacore tuna CPUE in Zone 1, Zone 2 and Zone 3. Model selection was based on Akaike Information Criterion (AIC), R2 values and significant parameter estimates at p < 0.05. The final models for albacore tuna CPUE in all three zones incorporated all three independent variables of LOTI, PWI and PDO. From the findings it can be said that the climatic conditions of LOTI, PWI and PDO play significant roles in structuring the stock dynamics of the albacore tuna in the Eastern and Western South Pacific Ocean. It is imperative to take these factors into account when making management decisions for albacore tuna in these areas.

Modeling seasonal variations of ocean and sea ice circulation in the Beaufort and Chukchi Seas:A model-data fusion study

A 3.8-kin Coupled Ice-Ocean Model （C1OM） was implemented to successfully reproduce many observed phenomena in the Beaufort and Chukchi seas, including the Bering-inflow-originated coastal current that splits into three branches： Alaska Coastal Water （ACW） , Central Channel, and Herald Valley branches. Other modeled phenomena include the Beaufort Slope Current （BSC） , the Beaufort Gyre, the East Siberian Current （ ESC）, mesoscale eddies, seasonal landfast ice, sea ice ridging, shear, and deformation. Many of these downscaling processes can only be captured by using a high-resolution CIOM, nested in a global climate model. The seasonal cycles for sea ice concentration, thickness, velocity, and other variables are well reproduced with Solid validation by satellite measurements. The seasonal cycles for upper ocean dynamics and thermodynamics are also well reproduced, which include the formation of the cold saline layer due to the injection of salt during sea ice formation, the BSC, and the subsurface upwelling in winter that brings up warm, even more saline Atlantic Water along the shelfbreak and shelf along the Beaufort coast.

Large Active Faults and the Wharton Basin Intraplate Earthquakes in the Eastern Indian Ocean

In recent years,great earthquakes occurred within the Wharton Basin in the eastern Indian Ocean,and they have been associa-ted with active faulting on the ancient oceanic crust.Large seismogenic faults were thought to be the fault reactivation on the ancient oceanic crust,but these phenomena are still unclear and require examination.This study used high-quality multibeam bathymetry and multichannel seismic data collected over the northern Ninetyeast Ridge to investigate detailed fault geometry,structure,and activity.We recognized 12 large linear active faults by integrating bathymetry maps and multichannel seismic reflection profiles.Our results showed that these faults have high angles,and they all displaced the basement and propagated to the seafloor with distinct fault scarps.They trended NWW-SEE with a spacing of 10–40km and were parallel to each other and the nearby subfault of the 2012 great intraplate earthquake,suggesting similar stress fields.These faults are also in agreement with the orientations of magnetic isochrons,implying their formation by seafloor spreading.Furthermore,regarding the strike-slip focal mechanism of 2012 earthquakes,we proposed that these faults were created early by a normal spreading process and then evolved into a strike-slip pattern since the ancient oceanic crust ap-proached the subduction zones.

Bio-inhibitive effect of an algal symbiotic bacterium on corrosion of magnesium in marine environment

It is a longstanding and challenging task to develop sustainable environment-friendly and cost-effective corrosion-protection technologies for Mg alloys, especially under marine conditions in which corrosion can normally be significantly accelerated by bacterial activity. However,this paper reports on the corrosion of highly active Mg interestingly inhibited by an algal-symbiotic bacterium Bacillus altitudinis. The corrosion of Mg in the presence of the bacterium drastically reduced by one order of magnitude after 14 days of immersion. This means that the algal-symbiotic bacterium widely available in natural ocean environments may be employed as a green and sustainable inhibitor in the marine industry. Based on electrochemical measurements, surface analyses and microbe experiments, a combined inhibition mechanism is proposed in the paper to interpret the interesting corrosion behavior of Mg.

Potential impacts of climate and anthropogenic-induced changes on DOM dynamics among the major Chinese rivers

Dissolved organic matter (DOM) is closely linked to human activities in drainage basins and plays a crucial role in maintaining ecosystem functioning and reflecting environmental quality. However, the impacts of climate and anthropogenic-induced changes on DOM in riverine systems under increasingly warming conditions still need to be better understood, particularly at large regional scales. To address this knowledge gap, we analyzed a dataset containing 386 published measurements for nine major Chinese river systems, examining dissolved organic carbon (DOC) concentrations and optical properties of chromophoric DOM (CDOM) under diverse envi- ronmental conditions, including mean air temperature, precipitation, surface solar radiation, population density, and land use. Our findings indicate that riverine DOC concentrations are significantly higher in northern China (at ∼46.8%) than in the south. This disparity is primarily due to the high input of soil erosion-induced DOM from drying-affected lands (57.0%), farmland (49.1%), and forests in the north. The high temperate and strong hydrological conditions would lead to DOM degradation easily in the riverine system in the south of China. Our study highlights that various climatic and anthropogenic factors, such as agriculture, vegetation coverage, soil erosion, surface solar radiation, and precipitation, individually or in combination, can affect DOM dynamics in river systems. Therefore, considering alterations in DOM dynamics resulting from climate and environmental changes is crucial for carbon-neutral policies and sustainable river ecosystem assessments.

Microbial carbon pump shapes chemical signatures of refractory dissolved organic carbon in ocean water column

The global ocean sequesters a great amount of dissolved organic carbon(DOC),which is mainly originated from indigenous microbial activities(such as photosynthesis and chemoautotrophy)in the water column,as well as various exogenous sources such as riverine input,sediment mobilization,aerosol dissolution,hydrothermal vent effusion,and others(Cai and Jiao,2023).

Study on 10 kVDC Powered Junction Box for A Cabled Ocean Observatory System

A cabled ocean observatory system that can provide abundant power and broad bandwidth communication for undersea instruments is developed. A 10 kV direct current （kVDC） with up to 10 kW power, along with l Gigabit/sec Ethemet communication, can be transmitted from the shore to the seafloor through an umbilical armored cable. A subsea junction box is fixed at a cable terminal, enabling the extension of up to nine connections. The box consists of three main pressure vessels that perform power conversion, power distribution, and real-time communication functions. A method of stacking modules is used to design the power conversion system in order to reduce the 10 kV voltage to levels that can power the attached instruments. A power distribution system and an Ethemet communication system are introduced to control the power supply and transmit data or commands between the terminals and the shore station, respectively. Specific validations of all sections were qualified in a laboratory environment prior to the sea trial. The ocean observatory system was then deployed at the coast of the East China Sea along with three in situ instruments for a 14-day test. The results show that this high voltage-powered observatory system is effective for subsea long-term and real-time observations.

A numerical study on seasonal variations of the thermocline in the South China Sea based on the ROMS

On the basis of the regional ocean modeling system （ROMS）, the seasonal variations of the thermocline in the South China Sea （SCS） were numerically investigated. The simulated hydrodynamics are in accordance with previous studies： the circulation pattern in the SCS is cyclonic in winter and anticyclonic in summer, and such a change is mostly driven by the monsoon winds. The errors between the modeled temperature profiles and the observations obtained by cruises are quite small in the upper layers of the ocean, indicating that the ocean status is reasonably simulated. On the basis of the shapes of the vertical temperature profiles, five thermocline types （shallow thermocline, deep thermocline, hybrid thermocline, double thermocline, and multiple thermocline） are defined herein. In winter, when the northeasterly monsoon prevails, most shallow shelf seas in the northwest of the SCS are well mixed, and there is no obvious thermocline. The deep region generally has a deep thermocline, and the hybrid or double thermocline often occurs in the areas near the cold eddy in the south of the SCS. In summer, when the southwesterly monsoon prevails, the shelf sea area with a shallow thermocline greatly expands. The distribution of different thermocline types shows a relationship with ocean bathymetry： from shallow to deep waters, the thermocline types generally change from shallow or hybrid to deep thermocline, and the double or multiple thermocline usually occurs in the steep regions. The seasonal variations of the three major thermocline characteristics （the upper bound depth, thickness, and intensity） are also discussed. Since the SCS is also an area where tropical cyclones frequently occur, the response of thermocline to a typhoon process in a short time scale is also analyzed.

A CIP-Based Numerical Simulation of Free Surface Flow Related to Freak Waves

An enhanced numerical model for simulating two-dimensional incompressible viscous flow with distorted free surface is reported. The numerical simulation is carried out through the CIP （Constrained Interpolation Profile）-based method, which is described in the paper. A more accurate interface capturing scheme, the VOF/WLIC scheme （VOF：Volume-of-Fluid;WLIC：weighed line interface calculation）, is adopted as the interface capturing method. To assess the developed algorithm and its versatility, a selection of test problems are examined, i.e. the square wave propagation, the Zalesak’s rigid body rotation, dam breaking problem with and without obstacles, wave sloshing in an excited wave tank and interaction between extreme waves and a floating body. Excellent agreements are obtained when numerical results are compared with available analytical, experimental, and other numerical results. These examples demonstrate that the use of the VOF/WLIC scheme in the free surface capturing makes better results and also the proposed CIP-based model is capable of predicting the freak wave-related phenomena.

Jurassic Hornblende Gabbros in Dongga,Eastern Gangdese,Tibet:Partial Melting of Mantle Wedge and Implications for Crustal Growth

The Gangdese batholith, more than 2500 km in length, is composed mainly of JurassicMiocene igneous rocks. This batholith is one of the most important constituents of the Tibetan orogenesis and provides an ideal place for study of Neo-Tethyan ocean geodynamic evolution and plateau uplift. Recent studies on the Gangdese Jurassic felsic magmatism highlight its juvenile source. However, important aspects concerning the genesis of the juvenile magmatism and related deep geodynamic evolution are still unclear. Here, we report detailed petrological, geochronological, geochemical, whole-rock Sr-Nd isotopic, and in situ Sr-Hf isotopic data for a recently identified hornblende gabbro in the Dongga area, southern Lhasa sub-block. This hornblende gabbro is dominated by hornblende and plagioclase, dated at Early Jurassic（ca. 180–190 Ma）, and characterized by a narrow compositional range in SiO2（49.38wt%–52.27wt%）, MgO（4.08wt%–7.00wt%）, FeO（10.43wt%–11.77wt%）, Na2O（2.58wt%–3.51wt%）, and K2O（0.48wt%–1.53wt%）. It has depleted isotopic signatures, with whole-rock（87Sr/86Sr）i ratios of 0.7033–0.7043, εNd（t） values of ＋4.90 to ＋6.99, in situ plagioclase（87Sr/86Sr）i ratios of 0.7034–0.7042, and zircon εHf（t） of ＋12.2 to ＋16.8. Our results integrated with published data suggest a model of Gangdese juvenile crustal growth by a subduction-related water-enriched mantle wedge. The hydrous partial melting of the lithosphere mantle was triggered by the dehydration of a Neo-Tethyan oceanic slab. This mafic magmatism emplaced in the middle-lower crust of intraoceanic arcs or active continental margins, leading to Jurassic juvenile crustal growth in southern Tibet.

Modeling of normal faulting in the subducting plates of the Tonga,Japan,Izu-Bonin and Mariana Trenches:implications for near-trench plate weakening

The plate flexure and normal faulting characteristics along the Tonga, Japan, Izu-Bonin and Mariana Trenches are investigated by combining observations and modeling of elastoplastic deformation of the subducting plate. The observed average trench relief is found to be the smallest at the Japan Trench(3 km) and the largest at the Mariana Trench(4.9 km), and the average fault throw is the smallest at the Japan Trench(113 m) and the largest at the Tonga Trench(284 m). A subducting plate is modeled to bend and generate normal faults subjected to three types of tectonic loading at the trench axis: vertical loading, bending moment, and horizontal tensional force. It is inverted for the solutions of tectonic loading that best fit the observed plate flexure and normal faulting characteristics of the four trenches. The results reveal that a horizontal tensional force(HTF) for the Japan Trench is 33%, 50% and 60% smaller than those of the Mariana, Tonga and Izu-Bonin Trenches, respectively. The normal faults are modeled to penetrate to a maximum depth of 29, 23, 32 and 32 km below the sea floor for the Tonga,Japan, Izu-Bonin and Mariana Trenches, respectively, which is consistent with the depths of relocated normal faulting earthquakes in the Japan and Izu-Bonin Trenches. Moreover, it is argued that the calculated horizontal tensional force is generally positively correlated with the observed mean fault throw, while the integrated area of the reduction in the effective elastic thickness is correlated with the trench relief. These results imply that the HTF plays a key role in controlling the normal faulting pattern and that plate weakening can lead to significant increase in the trench relief.